Rim Strapping
Loose Needles
Timing Degrees
Evolution of Cota
Seal Frustration
Shifting Difficulties
Successful Road Race Modification
ELECTRONIC – INTERNAL ROTOR
There are two reasons that the Motoplat ignition does not create a spark. First, for some unknown reason an internal short occurs and it just quits. The second is the more likely and that is what I will address. There is no way that the ignition can be damaged for the spark to be lost by removing the flywheel and stator unless there is physical damage inflicted on the unit by carelessness with tools. Knocking it off with a hammer would be one of these. Removal with a proper puller of the flywheel and removal of the stator with a common screwdriver is not. There is a greater amount of heat and vibration occurring during engine operation then proper removal and assembly can afflict. These are the things to look for.
1. Check and reset the timing if needed.
2. The ignition coil on the frame must have the metal mounting tab in contact with the metal surface of the frame.
3. Check all wiring for any breaks. This is easily done with your volt-ohm meter on the ohm test mode.
4. The only way you can check for spark is to have the top end assembled and all of the electrical components hooked up. Install a new spark plug into the coil cap of the high-tension wire, ground it against the engine, and rotate the engine rapidly. This type of ignition needs to be spun faster than the external flywheel type because it has magnet proximity of lesser radius and the magnetic flux occurs with the passing of a magnet past the core to the primary coil windings. If the kick-starter is unable to spin the engine fast enough then elevate the rear wheel, select top gear, and spin the engine using the rear tire.
Note: These electronic ignitions can short in the stator if the components are connected and the sparkplug isn’t grounded when the engine is turned over. This is not a common problem but it never hurts to take precautions.
5. Disconnect the kill button and try again. Some kill buttons will short. The ones I use are an aftermarket copy of the two-wire Yamaha kill button. I have not found any failure of this unit.
6. If these steps do not provide a solution then you can send it to Motoplat USA and they can test it. It takes special equipment to do this. The typical way a home mechanic tests the stator is to replace it with a stator on an engine that has proven spark.
Note: You might think that the rotor may have lost its magnetism. These are permanent magnets not provided by Lucas. I have not found any to have lost any magnetism. This may be a test performed by Motoplat USA. Loss of magnetism is a rare occurrence.
This seems to be a secret. There are a number of you that know this secret but there are quite a few that don’t. I was one that didn’t for a long time.
I’m a rather large fellow. I’m talking 250 lbs. plus. I assumed that I would need a bit more pressure in the tires than were recommended by those that were the more successful racers (read lighter). I beat myself up for about 25 years. I built a 1973 VR and proceeded to slip and slide as I had always done and expected the magic of the VR to vault me into a trophy. It didn’t happen. No way. I had been running around 20 to 24 pounds in the front tire and about the same in the rear. I found myself being passed by better riders that were laying their bike down on the cases in passing me and then disappearing into the dust within a couple of turns. The straight-a-way speeds were about the same. It was the cornering speeds I couldn’t attain. Mud was even worse. I was slipping, sliding, and falling while being passed by novices racing on trials tires.
Now that I have got your attention, here are the facts. Montesa provided recommended pressures for there MX bikes. I started following them. I found I was hooking up everywhere. Only my weight was what was keeping me from success. Well, that wasn’t all. I’m blind in one eye and a lack of talent fit in there somewhere.
I checked owner’s/parts manuals for VR, 125 MX, 250 GP, LaCross, etc. On dry and hard ground you put 13 psi in the front tire and 10 psi in the rear. In muddy conditions and sandy conditions the pressure is 11 psi in the front tire and 8.5 psi in the rear.
There is some additional maintenance that you will have to perform.
Don’t lock the valve stem to the rim with that valve nut. Snug it up finger tight against the cap. This allows the tube to slip a little bit and not tear the valve stem causing a flat.
Your tires will creep around the rim. Usually the rear tire will creep more than the front tire and you will have to adjust this tire more often.
Add this to your maintenance before each race on the rear tire.
Secure the front of the bike.
Elevate the motorcycle.
Deflate the rear tire.
Loosen the rim locks.
Pry the bead off the left side of the tire.
Work the tire back where it belongs. Use of a dilute soapy water solution is helpful.
Remount the tire bead.
Inflate to about 20 lbs.
Tighten rim lock(s).
Deflate to 10 psi.
The front tire should have only one rim lock, the rear tire two. You should figure out how to adjust the front tire on your own.
If you think that soapy water will just let it slip more easily, it doesn’t. I’ve tried tire mounting fluids and a mixture of snake oils. It’s the rim lock that holds the tire, not mounting fluid.
(Yes the name is Duct Tape. I am making fun of the word Duct.)
Frequently, too frequently, motorcycle publications mention a way to do away with the wheel rim strap and use duck tape.
No! No! No!
The problem has to do with the spokes and spoke nipples resting against the inner tube. If not protected, abrasion will eventually wear through the inner tube and give you a flat tire. The factory uses a rubber rim strap to cover the nipples and spokes and it does a very good job of it. If you want to reuse a rim strap then check for cracks and rot that would allow it to separate by stretching it by hand. If it hasn’t broken then it can be reused. Replacement straps are available from your local motorcycle source and can be replaced for very little cost.
The only disadvantage of a rim strap has to do with occasional slippage when mounting a tire or difficulty in installing rim locks. When using a rim strap and rim locks, the strap will hold the lock next to the wheel. You must press in the lock toward the inner part of the tire to allow the bead to drop into its correct place. If you use a rim strap then you must deal with it.
The use of duct tape creates a number of problems dealing mostly with older application.
1. If it is used on a chromed rim it will lift the chrome, create rust and jam up the spoke/nipple fastening. You will have to cut the spokes off and the rim and spokes must be discarded. The adhesive does one of two things. It either becomes gooey or hardens. The goo attacks the chrome and lifts it and then attacks the spoke/nipple joint. If it is dry it has hardened into a mass that is very difficult to remove. It can do both over time.
2. On alloy wheels it usually hardens and has to be scraped, cut, or dissolved off. All methods take an inordinate amount of time and make any spoke repair miserable. If you are dealing with a vintage dirt motorcycle this can be the difference in enjoying or not enjoying the process.
I have used a separate method that has worked on most of my wheel rebuilds. I use plastic electrical tape. It can be purchase in packs of 10 rolls and is relatively inexpensive. All spokes must be no longer then one thread above the head of the nipple. If any are too long then they will have to be cut off or ground down. I start with a clean rim at the valve stem hole and make three passes around the wheel. The first past is off a little to one side; the second to the other side about even with the edge of the first pass, and the last is down the center. I have at least 2 layers over all spoke ends. I use a box cutter to cut open the holes for the valve stem and all rim locks. This accomplished what the duck tape is intended to do.
There are a few benefits.
1. When removing the tire you are faced with a plastic strap that is much easier to remove. Usually I can take a box cutter and cut across it and the strap falls away. I have even used a screwdriver to snap the strap.
2. In the rare instance when the adhesive has fastened itself to the rim it is much easier to remove and the spokes and nipples are rarely locked together.
3. You will have to use new tape every time you remove the tire for wheel maintenance. Odd! That’s what you would have to do with the DUCK TAPE.
Note: When assembling wheels the spoke threads should have a spot of anti-seize put on them. This helps when retightening spokes. RETURN TO CONTENTS PAGE
Many of the Montesa models of the late 1960’s and early 1970’s didn’t use caged needle bearings on the wrist pin in the small end of the connecting rod. When removing the piston there is a shower of loose needles onto the bench, top of the engine case and into the crankcase. This article is to explain a way in dealing with the removal and assembly of this unusual bearing solution by the engineers of Montesa.
Early 175 and 250 models used an oillite bronze bushing for connection of the connecting rod to the piston pin. When this is subjected to severe service it doesn’t carry the load well. When the engines were produced in the mid ‘60’s they were equipped with a caged needle bearing. This needle bearing was weak because of the sparse number of needles. The bearing needed replacement more often. The 20:1 oil ratio wasn’t adequate with this bearing. LaCross’s beginning with serial number 23M0231, Scorpion’s at 24M0401, and 250 Impala’s at 25M0201 were fitted with 28 uncaged needle bearings as a replacement for the earlier bushings and caged needle bearings in order to support the increased load. They are a direct replacement for the earlier models. The loose needles continued to be used into the early ‘70’s in all Cappra’s up to the VR and the 247 Cota’s to serial number 21M13106. They were used in all 123 Cota’s (only 26 needles) and all Cappra 360 GP’s and DS (30 needles) models as well.
You will need at least one special tool to remove the piston and help in its reassembly. Go find an electric paint remover. It looks much like a hair drier but is typically adjustable for 750 degrees or 1,000 degrees. Some go higher. They are cheap. I found mine for under $15.00 at Sears. This is a much better heat source than a propane torch. It doesn’t concentrate the heat in such a small area and is much faster.
1. Place the engine over a cleared bench or table. You might want to place a few sheets of newspaper down under the engine.
2. Remove the head and cylinder.
3. Pull the piston up and stuff rags or paper towels around the crankcase opening.
4. Remove one wristpin-retaining clip.
Note: The wristpin is a very snug fit. You don’t want to hammer the wristpin out. This can damage the connecting rod.
5. Secure some type of drift that will fit into or against the wristpin that is smaller than the wristpin hole. I use a large common screwdriver that wedges into the hole near the wide end of the blade.
6. Put on a pair of cotton work gloves.
7. Heat the piston with setting on high for 2 to 5 minutes.
8. Grasp the piston with one gloved hand and push the pin out with the drift away from the remaining retaining clip. It should push out easily.
When the pin and drift is removed the piston will easily lift free. You will see a shower of needles and two location washers fall and scatter around the workspace. Pick up the needles and spacer. Count the needles. If you don’t have the correct number then one or more might
have fallen into the crankcase. This is why you stuffed the rags into the crankcase. A pencil magnet will help in the recovery. I have measured used needles against new ones to the 10,000th of an inch and have never found any difference. I haven’t reused any because I have access to new ones but in a pinch I would likely reuse. . RETURN TO CONTENTS PAGE
Montesa flywheels are fastened onto a tapered shaft. The woodruff key is only a location device. It is used for location purposes for ignition timing. The key does nothing else. There are 2 flywheel pullers for all vintage Montesa flywheels. They thread into the flywheel with right hand threads. The flywheel nut, on the other hand, is a left-hand threaded fastener. The two sizes are 27mm x 1.25 thread pitch and 30mm x 1.5 thread pitch. You must have the engine number to order the correct one. There was a change in at least one model from one to the other during its production.
If you find a part number in a parts book that doesn’t have these numbers then there are super cessions to them. As a rule, any part number with a D prefix is a 27mm and any part number that is all numbers supercedes to the 30mm one. Check for prices in the parts listing.
Steps in flywheel removal:
Hold the flywheel with some holding device. If you have an air impact driver then a hand will do.
Use a socket wrench. A 22mm or a 7/8” size will fit.
Turn clockwise to remove flywheel nut. This is a left hand threaded nut.
Remove the lock washer. This is a left-handed lock washer so don’t lose it.
Install the appropriate flywheel puller by turning it clockwise and turn it until it bottoms.
Note: This is important. Any less and the threads will strip on the puller.
Fasten the appropriate wrench to the center bolt of the puller.
Turn the bolt clockwise until the flywheel pops free. Here again an air impact driver will do the job quite nicely. If you are doing it by hand then use about an 18” break-over with ½” drive and a strap wrench to hold the flywheel.
This flywheel should torque to 72 lbs. ft. when reassembling. The factory installation may be a bit tighter. All of the flywheels I’ve removed from Montesa engines have been done this way.
Heat doesn’t work. The crankshaft and the flywheel hub are steel. The metal was cleaned of all oils and contaminates before they were installed and both metals expand at the same rate. You will likely damage the coils on the stator when you use heat.
Before you reinstall the flywheel you should clean all oils from the taper in the flywheel and on the crankshaft. Use alcohol or electric contact cleaner. Don’t touch them with your fingers.
USE A 2 OR 3 JAW CLAW DO NOT PULLER
These will destroy the flywheel. . RETURN TO CONTENTS PAGE
Beginning about 1968 engine designs changed. Up to this time most models had long studs that were used to retain both cylinder and head. These 10mm bolts were quite long. Due to expansion rates for the aluminum of the cylinder and head versus the steel stud the torque values on a cold engine were light. The engine casting was unable to handle much torque and would distort slightly and/or the stud would want to pull out. This torque value was 11 to 15 lbs. ft. To have a more secure fastening of the cylinder to the engine, shorter and thinner 8mm studs were fitted and the cylinders were modified to accept a sleeve nut.
This nut (part #3360.161) was sized to fit in the 11mm hole. To accommodate a tool one end was made to accept a 7mm Allen wrench. These sleeve nuts also have the torque of 11 to 15 lbs. ft. but they only have to hold the cylinder to the engine cases. They don’t have any other task. The cylinder heads may then be torqued to 21 to 25 lbs. ft. These engines don’t have a head gasket. The addition torque will more likely resist leaking a bit more than the former through-bolt designs. Neither design has a tendency to leak if proper assembled.
With the new attachment it was necessary to move the cylinder head fixing studs 45° around from the base studs to. Typically a boost port was inserted between a modified casting on the intake side allowing for a 3-transfer arrangement. This is found on the 247 and later Cota’s as well as most of the Cappra’s. Anytime you see the cylinder fixing nuts located front and rear and left and right on the top of the cylinder the engine will have these sleeve nuts. The 360 Cappra GP’s and DS’s also have these nuts. They are beneath brass inserts (3660.174).
If you are going to take an engine apart it is necessary to deal with these nuts. The cylinder will not come off without destroying the cylinder and/or engine cases if you attempt it. Scratch that. The exceptions are the 360’s. The 360 GP’s and DS’s have such strong cases you would have to use explosives to damage them. O yes, the only likely damage you can inflict on the cylinder is breaking fins. When you get that cylinder off you will see why. Heft it. These things are heavy.
Water can get into the holes and cause corrosion between the cylinder and nut as well as the nut and stud. This will make them difficult to remove. This is more prevalent on the 250’s.
Ratchet Extension Tool
Torque wrench
Pencil Magnet
Dead blow hammer
Procedure for removal:
Remove Cylinder Head.
It will typically take a 17mm socket to remove the 10mm nuts.
Insert 7mm Allen wrench into hole and engage sleeve nut.
Turn counterclockwise and unscrew from stud.
Remove with pencil magnet.
Tap cylinder with rubber or dead blow hammer to loosen connection. Strike against the edge of the fins, not on top or bottom of them. You can also strike beneath the intake manifold and exhaust port. Do not use a hard hammer.
Slide cylinder up part way.
Press rags or paper kitchen towels in crankcase beneath piston.
Remove cylinder.
his all seems very simple. About 1 out of every 2 engines has a severely stuck sleeve nut. You can soak the nut with liquid wrench or any number of penetrating oils and let it stand for a day or more. I haven’t the patience. Even after a week of using penetrant it only works about 1/10th of the time. What to do, what to do? Heat? Doesn’t work. Maybe the stud will pull before the Allen wrench rounds off the inside of the nut. Been there, done that. The sleeve nut will round out. Once you rounded out the nut it’s time to drill.
Drilling:
Get some cutting oil and an electric drill.
Select a suitable sharp drill bit. Make the selection of a size that will only drill the stud out. Remove all of the sleeve nuts that can be removed.
You don’t want to drill into the cylinder casting.
Start drilling. This will take some time but at least you will feel like you are doing something.
Remove chips occasionally with the pencil magnet.
Measure your progress in some fashion.
Resume drilling. Eventually you will destroy enough of the stud to remove the cylinder.
Use locking pliers and remove the remains of the stud.
Order another stud and nut.
There are special steel washers at the bottom of those holes for the sleeve nut to press against. If they fall out; save them. If they stayed in the hole, leave them there. Just remember to return the washers to the correct holes on reassembly. Clean all nuts and loose washers. Use a 7mm x 1.00 tap and die to clean the threads.
Reassembly: I am assuming that you have managed to get the cylinder over the piston and rings and seated onto a fresh cylinder base gasket.
Replace any steel washer that escaped from the sleeve nut hole (s).
Apply a small smear of anti-seize to the internal threads of the sleeve nut. (You don’t want to go through all of this again)
Using a 7mm allen wrench turn the nut down and seat against the washer.
Use a torque wrench to tighten fasteners to recommended torque.
Assemble head to top of cylinder.
The question will come to you about where to get a 7mm allen wrench. I purchased mine from Sears. If you don’t have a good hacksaw blade you can get one there also. You can also get a 7mm socket. Sear’s has them in ¼” drive. If you don’t have an adapter then get on of those too. Sear’s tools are of uniform strength but are not hardened like some tools. They are strong enough for the job. A hacksaw blade will cut them. Cut off the short part of the L.
Assemble this tool in this order:
Insert the long segment of the 7mm allen wrench into the sleeve nut.
Place the socket on the other end.
Install adapter(s).
Install torque wench.
Torque away.
Note: The 360 GP/DS models have a bolt inserted over the sleeve nut and therefore hide it from corrosive forces. You just have to remember the nut is there when removing the cylinder of one of these models. They won’t fall out. The inserts above them will retain them. You will hear them click every time you turn the cylinder over. Anti-seize will have to be applied to the threads on the stud before installing the cylinder instead of on the inside of the sleeve nut.
A SIMPLE WAY TO TIME USING A PIECE OF BAILING WIRE, AN OLD SPARKPLUG, A PLASTIC PROTRACTOR, AND A CONTINUITY DEVICE.
Tools Needed:
1. A length of bailing wire about 18” to 24” long.
2. One thoroughly used/fouled 14 mm short reach sparkplug.
3. One bolt 3 to 3 ½” long with a 3/8” x 16 threaded bolt with threads at least 1 ¾” long. (I used an allen bolt)
4. Use of a 3/8” x 16 pitch taper tap.
5. One plastic protractor about 6” long on it long edge.
6. One 4” long piece of fresh duct tape.
7. Two alligator clipped patch cords approximately 1 foot in length with alligator clips installed at both ends.
8. One detection device such as a buzz box, continuity light or volt/ohm meter with internal battery supplied.
9. One appropriately sized flywheel puller.
10. Three common screwdrivers; one medium, one slender, and one small enough to turn setscrews in connector block if necessary.
11. One long nose pliers. (Needle nose)
12. One very small adjustable wrench. (6 inch or smaller)
13. A ½” piece of electrical tape.
Fabricating piston stop:
1. Secure sparkplug in a vise.
2. PUT ON SAFETY GOGGLES.
3. Use a center punch or small cold chisel and a small hammer, break up and drive out the porcelain center and wire core.
4. Break off ground wire.
5. Cut threads through the metal body of the spark plug with tap.
6. Remove gasket.
7. Insert bolt from the top and twist it into the spark plug shell.
8. Clean up area.
Fabrication of alligator patch cords:
This doesn’t need to be anything special. Use light wire and alligator clips that are about an inch long. You can find them with cramp in straps and screw tightening forms. I prefer the cramp on version. I also solder the wires for a more permanent connection. You can find all of these items at your local Radio Shack.
Setting up to find top dead center:
1 .Remove flywheel.
2 .Loosen the small nut on the points and remove the pigtail that is connected to the points. It is unnecessary to tighten the nut down. Tuck the free wire out of the way of the flywheel so it won’t tear away when the flywheel is turned by hand in later steps.
3 .Remove sparkplug from the cylinder head.
4 .Screw in finger tight the fabricated sparkplug shell with the bolt inserted about 1/3 of its length into the plug shell.
5 .Replace the flywheel by hand but do not fasten. You should be able to remove the flywheel by hand.
6 .Tape the protractor with a piece of duct tape so that the center of the protractor is over the center of the crankshaft. The 90° should be somewhere a little to the left of the top of the flywheel and positioned so that the gap in the flywheel is positioned over the points.
7. Tie the bailing wire around two stationary points. (I usually tie it around the shift lever shaft and the kick-start shaft. In lieu of the shift shaft just wind it around some anchor point.)
8. Turn the flywheel with the hand back and forth over top dead center while screwing the bolt in the sparkplug shell down toward the piston until the rotation of the flywheel stops against the piston.
9. Bend the free end of the bailing wire so that it points to the 90° point of the protractor.
10. Rotate the flywheel away from the stop and turn it until it stops again.
11. Note how many degrees it is from the 90° point. (Example: Say it reads 76°.) The difference would be 14°.
12.Rebend the wire to half the degrees between the 90 and what ever you found indicated. (Example: 83°) This is top dead center.
Setting timing: This pertains to those models with the flywheel on the right. Reverse the rotation for advance and retard if the flywheel is on the left.
1. Rotate flywheel until points can be seen through the flywheel hole and the points are open to their largest gap.
2. Loosen point set screw.
3. Under close inspection you will see a fixed stop on the stator and a notch on the point plate where a common screwdriver blade will fit. Turning the screwdriver with the setscrew loosened you will see the gap of the points open and close.
4. Insert a thickness gage between the points.
5. Adjust with the screwdriver until the thickness gage will slide through the points with a little drag. The points should not be seen to open or close when the gage is inserted and withdrawn. Typically the gap should be .014” to .015”.
6. Tighten the setscrew.
7. Clip the alligator patch cords to you continuity device with one end connected to the frame or engine. This is ground.
8. Wrap a piece of electrical tape around the other clip to insulate it from contacting the metal of the flywheel and surrounding metal. Connect this clip to the points blade spring or the nut. (You remember the nut that you loosened to remove the condenser pigtail.) Use the long nose pliers to fasten the clip to the nut. Your fingers won’t fit.
9. When you rotate the flywheel before top dead center you will, at some point see a change in signal. Note the degrees on the protractor. This is the point where spark takes place.
10. To adjust the point in which the timing is supposed to take place, remove the flywheel and loosen the 3 screws that secure the stator to the engine.
11. Rotate clockwise to retard and counter clockwise to advance. You will have to remove the flywheel each time to turn the stator.
12. Once the correct timing has been located, remove the flywheel once more and tighten the three stator screws.
13. Replace the flywheel. Check that the timing has not moved.
14. Remove the flywheel again and fasten the pigtail of the condenser to the points.
15. Replace the flywheel and torque to 72 lbs./ft. or to that recommended for your model.
16. Replace all pieces on the engine and tighten snugly.
You have now set your timing. Easy wasn’t it. Next time you can do it in as little as a half hour. . RETURN TO CONTENTS PAGE
The 247
Month/Year Model Frame # Modifications
July 1968 Big Hub 21M 0 First Cota 247 in production ser
White Frame 21M 0500 Frame with “tab” support, rear fender
New chain guard.
Exhaust modification
Exhaust port with 2 exhaust webs
Air box modification (3 screws)
Nov. 1968 21M 1191 Chain guide
April 1970 21M 1800 New footpegs
New gas cap
Seat Modification
Rear sprocket – aluminum
October 1970 21M 2505 Triple Clamps – aluminum
March 1971 Small Hub 21M 3000 rubber fin dampers fitted
New Engine New color of frame
Gray Frame New forged lower bracket
New fuel cock
New front suspension
New fin arrangement on head
Muffler changed
New, smaller pinion gear flywheel
weight
New air cleaner assembly
March 1971 21M 3125 Polished brake/backing plates polished
March 1971 21M 3372 New kickstart idler gear
June 1971 21M 3750 New black handlebar grips
New rear brake lever
New cylinder sleeve
New crankcase
New countershaft sprocket
New kickstart idler gear
New cylinder
July 1971 21M 3789 New piston assembly number
July 1971 21M 3825 Rear shock absorber changed
September 1971 21M 4382 New chain tensioner
New plastic chain guard
September 1971 21M 4456 Head now fixed to cylinder with stud
and washer/nut fasteners
December 1971 21M 5288 New kickstarter return spring
February 1972 21M 5394 Part number change for countershaft
Sprocket
July 1972 Version with 21M 6600 New rear fender
rear muffler New rear muffler
Smaller tank/seat combination
Front Fork accordion boots introduced
New throttle assembly
New rear brake part number
New addition of a rear silencer
New lights and switch assembly
New speedometer and drive system
July 1972 21M 6700 Rear muffler change
Carburetor change (float bowl drain)
Countershaft sprocket changed to 10
tooth
December 1972 Left Side Shift 21M 8100 Left Side Shift arrangement
New fuel cock
Addition of spacer above rubber stop
on rear shocks
New thin ring and piston set
Change to top of air box intake
New shift lever
May 1973 21M 9702 Change to ridgeless rear wheel rim
August 1973 21M 11001 Steering lock included
Handlebar without integral lever perch
September 1973 21M 11152 Incorporation of cylinder fin damping
Rubbers
September 1973 21M 11240 New Pirelli rear tire
October 1973 21M 12115 “Twin-air” air filter
February 1974 Black Frame 21M 13107 New black frame/swingarm
New fuel cock (VR style)
Feb. 1974 21M 13291 Carburetor with float bowl drain
April 1974 Cota 247T 21M 13820 First 247 Trail
Larger tank/seat assembly
11 tooth engine sprocket
Shrouds on rear shock absorbers
December 1974 21M 17218 Natural colored rubber grips
June 1975 21M 19228 New front fork damper modification
Ulf Karlson signature
Addition of lever/perch covers
New pattern forged shift lever
New spark plug cap
August 1975 Cota 247T 21M 19779 Basic trail version for the UK
July 1975 21M 19872 Relocation of clutch arm to top of case
July 1975 21M 19979 Aluminum chain adjusters
September 1975 21M 20042 Electrical wiring installed on top of
rear fender
February 1976 21M 21318 Handlebar made of aluminum
February 1976 21M 21381 Rubber cover over top of carburetor
May 1976 Cota 247T 21M 21482 New tank stripes
September 1976 21M 21962 Plastic throttle, aluminum handlebar
October 1976 21M 22062 New seat
March 1977 21M 23035 New gas tank cap
July 1977 21M 23635 Engine displacement of 237 c.c. for
French competition
October 1978 21M 24389 steel rear sprocket
June 1978 Cota 247C 21M 25137 237 cc,
New fuel cock
New front suspension
Plastic air box
July 1978 Cota 247 21M 25307 New gas tank “348 Cota type”
14 Oct. 1980 21M 27337 The ultimate Cota 247
I have assembled a number of Montesa engines since my first Impala. In the last few years I have found that the shift shaft seal, #0099.2232, on about one half of my rebuilds would pop out when closing the central engine cases. This usually required the re-splitting of the cases with all of usual problems in reassembling the gears, shims, and gasket. I would occasionally press the cases together and the lip of the seal would turn out on the shift drum. I could ease the lip back with the aid of a used and rounded small common screwdriver. This was not the best plan because the tension spring in the seal may not seat. If this seal doesn’t do its job then transmission oil will contaminate the primary oil and cause the clutch to drag excessively and reducing the lubrication of the transmission.
This is caused by a sharp edge on the shift drum. The new seal is smaller on the lips than the worn seal that was removed. This will wear in with use but as a new seal it presents an edge that will not easily slip over the edge on the shift drum. There are a number of steps that must be done in order for the seal to slip into place when assembling.
You will need a few items: (1) a medium carborundum whetstone. (2) 280 grit aluminum oxide coated abrasive. (3) Fine, single cut, 8 inch round file. (4) Multi-purpose grease. (5) Patience.
Steps should be taken in order.
With the engine cases separated and clean and with the seal removed, file a slight chamfer on the edge of the seal-receiving hole. It only needs to have the sharpness removed and shouldn’t be more than 1/32” in width. It shouldn’t have any roughness. A fine file should be sufficient but it can be sanded lightly.
After cleaning press the seal into the hole without lubricant. It should be dry. If you have chamfered the hole properly the seal should go in without tearing. Drive it in until it bottoms.
Remove the shifting forks from the shift drum noting how they came off for later assembly. Also inspect the shift fork guide pins for excessive wear. Replace if necessary.
The edge on the shift drum that must be eased is located behind the gear on the shift-plate end and behind the groove of that gear. Using the whetstone, round the area on the drum. You can check progress by touching the edge lightly and running it around the drum. Polish it with the abrasive paper.
Clean all areas of abrasive.
Pack the lip of the seal with grease.
Reassemble the shift forks to the shift drum.
You are now ready to close the cases.
If you have a metal lathe then mounting the drum in a 3 or 4 jaw chuck and spinning the drum while using the whet stone and abrasive can do the job quickly. . RETURN TO CONTENTS PAGE
There are occasions when it is necessary to remove the shift mechanism from the engine. Those with a left side shift can generally be removed entirely while those with the shift on the right will require the separation of the center cases to remove the shaft. A snap ring inside the left case half retains the right side shift shaft.
The shift plate assembly can be removed in either case inside the primary after removal of the primary cover. When disassembly is necessary due to worn parts or curiosity you will find it assembled in a logical sequence in this order:
1. Two 5 x 25 mm bolts
2. One locking plate
3. One cover plate #0266.101
4. One spring #0266.014
5. One fitting #0266.105
6. One plate #0266.102C with #0266.103 pin inserted or shaft 2166.118.
7. One plate #0266.013 or #4366.013, four or five speed respectively for the right side shift models. Etc.
What this is leading up to is the shaft with #0266.005, #3466.005, and #2166.005 for the right side shift models and #2166.036 for the left side models. When you look at the end of this shaft you will note that it has a long slot across its face containing a light spring and engagement pawls. You think it is centered. It isn’t. It’s slightly off center. The shaft when placed upside down will give you; at the most, two gears. Rotate it 180 degrees and reassemble. This should bring all of your gears back.
The slot should be off center above center. This will not be horizontal but turned a bit clockwise. The plate suffix ….012, called a gear, with the pawl engagement notches must be placed correctly. This plate will have the number of shifts available pressed into the front of the plate, these being 4, 5, or 6.
Another problem can occur with a damaged pawl spring. If it has become weakened or bent it cannot provide adequate spring pressure to press the pawls into engagement. It will need to be replaced. Restretching it or rebending it won’t provide adequate tension. The spring is an inexpensive item costing less than $2.00. This is an extremely rare occurrence but it happens.
The service information advises you after the engine cases are closed to work the gears by hand to see that selection of all gears occur. Use the shift lever on the splines and not a pair of pliers to rotate the shaft. Pliers will damage the splines. The detent plunger on the shift drum should be installed. The hex head cam that is fastened with a 6mm nut and lock washer to a 6mm case stud should center the stop plate for the initial
adjustment. This adjustment is for firmly engaging the first and top gear. Engage first gear. Check to see if it is fully engaged. Adjust if necessary. Manually work through the gears until top gear is engaged. If it is not fully engaged go back to first gear. Readjust the cam. Relock the cam and try again. All of the intermediate gears should readily engage. If you think to scribe a mark with a metal scribe on the cam to a reference point on the engine case this adjustment may not be necessary for future assemblies.
If the pawls are excessively worn they should be replaced. You might have noticed that they do not engage along the full width wedge surface. You may get by with installing them the other way around. Damaged shift pawls do not allow a smooth engagement when shifting gears. Missing gears is best suffered by other manufactures machines.
Check for bent shift shafts. The shaft will drag against the cover and not return smoothly or at all. This is more common to the right side shift models. The only good way to fix this is by replacement. Straightening the shaft is difficult. On right side shift models it is nearly impossible. . RETURN TO CONTENTS PAGE
Carburetor: Recommended starting point for sea level.
Amal 389-B/30 MC 30 MM Mikuni of 32 mm with similar main jet and pilot jet number.
Main Jet: 260-290 Throttle valve in same number is a good place to start.
Pilot Jet #35
Throttle Valve 3.5 mm
Needle DA
Middle Jet 105-A
Stock Impala porting:
Bore: 72.5mm
Stroke: 60.0mm
Exhaust Opens: 102 degrees ATDC
Transfer Opens: 118 degrees ATDC
Modified porting: Cylinder head modifications:
Bore: 72.55mm Have head machined so that pumping
Stroke: 60.0mm Pressure is between 145 and 150
PSI. Exhaust Opens: 96 degrees ATDC This is best done on a lathe. A
little trial and error is necessary.
Transfer Opens: 118 degrees ATDC
Other recommendations:
Ignition timing should be 27 degrees BTDC (4mm)
Oil ratio must never be leaner than 20:1 (Quart to 5 gallons)
Recommended oils: Yamaha R (synthetic), Castrol 2 stoke-petroleum base. I’ve heard good things about Duralube, Silkolene, Maxima, and Golden Spectro.
A velocity stack in combination with an airfilter will increase performance and help keep the spark plug from “whiskering”.
175 (3M, 4M) or 250 Impala (25M), 250 La Cross (23M) or El Diablo (13M) transmissions should be used instead of the Scorpion transmission if this is your choice. . RETURN TO CONTENTS PAGE
Your motorcycle may be smoking for one or both of these reasons. One, your carburetion is too rich. Two, your exhaust is fouling with excess unburned oil. Both can be rectified. The first by a spark plug check and subsequent changes to pilot jet/air screw adjustment and main jet reduction. If the engine is running fine than the second smokier solution may be appropriate. It involves a LOT of smoke and an oxy-acetylene torch.
The exhaust is removed and a fire is lit with a flame of oxy-acetylene mix. Once the fire starts the acetylene gas is turned off and the oil in the pipe becomes the fuel. The oxygen is still supplied by the torch. It will burn until the flame consumes the last remnants of oil. A rosebud tip or a cutting tip, without use of the oxygen lance, can be used. The only problem with this is the heat might be great enough to burn through the pipe somewhere. I haven’t found this to be true yet. It will burn any aluminum that might be in the pipe and it will certainly burn any fiberglass if any is present.
Recommended ratio is 20:1. That is a quart to 5 gallons. This is recommended for all Impala’s, Scorpion and King Scorpion, and 247 Cota’s. If in doubt check the Montesa parts/owner’s manual for its recommendations. I recommend you follow Montesa’s recommendations. Golden Spectro can be used at that ratio no matter what the can says or a parts person might say at any motorcycle shop. These old engines have marginal bearing sizes. Most of the Montesa engines use the same bearings as the first 175 Impala that produced about 16 Spanish horses. A third bearing was added to the power takeoff side of the crank and is somewhat isolated from the crankcase premix on any of the 5 speed Cappra’s and Enduro’s. Bearing sizes did not change until the VA series in 1976.
Other oils I have tried with success are Full Bore 50 wt., Castrol 2 stroke petroleum base, Yamaha R, Schaeffer’s, and Maxima. . RETURN TO CONTENTS PAGE
06/06/2003
I have given some thought to the use of the word mudguard. It seems that the British have adopted the word to describe and item that guards mud. Since we in the U.S. don’t have that much mud to guard and we rebel against its accumulation we tend to fend it off if it attempts to become a part of our vehicle. We, therefore, have adopted the word “fender” to describe this item. I thought you might be curious.