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1966 CM91.... where to begin

This is a discussion on 1966 CM91.... where to begin within the Vintage forums, part of the Types of Bikes category; I just scooped this old beast up and she's had a hard life it would appear. It is pretty complete, ...


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Old 09-30-2010   #1
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Default 1966 CM91.... where to begin

I just scooped this old beast up and she's had a hard life it would appear. It is pretty complete, with the exception of; ignition key, air box/ tube, side covers, and of course title. When I picked it up the crank case didn't have any oil in it because it had an improper drain plug, and no dip stick, all those conditions have now been remedied. She isn't seized, and I'm having a local lock shop try to make a key to fit, once I have it I'll check for spark, rebuild the carb and see if it will start for me. Here are a few horror pics.




Any ideas what else to do, I'm new to the whole two wheeled thing. Also, if anyone knows where I can find some body parts other than eBay? I also need a manual, wiring diagrams, torque specs etc. All help is greatly appreciated
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Old 10-01-2010   #2
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starting to reconsider the engines health, after I put oil in it I kicked it over for a little bit and it seemed loose, but with plug out I noticed the piston did not appear to be moving, so I used a pencil to mark depth and kick it some more. Took off the upper valve cover to make sure something worked, and even though the valve was moving the pencil wouldn't go in any further. Starting to wonder if I might have a broken connecting rod.

I do have a key now, and just have to get my battery charged to check for spark... but that won't count for much if I have to open up the case.
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Old 10-02-2010   #3
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Engine off bike, cylinder and head off engine as well as piston. Connecting rod good, internals look good too, but there was water that appears to have sat in the inlet valve area. Soaking that now to get some of the rust broken up before diving in ant removing the valves. I might be able to save it.









Last edited by haddockkl; 10-29-2010 at 10:06 PM.
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Old 10-14-2010   #4
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I have nearly all the parts I think I'll need on the way, going to split the case and take a look inside, clean out the old varnish and replace any worn or rusted bearings. The cylinder bore looked really good, right up until where the piston had been sitting for who knows how long, so that's getting bored over .25mm and getting a new piston/ rings, the old one had a little lateral wobble anyhow. Need to get the valves out but haven't found the right size tool for it, but going to replace both valves if I have to. Once everything gets put together... then I get to see if I have spark, and might have it running before the snow falls. If it'll run it might get a victory lap around the neighborhood before it gets pulled to pieces and have everything refinished.
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Old 10-26-2010   #5
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This thing's getting stupid, got the cylinder honed, blasted, repainted; the head soaked of all carbon deposits, rust soup, and getting valve seats re cut + new valves. After that it'll be time to clean up and out the bottom end and get it put back together and see if it'll roar like... something small and comical.
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Old 11-07-2010   #6
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Well the deed is done and the engine has been gone through. Removed a huge amount of sludge from the centrifugal oil strainer and the filter screen. Also inspected all my bearings and everything cleaned up well, then got to spend two days scraping gasket material. So last night I put everything back together without my manual handy, as a result I need to reset the timing and figure out why it won't shift now. Things to do still but progress made.
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Old 11-14-2010   #7
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This sad little bastard. I took the engine, pulled it apart, put it back together again... missplaced a thrust washer so it came apart a second time, reassembled it and left out the rubber gasket for the timing chain between the cylinder and the head... took the head off and put it in and now it's finally in one piece. Everything inside looked good other than the sludge on the filter screen and in the centrifugal oil filter, both of which I'm pretty sure are clean for the first time since it was new. Oh, I also didn't have the right gasket for my oil pump, I was using a CS90 Gasket set, only had to modify the case gasket slightly but everything else was perfect, save for a different style oil pump, so I made a new one out of printer paper.

So after reassembling the engine, adjusting the valves and points and making sure oil circulated I put it back on the frame, along with a new fully charged battery. Try as I might however, I couldn't get any spark, forgot to put in a new condensor so I have that to do, but now it's time to chase the gremlins out of the wiring, which in places is pretty rough as the head light bucket had been a mouse nest when I got it and some wires are stripped of insulation. Time to break out the multi meter.



Last edited by haddockkl; 11-14-2010 at 03:44 PM.
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Old 11-20-2010   #8
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The beast has fire! After going through the wire loom in the back, pulling out the ignition switch, and generally scratching my head I did the following.
Seeing I wasn't getting any spark I pulled off the points cover to see if I was getting any there, but instead of finding spark, I found that the cam wasn't rotating... so that meant the crank wasn't turning and lead me to the clutch. Thinking to myself "that was the only damn thing I didn't have down to nuts n' bolts" I figured I was in for some friction disks. Doing what any amature mechanic with the interweb at their disposal would do, I ran and searched clutch disassembly. Fortunatley the first thing I found was a walk through of how to adjust the clutch. Mind you, my Clymer manual told me how... to do the exact opposite of what I should have. After adjusting the clutch I was getting the engine to turn over finally, but still no spark.

Next I wen't through the wire loom under the tank, and pulled out the ignition, might have pulled the condensor but I haven't found it yet. Anyhow, the ignition has 5 wires, one of which had worn through the insulation, and while doing an Ohm test I found that the switch wasn't really turning off. Well I taped over the hole in the wire, and turned the switch a few dozen times, and I was finally not getting any continuity when the key was turned off, so I wen't to my local hardwear store and got all the screws I was already missing and went to work putting everything back together.

With all things in their proper places I pulled the plug out and started kicking, no spark, so thought I might check the points again but held short when I realized I hadn't plugged in the condensor lead to the points. After that I was able to get a little blue ark, and was able to repeat it a few more times before my already semi charged battery wouldn't take anymore. So now it's time to charge it up and put a fuel IV to the carb and see if she has thunder in her belly.
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Old 11-28-2010   #9
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Some progress has been made, but not all in the right direction. Had everything together and was trying to fire it, but kept getting puffs coming out the intake. Turned out my timing advancer had been reversed when I took it out the first time, and was firing right between the exhaust valve closing and the intake opening. Then I got the timing set with my home made test light, got everything put back together but I can't get it to fire now, and while I'm watching the points they are irradically opperating because I've got so much clutch slippage I can't get a good solid kick in on it, sometimes I can get two or three sparks, but never more than that, usually only one or two. So with that knowledge I'm going back into the engine and pulling the clutch off when I've got time and taking a look at the friction disks. It might be nice to see if this runs before full on winter gets here.
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Old 12-12-2010   #10
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So I got the clutch out and the old disks were burnt black, there was so much slippage that I had thought I was getting compression when the engine was seized, and when it was freed up I was lucky to get two compressions on a kick, often only one or none at all. So I got new plates and disks, all except clutch plate A because it had been discontinued, but it was the best looking of the old disks anyhow. Soaked the new disks for a few days in fresh oil and cleaned out the clutch basket, popped it all back in and it turns over like a champ now. Sadly I haven't had time to feed it some more fuel and see if she'll start, but I'm trying to source an exhaust because the old one was dented halfway shut.


I also took out the old rectifier and put together a new one with a modern solid state unit, I pirated the old wiring off the old unit to maintain the proper colors, but I don't need it in to test for spark and get it running, she just won't charge.

Last edited by haddockkl; 12-12-2010 at 09:54 PM.
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