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Old 05-26-2012, 01:23 PM   #1
Droz88 OP
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Yamaha enduro won't start.

It's a 1973 yamaha CT3.

-New spark plug
-New contact breaker
-Fresh 20:1 fuel
-Rebuilt and cleaned carb
-New K&N air filter
-Engine has compression of 120 PSI

I am at my wits end with this thing. The only thing left for me to check is the timing but I cannot find a good resource online telling me how to do that. The service manual is very vague about it and specifies using a dial indicator which I don't have. How do I check timing?
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Old 05-26-2012, 03:18 PM   #2
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Ok I found a video on youtube and checked for TDC and measured 1.8mm before TDC. It look like the timing on this thing is WAYYY off. It's about 90 degrees off...

After looking over the flywheel and stator I can't figure out why this timing is so off. Any ideas?
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Old 05-26-2012, 03:32 PM   #3
Donkey Hotey
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Sheared key on the crankshaft? The flywheel could have rotated with nobody knowing. It happens. If it hasn't run for you, it could have sheared that key for the previous owner, they never knew why it didn't run, then parked it.

You might also check the crank seals. If they are leaking, you won't get proper fuel induction. Take the plug out, put your hand over the carb and crank the engine through a stroke. It should suck your hand firmly against the intake.
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Old 05-26-2012, 04:01 PM   #4
baloneyskin daddy
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He said it had new points so he had the flywheel off and you'd think would have seen a sheared keyway, But that sounds like the problem to me also. Its possible he dislodged the keyway reinstalling the flywheel.
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Old 05-26-2012, 04:07 PM   #5
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I suspect the key fell out and he did not notice while re-installing the flywheel.

If you need a replacement key make sure to use the correct metric key.
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Old 05-26-2012, 04:56 PM   #6
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Alright it turns out that it was a sheared keyway. I put a good keyway in when I re-assembled it but it must have sheared when I kicked it 1000x trying to start it last week. Well I just ordered a new key and I'll try again next weekend. If it doesn't start I'm done with it and just selling it.

Droz88 screwed with this post 05-26-2012 at 05:38 PM
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Old 05-27-2012, 01:42 AM   #7
AC Swank
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Don't give up, these bikes are fairly easy to get going and still a lot of fun to ride.

BTW, when I purchase flywheel keys, I always buy two, one to use, one to lose.

Good luck!
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Old 05-27-2012, 07:49 AM   #8
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Flywheel keys are only an alignment devise and have very little shear strength, if you are shearing keys you are not getting a good connection between the crankshaft and the flywheel. The tapered connection is what holds the flywheel to the crankshaft from turning.
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Old 05-27-2012, 08:02 AM   #9
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Quote:
Originally Posted by Strong Bad View Post
Flywheel keys are only an alignment devise and have very little shear strength, if you are shearing keys you are not getting a good connection between the crankshaft and the flywheel. The tapered connection is what holds the flywheel to the crankshaft from turning.
That's probably what caused it. I don't have a torque wrench so I am only tightening the flywheel nut as much as I can before the engine starts to turn over with a regular socket wrench. When the new flywheel comes in I'll make sure it's not going anywhere.
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Old 05-27-2012, 08:02 AM   #10
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Quote:
Originally Posted by Donkey Hotey View Post
Sheared key on the crankshaft? The flywheel could have rotated with nobody knowing. It happens. If it hasn't run for you, it could have sheared that key for the previous owner, they never knew why it didn't run, then parked it.

You might also check the crank seals. If they are leaking, you won't get proper fuel induction. Take the plug out, put your hand over the carb and crank the engine through a stroke. It should suck your hand firmly against the intake.
Yes thank you. I'll check that today too and see if there is a good suction.
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Old 05-27-2012, 08:14 AM   #11
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Before putting the flywheel on ,take a little valve lapping compound and put it on the taper and spin the flywheel back and forth to remate the surfaces. Be sure to clean it off thoroughly afterwards.. Another trick I've done is made keyways fron valve shims. They're very hard and if you have an assortment you can find a real tight fit.
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Old 05-27-2012, 10:31 AM   #12
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Quote:
Originally Posted by baloneyskin daddy View Post
Before putting the flywheel on ,take a little valve lapping compound and put it on the taper and spin the flywheel back and forth to remate the surfaces. Be sure to clean it off thoroughly afterwards..
Good idea.

Quote:
Originally Posted by baloneyskin daddy View Post
Another trick I've done is made keyways fron valve shims. They're very hard and if you have an assortment you can find a real tight fit.
Bad idea. You want the key to shear, less damage to the crank if it does try to spin.
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Old 05-27-2012, 10:35 AM   #13
Droz88 OP
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Quote:
Originally Posted by baloneyskin daddy View Post
Before putting the flywheel on ,take a little valve lapping compound and put it on the taper and spin the flywheel back and forth to remate the surfaces. Be sure to clean it off thoroughly afterwards.. Another trick I've done is made keyways fron valve shims. They're very hard and if you have an assortment you can find a real tight fit.
Will do. Thanks.
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Old 05-27-2012, 01:25 PM   #14
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Alright I pulled the spark plug and put my hand over the carb to test for vacuum. There was vacuum but it was felt a bit weak. I can't objectively tell whether it was in fact weak or if it would be considered good. It did not pull my hand "firmly", but I could tell that there was in fact vacuum.

I might as well just replace the seals. Can anyone tell me how to replace the seal on the right hand side? The one on the left looks like it just pries out and the new one gets tapped in. It looks like i'll have to pull the engine halves apart in order to get to the one on the right, but I can't really tell. The factory service manual for this bike really sucks.

Oh and I have the cylinder head bolts tightened pretty tight. The service manual says 14-17 ft/lbs but I have them way tighter than that. Originally when I did a compression test the engine only had 20 psi. I checked the cylinder heads and they were pretty loose. I cranked them down a lot and got the compression up to 120psi. Could worn out oil seals cause low cylinder compression?

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Old 05-28-2012, 09:24 AM   #15
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I'm only using the valve shim rig in cases where theres already damage from multiple key shearings and the slots are a little oversized from the rocking action that takes place before the key actually shears. It works to stave off replacing a crank end and flywheel and if you shear one of these off thats your only alternative anyway.
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