Diagnosing odd blowing (not sucking) on intake after breakdown...cam timing?

BillyO

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I'll try to shed some light on the subject here, but understand, I have never done this on a motorcycle engine, only automotive engines. But a 4 stroke is a 4 stroke, so....
- you know which cylinder is #1 (because I don't)
- you know which way the engine rotates when running (again, because I don't, but I can imagine the same rotation as the drive chain)
- you've already got the basics, hold your finger over the #1 plug hole, rotate the engine forward, when the compression begins to blow against your finger you're on the compression stroke.
- now, take a piece of wire (14 or 12 gauge household wire) and put it into the plug hole until it hits the piston. Please make sure the wire is long enough so that it doesn't fall in and you can still control it. Continue rotating the engine, slowly, and watch the wire rise up as the piston pushes it up. You should adjust the wire often to make sure it doesn't get jammed. As soon as the wire starts to go back down, you've just passed TDC. Rotate the engine forward and back ever so slightly, watching the position of the wrench you're using, until you feel confident you have the piston at the top. That is TDC.
- check your other settings/markings to see if everything aligns as its supposed to.

I'm sorry, but I cannot say if you can loosen the cam chain adjuster enough to move the chain a cog or two. You could try, but as I visualize the engine, if the chain is loose at the top, its also loose at the bottom and you run the risk of the chain coming off the sprocket at the bottom as you try to reset the top. Someone who's been inside one of these may know better. Maybe that's what happened and the chain is no longer on the lower sprocket...but I don't know what the engine innards look like.

Hope this helps you find TDC though.
 

Indydave

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Thank you. Yes, I'm nearly 100% sure I have it at TDC (and the piston is indeed within less than an inch when plug is removed). I MAY have lost spark bc my socket may have pushed the two pulse generators too far from the big nut I used to turn the crankshaft. I will try to return them to the proper position.

FINGERS CROSSED that will solve it tomorrow.
 

Indydave

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UPDATE: I just finished doing a compression test and it pretty much confirms that the valves got bent when the chain slipped. I got 100 PSI on number four and zero on 1-3. I repeated the test and got zero again (with plugs out and throttle open.

So would anyone want to buy it for $600? Any other 79 with 31,000 miles would be ready for a valve job anyway.
 
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