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Timing Issue

2384 Views 32 Replies 5 Participants Last post by  shadetree
I am brand new to this forum, just thought I would seek some assistance with what I have going on. I purchased a '98 Foreman 450S, and just the other day, it "pecking." Adjusted the cam chain both clockwise and counter clockwise. Turning it counter clockwise caused it to smoke, so I turned it back clockwise and it continues to smoke. Took the valve cover off and spun it over using the electric start and noticed that only the intake push rod is moving. Could it have jumped time and bent a valve? Strange thing is that it fires right up, rides fine, and lacks no power, just pecking loud and smokes. Any help would be appreciated! I would think if it jumped time, it wouldn't have any power, or would run rough. None of this is happening.

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There is a cam chain tensioner adjustment under the exhaust pipe right at the head. I removed the plug and used a flat head screwdriver to turn it both directions to try and get rid of the "peck" from the chain. It didn't help the sound, so I am thinking it needs a chain. Just trying to figure out why the exhaust rocker is not moving, and the pushrod is not traveling. Going to have to tear it down I guess. It just had a top end rebuild right before buying it.
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I have taken the head and jug off. Found no issues. Removed the front cover found no issues. Checked can lobes no issues. No issues with lifters or push rods and no issues with the cam chain. How do I know of it jumped time? Can't see the crank shaft with the clutch in the way.
The rings LOOK fine. The cross hatch was gone from the cylinder for sure. But its just weird that it is all of a sudden. The exhaust valve was coked from the oil of course but no major issues to the naked eye.
I'm trying to figure out how to post a video to show you.
It has side to side, like front to back but not vertically. Sliding in between the two retainers some.

In these engines is there supposed to be ANY movement in the rod on the crankshaft? Slight aide to side movement like the wrist pin but not much
So if I check the decomp, what exactly am I looking for? I mean if I make sure it locks and unlocks, how will I know if it is bad?
I checked the timing last night (putting the engine to TDC and checking the cam sprocket to the mark on the case). Everything was as spot on as it can be. I am thinking about pulling the cam tonight and check the decomp to see if it is hung up because there was a little bit of rattle when the engine was running before the tear down. The service manual is kind of vague to me as far as how to check the decomp with the cam removed. Any special or weird instructions that I am not aware of?

Also, it looks like the crank and rod have a little "blu-ing" from where maybe it had been hot before? Any pointers on checking the bearings to know if they are salvageable? Other than trying to rock it up and down and back and forth?

Just want to hit as many issues as possible before putting it all back together.
Is this considered "failed?" There is one straight edge and one jagged. Almost looks chipped. Moving the springs up and down it seems like the decomp gets hung up. Normal or no?


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Well I'm not sure what else to check at this point then. I guess I'm going to put new stem seals and a set of rings in it and hone the jug, new can chain and tensioner lifter, and run it.
Does it help if I mention that I mic'ed the cylinder? Almost perfect at 90mm.
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Measured my ring end gap have stroke. .028" on wiseco rings. I'm going to say it probably needs to be bored.
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I did not get a measurement at the top. Dangit. I took it to the machine shop to get it bored over. Going with a 4825M09050 Wiseco setup. So far its getting complete gasket kit top end and front cover seal. New can chain and tensioner and lifter. Getting new cam and bored over.
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Fish, thank you for the information. I checked for side to side and wobble on the small end and the crank end. Barely side to side on the crank. No "rocking" on the small end.
Update on the situation:

Removed the engine from the frame to get a better look at things. Tore the engine down and checked the hard parts. Did not split the case though. Checked for play in the rod, and play on the crank. All looked good in the lower end. Used oil/gas mix to flush out the case as best as I could. Replaced the camshaft due to the decomp ring hanging up, along with the cam chain, and clutch pack on the change clutch. Had the cylinder bored to 90.5 and put a 4825m9050 Wiseco piston and rings in. Lapped the valves, changed the seals, and reinstalled. Fired it up for the first time yesterday and all seemed fine. Quiet, except the HMF exhaust being loud (LOL). Going to put the plastics and all back on and take for a spin.

Thank you all for the help that you've offered. Definitely helped along the way!
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