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Loud "TAP" when piston reaches TDC, normal?

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Hey guys, 

 

So Ive been trying to figure out why my engine has been having this knock sound for awhile now, i have a couple other threads going on this issue, but I still cannot figure it out. I have removed the top end and checked the crank shaft for movement and there is zero side to side or up and down play. I have replaced the piston and rings, the old one was in near perfect condition but I decided to replace for peace of mind. I cleaned the valves and head but did not replace any of that yet. My valve clearances are in spec although the right intake valve has no shim. So I'm thinking at this point that it's either something to do with the valves, I just don't know what. Any ideas? 

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Why is there no shim in your right intake valve if its that worn out it needs to run without a shim I would not be runing that motor you are asking for a big repair bill get your topend overhauld sounds like its long overdue.

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If there's a valve with no shim, that's your noise. I assume there's no shim in there because even the shortest shim will cause the valve to hang open, which means your valve is shot. Time for a valve/guide/seat job, and springs.

Do NOT run the motor, please.

Edited by Eddie8v
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It's so zeroed you use no shim....... i triple dog dare you to run a hare scramble and post pics

Edited by zotis777

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It's absolutely from the top, last night I took the valve cover off and listened closely while slowly turning the motor and found that as soon as the decomp lever passes rocker arm it makes that loud click could something be wrong there?

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I wondered from your first post if that may be it, that should only click through the kick stroke. You might look that assembly over and make sure the spring is oriented correctly. Might as well do the mod while you're in there.

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I haven't really needed to but I was thinking I might do it when I check my valves next. Mine was a hard starter after I let it sit for a few months but after a good carb cleaning and a couple tweaks it usually starts in 1 or 2 kicks now, and I subscribe to the theory "if it ain't broke don't fix it". The theory behind the mod is sound though.

Your missing valve shim is another matter. I bet the last time it was shimmed it was accidentally dropped during reassembly and since it spec'ed okay nobody questioned it. I don't think I would run it without a shim, maybe try putting a 1.2 mm ( the thinnest I think ) and see if it is still in spec. My guess at this point is that your auto decompress arm is not springing back out of the way like it should. Let us know what you find.

Edited by mdwsr

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I had a mechanic look at it yesterday and he's pretty sure it's the cam chain making the noise. I re shimmed the RT intake valve with a 1.70mm and it's in spec not and starts and runs much better. As the auto decomp mechanism I think that is pretty sound, from what the manual says to inspect it looks good. I have a timing chain on the way so I'll let you all know if that is the issue or not.

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Remove your decompresser from the cam no need to remove the cam to do this if the noise is gone you now know what it is as you said its right after the decomp rolls of the cam they do make a loud tap its normal.

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I know what the decomp click sounds like, and the sound I'm hearing is close that but it doesn't stop when the motor is running, even at high revs. I'm ruling decompressor out unless replacing this cam chain doesn't fix it.

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Mine is quiet at idle so something is up. I read another thread on this type of tap sound on another forum and he hasn't reported yet what he found. It makes me curious though. This other guy had some discussion about the cam chain too so maybe you'll get lucky.

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