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Dwight Williams

Bayou 250, questions about timing chain and valve/piston contact

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Ok, so I bought a 2006 bayou 250 for 200 bucks, kid couldn't start it and had no idea why it wouldn't run, I pulled the rope and felt what I thought was valve to piston contact, he wanted 500 and I talked him down to 200 and brought it home.  Sure enough, timing was way far out, timing chain incredibly loose.  So for fun I re-tensioned the timing chain and re timed it, got about 120lbs of compression, pretty low.  I cannot get the chain very tight but the the tensioner seems to work fine, the chain guides don't look very worn.  Also, when I took the head off the valves don't look bent and the piston has no discernible marks on it.  Is this an interference engine?  I sure thought I felt some contact with the pull rope but maybe no permanent damage was done?  Anyway, I plan on doing a full top end job as well as timing chain tensioners and hopefully that'll cure it.  Is there any reason other than chain stretch (I measured it and it's ok) or guide wear that would cause the chain to be so loose?  Thanks!

 

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Sounds strange that the chain is so loose. I would check the  lower cam chain sprocket to make sure a tooth is not gone causing the chain to be so loose. 
How did you measure the chain? 

Are you 100% sure the tensioner is correct and all parts are in place?


When you took the compression reading did you take it with throttle open or closed?

Check the decompression device as well for proper operation  

Bent valves are somewhat hard to see and they could not be seated properly but i agree that you  should see a mark or two on the piston because you know the previous owner cranked the hell out of it. So maybe the timing was out just far enough but not far enough  to collide with the piston? 
 

For the price you paid and if the atv is clean then a full top end tear down sounds  in order and is worth the  investment but i would change  the chain and inspect the lower sprocket as well. 
 

Good luck.  

 

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I checked compression with throttle open, decompression lever is fine.  I'm still not sure about the chain, it's weird that it's so loose.  No marks on piston, cam and rockers look good.  There are some fine scratches on the cylinder but nothing serious.  I just got a puller for the flywheel and I'll take it off tonight to inspect the lower timing chain sprocket.  Timing was out to lunch, I'm sure the valves hit the cylinder but if only pull rope starting (electric starter clutch is bad) maybe it wasn't enough to bend hurt anything.  

I know for sure the tensioner is correct, it wasn't when I started and that's why it jumped time.  

 

I measured the chain with an engineering metal ruler.  I'm not sure what else to measure it with.  I'm going to do the top end, order a new chain, inspect everything and put it back together.  It's just weird to me that the chain was so loose but I suppose once it started jumping on the gear it could have really stretched it out.  I have two other Bayou 220s and the chains are nice and tight, although I still can't get spark on one of them (see my other thread).

 

Thanks

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