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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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I tore it down, intake valve is bent, I ordered both.  Cylinder is pretty scratched up, timing chain is really stretched.  I ordered a stock piston and ring set but now I'm wondering if it'll have to be bored out to a bigger size just to clean it up.  I tried a ball hone and it didn't really touch the scratches.  I think once I get the top end all done it'll be ok.  I was tempted to put it back together with the scratches but I know better, why do all that work and have it smoke or have low compression (or both) and have to do it again.  I'll take the jug to a machine shop this week and drop it off to be done right.

Bayou250_scratches.jpg

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Figured there would be a bent valve. Makes sense on the stretched chain as well. Nice work on the tear down. 
The dark spots in the cylinder head are they scratches or gouges ? If not then its not in bad shape. I quick cylinder honer on a drill would work fine with a fresh piston and rings. If the dark spots are in deed deep scratches or gouges then yes its going to need a machine shop. But keep in mind going a bit bigger usually will need a bigger jet kit on the carb.  

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The dark spots are just grease/dirt from my fingers, I got the new piston and rings but I'm perplexed.  There are no markings on the rings.  The originals only have a mark on the second ring down, and it's supposed to have a taper according to the manual.  The new rings have no marks whatsoever.  I'm sure the oil rings don't matter but the compression ring should.  I can't see the taper with my naked eye.  The old one doesn't appear to have a taper either but it may just be worn down enough to not see it anymore.  Anyway, if the ring has no marks does that mean it can go in either way?  The instructions are generic but they do state that that the marks go up (assuming there is a mark).

 

Thanks

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If the dark spots are just grease from your fingers then yes the cylinder is fine.  
The ring should be tapered and not noticeable to the eye without really looking at it or putting  it up agains a flat surface like a smooth piece of steel or on a metal ruler but its tough to see. 
Did you look on the flat spot of the rings, the rings are usually marked there?

 

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Yes I looked at the rings very closely, no marks.  The mark on the original is very easy to see.  No writing, no dots, stamps, paint etc.  Just plain black.  I'll check for taper with a straight edge, thanks for the tip!

 

 

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What I would do is take a stainless steel corner square and place it down on a flat surface. Then put the ring in the corner of the square and check for the slope against the edges of the square and then flip the ring over and check again.    

Edited by Frank Angerano

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I checked and re-checked.  I found what may be a slight taper but barely noticeable.  I was able detect it on the old ring.  After measuring over and over using speed square on a flat quartz countertop I go somewhat consistent results.  I suspect it has no taper though since there were no markings.  Anyway, it's ready to go back together as soon as I get the new valves - they should be here tomorrow.

 

thanks

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Yes, new seals all around.  I currently have 3 quads in different states of repair now - I just got another project this week and I'm tearing the top end of it down today.  Stand by for more questions LOL..

 

Thanks!

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So I got this all put back together, runs great, idles poorly (chinese carburetor).  I should be able to get that adjusted out.  Anyway, I've got a little smoke from the tail pipe when I rev it up.  Also quite a bit of smoke from the base of the exhaust where is comes out of the cylinder, like it's leaking somewhere?  I cracked a banjo bolt up top and the oil pump seems to be working fine, no rattles from the top either.  It's got maybe 5 minutes of run time on it.  How long should I give it before I'm concerned?  I know the cylinder had a few scratches but it was at 120-125 psi before I tore it down, so I figured it couldn't be all that bad.  

Also there is quite a bit of chatter from the right side when I put it in gear, I'm assuming the clutch has some issues so I'll be tearing into that.

This thing has had a rough life but it sure seems to run strong now.

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China carbs are the worst! Never had any luck with them. The smoke by the exhaust is usually a valve cap seal, did you change the rubber seals ? If not simply pull them and add a little high heat silicone and put back on.  Leave the rubber ones in place with the silicone and clean them of any oil.  
What do you mean you broke a banjo bolt? Did you replace it ? The noise is most likely the  clutch. When you start to move the noise should stop, if so then its clutch chatter and will need some work. Maybe new plates. 

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I didn't break a banjo bolt, I cracked it, as in 'crack it a bit' to see if it spit oil, and it did.  Sorry if I wasn't clear on that.  Anyway, the kid I bought this from threw parts at it, a starter and solenoid (he wired the solenoid wrong so the starter spun backward), and a carburetor.  Turns out the original carb was in pieces in a bag with bolts, etc that he gave me.  I put the carb back together and it fired up and ran perfect.  I adjusted the idle again and took it for another ride.  It runs fantastic, and when I got back, no smoke and no clutch rattle!  I assume the clutch just needed to be wet again after sitting.  I can't believe how good it runs, just perfect.  I'm starting to feel that my $250 investment wasn't so crazy.

The brakes however, are terrible, and one back wheel is on backward and bent.  It pulls pretty hard to one side because the back tires are different sizes.  I still have plenty of work to do but this last ride made my day.  Onward and upward.

 

IMG_0534.jpg

IMG_0535.jpg

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Good stuff brother, OEM carburetors are the best! Im glad it runs good. 
I would get the proper tire on the rear sooner then later. One tire is spinning faster then the other and thats not good for a rear differential. 
I have seen a few racks for them on various sites as im always looking for parts.  If i come across some I could put you in touch with the vendor if your looking.  
 

 

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Thanks, I'm watching a few on Ebay as well, I appreciate you keeping an eye out though.  I've got a few parts here and there too, let me know what you're looking for.  I was planning on putting tires on it but it looks like I need a wheel now as well, it's pretty bent.  I agree about the OE carbs, I'll always take one, crusty or not.  Once cleaned up they run like they were made for it (hmmmmm).

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