Cams and Cam Chain setup

Hey Guys

 

I'm butting my head at the moment trying to get my cams set up properly after re-shimming the head. :banghead:

I set the marks up according the manual but when I release the chain tensioner and do a full rotation of the motor, when I hit TDC, the cams are slightly shy of their marks, when I advance both cams 1 tooth, then they reach their marks slightly before TDC. :bonk:

The chain tensioner still has a bit of movement left to keep tension on the chain, but I was wondering if this problem could be caused by a stretched chain?

 

Also just to double check myself, there are 3 marks on the flywheel 2 are joined by a straight line (looks like a really wide H or an I laying on it's side) I assume these are possibly 10 and 5 degrees before TDC and then there is a third mark on it's own which I assume is TDC, it does seem correct after testing the movement of the piston with a long thin screwdriver>

 

I also still don't have the right shim in the centre intake valve, I couldn't get a 0.05mm feeler gauge in there so shimmed from a 181 down to a 170, but after installing the new shim I still can't get the 0.05mm feeler gauge in so I'm going to try a 160 shim now.

 

Thanks

 

 

 

 

Sounds like you have a worn out cam chain and possibly worn out tensioner too.

 

When installing cams, you do not have to install the tensioner to confirm you have it right. Just poke a screw driver in the tensioner hole (gently) or simply pull the cam chain back slightly on the intake cam.

 

When smimming, do the math, do not trial and error it.

Sounds like you have a worn out cam chain and possibly worn out tensioner too.

 

When installing cams, you do not have to install the tensioner to confirm you have it right. Just poke a screw driver in the tensioner hole (gently) or simply pull the cam chain back slightly on the intake cam.

 

When smimming, do the math, do not trial and error it.

 

Thanks William, OK I'll get a new Cam Chain

 

For the shimming , I could not get a 0.05mm feeler gauge in so followed the manual for a 0.00 to 0.04 clearance and installed the 170 from a 181 but the valve has obviously receded further than that into the head. The valve was obviously open all the time. :excuseme:

The exhaust valves worked out perfectly, I re-shimmed from a 184 to 180 on both of them and now my clearance on those is right at 0.20mm, the outer intakes are both between 0.1 and 0.15

 

This is my first offroad bike which I bought 3 weeks ago so still lots of learning to do about the little tricks.

 

Thanks for the help :cheers:

If your to the point of needing to go to a 160 from a 180 shim ( or More) the valve is trashed. if you get clearance it will be gone again in no time. the face of the valve is cupped out and the seat is damaged to match. If your going to keep the bike you should pull the head and fix the issue. there is no other way. The worse news is that lots of other parts are probably worn as well. :(    

I agree with Geofitt.

Sadly, it is not uncommon for a person to wear a bike out and instead of being honest and servicng it, they unload on an unsuspecting buyer. I'd wager the seller just shimmed the bike to make it run and dumped it on you.

 

Fix it correctly or a more expensive bill awaits.

If your to the point of needing to go to a 160 from a 180 shim ( or More) the valve is trashed. if you get clearance it will be gone again in no time. the face of the valve is cupped out and the seat is damaged to match. If your going to keep the bike you should pull the head and fix the issue. there is no other way. The worse news is that lots of other parts are probably worn as well. :(    

 

I was afraid someone might say that. :(

If the 160 works out OK for clearance, what sort of time do you think it will have before it closes up again? I've already had to throw a new fuel tank and lots of other goodies at it, just can't afford to get the head done right now. Was hoping to get a few hours on it to start learning how to ride before I pull the head off.

I agree with Geofitt.

Sadly, it is not uncommon for a person to wear a bike out and instead of being honest and servicng it, they unload on an unsuspecting buyer. I'd wager the seller just shimmed the bike to make it run and dumped it on you.

 

Fix it correctly or a more expensive bill awaits.

 

William can I get away with just doing the one valve or must all 5 be done together (I know that's the correct way, but is it an absolute must)?

How long will it run before you have a failure? Five minutes, five hours, more/less? No way to know but... once the valves 'begin to move' the process continues untill the valve fails. Normally, you can shim safely once or twice. After that, it is a ticking time bomb and the risk of catastrophic failure rises dramatically. Not worth a 5 times more expensive repair bill just to squeeze a few more rides out of it.

 

I would do all five valves. I would also pull the barrel, inspect the rings, piston and barrel bore, service as needed.

A few rides only,  maybe more if you keep the revs lower. at this point there's no harm in putting extra clearance in there, if you end up at .20-.25mm ( .008-010") it won't hurt any thing and it might give some extra time on it. The 250 valves are pretty thin in the margin area and give up fast once they start. 

Thanks William1 and Geoffit

Wow so much for buying an older cheaper bike

 

I know it's a difficult question to answer but on average how long would a new set of valves last before this happens again, based on an average weekend rider just doing trail rides and no competition riding?

If you get a good valve job ( seats cut) and put in new springs and valves it should all last for a long time, make sure who ever does the head checks the guides as well. For trail riding check into the kibble white SS valves they might save some$$ and last even longer.

Thanks Geoffit.

 

Got prices today on the machining and it's not too bad, the valves are a bit scary though .

 

Thanks for the help guys :thumbsup:

Shop about. There are complete OEM valve kits (valves, springs, ect) for about $200 on Ebay, I think.

Shop about. There are complete OEM valve kits (valves, springs, ect) for about $200 on Ebay, I think.

 

I think I'll do that William, thanks.

Got hold of my local Yamaha dealer today and they want to charge me $500 just for the valves :naughty: , Ebay here I come

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now