HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
jw423

"Pads" For valve adjustment.

12 posts in this topic

I'm new to the new dirt bike thing but how long and do other bikes have this change the pad to adjust the valves thing going on? Doese anyone know why the new system? It sure seemed a lot more easy to just loosen a nut and turn a screw. My 2006 quad has the old way of adjusting. Is this a Yamaha thing? Do you guys like the pads? Seems nuts to me but I guess there must be a reason....:)

Share this post


Link to post
Share on other sites

99% of modern engines (IE, those in the last 20~30 years) use pad/shims or some variation. The screw/nut/ball time is more prone to wear and as they wear, adjustment becomes near impossible always loose due to the ball making a 'pocket').

Because the shim method is so wear free, adjustment is infrequent and when it does need adjusting, it is because the valves are beginning to recede and out of adjustment valves are a sign that a overhaul is imminent.

Share this post


Link to post
Share on other sites

When the cam sits directly on top of the valve lifter, which sits directly on top of the valve, how else would you do this?

Share this post


Link to post
Share on other sites
99% of modern engines (IE, those in the last 20~30 years) use pad/shims or some variation. The screw/nut/ball time is more prone to wear and as they wear, adjustment becomes near impossible always loose due to the ball making a 'pocket').

Because the shim method is so wear free, adjustment is infrequent and when it does need adjusting, it is because the valves are beginning to recede and out of adjustment valves are a sign that a overhaul is imminent.

Cool thanks for the input. My old bike is a 1990 XR250R and my 2006 Suzuki Vinson both have the old style of adjusters. I can see how the shim leaves less movable parts. So I guess this is the norm now. Do you know if the shims are make and model specific? Or is there an industry standard.. ya right huh.

Thanks again.

Share this post


Link to post
Share on other sites
When the cam sits directly on top of the valve lifter, which sits directly on top of the valve, how else would you do this?

Well you make a good point and I see how the pad is the best way to adjust that system. However having the cam sit directly on top of the valve is not the only way to build a head. How about having a hydraulic lifter in there, now even less adjusting eh.

I was just trying to find out what the norm is now and why it is designed that way. maybe I wasn't clear.

Share this post


Link to post
Share on other sites
... having the cam sit directly on top of the valve is not the only way to build a head. How about having a hydraulic lifter in there, now even less adjusting eh.
It's an engine designed to be used in competitive racing, and run at speeds that would have had you declared insane for suggesting them in the same sentence with "reliable" as little as 20 years ago. Hydraulic lifters are not suitable for such applications.

As far as other layouts for the valve train, it's true, there are other ways, but none as simple, effective, and reliable with as few moving parts and as little total valve train weight to be managed at high rpm. Also none which produce so little total wear.

Besides, where the Yamaha engine is concerned, you won't really be doing that much adjustment, anyway.

There was a similar setup used in the original Kawasaki 900cc Z-1 engine wherein the adjustment pad sat in a pocket on top of the lifter. This meant that the cams did not have to be removed to adjust the valves, but it did require a special tool for the job, and raised the possibility of damaging the valve train during an adjustment. I'm not certain why the setup was dropped, but it was.

Share this post


Link to post
Share on other sites
Cool thanks for the input. My old bike is a 1990 XR250R and my 2006 Suzuki Vinson both have the old style of adjusters. I can see how the shim leaves less movable parts. So I guess this is the norm now. Do you know if the shims are make and model specific? Or is there an industry standard.. ya right huh.

Thanks again.

No, other than diameter (of which there are a few) If a bike uses a 9.48 Dia. shim, then any 9.48 dia. shim will work assuming it is the right thickness of course. I think there are like three diameters used in a majority of bikes. So if you serviced bikes for a living, you'd own three kits.

Share this post


Link to post
Share on other sites

Shims over buckets were dropped because they were occasionally spit out at high RPM. Imagine that mess.

Share this post


Link to post
Share on other sites
Shims over buckets were dropped because they were occasionally spit out at high RPM. Imagine that mess.

I had heard tales like that, but I haven't ever seen any hard evidence to support them. Strikes me as credible, though.

Share this post


Link to post
Share on other sites

Was more a problem with street bikes, and rare. I had a coupla bikes in the early to mid eightys with the shim over arrangement and no issues. Special tool was cheap ($10+-) and much easier than pulling cams.

Share this post


Link to post
Share on other sites

Just occured to me, with shim over, possible wear on shims due to direct cam contact? Could add an extra step to adjustment.

Share this post


Link to post
Share on other sites

My XT350 Yamaha has shims over buckets. So far, none have jumped out. Nor has any wear been apparent. There is a pretty large contact patch (fat old cam lobe) and at 14,000 miles, not nticable wear. Seems to, the bucket tends to rotate about and the cam does not hit the same point.

Share this post


Link to post
Share on other sites

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
Sign in to follow this  
Followers 0