Shim Under Bucket

I'm working with a 650 engine that uses shims under the bucket.  What a pain to get the correct gap!  I'm thinking about converting to shim OVER bucket.  Has anyone ever done this?  Is it as easy as I think it is...just pull the buckets and replace them with the old style?

There must have been a reason they did this.
Steve

wrote:

There must have been a reason they did this.
Steve

 

Higher reving while effectively eliminating risk of spitting a shim ??
 

It may have been a bit cheaper to make the components, as far as operation they both perform the same unless a higher lift cam is used in the 900 style.

I have been a 650 owner for over 35 years, once you adjust the shims you get pretty good at doing it. True its not as fast as the 900 style to change a shim, but once you get use to it you find little tricks to make it quicker and easier. I don't find it challenging at all.

900 tappets are a direct fit for the 650 but you will probably need to fart around getting the shims correct after the swap. I am not sure if there is clearance to use the 900 shim change tool due to the differences in the head casting - That may be the only issue but I doubt it would be a problem.
 

No problem using the shim over buckets from a 900/1000.
You need to use the matching 900/1000 spring retainers as well as i'm sure you already know.
The limitation. just like the 900/1000 is the lift of the cam used so around 410 lift is the max although some cam manufacturers have state 418 before going to shim under.
The main reason for shim spitting is the groove around the top inside lip of the bucket.
When the cam lift is so high that it sweeps right to the edge of the shim it tips the shim into the groove which can eventually flip them out like tiddlywinks.
Back in the day tuners would fill the groove with silver solder etc to prevent this and some companies like RC Engineering produced lightened aftermarket buckets without the groove for racing...    See attached pic...

 

Thanks for the replies.  I wanted to make sure before going ahead.  At my age I doubt that I'll be getting the engine up into high revs!  Glad to learn that I need to change the spring retainers as well.

Converting seems like a lot of extra fussing.  The cams are easy to R&R once you get the hang of it.  Just be careful to not strip the cam cap threads in the head.

wrote:

Converting seems like a lot of extra fussing.  The cams are easy to R&R once you get the hang of it.  Just be careful to not strip the cam cap threads in the head.

Perhaps.  But the engine is currently apart, so it's an ideal time to do it if one wanted to, and it only gets done once. 

With shim over bucket all you need to do is remove the valve cover, check clearance and pop the shim if necessary.  With shim under bucket you have to remove the valve cover, check the clearance and then remove the top cam chain tensioiner, pull the cam, pull the tappet, change the shim and potentially re-time the engine before re-assembling.  I see the former to be much easier than the latter.

I have to measure the cams before converting, just to ensure they are not high lift.  But I don't think they are any higher lift than a Z1 cam.

 

I needed to replace only one intake valve shim.  I locked the chain to the sprockets with zip ties (and put paint marks just in case), & locked the cam chain tensioner.  I unbolted the cam and moved it up and forward out of the way and kept everything taut with a bungee up around the frame....swapped out the shim and everything went right back into place. I imagine you could then do the exhaust cam the same way.  It wasn't bad really

Changing valve shims with shim under bucket is not that much of a hassle in my book. Every time I checked my valve clearances I usually only had to change  one or two shims at most.

And yes I have pulled the exhaust cam without pulling the intake cam first. I just roll the cam out of the way so I can remove the shim bucket to get to the shim.

One thing I always do is pull the tach drive gear before I bolt the exhaust cam back in place!!!! I have seen many people deform or smash the tach drive gear on the cam or bend the tach drive gear. Which is NLA from Kawasaki anymore!!!! 

 

I try to remember to do it every time. I hate the dredded click and find I bent one.
Steve

Just because you haven't figure it out does not means that you need to change it it is a simple procedure that if you get it right you will only have to disassemble and assemble one time, measure the gap in each cylinder, open and measure each shim and do the math to get the right clearance.
if your current gap is to tight open put smaller shim were needed and put back together measure and do the math again. its not so complicated just not as easy as 900, but for some reason they did the design like that.
Also make sure to do not damage the threads of the cam caps screws and do not over tighten, the screws snap easy and then you have a big issue to remove that screw out.