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Trimming valves

  • Thread starter Thread starter snyderman
  • Start date Start date
S

snyderman

Guest
I am moving this question from the general maintenance forum to this one in hopes of getting a response. I am restoring a 1978 gs750. The engine was froze up and I had to remove the head and apply direct pressure to the pistons to get things moving. So I decided to rebuild the top end. I don't think the PO adjusted the valves, at least not enough. The bike has 33,000 miles, but 2 of the valves were so burnt they had to be replaced. I had a valve job done at a reputable shop. They replaced seals and ground the guides and seats. Now I recently heard (from a post about valve jobs) that I may need to have the valve stems trimmed. I would like to measure things before I put everything back together, mainly because of the gaskets. They put the valves back in the head. the engine is still tore apart. So I am wondering if I could put the tappets shims and cams back in the head, bolt down the cam housings or covers, then rotate the cams to the proper place, and check my valve clearances with just the head on my bench.

What do you think?
 
Yes, that is the way to do it. Just install one cam, shim it, remove it, install the other cam and repeat. Then recheck once installed and torqued down.
 
Yes.

Just be very careful not to put pressure on the valves that are sticking out.
 
Yes, you can do that. Make sure you elevate the head off the work bench while turning the cam. Best thing is to use only the small valve springs so the cam will be easier to turn.

How much you need to remove from the valve, if at all, depends on how badly damaged the valve and seat were. I worked on one head with oversize intake valves and all the valves were showing no clearance with 2.15 shims installed. I'd target getting the clearance right with shims no thinner than 2.50's so you have some wear room.
 
If you don't already have one, it helps to have a "checking" shim that is considerably thinner than what you expect to use. By installing a shim that is too thin, you will have extra clearance, which is a LOT easier to measure than "negative" clearance, or anything less than your thinnest feeler gauge.

This would also seem to be the perfect time to point you to the invite in my sig.
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There's also a "nub" on the underside of the buckets which is the point contacts the valve stem. Given a proper end mill that can be ground down a bit as well without removing the valves. Since your head is still off it's not a big deal to remove the valves and machine the stems though.
 
Thank you all for the help and information. You guys are great! This forum is awesome!
 
If you are revering to tipping" the valve stems to get them back into the middle of the shim range, the shop the did the work should have done that as part of the valve job.
 
Big Jay said:
If you are revering to tipping" the valve stems to get them back into the middle of the shim range, the shop the did the work should have done that as part of the valve job.
Click to expand...

The work was done over a year ago. I will ask the shop if that is their practice. I am going to shim my valves with the head on the bench anyway.
 
snyderman said:
I am going to shim my valves with the head on the bench anyway.
Click to expand...
I have never done a valve clearance check with the head on the bench, but I would probably recommend a double-check of clearances once you get the head back on the engine.

.
 
Steve said:
I have never done a valve clearance check with the head on the bench, but I would probably recommend a double-check of clearances once you get the head back on the engine.

.
Click to expand...
Probably a good idea. I really just want to make sure that my valve stems are not too long. I will start the bench top process around New Years. I will post on my project thread. But considering the pace I work at, it could be awhile before it's done. When I get the engine back together for a final check will be midsummer at the earliest. One good thing about my glacial pace is that I have plenty of time to research the tasks. I could have easily had my engine back together with valve stems that are too long if I had rushed.
 
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