Opinion on valve replacement

[bbmcw]

I have a 79 GS550L. I just recently tore down the motor to replace leaking valve seals. Right before dissambly I measured cam to tappet clearances. Most were very tight(.0015). I am considering replacing valves while I have it apart. According to the speedo it only has 13,000 miles. Inspection of the valves currently in the head show no cracks that I can see. Since its already apart do you think it worth the cost of a new set? I know it will have to be reshimmed anyway. I plan on keeping this bike for a few years. This is my first tear down too. This site is awesome with all the info it contains. Already saved me many hours in STUPID mistakes.. Thanks to all.

 

[Guest]

With the low miles valve replacement is probably not needed. You increase the valve clearance with shims. Now an eight valve expert can step in.

 

[hampshirehog]

If your valves look ok they probably are ok. You should measure stem diameter - inlet service limit 6.90mm, exhaust SL 6.805mm and the valve stem / guide clearance - inlet .02-.05mm, exhaust .03-.06mm, though on 13k these should be fine. Probably just cleaning the carbon off and lapping the valves in again (that's what I'm doing tonight on my S - yawn) is all you'll need to do. When you put the valves back in the guides a smear of Molyslip is a must.

 

[catbed]

you shouldnt need a valve replacement as chef said, unless you have a bent valve, like mine. at 24 bucks a valve, that adds up to like 200 bucks, a lot of money, at least for me anyway.

you didnt have to take the head off to replace the seals.

 

[bbmcw]

I tried the compressed air in the cylinder trick but could not push the tappet down to release the spring. Is there a trick to that too? I'm just a rookie ya know LOL

 

[Guest]

You need a spring compressor. I'd just pull the head and clean it up and replace all the valve stem seals. It's not as hard as you think.

 

[DimitriT]

You don't need to replace valves unless the get burned.

I've seen tools for cars which allow you to compress the springs
without removing the head but I haven't seen anything for these
bikes. Maybe you can build a lever with a fitting attached to it.
Not sure how you'd get to those inner valves, though, and getting
those split cotters on and off with the head still in the bike will
be fun times.

I think you're better off pulling the head for this job.

 

[catbed]

I tried the compressed air in the cylinder trick but could not push the tappet down to release the spring. Is there a trick to that too? I'm just a rookie ya know LOL:smile:

what did you use to get the compressed air into the cylinder?

 

[bbmcw]

I have a compression test kit. I just removed the needle valve from the test hose. Screwed it into the cylinder and pluged the test hose into the compressor.

 

[hampshirehog]

You can replace the valve stem oil seals with the head in place if you can find a method of holding the valve in place. Compressed air - though it will slowly leak and you'll have to keep the pressure up; or you can thread in cord underneath the valve until you've got enough squeezed in to hold the valve up. You then have a devil of a job compressing the spring without marking the barrels where the valve buckets sit. I've never done it and I bet it's not easy + you could bend a valve. Whipping the head off is a pretty easy job on a GS - an evening's work - and you can give everything a good clean up while you're in there. And as long as you can count to 20 (rivets on the cam chain) setting the timing is straightforward.