90PSI warm on all 4 cylinders, no valve clearance at all

[1980GS1000E]

A lot of guys here run the valves at .09-.10 to be on the safe side. A valve with clearance is a good thing.

[OMGCat!]

If your bike has no clearance then you are definitely on the right track to getting rid of your running issues by doing a valve adjustment. You're chasing your tail otherwise as no amount of tweaking fuel or air is going to mask compression loss due to valves in the process of burning themselves.
I always set my valves (cars or bikes) to the max clearance or even a touch above if I only have aftermarket shims that go in .05 increments. It might be a tiny bit noisier but you will be a lot better off in the long run.
With valves a little more clearance is MUCH better than less.

When I did the valve adjustment on my FZR600 nearly all intake valves were at no clearance. I started with decreasing shim thickness by the .20 (which is the spec) and went from there. I still had to go back and put thinner shims in several of the buckets. This means 6 of my 8 intake valves were OPENED by around .1mm while the bike was running. This is BAD. The bike needs compression to run and squeezing super hot gas through a small opening is kinda how a cutting torch works.

Hopefully you won't have such severe lack of clearance though. The FZR is known for having valves with the harness of dry play doh and I know I may get one more adjustment before it's time for a valve job.

Suzuki built there bikes a bit tougher, the GS bikes especially.

On my GS700 with the clearance set to max spec I almost doubled my last clearance setting interval (around 14k miles) and when I checked them only three were a touch below min spec.
I usually only set them at 10k instead of the recommended 7 just because I've become aware of the wear patterns in this bike over the years.

[Nessism]

This is what the valves look like when you don't adjust them. Hopefully your engine isn't damaged like this one was...

[lemonshindig]

This is what the valves look like when you don't adjust them. Hopefully your engine isn't damaged like this one was...

I hope not. But it's possible, I put 800 miles on this bike a few weeks ago, before I had ever touched the valves.

-Matt

[Steve]

Is that normal? Being off by a single size can result in low compression and poor running?

Think about it for just a moment.

The minimum clearance is 0.03mm.

The interval in shim sizes is 0.05mm.

You could have a valve being held open by 0.02mm, change it one shim size and it would now be at the minimum clearance.

.

[lemonshindig]

Well, there's one valve in which I measured .003-.004" clearance with a 2.65mm shim, formerly had a 2.75 installed with less than 0.001". I installed a 2.70mm shim, and now I'm still less than .001" clearance. I had 5 other valves measure the exact same way, and all of them are showing 0.003" with the new 2.70mm shim, so either that one new shim is really closer to 2.75, or it isn't fully seated. I don't have a mic handy, but I'll run it for a bit then check the clearance again. I might swap that 2.70 for a different one and see what happens.

Still waiting on one last shim, can't run it until i get that and bolt it all back up, but i did a cold compression check on cylinder #1, came up with 140psi. Hot damn!

[Steve]

If you installed a 2.70 in place of a 2.75 and still don't have enough clearance, try a 2.65.

Hopefully it does not need anything smaller than that, but only because that would mean possible problems due to burning valves.

.

[lemonshindig]

Well, got all the valves adjusted (Thanks GS Shim Club!), it was looking promising, .002"-.004" on all 8 valves. Also reset the points, one was at 5 thousandths instead of 14.

Went for a ride, WOOOOOOOOOAH. It was FAR more powerful than before. After heating up a bit, though, it started missing. Not as bad as it had before, but it was missing. I could possible chalk this up to carbs needing adjustment and sync.

But I pulled up back home and ran a compression check, 85-90 psi on all four. One of my compression testers would run up to 90 and then start draining back down, the other read 85-90 and stayed there until i let the pressure out of the line. I tend to believe the second one, I think my first tester has a leak.

Anyhow, I still have bad compression. About the only thing I can think of is to check the valves again. Maybe the valves and seats were covered in carbon deposit, and a quick run cleared it out and now my valves are all tight again? Far-fetched, but it's all I've got before deciding my engine is toast.

[tkent02]

Anyhow, I still have bad compression. About the only thing I can think of is to check the valves again. Maybe the valves and seats were covered in carbon deposit, and a quick run cleared it out and now my valves are all tight again? Far-fetched, but it's all I've got before deciding my engine is toast.

Could be this, could be the rings are a bit stuck still.

Recheck the valve clearances and ride it a thousand miles or so before deciding anything is toast. After that check the compression again. You did open the throttle during the test, yes?

[lemonshindig]

Could be this, could be the rings are a bit stuck still.

Recheck the valve clearances and ride it a thousand miles or so before deciding anything is toast. After that check the compression again. You did open the throttle during the test, yes?

...no...

Hold for a second set of numbers...

[tkent02]

If you got 90 with the throttle closed, you have some serious compression.

[lemonshindig]

145-150 all the way across. I can settle for that.

Good indication that the 12k on the odometer is a real 12k?

[tkent02]

Congrats, you fixed it. Well, at 112,000 the compression could be exactly the same. My old 550 was that tight at 120,000 miles.

Look at other things, footpeg pivots, footpeg rubber, shifter rubber, paint rubbed off the frame from boot heels, pits on the leading edges of everything, chips in the paint under the frame, a uniform layer of black crap underneath the bike. Loose levers and things, just overall wear and tear. People can replace all these things, but they almost never do so if this stuff looks like a low miles bike it probably is.

[Nessism]

Engine should be warm before testing too.

[lemonshindig]

Engine should be warm before testing too.

Good 'n toasty both times.

Opening the throttle was the ticket.

Thanks guys! I'll get her synced and ride on.