How bad can a valve clearance be and still live?

[Guest]

I've just begun to clearance valves on a GS850 that's new to me.

#4 exhaust is puzzling me. It had a 2.80 shim in it, and I still don't have clearance in spec after going all the way down to 2.45. That's my smallest shim. Can it possibly be that bad and still live? It seemed to run on all 4, although I had some misfiring on the right side. I didn't run it either long or hard before I get it running right. What's the likelihood of the valve burning?

Is it possible I am just checking clearance wrong ? I followed cliff's guide.

A side note: The 2.80 shim I took out was NUMBERED 2.30. Clearly. Someone put a shim they thought was 2.30 and forgot about it?

What's the last resort if the shims needed drops below 2.30?

[adamchatum]

Did you happen to do a compression test before checking the clearance? If you had a 2.80, and then put in a 2.45, and still had no gap, likely that valve was never seating and you would have very little or no compression on that cylinder. Theirs a good chance your valve could be burnt from not dissipating heat to the valve seat.
I had to change an exhaust valve when I bought my GS because the previous owner never checked the valves. It was burnt and cracked. Only 10 psi on that cylinder.

[86turbodsl]

I didn't do a compression check. I bought this head off ebay, off a bike that was being parted out. With that 2.80 shim in there, marked as a 2.30, makes me wonder if nobody could get it running right so they just parted it. It runs and starts ok, if a little tough, and when running, it seems to run on all 4, but with a bit of misfire on the right header pipe. Not continuous, just every few seconds. It revs up ok when warmed up in the shop. I took it out very briefly on the road 2 x and once on a 5 mile trip, only driving about 50mph in 3rd gear. Stayed under 4000-ish rpm, and it ran ok, but not great. when I got to the stop, shut it off and it backfired. sat for 1/2 hour, and drove it home same way. No backfire that time. I've been trying to tune it and it didn't have much effect. Still starts and runs, but with a bit of misfire on right side. Tore into it tonight, and found most valves tight. Dropped down 1-2 sizes on most, and this one that won't loosen up. I'm waiting on a set of shims down to 2.30 from Z1 now.

I'll locate my compression tester tomorrow but I'll have to wait until the shims are sorted before I compression check it.

[Big T]

If you need a shim thinner than you can buy, Have the Shim club custom make you a couple of thinner ones

That's what I did

[86turbodsl]

Yeah, I'm a little worried that #4 won't clearance with 2.30. That's why I asked the question. Doesn't seem like the cylinder would run with that negative of a clearance, so I am confused. Could there be something I'm doing wrong measuring? Or a cam lobe with something stopping the gauge from entering? There is a funny looking pattern on the lobe. I'll try and take a picture of it tomorrow.

[Nessism]

Case study of why you always break down used heads, check everything out, change the valve stem seals, and adjust the valves before installing.

[86turbodsl]

The most expensive bike is the free one your buddy gives you. You have no idea how much I've spent to get this free bike back in shape... I'm tired of it.

[hampshirehog]

Have you checked that there isn't a bit of muck on top of the bucket that's stopping your shim from sitting properly?

[86turbodsl]

Just pulled the shim again and checked under it. I really think it had a 2.35 shim in it at one time, somebody checked and found it needed a 2.30, and put a mismarked 2.30 which was 2.80 and it never ran right, so it was parted. I'm hoping anyway.

A note to anyone reading this doing valves - MAKE SURE you follow the book procedure for cam positioning. The clearances TIGHTEN when you put the cam in the correct spot. I got bit by that one too. I was moving the cam for each lobe instead of checking each complete side in the correct spot. You have to measure in pairs per position.

[1948man]

What makes you sure that a shim labeled 230 is actually 280? Did you measure it with your calipers? If not, maybe the 245 you put in merely made it tighter than the 230 that was already in. If so, having a thinner shim made might be the answer. It would be great to get one really thin shim to use as a measuring shim before you order a 225 or 220.

Also, will the shim labeled 230 spin in the bucket? That would indicate there is at least some clearance with the 230 shim in there although probably lower than your thinnest feeler gauge.

[Nessism]

What number shims or on the other valves? Are they all thin like that one?

Most GS heads I've seen have shims much thicker than 2.30. Either that head has a LOT of miles on it, or someone cut the valve seats before.

[86turbodsl]

My shims vary between 2.40 and 2.65. I know they're kinda thin. It was the only head I could find on ebay at the time. The old 79 head when I got it in the box had 3 broken exhaust bolts with 3 broken off easy outs and a completely mangled attempt at removing them including a bunch of removed material around one or two of them.

I know the shim thicknesses as I am measuring them with a digital caliper. The 2.80 shim is VERY CLEARLY marked 2.30. It's not rubbed off. It's about the clearest of all the marked shims I have.

I'd like to find a really thin shim, but they seem to be pretty rare. I may try and make one at work on the surface grinder maybe.

[86turbodsl]

Well, update, the 2.30 shim I got in the mail today got the valve clearance on the #4 exhaust down to between 0.04 and 0.05mm. So my hypothesis was right, it was supposed to be a 2.30 and it got a 2.80 due to mismarking. Now to run it and see if the valve is burned.

Now all the valves are in spec, from 0.04 to 0.10 based on what I had on hand. I could probably change a couple for looser, but it'll work for now.

[1948man]

Good news!! Hope everything works well.

[86turbodsl]

Well, I got my answer tonight. A valve cannot be held open 0.5mm and survive, no matter how easy you run the engine. Put it all back together and ran it, started harder now with more clearance, and #4 is cold. No compression. Running on 3 cylinders. I guess the head is coming off this winter...

Any advice on repairing valves?