Clearance Conundrum: The Curious Case of Absent Valve Clearance

[GRom4232]

Hello, good people! First of all, I'd like to thank you for providing all the knowledge a complete newbie would need in resuscitating and maintaining a motorcycle. All the forum questions, discussions, and guides have been invaluable to getting my newly acquired 1979 XS1100 actually running. Hurray! However...

Here's a curious problem I ran into. I noticed that the bike suffers from compression issues--across all cylinders, I get a pressure reading of 105psi. The consistency is great, but the general level of compression is not. So, today I checked my valve clearances, and noticed something strange: there weren't any clearances to check. All the lobes, when rotated away from the shim pads, still made contact. Is this another proof that the previous owner(owners?) was(were?) not very tech-savvy, and swapping shims would get my baby rolling, or does this indicate a more serious problem? Mind you, this is my first bike, and I'm learning as I go along. So, please, use small words

Also, not having the tool to keep the valves depressed, I did not take any shims out to look at their sizes. Would that help in determining the problem?

[skids]

Well, to start with, all of your shims need to be thinner to start with. You need some clearance to start with to decide how much more you need. Geez, I wonder why there is no valve contact with piston crowns!

[James England]

As valves wear, they do so into the valve seat in the cylinder head. This reduces the valve clearance because the valve stem end gets closer to the cam. This means that, usually, progressively thinner shims are needed in order to get the tolerances right. Worn valves get quieter on the XS1100. The XS11 engine is quite noisy from a valve gear point of view, so a quiet top end usually means that the valve clearances are too tight. So, as the miles go by and the valves move towards the cams, the shims needed get thinner and thinner.... that's why you often see loads of thicker shims on eBay.... nobody needs them.

From the sound of it, you need to get your valve clearances adjusted correctly asap.

[GRom4232]

Thanks for replies, gentlemen. I am now considering ordering up the tool, and at least getting a look at the shims. If I were to order replacements, would any 29mm shim of correct depth do? I've read somewhere on the forums that Kawasaki used the same shim formats--could I stick 'em in my beast, and make it behave?

[bikerphil]

Yes, any 29MM shim...

http://www.newmotorcycleparts.com/mo...lve_shims.html

[crazy steve]

I doubt if you have zero clearance, that would mean the valves are open and you wouldn't have any compression....

You're probably in the .001-.002" range (which will result in low readings) but finding a feeler gauge that small is tough. Usually .004" is the smallest you can find. Do check them, if you can't get a .004" gauge in there then you'll need to go three sizes thinner on the exhaust and two on the intakes... at least.

And you did check compression with the throttle held open or the carbs off, right? Failure to do either of these will give low readings too.

And as an alternative to using the valve tool, there's this....
http://www.xs11.com/forum/showthread.php?t=35434

[BA80]

You've got some work ahead of you. You might swap what you have around a bit and get as many as you can in spec with what you have before you start buying shims.

[GRom4232]

Carbs? You must mean spark plugs, yes? They were all removed during the test. As for the throttle, I can not say. As I said, this is my first motorcycle; I do not have the tools necessary to diagnose it. Thus, the compression test was run by my friend--I do not know if he held the throttle fully open when turning it over. I understand that open throttle can give much higher compression readings, and I plan to re-test. I do not have a kick-start arm, so I will use the electric start. But now that we know the shims to be too thick for the old valves, should I address that before re-checking compression?

[crazy steve]

If the carbs were on the motor and the throttle wasn't held open while checking, you'll get low readings. And yes, you want the plugs out too..

Do check your valve clearances with feeler gauges, you won't be able to 'eyeball' that. Correct specs (cold) will be .008-.010" on the exhaust, .006-.008" on the intakes. The 105 number would be pretty typical with a closed throttle...

[GRom4232]

I do have a metric feeler gauge set I used to check my clearances. Picked it up at the local AutoZone for around $8. The smallest blade is .04mm. No eye-balling there

Oh, so the carbs should come off? The factory-specified compression range is what I'm shooting for. I assume, this range is established with carburettors on, yes? So what are the compression readings I should be looking for under ideal conditions (plugs out, valves set, carburettors off, full throttle)?

And thanks again for helping me out

[natemoen]

Don't get Hung up on compression readings! You have even.compression across the cylinders, that is all you need to know. Whatever you end up with after reshimming will end up coming up even higher after you run the bike and the rings loosen up and repeat in.

Do reshim, don't worry with the compression test.

[DGXSER]

Oh, so the carbs should come off? The factory-specified compression range is what I'm shooting for. I assume, this range is established with carburettors on, yes? So what are the compression readings I should be looking for under ideal conditions (plugs out, valves set, carburettors off, full throttle)?

The carbs do not need to come off, you just need as little restriction as you can to air getting into the cylinders, so simply holding the throttle at wide open is the normal way a compression check is performed. Factory compression is 142 PSI +/- 10%. The key being the +/- 10% across the cylinders, meaning all the numbers are within +/- 10% of the avg number.

I would definitely re-shim the valves before you bother rechecking your compression.

Honestly, my bike has about 100 PSI compression with full throttle and all the valves properly shimmed. I plan to do a leak down on it in the next few weeks to see where the problem is so I can plan a winter rebuild or repair. But it runs pretty well as is and I do not notice any large lack of power from the beast.

[GRom4232]

Hello again. I successfully re-shimmed the valves using the no-tool method. (On reassembly, dropped a nut into the oil pan, and while removing it, discovered that the mufflers were only superficially slipped over the pipes, and the left one considerably cracked--that's another story). Now, the compression readings I get, with the bike cold, are 170-175-165-175. I suspect carbon build-up. Am I right to think so?

[BA80]

"What are you rebelling against?"

What have you got.

[crazy steve]

...Now, the compression readings I get, with the bike cold, are 170-175-165-175. I suspect carbon build-up. Am I right to think so?

Not neccesarily. The factory numbers are low IMO (probably to prevent too many warranty complaints), and I've seen numbers in that range or higher on more than a few motors. These ran fine (on regular grade fuel no less), so I wouldn't be concerned. Several have reported numbers higher than those after a ring replacement and thoroughly cleaning all carbon out, so you should be good to go.

You're within 10% between cylinders, it's good...

I'll also note that the numbers may go up more after running the bike some; when the valves get really tight, they tend to get slight carbon build-up on the valve/seat faces and that will go away after running the bike a bit.