checking valve clearance...help?

Okay, is maximum clearance obtained when you rotate the cam lob 180 away from the shim?

At what looks like 180 degree I get a measurement. If I rotate the came 10 or15 more degrees I get a bigger measurement.

So is 180 the max spot or just the proper spot.

 

According to my Clymer manual, "In order to obtain a correct measurement, the lobe must be directly opposite the lifter surface".
I don't believe I have ever encountered a camshaft that would have a greater clearance anywhere other than directly opposite the lobe. You might want to put a micrometer to it and see how the dimensions stack up against factory specs. Don't want to suggest you could need a new camshaft but..............................

 

I think I need new eyeballs. both measurements indicate a need to drop one shim size. Have the correct size on another that needs to drop one also. So I'll only need to order one shim!

Thanks.

 

What model do you have?

I have the '82 Seca 750

Mine are spot-on what they are supposed to be at 180, and slightly larger at the sides too, but I'd say it's more like a 45 degree turn. I wouldn't worry about it.

 

It didn't matter did it? The book says 180 degrees; yes on SOME cams you can find an area with greater clearance but the difference is generally not enough to make a difference.

How many miles are on your bike? I would NOT re-use a shim; if you need two then get two. $7.50 vs. the cost to repair a trashed top end just ain't worth it. (IMHO.)

 

Fitz,

Every shim I have in there but the ones I change will be "reused". What's the difference if its "reused" in a different bucket. Some of them may have 40k+ on them and some of them are surely newer than that.(they may all be newer, but I can't say as this will be the first I had to change). I micro'd them all and they all still read dead on to what they report. Should I replace them all with new ones every time one needs replacing?

Perhaps I'm missing something here, but I don't get that one.

 

I am not really very experienced with these engines so don't put too much stock in what I say but I recently had to replace the head on my 750 as the oil pump stopped pumping (the sprocket just came loose one day). The new head was from a neglected parts engine at the local shop and after reseating the valves every shim was well out of spec. I then took the shims from the other head and mixed and matched until I only needed two new shims to get things back in spec.

However, a week or so after (maybe 45 minutes of riding during the week max) I swaped the shims I had the valve cover off to take a look at things and I noticed that most of the shims looked like they were wearing through the dull surface coating (I presume it is some kind of carbon hardening) to the nice shinny surface below. I also noticed a very ample supply of really small flakes of metal in the oil around the shims on the head.

Since then I continued to ride the bike and as far as I can tell from compression tests and the bike's performance the engine has only improved (though only a small amount). So I would say that it is definitly a bad idea to reuse the shims if the surface finish looks at all worn though if you do reuse the shims the engine can probably handle it (considering I swapped around every shim in the engine and mixed and matched with the shims from a different head).

I think the main point is not to avoid swapping the shims but to replace them as soon as they become worn. Though like I said I don't have very much experience with these engines or engines in general so don't put too much weight in what I say.

 

Any chance you put those in upside down?

 

I am actually 100% sure that I put them in correctly. I think that the issue just came from them being old and worn.

One other factor that probably contributed to the flakes of metal in the oil was the fact that after the previous head distroyed itself I didn't completly tear down the engine and clean every passage to remove the metal flakes that may have built up from the highly accelerated wear. I simply did an oil and filter change and left things at that.

I suspect that the shims actually have a semetrical hardening and that the only reason not to flip them over is to keep from rubbing off the printed size number.

 

There is no "finite life" published for shims as far as I know.

The factory service manual says to use NEW shims when replacing them.

That's what I do. Blind faith persuaded by the argument of $7.50 versus potentially hundreds of dollars.

I do know that each shim develops wear corresponding to its cam lobe. I know the shims rotate during operation and they DO wear, and on both sides.

I replace shims with new ones because the factory said to and I have NO compelling reason to do otherwise. The factory didn't say to use worn shims from other valves in the same engine if they measure ok, they said to use new ones.

For me, it's false economy to do otherwise. Not as bad as gluing delaminated brake shoes back on yourself, but close.

Others may have a different opinion.