Valve wear advice

[rputney01]

I pulled the head and checked the valves and springs against the specs in the manual. The springs and exhaust valves are well above the service limit. The intake valves are right at or just barely above the service limit. Should I replace all the valves, just the intake valves or none of the above? This bike won't get a lot of miles put on it, so I don't want to spend money I don't need to. On the other hand, I don't want to create problems down the road by saving a buck right now. If I'm going to bite the bullet and buy valves, should I go with the stock Suzuki valves or upgrade to APE stainless steel?

Your thoughts and opinions are invited. Thanks.

[Nessism]

What are you measuring? Valve stem diameter or ?

[rputney01]

What are you measuring? Valve stem diameter or ?

Yes. The valves are all slightly enlongated, but the diameters are barely above the service limit.

[Nessism]

Yes. The valves are all slightly enlongated, but the diameters are barely above the service limit.

I've never heard of valves elongating. That's a new one on me. Can't see a spec in the service manual either. Please explain.

With the valve stem diameter at the service limit, the valve to valve guide clearance will almost certainly be over the limit. To measure valve stem to guide clearance you need to do the "wobble test", the service manual shows how and the spec is .004" or less. Interestingly, there is some conflicting information regarding the valve stem to guide clearance service limit between the various Suzuki service manuals. For example, in the original GS850 manual the maximum clearance is listed as .004", just like the original 1000 manual, but in the later year manual supplements the spec allows .014" clearance, which is HUGE. My opinion is that this later spec is way too much, so I stick to the original number.

[rputney01]

[QUOTE=Nessism;1424398]I've never heard of valves elongating. That's a new one on me. Can't see a spec in the service manual either. Please explain.

Maybe stretching or lengthening would be more accurate. In short, the old ones are longer than the new ones, which makes sense I guess. That is why the shims are different thicknesses. I didn't see anything in the manual either. I just compared a new one to an old one.

Pics:

New



Old



Diameter - Service limit is 6.90



Finally, the buckets show wear as well. Does this mean they need replacing also?



I did the wobble test and there is some movement, but not a lot. I'll do more checking. Thanks for the advice Ed.

[rustybronco]

If I may interject my two cents into this.

the stem on that valve looks just fine. you said the valves appear to have very little wobble but you haven't measured it yet. I think you'll be just fine re-using them if the wobble measures okay.

you'll need to use a good Micrometer to measure the stems instead of those calipers you are measuring with. it's the calibration of the calipers I'd be concerned with, not the valve stem diameter. how much over discard did the new stem measure?

[Nessism]

Yea, as Dale says, you need a good micrometer to measure the valve stems, one that measures in .0001" increments. To measure the wobble you need a good dial indicator. It's a little tricky to get the indicator in the proper position so have fun with that.

So going back to the true service limit for valve stem to guide clearance, after noticing the later manual supplements allow such a wide clearance I checked some other service manuals and I can't find any others that allow as much. So based on what other manufactures allow, and the early manual numbers, I recommend sticking to .004" or .005". More might be okay, but I like my valves tight!