Set Valve Clearance at High End of Spec?

[DCKJR]

If a clearance on a particular valve is out of spec and requires a shim change to bring it into spec, does it make sense to pick a shim that sets the clearance at the high end of the spec rather than at the midpoint of the clearance spec?

I am assuming that, as the mechanical parts that affect valve clearance wear, the clearance gets smaller (correct?) so the upside with setting it at the high end means the valve clearances would stay in spec longer.

Is there a downside to setting the clearance at the high end of the spec?

Thanks in advance for the input.

Dudley
97 ST1100

 

[skyboybry]

The valve components can wear in two ways. If the valve clearance is tight, that means the seat has worn and reduces clearance. If the valve is loose, it means either the cam or bucket is worn and will increase clearance.

So if you find one that's loose, chances are you'll find it's loose if it ever needs be adjusted again. The same if it's tight. I doubt there's any advantage to doing as you said, as valve components can wear in both ways at the same time, there's too many variables such as fuel quality, oil viscosity breakdown, heat, etc.

From what I've read here, I think that the majority of owners have been finding ST valves are tight when they need adjusting, but I'm not sure of that. It's better to have a valve that's slightly loose than one that's too tight. Burnt valves are the result of that. Too loose though and you'll have accelerated wear on the cam & bucket.

sbB

 

[RaYzerman]

The valve components can wear in two ways. If the valve clearance is tight, that means the seat has worn and reduces clearance. If the valve is loose, it means either the cam or bucket is worn and will increase clearance.

So if you find one that's loose, chances are you'll find it's loose if it ever needs be adjusted again. The same if it's tight. I doubt there's any advantage to doing as you said, as valve components can wear in both ways at the same time, there's too many variables such as fuel quality, oil viscosity breakdown, heat, etc.

From what I've read here, I think that the majority of owners have been finding ST valves are tight when they need adjusting, but I'm not sure of that. It's better to have a valve that's slightly loose than one that's too tight. Burnt valves are the result of that. Too loose though and you'll have accelerated wear on the cam & bucket.

sbB

Agreed. Good explanation. I do cheat on the side of being looser than nominal and never tigher than nominal.

 

[gregj]

Ditto. When I would adjust the valves on my VTX, I would adjust them to the lower end of the spec, mostly to reduce valve train noise. I would have to do them again in about 8K, so I knew it would never be a problem. Given what one has to do to adjust the valve clearnce on the ST, I would opt for the looser side of the spec.

 

[Byron]

The cam and buckets are hardened and unless the engine has been subjected to a lack of lubrication there is no noticeable wear on these parts from what i have seen. The valves and head are a different story and this is were the vast majority of wear is found. When the valves or head wear the gap gets smaller between the cam and the bucket. By adjusting the valves on the loose side of the spec you buy yourself a little more time before the next adjustment.

The 16K mile service interval is there for a reason. My guess is that Honda believes that if a valve is at minimum spec at check "A" it will not be out of adjustment far enough to cause damage at check "B" the next service interval. In fact you will see where there doesn't seem to be any difference with some valves even after 16K miles.

Depending on the shims you are using you may not be able to set a valve at max spec. One size may put it in the middle and the next shim may put it over. There is nothing wrong with this it's just the way it works. Also, always double check the clearance after changing shims to verify the finished clearance. Even if the shim is marked one size nothing stops it from being under or over size.

My personal feelings are; middle at spec is good, loose and in spec is OK, tight and in spec is OK. However, if that side has to come apart because of an out of spec valve then the tight and in spec valves gets adjusted too. Otherwise it/they will do until the next check if you don't want to take things apart.

 

[hojo in sc]

I've always heard that if you make an adjustment, make them on the loose side. Of course, this was from a site that isn't an ST, but on a bike where the clearance needs more frequent checks, and more frequent adjustments.

 

[DCKJR]

Thanks all for the feedback.
I have one valve on 3 of 4 cams that is .001" below spec (ie tight). The rest of the valves on those 3 cams are at the tight end of their spec. So I'll change all of those shims on all valves under those cams to make the gap toward the loose end of the spec.
I'm finding that pulling cams is a pain and if there is no down side to going loose (but within spec) then I'll do that to reduce the frequency of having to do it.

Dudley

 

[STPaulK]

My 94 ST1100 had one exhaust near the edge of the tight spec for the 100k miles I owned it. I was always thinking about centering it but later on it became more of a curiosity to see if it would ever hit the spec limit, it never did. Since I sold it to a friend, I'll be able to keep an eye on it for longer.

 

[billo]

I find that simply re-torquing the camshaft sometimes brings a marginal valve in spec. This worked on that my FZ1 more than once. I had one stubborn tight valve that I brought to the dealer. The service invoice came back "all valves in spec." When I asked the mechanic about it he stated that if the feeler gauge feels right anywhere in the rotation of the camshaft that the clearance is ok. The reason being that, generally speaking, TDC is given because it is most likely the loosest spot on the cam but not necessarily. Anybody?