Valve Shims

[Son_of_Dog]

So I've been working on a valve shim job with the help of the tool designed by Rocket Scientist and loaned to me by 1olbull . I've got all of my relevant shims measured and the measurements are as follows:


My question now is should I be shooting for 0.10mm clearance or 0.15mm clearance on intake? On the exhaust, should I be shooting for 0.15mm or 0.20mm clearance? My assumption at first blush is that I should be trying to get the clearance as small as possible on both intake and exhaust shims, but I'm not sure that is the case.

[EasTexOutlaw]

These bikes get tighter clearance as they wear so I would think go for the high side

[1olbull]

So I've been working on a valve shim job with the help of the tool designed by Rocket Scientist and loaned to me by 1olbull . I've got all of my relevant shims measured and the measurements are as follows:

My question now is should I be shooting for 0.10mm clearance or 0.15mm clearance on intake? On the exhaust, should I be shooting for 0.15mm or 0.20mm clearance? My assumption at first blush is that I should be trying to get the clearance as small as possible on both intake and exhaust shims, but I'm not sure that is the case.

Gage,
Nice work so far.
I am attaching some revelent files that may be informative and/or helpful.
WOW seven shims! After 60K miles I needed only 1 shim (intake 6).

Based upon your data, I would shoot for the mean at .17mm clearance on the exhaust.
Add the appropriate clearance difference to the shim thickness' then find the closest shim dim. you can.
e.g. your shim #1 (2.715) should be changed to 2.825 - #2 s/b 2.875 - #3 s/b 2.890 - #4 s/b 2.815 - #5 s/b 2.885 - #6 s/b 2.920.
I would ignore #12 intake as it is well within tolerance.
HTH,
Steve

[Mad Dog]

Lots of good information there, great form for with the go/no go, and you did the math for shims required too! Thanks Steve! So, my last conversation with him was about whether the tolerances got tighter or looser as the miles went by, any insight on that question?

[FE_rex]

Lots of good information there, great form for with the go/no go, and you did the math for shim reqired too! Thanks Steve! So, my last conversation with him was about whether the tolerances got tighter or looser as the miles went by, any insight on that question?

Valve seats wear - clearances get tighter. If left too long, valve will have zero clearance and will not seal.

[1olbull]

Lots of good information there, great form for with the go/no go, and you did the math for shims required too! Thanks Steve! So, my last conversation with him was about whether the tolerances got tighter or looser as the miles went by, any insight on that question?

Many claim the clearance decreases with wear. However, as seen in Gage's case, all exhaust clearances have increased.
Wear produces clattering valves, so I remain unconvinced either way. In past years, when adjustment was necessary on cars, I just measured and corrected clearances after they started getting noisy.

[Mad Dog]

Exactly, his clearances increased with wear, at least on the exhaust side, assuming they were within tolerances when installed. I saw the same thing when I did mine, the diagram is attached, clearances before I started are the numbers shown.
Hence the question. Could wear on the shims or cam lobes account for it? That doesn’t really follow because it’s notably different between exhaust and intake on both the bikes we’ve done. I’ve heard carbon build up on the exhaust side offered as an explanation and not sure I buy that either, those valves have got to seal, hard to imagine that happening with an appreciable amount of carbon build up on the surfaces. My unknown variable on both bikes is what the clearances were when installed.

[Rocket Scientist]

I had a Honda V-65 Magna that the previous owner had allowed the valves to go tight, and it definitely had carbon on the valve faces. I had to pull the heads, clean the valve faces, then re-lap the valves. Kept them adjusted after that and had no more problems.

[FE_rex]

My experience - motorcycles, drag cars (SBF, FE and BBF), diesel tractors, utility engines (mowers, trenchers, UTV, etc) air, oil and water cooled.

80-90% of the stuff I work on decreases lash as valve seat recesses. Increasing lash is caused by something in valve train wearing quicker than seat - which is fine as long as it is not failing. It's just increasing is not as common as decreasing lash in my experience. Good example of a systems that can increase lash are flat tappet cams, rockers with "sled" or "ball" fulcrums, poorly set rocker/valve/push-rod geometries, springs with too little or too much seat pressure, etc.

MOST cases - I would would bias my lash to the loose side. As a rule, I try not to leave the lash in the tightest 1/3 of the allowance (assuming lash is decreasing)

In some HIPO engines, I would run on the tight side of lash just to get more lift on the cam. I would also use lash to make minor changes in cam timing. These would be engines that would have valve checks nearly every weekend, with a full engine eval, freshen-up every 100 -150 passes.

Main Points -
Monitor and track your lash to see if it is an "decreaser" or "increaser" on a valve x valve basis (exhaust/intake cylinder number etc)
Get worried if an "decreaser" becomes an "increaser" or viceversa, get especially worried if lash drastically changes
Avoid to little lash on a mechanical valve train as you run the risk of the valve not fully sealing. Too little is typically MUCH worse than too much. Beware - too little is quieter than too much.

[EasTexOutlaw]

Exactly 👍

[Speedy]

Right on. New or freshened motors will increase lash clearance at first and then gradually decrease over time. At first cam lobes and bearings wear in, which increases lash clearance. Then over time valve faces and seats wear which decreases lash. Set lash on a used motor towards the looser side and tighter on a fresh build. Watch for quick changes.

[Mexican]

Is all Chinese to me

[Tripps]

It's all Spanish to me.

[Mad Dog]

Interesting, I would expect then that if lash is increased on a rocket motor the primary cause would be build up on the valve seats and would likely result in some loss of compression because of blow by...sounds like the beginning of burnt valves to me...hmm.

[1olbull]

Right on. New or freshened motors will increase lash clearance at first and then gradually decrease over time. At first cam lobes and bearings wear in, which increases lash clearance. Then over time valve faces and seats wear which decreases lash. Set lash on a used motor towards the looser side and tighter on a fresh build. Watch for quick changes.

Kewl, Blain!
We are all correct!