Valve shimming question

[Nook]

Howdy there,

I've done about my 20th valve gap checking and testing on someone's SHO, and I am always surprised to see how many of these gaps are still within the allowed specs. The average mileage I would say is about 110K for them, as low at 55K but as hign as 170K. Of the 20+ cars I have checked, I have only found 3-4 valves that were out of spec, needing reshimming. Two of these were on one car, and the cam lobes were hosed too.

Am I just getting lucky, or are you shimmers also finding the gaps staying well within specs,

N

 

[Nook]

That 3-4 number doesnt't count people that wanted their shimming set to the slim end for all valves on purpose, to get the most lift from the cam.

N

 

[twr]

Although not required, it is generally recommended to bring the gap to the minimum clearance. My shims were still with in spec, albeit past the nominal (recommend) gap.

 

[sdpatt]

You have just had a lucky sampling set. I just checked the Gapping Worksheets of the last 5 gapping jobs I have done (not including my car), and found the following number of gaps out of the limit on the high side: 2, 6, 9, 9 and 11. One of those gaps was as large as .432mm on a specified range of .25mm-.35mm for an exhaust valve gap.

Many of the gaps are within the allowed range, but the shims should also be inspected for unusual wear. The type of wear that will damage cam lobes if not corrected with a new shim surface.

On the gapping I did on my car last Saturday, only one gap was at the high limit (.356mm on an exhaust valve gap), but there were two shims that showed unusual corrosion (non-wear related) patterns in the contact area. One of these resulted in visible cam lobe abrasions. If I had not replaced those two damaged shims, the cam lobes would have paid a high price.

 

[Bizzy]

I thought the shims were the wear item and should be flipped over or replace with new when doing the valve lash? Is this not the case? Cause I'm thinking aobut my 70k mile ones right now.

 

[Yamaha V6]

I've had very few be mostly in spec, mileage from ~70k - 160k typically.

Most shims show normal wear patterns, some have looked downright mean. Only a couple of cams that exhibited any noticeable wear / marks.

I've had some of my customers' be way out (like .019-.020" on an exhaust, and .017" on an intake, IIRC). Can you say, "I want new valve springs?"

 

[SHO Boom]

I have only seen a few engines with more than 2 or 3 ourt of spec. All of mine wer ein spec, as well as Centaurs3200, but FOR SHO had many out of spec, two were so bad that even a 2700 didn't bring it back into spec, many other equired a 2600+ shim to correct.