Yeah, I know I should always keep lifters etc matched, but hey, sometimes you just cannot:

I've got a B20 wich I put together with a used C-cam (has run aprox 5k miles in other engine), used lifters (have run aprox 10k miles on different cam en engine) and used pushrods (also yet other engine/lifters).

Started this engine up first time. I adjusted the valves while hot. Very silent valve train. Drove 10 miles. Loud nock. Valve clearance on cilinder 3, intake, about 1 mm. Not so good. Measured valve lift (wiped out lobe I fugured?) compared it with other cilinders. No measurable diference. Took out the pushrod to have a look at both ends/tips. All fine. Re-adjusted. Drove 20 miles. Same story. No dif in valve lift. Drove 50 miles. Same story. Again no dif in valve lift.

I'm stunned. What can possibly cause this? Is my lifter shortening somehow? Is my pushrod shrinking?

Thanks, ben
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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Loosen the adjuster and push the rocker to the side. Is there appreciable play at the shaft or (feel with finger or use mirror) nasty wear marks?

If not, go to local shop and get a brand new chevy lifter. Lube it well with assy-lube and do another cam break-in. The lifter must be going wonky, no other solution and the sooner it is pulled out the better the chance of saving the cam.
The ends of those things aren't all that thick. 2mm wear at the valves would be about 1.3mm at the lifter and there isn't a lot more metal to go!

Mike!

This is pure speculation, but could it be possible that, because the cam and lifters were worn in differently, after a bit of driving the guilty lifter just finds a position of least resistance on the cam and stops rotating where it sits lowest? That wouldn't explain why it doesn't stay in that position while you adjust it, but who knows, the world is full of mysteries.
Bob S.

Well, if it actually did stop rotating it would certainly increase wear in that lifter and cam lobe. So that could explain the extreme shortening of the lifter.

The lifters however are all free to rotate in their bores. Also, even if this guilty one stopped rotating, I find it hard to see how a lifter would wear down aprox. 2 mm in 30 miles. Seems virtualy impossible to me. But then again, like you said, the world is full of mysteries...

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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

The lifter may be going concave, which is what happens when the geometry of the lifter-cam fails. The 1mm lash is .040 inch, which is a lot. Monitor it, and check the protrusion of the adjustment stud from the rocker arm - its always a rough indicator of a failed lifter.
I have been re-profiling lifters for some time now. It takes a valve grinder and a metal lathe to do it, but it restores and improves the lifter profile to allow use on a new or used (in good shape) camshaft. Exchanging worn lifters to worn cams is fraught with peril, unless at least one or the other is returned to a correct profile.
When the bottom of a lifter breaks away, you'll know it....
Rhys

About restoring lifters: I had been thinking of doing that myself too. I decided not to cause I thought the bottom surface was hardened and I would only expose softer metal. Maybe I will afterall (since it looks I might have to pull the head again...)

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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Having rebuilt a B20 (via the good instructions of the VClassics site and frendly email advice of Phil) I agree with what Danny said.

Having rebuilt a few engines aswell, offcourse I agree with Danny too. Thats what I stated in the first line of my post. I know I'm being norty here. I don't realy need confirmation on that.

But: can a lifter (it's not the cam lobe, since lift is unchanged) wear at a dizzling rate of 1 mm / 10 miles of driving? There should be quite a bit of metal shavings in my oil by now then... Hmmmm.

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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Two old saws I learned when I started working on a construction site were:
Measure twice - cut once.
All you need to know to be a plumber is that s#!* flows downhill, and Friday is payday.

When I began working on cars, one maxim I recall being drummed into my head was:
You don't change the cam without changing the lifters. And vice versa.
If you're tearing down a motor and you think you might be using the same cam and lifters again, you must keep them in their same old relationship upon reassembly.
Or else...

The one I came up with after borrowing a LARGER breaker bar when attempting to loosen some large, frozen nut was: Torque is cheap.