Re: [T3] ? Mystery of the Clacking Valves ?

[Jim Adney <jadney@vwtype3.org>]

On 11 May 2011 at 22:38, David Yaghoubian wrote:

> Hmmm. Since the adjuster locknuts and stands were tight the first 
> time I checked the clacking valves, and the condition then 
> essentially repeated itself within 20 miles, I guess that leaves the 
> pushrods collapsing, which we should be able to determine by 
> comparing the two sets.

 I've been trying to think of all the things that could cause the valve 
clearance to grow. Here's what I can come up with:

1) valve adjusters came loose

2) rocker stands came loose

3) cam surfaces have ground down

4) lifters faces have ground down

5) pushrods collapsed

6) tail end of valve wearing down

7) Rocker wearing on the rocker shaft

You've eliminated 1 & 2. 

3 would explain this happening on both sides, except that I don't think cams 
ever fail on the "flat" part of the profile, and it would be quite unusual for 
ALL four lobes to fail at the same time.

4 is common if the lifters are wrong. Did they replace the lifters? (with 
something that might not have been of OE quality)

5 I've never heard of, but I suppose it's possible. The steel ends are just 
pressed into the ends of the alum tube, so the ends of the tube could mushroom 
and let the ends sink in farther.

6 happens, but on all 8 valves at the same time???

7 could be explained by pushrods all the wrong length

Some of the problems above could be made worse if the pushrods are the wrong 
length for your engine. Oil normally gets pumped up the pushrods to lube the 
rocker arms. If the geometry is way off, the hole in the end of the pushrod 
won't align with the hole in the rocker socket. That could cause wear problems 
at the rocker end of things.

In the end, I'm puzzled by your description of how large the gap was. If this 
happened to most engines, I don't think you'd have enough adjustment to take it 
up 3 times.

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI USA

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