What are acceptable valve guide limits?

[andreic]

New question: how can I tell if my valve guides are too worn out and need replacing, or if I can use them as they are? I have read about a wobble test, and I also read all kinds of allowable tolerances, but I am not sure what to believe.

The story is that the heads I have for my rebuilding project (that I acquired a few weeks ago) have been worked on some time ago, but I have no idea if the work was done right. A local machine shop (who does not regularly work on VW or Porsches) looked at my heads and said very dismissively that they clearly need to be rebuilt. They told me that they found clearances of 0.003/0.007 on the exhaust/intake valves guides. They said that they did not look up in the book the allowable tolerances, but that these are way too much.

On the other hand on a forum for Porsche 928's (I know, not aircooled, but...) they listed an acceptable valve-to-guide tolerance of 0.5mm = 0.019in. That is much better than what my machine shop found. So I am totally confused as to whether I need new guides or not.

Thanks.

[Dave at Pelican Parts]

Which engine?

1.7 and 1.8--
ID intake valve guide wear limit: 0.3173"
ID exhaust valve guide wear limit: 0.3567"

Rocking limit for both valves in their guides: 0.0354" (measured with VW fixture VW 689/1)


The 2.0 limits--
ID intake valve guide wear limit: 0.3173"
ID exhaust valve guide wear limit: 0.3567"

Valve guide/valve stem clearance: 0.047"

--DD

[John Rogers]

Some things I would be concerned with are: first the shop does not regularly work on air cooled engines and more importantly they did not use any manual or spec book to see what clearances should be?! If it were up to me, I would find another shop with air cooled engine experience.

[andreic]

I am anyway moving my business to another shop with more experience in aircooled engines, but I wanted to get an opinion form the forum.

But in any case I went today back to the shop and asked some more questions. Here is what they told me they did: they pulled the valves out from their closed position about 1in, and used a dial gauge to measure the amount of "wobble" or lateral movement. Their measurements were (for the intake valves) 0.007" along the longer axis (transversal to the length of the head) and 0.003" along the perpendicular axis.

For the exhaust valves both measurements were 0.003".

These measurements seem to be well within the 0.0354" tolerance that DD wrote. Should I be worried by the fact that the valve guides are slightly oval?

Thanks.