Valve Guide Sizes

[chris_seven]

I have been looing at valve guide sizes and don't quite understand some of the parts that are available.

According to the `1978,79,80and 81 Spec Book the following sizes are shown:

Standard 13.06
1st Oversize 13.26
2nd Oversize 13.46

The guides on sale seem to be offered as follows:

1st Oversize 13.08
2nd Oversize 13.26

Has there been a change ? as the PET doesn't show sizes.

Also does anyone know the difference between the early guide 930.104.321.50 and the guide shown on the PET in 1989 which is 930.104.321.53

The are both available from Porsche with the '53' part Number being about 25% cheaper.

I was speaking with Serdi and they have the same part for all years.

Does anyone know the difference?

Thanks

[cgarr]

As I understand it, what is offered is First replacement, then first oversize then second oversize. Maybe they are confused between first replacement and first oversize?

In any case I always buy the larger guide, which is usually cheaper, then turn them down to fit with proper interference.

[chris_seven]

Sounds plausible - Thanks

[matt demaria]

The current theory is that when the 13.06 valve guide is removed the guide boss hole is bigger and a new 13.06 will not have the proper press fit. So the replacement is 13.08 (one thou bigger) made to compensate for the broaching of the hole.

[chris_seven]

We have found if you warm the head carefully and press out the old guide a standard size guide seems to work.

Serdi have suggested carefully machining out the old guides.

They tell me that in the UK they normally supply standard guides and that they only stock a small number of 1st Oversize and don't stock any 2nd Oversize.

I guess making them slightly bigger is a reasonable idea to be sure they will not fall out when the engine is hot.