head damage during valve guide replacement
 

I received the heads back from the machine shop and noticed that one of the heads was damaged during the replacements of the valve guides. I called the machine shop and sent a picture of the damage (below) and he said not to worry, that this happens quiet frequently on 993 heads and that I should assembly as is.

I would appreciate your advice on this.

Thankshttp://forums.pelicanparts.com/uploa...1341276336.jpg

Where is the damage?

Yeah, not very clear on that pic. I think this one is much better. Let me know what you think.
Thanks

http://forums.pelicanparts.com/uploa...1341278441.jpg

Not acceptable.

So that piece is going to expand and contract a few times if you install it. Then a piece will break off and wreck the inside of that cylinder then the turbo is next!
I woulsd suggest you get buddy at the machine shop to replace the head then go somewhere else if he said what he said. Proves that there are few real engine builders left out there.

wow

that's not good. blending that crack out will not work. and that cracked piece might break off and you know where it will wind up. welding it up??? still have to remove the guide and re machine it.

It could happen frequently if you frequently remove the valve guides incorrectly.

It's not uncommon to get a small crack in that location, but that's not what I'd call small. I wouldn't use it.

Give us all a hint as to what machine shop it was. Or at least what state its in. I have started burning oil past my intake guides and seals after just a couple thousand miles. I wonder if it is the work of the same shop. I am told that this happens when they try to make american size guides work?

"Proves that there are few real engine builders left out there." Amen.

That is a scary photo. I doubt that would last 15 minutes of run time. It that machine shop familiar with Porsche at all?? It looks like they picked a guide that was too large and just hammered it in. Awful. :(

For the time being I am reserving the name of the machinist!!..but it has been a terrible experience

Could you give let me know what my options are here in terms of how to repair this?

Thanks

Id talk to Steve W or Henry @ Supertec.

Options in order of perfection/$/risk:
1-Replace Head
2-Weld/machine/replace guide
3-Remove the broken area as it is not serving any purpose now and could break off and enter the combustion chamber. The majority of the clamping force is above that area provided it hasn't cracked too and the guide was installed with the proper interference.

Well, I don't claim to be a Pro Porsche Engine builder but I would not use it. The shop should replace
it.

Steve

73 911 T MFI Coupe, Aubergine

Shocking, as that whole guide will soon be moving along with the valve. Don't lose hope, get it fixed properly though. I have seen people run these things and the whole thing moves around for a bit before it goes, and it goes quick.

I recently gave my heads to a local head builder who had a great reputation but admitted himself that he rarely worked on Porsche heads. After looking at them he came back to me and told me that the new guides he purchased from our local Porsche supplier were too large to fit correctly and would have damaged the heads. He said he could have the guides remade to the correct size. I gave him the job. Any engineer worth a pinch would know how to measure his work, what the tolerances were, and would not take things on face value.

I recently finished a rebuild. Upon tear down I thought I would save some money so I disasembled the heads and removed all the valve guides. When I took the heads in to the machine shop he said that I gauld the heads because of the way I removed them. Needless to say it cost me an extra $220. to machine the valve guide bores. Lesson learned.

A lot of people do not de-coke the valve guides before driving them out of the head for replacement.
If you do not remove the built up carbon deposit on the guide...when you drive the guide out (to the spring side) the hard carbon will damage the head (requiring over size guides).
Just a quick heads up.
Bob