I isolated it by using the stethoscope and confirmed it by taking the lower valve cover off and going right to the valve. I can move the valve stem side to side probably a mm in each direction. The valve guide has less than 10k on it too. In addition, in my discussions about this issue with Neil Harvey at Performance Developments, he said he has had examples of this happening - loose guides making tapping noises.

When I have the motor out, I'll look around some more, but I feel pretty good this is the problem.

If the guide itself is loose, that would be different.
My SC had worn guides, and valve stems (200k+ km) - I replaced both. One guide was cracked and ready to drop into engine. But the engine still had no noises.
Weird it would fail like that - old valve stem in new guide?
Alan

Neil did my valve guides. Back when I sent him my parts, I shipped him a set of new valve guides that I acquired in a rebuild kit. He indicated that he preferred to use his own guides (which I agreed to), as loose guides can cause all sorts of problems including noise, and he wasn't familiar with the ones I provided.

A few things could have caused the valve guide to prematurely fail. Bad materials, faulty guide insertion technique, bent valve(slightly), piston/valve contact during cam timing, misalignment of valve guide to valve seat, or valve/guide oiling failure (spray bar clog).
I know Don used the best materials and builders in his engine after seeing his build posts. That engine is a work of art! :cool:

AGREED! Every time Don goes into that engine, it only gets better!

Now the question is, do I send all 6 heads back to the machine shop for inspection....

Yes. IMHO I would also send the cam towers for inspection of spray bars......just to be on the safe side.

Hmm. Well, if you were reluctant to strip the rest of it (understandably) then you could send just the faulty one, and ask for opinion of cause. Depending on result, you may not need to send rest.
Or, since you have had to strip one side of motor to get one head off, you could send the other two, and see if any issues arising - before stripping all 6.
I think that is what I would do. Bugger all extra work to take other two 'good' heads off, and see if they are as good as they should be.
Alan

Don,
You answered your own question my friend. If you can move the remaining valves as you did on the #3 exhaust, then you have to remove that head as well. I would think this is a fairly quick test. Walt at Competition Engineering told me that exhaust guides fail more often than intake guides, which makes sense.

He also told me that the material that Porsche used for guides in many engines was metallurgical junk. Perhaps you only got one of those in your rebuild. I don't think you can tell by visual inspection.

Good Luck,
Mark

Don any more progress?

I have a lot of experience dropping my motor, so by tomorrow noon, I should be able to confirm the problem. I can drop the motor, have it on a stand, and have it torn down to the cylinders in about 4 hours by myself. Kind of sad actually,....

Yes but that's what makes you ...you. Just to drop a name I use bill at Extreme Heads. He makes his own guides to tackle this very problem. He would be a good one to contact to get a better idea of the path you might want to take.

Don, you sound a little bummed. Understandable, I guess, but hang in there. There is a bright side, just think how hard it was when you tore your engine down for the first time. All those seized, corroded fasteners, all that frickin' grime everywhere.....
If I lived closer, I'd be there helpin' you.....purely for selfish reasons of course. I just want to see the beast! :D

Jerry - contact info?

I'll post some pics tomorrow, but not much to see really. Lots of carbon on the tops of the intake valves tho. Due to overlap?

http://www.xtremecylinderheads.com/

Xtreme Cylinder Heads Inc
3471 SW Palm City School # B
Palm City, FL 34990
(772) 286-1660

ask for Bill, he is a hell of a guy. He is a pic of his handy work.
http://forums.pelicanparts.com/uploa...1226197189.jpg

The casting wasn't ready when my heads were done but I was in the shop when he was on the prototype. This is the answer to any air cooled engine. So say a 910 or some early 2 liter heads are hard to find in good condition. No problem Bill has there castings made to where he can custom CNC any engine port configuration and any bolt spacing. Plus place the port at the location desired. basically there is no limitations. He had the heads beefed up where they need it so even on the big motors no more welding the fins to prevent cracking.

http://forums.pelicanparts.com/uploa...1226197663.jpg

The shop called to tell me the guides in both the intake and exhaust were severely worn, the exhaust guide being the worst. In addition, both valves are toast. The valve and guides have less than 5000 miles on them. During the last rebuild, I bought the valves and guides, new, from a reputable online Porsche parts reseller. Both were OEM replacements.

Looks like a valve job is in my future. But no silicon bronze guides.

Don,
Any new news?

Heads are at Xtreme Cylinder Heads in FL. They will be getting new manganese/bronze guides and stainless steel valves. They should be back in a couple of weeks.

My commiserations. To have a job like that go bad on you is the pits.
But I guess it could have been worse if you were not so alert - flogged out valve seats, overheating engine/valves, broken guides etc.
If I could give you a hand, I would.
I just had an engine builder friend suffer complete failure on his brand new race engine.
New crank grind. Showed up a line across one journal - but still dead smooth. Had it crack tested. Fine.
Assembled and installed engine. Still running in when it tore a bearing apart. The line turned out to be a defective crank casting, it opened up and tore the shell out of the bearing.
Sometimes life sucks. But I still find them more consistent than women.
Regards
Alan