cccscotland

Hi guys,

In the middle of a protracted engine rebuild due to snapped timing chain, and I've decided to replace the valve guides because after 80k miles they are a bit oval.

Porsche UK refuse to sell them for some reason, telling me they will only sell them as part of a completed head (over $10k for both), so I'm looking for alternative sources of valve guides.

The ones on Pelican Parts are oversized both in terms of the internal and external diameter, and so need considerable machining to make them fit.

Before I go down that route does anyone know of an alternative source for guides that are ready to fit? I see a couple of place stock inlet valves from a supplier called Technovance, but I've no idea whether these are oversize too, or whether they make exhaust ones as well.

Any help gratefully received, as ever.
Matt

beentherebaby

You might see if any competent local automotive machine shops offer K-Line guide liners or similar.

johnsjmc

In UK I,d try "ninemeister.com"

nick49

You mean the guides are undersized on the ID and oversized on the OD don't you? All gudes are typically this way and have to be to work. When you remove the old guide, especially in an alloy head, broaching occurs to some degree. In other words the guide hole becomes slightly enlarged compared to the original. If the guide was STD, it most likely would not have enough interference fit and would most likely move after installation causing damage. Larger OD on the guide allows for individual custom fitting. I generally machine the OD to match the particular hole in the head. The head can be slightly reamed as necessary as well to re-establish a straight round hole also. The ID must be undersized as when the guide is installed, the ID tightens up and distorts, more so in the area in contact with the head. All guides should reamed to size and honed after installation to the proper running clearance, more usually on the exhaust guides and usually more on both for hot running competition motors.

Good luck

Macster

Are you sure they're oval? 80K miles is not many miles for valve guides that have had good oil.

If the guides are oval there are several alternatives to replacing them. Frankly I don't like to disturb OEM valve guides unless absolutely necessary as long as the guides are mechanically ok. A bit of wear is not bad.

Anyhow, the guide bores can be knurled with a special tool that forms a spiral in the guide much like a thread forming tap forms a thread form in a hole.

The guide is then precision reamed to resize the guide bore to the proper size for stock valves with stock valve stem diameters. A side benefit is this process provides more oil flow to the guide and the valve stem than a plain smooth valve guide bore.

Another possibility is to cut the guide bores slightly oversize and then source either stock valves with oversized stems or have the valves made up with oversized stem diameters. It may be possible to hard chrome the valve stems and then grind then to size. You'll need a good automotive machine shop that really knows it stuff though. This if supported by the aftermarket valve industry (and it may not be) is not something to leave to the local gas station.

Also, have you tried to source the stock valve guides from a member country of the EU? While UK OPC's may not sell the guides separately a German OPC even a large Porsche parts supply house might.

Lastly, maybe there's a reason beyond greed the valve guides are not offered separately. Maybe the proper fitting of the guides and the machining of them is something the Porsche engine factory is best equipped to do?

Sincerely,

Macster.

Kevin

The intake guides from Porsche have always been soft. And yes they are showing minor wear. Macster > Matt stuffed his valvetrain from a broken chain.

Matt I have replacement guides manufactured for my head rebuilding that I have had done. Usually the rebuilder will have to invest in manufacturing them. If you don't have any luck, you can FedEx the heads to me and I will rebuild them for you.

Macster

Yes, I noted the engine suffered a snapped cam chain. I touched upon this by putting in the caveat that maybe the guides don't need to be replaced as long as they're mechanically sound.

From your post it appears the guides are not available unless one has an arrangement to have them built.

But I can't help but wonder if some other engine's guides would work? Maybe with a bit of custom machining? Nothing fancy, just a shortening of too long guides or maybe turning the outer diameter down a bit to fit the Porsche valve guide holes in the heads or turning the ends to accept the proper Porsche valve guide seals (or maybe some after market seals?) and of course properly siizing the valve guide bores to fit the valve stems.

There are a lot of engines out there and alot of valve guides.

Sincerely,

Macster.

calandri

Hi guys,

I d like to bring up this post as I am thinking of upgrade my turbo. I have 100K miles in the clock and a standard 1 bar flash for many years around 470hp. Now thinking of k16 billets and up to 550-580hp at crank.

My mechanic said that it is better to open the engine and do the heads, etc because of the wear of the guides. However, I understood that the most important part is the fueling line: injectors, fpr, and pump.

can the guides lead to a blown engine?

please share your expert opinion.

thanks

32krazy!

i had a lifter fail and bent 2 valves damaging the guides. i used a race shop that set and remed the guides to fit and have had zero issues since. if they oval they can allow the valve to move around a bit but i doubt they will blow the engine and you should at least see the signs prior