Cylinder head valve guide replacement?
 

Hello,
I’m looking to rebuild my cylinder head, are the valve guide replacement must be done by a specialist or is it possible to do it by myself?
Thanks
SmileWavy

Yes, it is possible to replace your own valve guides. I've done it, but not in a Porsche head. It takes familiarity with precision measuring tools, as well as a variety of unique tools that an automotive machinist typically has but the DYIer doesn't. Also, if you are replacing the valve guides, you are also going to want to grind the seats and the valves, and that takes other specialty equipment. In addition the sealing surface of the head often needs to have some light machining to remove a groove that has worn in. On my current 964 project, I trusted my heads to a well respected Porsche machine shop even though I've replaced guides and ground valve seats on a few different engines.

There was an excellent recent thread about replacing guides and grinding valve seats, but I couldn't locate it this morning. Perhaps someone can provide the link.

best valve jobs include the fly cutting of the valves and heads (triple angle cut). They always machine the heads flat again. It can likely be DIY but wont be as good as it can be.

Chris

This is a job that I would not want to practice or learn to do on my 911 heads. Way better to have someone who KNOWS AIRCOOLED cars take on the job.

If you have the FACTORY workshop manual the procedure is detailed.

As mentioned there is a specific procedure to R&R the old guides so you don't damage the head. Once the old guides are out you then must custom fit the new guides. Then they have to be reamed to size.

Then the valve seats have to be regound.

So, if you have a hydroclic press, drill press with angle plates, a lathe, the correct 9mm ream, an air hammer, the correct size drift punches, AND a valve seat machine, and you know how to use them, you are set to DIY your heads.

BTW, there are youtube videos showing the process.

It was easy to change them on my old 1600cm3 air-cooled VW but I for my Porsche engine I can find tools to do the job but I don't want to take some risks if I did a mistake the issue will not be as cheap than the beetle engine

With the newer aluminum bronze guides you have to hone them, not ream.
To get the guides in straight without an angle plate and press you need a ball or tapered plug that sits in the seat with a threaded rod going through the guide bore, through the new guide, a thrust washer and nut to drive it down. Use a wood jaw vice so you do not pull the heat off the head whilst installing the guide. Porsche guides do not have a shoulder or circlip stop so you need a precision spacer to get the installed height correct.

Not much different than a Beetle engine. I did my heads on both of the 911 motors I rebuilt. If you have the Factory workshop manual they have it well documented. If you have done it before and have the equipment at a shop where there is someone to help with the details you should be good to go. In my case I spent almost a week doing my heads and with the cost of the Neway set I probably didn't save much. But I am a diehard DIY guy.

FWIW, I actually used a unique, I think, method of removing the guides. I threaded the end of the old guides with a 10mm tap. I screwed a bolt into the guide. I then used my press by supporting the heads upside down on a deep socket the size of the valve spring. I put a long 1/4" socket extension down the guide and used that to press out the guide after heating the head. Worked perfectly and did not enlarge the guide's bore. I forgot to take pictures.

If you think that you're DIY enough to tackle the heads yourself (they really aren't that difficult to do, but use the manual and take your time).

You'll need to get a few things from Goodson like their valve guide driver (9mm).

You'll also need a 9mm reamer and a hone, along with some way to measure valve to guide clearance, usually snap gauges and a micrometer that reads down to 0.0001" or 0.001mm.

Heat the heads up in the oven, have your workbench and tools ready to go, with the new guides in your freezer (or dry ice if you have it available). Then, working quickly, remove one head from the oven (use thick leather gloves!) and quickly tap the guides out from the chamber side using the valve guide driver (us pros use an air hammer, but tapping with a hammer works too). Then quickly install the new frozen guides from the valve spring side using the same driver. If you use Canyon guides, they have a step on the guide to show you how far to drive them in. After that head is complete, go to the oven and tackle the other heads, one at a time until you're finished. Waiting for the heads to heat up in the oven will take longer than the actual work.

Some people drive the guides in and out without using the oven, but IIRC, the factory manual still says to use the oven method. Either method works, but if they were really rare heads, or ported with the guide bosses thinned to nothing, the oven method is safer.

Adding to that, some of the "standard" canyon guides I last recieved were a bit over sized. Didn't notice until the third head had a guide that would NOT go in. Had to machine the oversized ones to fit. Luckily, I had extras on hand.

BTW, I had always used an air hammer before this last job. A machinist friend said not to use an air hammer. True, if it slips or misses, your seat is toast.

Let me clarify the air hammer technique. Goodson sells the drivers specifically for air hammer use, so they have the proper shank to fit in the barrel. Also, use the weakest air hammer in your arsenal, so that you can carefully watch the guide get driven out. Now is not the time for your front end work, super heavy duty long barrel air hammer. It'll knock the guide out so fast that the barrel could hit the guide boss. Weak air hammer and a light touch. Knocking them out by hand doesn't guarantee success either, as you can have a glancing blow tap the head.

Good call on the size of the guides. Measure all of the new guides before hand, just to make sure they're not misboxed or something.

Thanks a lot for all these information.SmileWavySmileWavy
First I have to find the factory workshop manual to check the procedure in details. Actually in confinement for undetermined time I'll have to wait a little bit before to do a test on one cylinder head.

maybe some info in here for you also:

https://forums.pelicanparts.com/911-engine-rebuilding-forum/991556-diy-refurbishing-cylinder-heads.html

Hi thanks a lot for this very interesting link

SmileWavy