Valve Guide Renewal - Inserts vs. Full Guide

Porshaah · 08-12-2008, 10:54 AM

Fellow Pelicans

I was wondering if anyone had any negative opinions/experiences installing valve guide inserts vs. the complete valve guide?

TIA
Bill
90C2

cgarr · cgarr's Garage

Some of the old iron heads used this method, but since these guides can be knocked out very easy a sleeve would not be an option.

Porshaah · 08-12-2008, 02:23 PM

Craig
Thanks for your response.

Three machinists, two I consider experienced in Porsches and one having gone thru the Bruce Anderson course suggested the inserts first.
I've read there's a risk of damaging the aluminum head surrounding the guide while pressing it out and I thought if the insert is just as good, why risk the cost of having to purchase a new head? Would the method described in the shop manual using a spot facer to cut the protruding guide down from the camshaft side to the head surface and then pressing it out, be the prefered method to ensure success?

TIA
Bill
90C2

cgarr · cgarr's Garage

I leave the guide full length, tap the top of the guide with a 10x1.25mm tap and thread in a bolt then drill out the guide with a 3/8 bit to release some stress and drive it out with a punch against the bolt from the cylinder side. The key is to have the interference fit of the new guide correct so the casting does not crack. Out of a hundred or so heads done I have never had a problem. The only reason I can see you would have to face the guide top off is if your driving it out from the top and there is a shoulder on the guide.

Porshaah · 08-12-2008, 05:44 PM

Craig
Thanks again for your response.

To avoid cracking the casting I get the impression that there is more to it than just pressing in the new guide and assuming the valve guide hole in the head is the correct diameter. Is there possible machining on both the valve guide hole or the valve guide in order to get the correct fit? If that is the case what does one do if the valve guide diameter is too small or are there different diameter valve guides?

TIA
Bill
90C2

cgarr · cgarr's Garage

You can get first oversize which is for a standard size head (first replacement) or if the bore is larger you can get a 2nd oversize guide, I always measure the bore then machine the guide to fit the bore with the correct interference, usually .002 to .003 You really don't want to use a press, thats how these heads get broken, quick blow with a hammer knocks them right out.

Porshaah · 08-13-2008, 01:55 AM

Craig

Any heating of the head or cooling of the guide involved in putting them in or is the same method used in getting them out used to get them in - a quick blow of the hammer without any temperature difference?

TIA
Bill
90C2

cgarr · cgarr's Garage

No heat on the head but I do freeze the guides.

Porshaah · 08-13-2008, 03:54 PM

Craig

Excellent!

Thank you
Bill
90C2

Porshaah · 08-21-2008, 08:45 AM

Gentlemen

Is there any way I can rebuild the entire head without involving a machine shop? I believe I'm capable of determining if the valves and valve guides are worn and in turn replacing what is necessary usig Craig's method. But what about the valve seats - if they're worn I suspect I'll need to have them machined or can they also be renewed by a home DIYourselfer?

TIA
Bill
90C2

Eagledriver · 08-21-2008, 07:12 PM

When you replace the valve guides you must cut the seats again on the "new" center of the valve bore. This requires a machine such as a bridgeport milling machine and lots of skill. Most machine shops have a special machine set-up to cut the seats with the factory 3 angle cut in one step. Unless you have a milling machine you will not be able to do this. If you do, it will still be very time consuming. Unless you make minimum wage it will be more cost effective to have a machine shop do this.

-Andy

sww914 · 08:17 PM

A shop that I once worked at had a handheld seat grinder, it was kind of like a huge drill. It had a set of guides that wedged into the new valve guides and a set of stones to grind the seats at different angles. It worked great as long as the stones were well dressed. I remember it was loud as hell and cost over $1000.00. Cheaper to send them out unless you're doing heads every week.
They're all over ebay, search for valve seat cutter.

Porshaah · 08-22-2008, 01:24 AM

So I'm assumming a new valve seat is just a blank peice of metal with no angles cut into it? I don't see them listed by our host as an item one can purchase, so I'm guessing the machine shop either turns down hollow stock to the correct outside dimensions and they're press fitted into the head and angles cut in afterwards or there are standard valve seat blanks available that I'm not aware of? In any event it would make sense as mentioned by Andy above that after the seat is fitted onto the head, the angles are cut in relation to the valve guide - am I correct?

All responses welcome

Thanx again men
Bill
90C2

304065 · 06:11 AM

Bill,

Valve seats are not available "on the loose" from Porsche but are a fairly standard thing in the rebuild community (outside of just Porsche).

R&R seats is NOT the kind of operation that can be executed by the casual DIYer.

Here is a picture of beryllium copper seats made by Del West, these are required when you use Titanium valves to prevent galling. You can see what they look like, they have very precise dimensions and metallurgy (not just a hunk of pipe).

Here is perhaps a better photo from xtreme cylinder heads

xtremech · 09-10-2008, 04:57 AM

Quote:

Originally Posted by cgarr

I leave the guide full length, tap the top of the guide with a 10x1.25mm tap and thread in a bolt then drill out the guide with a 3/8 bit to release some stress and drive it out with a punch against the bolt from the cylinder side. The key is to have the interference fit of the new guide correct so the casting does not crack. Out of a hundred or so heads done I have never had a problem. The only reason I can see you would have to face the guide top off is if your driving it out from the top and there is a shoulder on the guide.

I also perform this operation very similar. We also go as far as to relieve the press from the the bottom of the new valve guide to insure that there will be no chance of cracking. Measure with a set of calipers from the spring pad to the shortest part of the valve guide boss and turn the press from that portion of the guide. It will give you a (pilot) also. Only turn .001 from the guide. Also, dry ice is readily available at your grocery store for cooling the guide. We use liquid nitrogen but dry ice is the next best thing....