Chris Lockhart

Ok, making decent progress assembling the heads. Definitely learning a lot. (Thanks Ake, and Rob!) The only issue I have at the moment is the shimming to get the correct spring installed height. With only 2 choices on factory shim thickness (1.0mm and 1.5mm) you're really limited as to achieving the correct in spec dimensions. It would be great if they also had a 0.5mm and 2mm shim thickness to chose from. Most I have been able to get in tolerance, but some are just over or under by a few thousandths. I also have one, (#4 aft intake) that was in spec without a shim at all. I'm looking at possibly getting some domestic V-8 valve spring shims in .015" that I can use to better adjust the installed heights. They're 1.250" OD, .625" ID, which is about the closest I can find to he factory shim dimensions of approximately 1.236" OD and .615" ID. I would think the domestic ones would be close enough to work. Any ideas, advice, or commiseration is appreciated.

Imo000

Leave the #4 without a shim. As for the rest, if you have to choose, stay on the looser side of the spec but a few thou of the spec will make no difference in performance.

GregBBRD

Porsche makes shims in both .5 and .25....

Not around PET, a computer, or my shop today, so I can't help you with part numbers right now.

Chris Lockhart

Thanks Greg. I'll look deeper. I've only found the two thicknesses so far.

Imo, thanks for the reply. If I can reasonably easily get the additional thinner shims, I definitely want to get the numbers as close as I can. If it's gonna be a huge deal, then I have no qualms about leaving them as is.

jcorenman

PET shows four shim thicknesses:
0.5mm = 944-105-465-02
1.0mm = 944-105-465-03
1.5mm = 944-105-465-04
2.0mm = 944-105-465-05

I didn't find a 0.25mm shim. My guess would be 944-105-465-01 but that is not a valid part#.

Chris Lockhart

Jim, thank you. I'm not sure what the heck I had looked at but I swear I had only pulled up the 1.0 and 1.5mm part numbers from somewhere. After reading your reply I went back to the PET to verify, and sure enough they are right there! Doh!! No clue how I missed them. Thank you (and Greg) for steering me back to the simple path.

Strosek Ultra

Chris, the correct installed spring height is for intake 35.5 to 36.0mm and for exhaust 34.5 to 35.0mm. The difference depends on 1mm more intake lift making the open spring pressure the same for both intake and exhaust. I use a caliper to measure the height from the top of the top retainer down to the base retainer which is slightly larger in diameter. The top retainer is 2.0mm thick so you have to take that into account. Some small modifications to the caliper might be necessary to perform in order to be able to get it down between the spring and the lifter bore.
Åke

dr bob

Chris--

Besides setting installed spring height, generally the spring shims keep the spring from wearing directly on the aluminum head. You'll want to have shims under every spring IIRC.

Unless the valves and seats are replaced and not ground well, headwork that includes facing the valves and the seats ALWAYS results in springs that need MORE shimming. Hard to fathom a valve spring that's stretched in service too. Scratches head...

Chris Lockhart

Thanks Ake. I had already completed checking/shimming the spring height on the right head but had a few that were just out of the tolerance. Now I'll buy some 0.5mm shims, which will allow me to get them all in spec.

Imo000

Yes he needs something under the spring but that's not the shim. It's a separate part.

Chris Lockhart

Just an FYI for anyone out there in Rennlist 928 land that may be quietly performing the same task: The 0.5mm Shim and 2.0mm Shim are apparently not a US item, and have to come from Germany. So, if you need some, you need to order them early and be prepared to wait. Local dealership gave me a lead time of 3-4 weeks, unless I wanted to pay double for air freight. Goodsons it is.

SeanR

Did you call Roger about pricing and how quick he can get them?

Chris Lockhart

Kind of. I called and left a voicemail about a different issue, and was going to speak to him about the shim when he returned my call, but he hasn't called me back yet.

Jerry Feather

What are they made out of? Why don't you just make some?

Chris Lockhart

He Jerry, I think they are hardened 1075 steel. Not 100% positive on that though. I just went ahead and ordered a pack of 50 from Goodsons. They are just a hair larger on the ID and smaller on the OD than the Porsche shims. Not enough to be an issue.