Shim ? For Setting Valve Spring Height
#1
Drifting
Thread Starter
Shim ? For Setting Valve Spring Height
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.
Last edited by Chris Lockhart; 09-26-2016 at 12:23 PM. Reason: Spelling
#2
Captain Obvious
Super User
Super User
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.
#3
Former Vendor
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.
Not around PET, a computer, or my shop today, so I can't help you with part numbers right now.
#4
Drifting
Thread Starter
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.
#5
Rennlist Member
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#.
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#.
#6
Drifting
Thread Starter
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.
#7
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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
Åke
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#8
Chronic Tool Dropper
Lifetime Rennlist
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Lifetime Rennlist
Member
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...
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...
#9
Drifting
Thread Starter
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
Åke
#10
Captain Obvious
Super User
Super User
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...
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...
#11
Drifting
Thread Starter
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.
#12
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.
#13
Drifting
Thread Starter
#15
Drifting
Thread Starter
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.