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In 1969, I was building a new aluminum block ZL1 427 engine with new Chevrolet parts. I also ordered two sets of the special head bolts required for the aluminum block. The bolts are about 7/16" longer than bolts used for cast iron blocks. The image below shows the markings on the heads of the bolts that are different than bolts for cast iron blocks. I still have one set (not for sale) just in case I ever build a ZL1 for my 66.
Any idea why GM didn't use studs then like the new version of the ZL-1 does ?
Thanks,
Rex
I don't know Rex. It might have been easier than inventing a new part number and part for the longer bolts. I'm sure they had a reason though. Maybe ease of assembly?
This was my other set that I sold on ebay 19 years ago. I wound up cancelling the auction before it ended because a guy in Detroit contacted me and made an offer I couldn't refuse. He was restoring a ZL1 Camaro. The bidding was already over $700.00.
In 1969, I was building a new aluminum block ZL1 427 engine with new Chevrolet parts. I also ordered two sets of the special head bolts required for the aluminum block. The bolts are about 3/8" longer than bolts used for cast iron blocks. The image below shows the markings on the heads of the bolts that are different than bolts for cast iron blocks. I still have one set (not for sale) just in case I ever build a ZL1 for my 66.
don't try and use them in CI blocks as some of the short ones on the exhaust side will bottom out. been there done that using them with aluminum heads and the hardened washers
Another issue with head studs with SAE threads on top is that many builders don't know that you can NOT use the same torque specs when installing the heads. The SAE thread increases the actual load by somewhere around 30% over what it would normally be. In other words, if the original torque spec is 65 ft lbs, it should be reduced by the amount of the thread count per inch of standard threads divided by the number of of threads per inch of the SAE thread. I still have the formula for calculating the correct torque value. I also figured out that if you divide the number of threads/inch of the standard thread fastener by the number of threads/inch of the SAE end, you can multiply by the results.
Below is the formula.
Another issue with head studs with SAE threads on top is that many builders don't know that you can NOT use the same torque specs when installing the heads. The SAE thread increases the actual load by somewhere around 30% over what it would normally be. In other words, if the original torque spec is 65 ft lbs, it should be reduced by the amount of the thread count per inch of standard threads divided by the number of of threads per inch of the SAE thread. I still have the formula for calculating the correct torque value. I also figured out that if you divide the number of threads/inch of the standard thread fastener by the number of threads/inch of the SAE end, you can multiply by the results.
Below is the formula.
its above my pay grade for sure. I guess NOS ones don't come up for sale too often? how long where they in service. and are the current ones any where close to the originals
Last edited by Nowhere Man; 09-22-2018 at 04:21 PM.
its above my pay grade for sure. I guess NOS ones don't come up for sale too often? how long where they in service. and are the current ones any where close to the originals
I was referring to using the formula that I posted to find out how much less torque is required to achieve the same clamping force when switching to SAE thread instead of standard.
Later, I'll post a VERY easy formula to convert torque from standard to SAE.
I don't think many builders used GM bolts when ZL1's were being prepared back then. I think most everyone used studs. (and screwed up the block by over torquing because of fine thread studs)
I think REX mentioned that the newest design AL blocks use studs instead of bolts.
I vaguely remember that the ZL1 block was a little over $1,000 dealer cost in 1969.
Edit: I just looked up the 3952318 AL ZL1 427 block. It was $950. dealer cost in Jan of 1972. The bolts were cheap. Long and short, 46¢ & .41¢ each. I'm pretty sure the block DL cost dropped a little from 1969. Pretty sure it was $1,050. then.
Well Mike..................................I wanted to understand your formula a little better, but my Calculus and Trigonometry classes are too far in the rear view mirror and fading fast...........................just like me. I have one NOS ZL-1 block (new version) left and I am trying to decide if it is best used in my 67 L-88 tribute car to replace the "mild mannered" ZL-1 that is currently in it or use it in my 57 project. Either way, I will use the recommended ARP studs and the open chamber heads built by Valley Head Service.
Now you got me wondering if the torque specs for the 074 heads using the ARP studs would require recalculating using your formula.
Well Mike..................................I wanted to understand your formula a little better, but my Calculus and Trigonometry classes are too far in the rear view mirror and fading fast...........................just like me. I have one NOS ZL-1 block (new version) left and I am trying to decide if it is best used in my 67 L-88 tribute car to replace the "mild mannered" ZL-1 that is currently in it or use it in my 57 project. Either way, I will use the recommended ARP studs and the open chamber heads built by Valley Head Service.
Now you got me wondering if the torque specs for the 074 heads using the ARP studs would require recalculating using your formula.
Nice new blocks! I bet the price went up a bit since 1969. LOL.
Later, I'll post a very fast/easy formula to calculate the correct conversion when switching from standard to SAE thread. Anyone can do it in several seconds.
I heard that some suppliers of main and head studs now do supply the corrected torque values for SAE thread. Clem may know as he was still active in engine building at least to a few years ago.
Nice new blocks! I bet the price went up a bit since 1969. LOL.
Later, I'll post a very fast/easy formula to calculate the correct conversion when switching from standard to SAE thread. Anyone can do it in several seconds.
I heard that some suppliers of main and head studs now do supply the corrected torque values for SAE thread. Clem may know as he was still active in engine building at least to a few years ago.
I thought for sure Duke would do the math.
I retired from engine building close to 20 years ago. I was told when using a washer on aluminum heads do not lube the under side of the washer next to the head as this will act as a thrust bearing and you will over torque the fastener. If the washer is smooth rough one side up on some 80 grit paper so it will grip the head surface and not turn when torqueing. the torque specs are only if one surface is free to turn not both. I remember GM head bolt washers had grinding marks that roughed up the surface
Last edited by PAmotorman; 09-22-2018 at 09:16 PM.
I retired from engine building close to 20 years ago. I was told when using a washer on aluminum heads do not lube the under side of the washer next to the head as this will act as a thrust bearing and you will over torque the fastener. If the washer is smooth rough one side up on some 80 grit paper so it will grip the head surface and not turn when torqueing. the torque specs are only if one surface is free to turn not both. I remember GM head bolt washers had grinding marks that roughed up the surface
I always assumed that the GM head bolt washers were ground to insure flatness against the flat machined surface of the cyl head. I think they were stamped originally which would result in a somewhat rounded surface. The machining would correct that. I could be wrong though.
09-21-2018, 08:27 PM
ZL1 Head Bolts
I have one NOS ZL-1 block (new version) left and I am trying to decide if it is best used in my 67 L-88 tribute car to replace the "mild mannered" ZL-1 that is currently in it or use it in my 57 project. Either way, I will use the recommended ARP studs and the open chamber heads built by Valley Head Service.
