| Its been years since on here. Finally got the Z back out and on the road. Back in 2008 I have the motor built. Its always ran great but seemed to slowly loose coolant over time. Just figured had a small leak and coolant was evaporating. Over the last couple week it started to stumble under boost and then started fouling #1 plug. I checked all the normal things and found no issues except oil in #1 cylinder. I did a compression check and #1 was 175 when all other 145-150 range. Blew out the oil and it came down to the 150 range. Put 30 PSI air into cylinder #1 at TDC and bubbling like mad in the radiator. The dam HG is leaking! Started looking into this and seems to be the norm with these dam metal head gaskets on a Z. What a nightmare. In Buffalo nobody will touch working on this so I started tearing it down. 16 hours later the heads with attached turbo's and down pipes are hanging out of the engine bay. The Cometic gasket is missing material at the 12 o'clock position of the bores on all three cylinders 1/3/5. No coolant was mixing with the oil at all. Piston #1 was steamed cleaned. All others looked fine. When I broke the studs loose I first tried to get a good read on what the studs were torqued down to. Somewhere between 95-100 ft/lbs seemed about right. At first look the HG was obviously deteriorated. I also noticed that the front block/head dowel pin did not look right. It was all dinged up and looked smaller at the top. With the head gasket on it moves up and down over the dowel pins. Mostly the one in the front by cylinder#1 where the failure mainly occurred. In order for the gasket to fit uniformly around the 88mm bore it had to be pushed and held up. If it rested down then the gasket would actually be inside the compression chamber. I think this is what happened when the head was torqued down .
I read some articles about these ARP head bolts back then not having the proper washers causing clamping force issues and max. torque limit of less than 100 ft/lbs. Not sure if I should reuse these studs or not. Threads were not galled looking but they may have exceeded max. torque limits and therefore junk. Anyways I just want to get this right and not ever have to do this again. I have new block/head dowels coming. New OEM head gaskets. My understand is that Cosmetic is junk and no longer used. Stock is the way to go with proper studs, washers and ARP joy jelly. In my opinion head gasket alignment over the bore was the true cause of the failure. Both head and block surfaces looked smooth at least running a fingernail over them did not catch. I have no means of checking flatness other than a simple straight edge. My plan is to get new dowels in the block and see how snug the OEM gaskets fit. Then just clean up the surfaces with a scotch-bright pad and torque the heads back down in pattern starting at 30, then 70 then 90. Any input from you engine builders is welcome. I just want to get this right. Do you think I should buy new studs with bigger washers?
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15:30:15 06/09/23
