I've got this same question posted on TDIclub (yeah, I know...). But I need to get some insight soon because I want to finish this job. So, any insight is appreciated.
So, I've got a 1998 Jetta TDI with an AHU motor. The head gasket was leaking compression into the cylinders. So, I pulled the head and had it reworked by a trustworthy shop (Kiwi Engineering in CT). He did a really nice job on the resurface (took off about .006), recut the valve seats to proper projection, and ground the valve tips to account for the resurface grind down.
So, I finally got to putting it back together. The head gasket was a Reinz 2 notch (good brand), and I had 10 new Febi TTY head bolts (German brand, but who knows where they're made these days).
I cleaned the head up, chased the threads in the head with a chaser (the threads were really clean), flushed out the holes with brake cleaner twice, and blew out the excess until dry.
Following the advise of Frank (head man who advertises here on TDI) and Jack at VWdieselparts, I lubed up the headbolts in order to get proper torque (the bolts were dry to begin with). I used some 10W/30 oil I had (synthetic, not sure if that matters), and I lubed them, and let all the excess oil drain off. So, the bolts just had a thin film on them for the install.
I set the head on the gasket with locating studs, installed the bolts, removed the centering studs, installed the last 2 bolts and began the torque process in sequence.
Stage I: 40 Nm no problems there
Stage II: 60 Nm, no problems there
Stage III: 90 degress turn in sequence, no problems there
Stage IV: another 90 degress rotation: When I torqued the #1 bolt in the sequence, it seemed a bit soft towards the end, but nothing major so I ignored it. But, when I got down to the #7 bolt in sequence, after I got thru about 80 degrees of rotation, I could feel the bolt start to yield slightly. It wasn't terrible, but it was notable.
Now, perhaps I'm being neurotic and this is normal. Perhaps not. I've just never experienced this on a head install before.
I just did a head on a 1984 Rabbit 1.6 D with the same head bolts and procedure (chase threads, blow out with brake cleaner, blow out with air), but in that case I used some 15w/40 Rotella dino-oil to lube the bolts. It was tough to torque, and none of the bolts started to yield. Granted, it had a fiber head gasket, so maybe it gives more than the metal HG used on the TDI.
The only time I've ever felt the TTY bolts yield on the head was when I tried to re-torque a fiber head gasket after it had already been completely torqued to proper specs.
So, is this normal? If it's not, the only things I can think of are:
1) The oil reduced the thread friction so much that I overtorqued the bolt.
2) The bolts are crap, and somehow Febi (a good german brand) is now producing the bolts in China or some crap. This would explain why only 1 (maybe 2) bolts seemed to yeild, while all others seemed fine.
I'm 99.9999999999999 % certain that the block is fine (i.e. not cracked in the threads) since the head was held on fine before, I cleaned the threads just until the chaser stopped (which was about 1/2 inch more than I guess I needed to go), and there was not enough oil on the bolts to cause hydrolock, since I let all the oil drain before I installed the bolts: there was only a miniscule amount that might have collected in the final 1/2 inch of the thread: not enough to crack the block. I can't see any external cracks on the block, and I didn't notice anything when I was cleaning the threads/deck.
At this point, I've just installed the head and none of the other components until I get a satisfactory answer on the matter. I'd rather just pull the head and put on a new gasket and bolts (only costs me $35), rather than have to pull all this crap apart again after putting it all back together.
Thoughts?
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