ZZ4, aluminnum heads (but no paper work). Anybody have a torque spec for the headers (I had to drop one to do some front end work)?

Thanks

 

assuming you have the hooker side pipes, I have never seen a torque spec. Make it snug but dont put your whole arm into it and start from the center and work out to the ends.

 

Yes Hooker side pipes. Yes center to out. Tighten cold, then at running temp, recheck after a few running cycles. I'm guessing 25-35 ft-lbs. but I really hate to screw it up.

 

Since the thread is in the aluminum head, you should use the spec listed with the head. Or, you can look up the 'standard' spec for that bolt size in an aluminum part. But, you need to put some kind of positive lock on the bolts so they don't back out (loosen). Since aluminum expands more than steel (with increased temps), the bolts will loosen...unless you use French locks, lockwired bolt heads, or something similar. Lockwashers will NOT get that job done.

 

I have no paper work that has torque specs for the heads, and realizing they are the limiting factor, hence my post.

I will research "positive lock" (although there are none on there on there when I took it off). I hadn't thought about differential thermal expansion/bolt loosening, but I understand what you are getting at. That's in interesting thermodynamic proposal.
1000* steel headers bolted to a 180* water-cooled aluminmum head. It seems the temps would be similar at each individual thread, but hotter externally than internally. But what is the temp differece at each thread? I'm not quite sure what difference it makes whether the head expands more or the bolt does as far as tighenting/loosening goes. Any ME's out there?

Torque specs at this point are kind of useless to me at this point because, and despite the fact that I took the headers off myself, there is no possible way to get a socket, much less a torque wrench, in the the spaces I have to work with. Therefore I have them in by what feels to be about 30-35 ft-lbs. Looking back it was kind of a dumb post from me, but you raise a good questions.

There was a silvery compound on the threads when I took the headers off which I am figuring was an anti-sieze compound. (I reinstalled today with a 2000* copper-based anti-sieze compound). I'll check on positive locks for the bolts.

Thanks for the advice 7T1.

 

Several folks use [Allen head] cap screws which have been drilled for lockwire. You can use a swivel-drive Allen wrench to tighten/loosen them and tie them in place with lockwire.

The difference in expansion rate between Al and Fe causes some temperature 'cycling' of the bolt and promotes loss of torque during the cooling cylcles. It's even worse if you use anti-seize compound on the screws. Another alternative is to get some aircraft quality aluminum bolts for attaching the headers to the heads.

 

alot of times it is also recomended that when threading into aluminum, you do it in 2 or 3 steps. it was something both BMW and Triumph recomend to their factory techs.

 

Bucky,
When you say "steps," can I assume that you are saying tighten, let the gasket compress, retighten, run til hot and tighten, cool, tighten, repeat until there is no more tightening to do? That's my plan. Let me know if it's a bad one. Thanks

 

for example say a fasteners torque spec is 75ft pounds. tighten all to 25, tighten all to 50 then to 75. doing it in steps helps the part being fastened to "settle" better than being torqued all in one fell swoop.

 

Got it. That's what I've done so far, gone around 4 times center to out. Still on stands right now, but will check torque after heating/cooling cycles. I'm sure it'll be fine. I just don't want to screw it up.

 

Headers will "crawl" around and loosen regardless of using whatever the manufacturer recommends for torque. If you don't go back and re tighten them several times, the gaskets are going to leak. Even using the positive locks, after several heat/cool cycles, they're going to be loose. As 7T1 stated=the different expansion rates will get ya' everytime.

 

Good idea. But I don't have the hardware right not and I've got them on and feel good that I've got the bolts snug, but more importantly haven't stripped anything. I'll continue to recheck them. I've had a header header gasket blow before (installed by PO) and I'll know it when it happens.

Are aircraft aluminum allen head cap screws with lockwries even available? All good thoughts. Thanks

 

That's the premise I'm going with.