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View Full Version : Correct way to set exhaust studs in head?


smcguyer
05-15-2015, 07:41 PM
Hi folks,
I have never seen a description on how to install the exhaust studs into the cylinder head. This is for a rebuilt head application; the studs were previously removed without drama and the threads seem ok. I have not tapped the aluminum threads (special tap might be involved).

Are the studs run down the bore until they bottom out, and perhaps a 14 ft. lb torque applied before installing the nuts? Or no torquing? Or, are the studs NOT bottomed out at all; and they are supposed to self-tighten when the nuts are torqued down ? ( I have never used bronze nuts before).

I suppose blue Loctite could be used, and will probably char/burn off later from the temperature. Or maybe a tiny amount of red loctite.

Thanks for reply from engine rebuilders...

lindenengineering
05-15-2015, 10:52 PM
Old fashioned mechanicing this--Learned from my dad in his garage/ shop fixing Vauxhalls & Hillmans at 9 years of age! Big GM fan my dad!:thumbup:

Take two plain nuts --same as the stud---In this case 8x1.25mm
Place them on the outer section of the stud threaded shank and lock with two wrenches.

Put a blob of loctite on the engagement thread and run down the stud into the head using the TOP nut as the driver. Torque to 20 nm if you have a torque wrench or use maxim "tight is tight" and "too tight is overtight" as my late dad (Grandad Harry--refered to by my boy's) often used to state!

Best of luck
Dennis

icarus
05-16-2015, 12:53 AM
The olde double nut trick!

It is amazing how many basic mechanic skills/techniques/tricks seem to have escaped modern "technicians"! (no offense to the OP, just stating from experience).

Icarus

crazyswede
05-18-2015, 04:58 PM
A nice new tap will work fine if you want to chase the threads in the head before you put the studs in. There is no need for some sort of special tap.

CJPJ
05-18-2015, 05:34 PM
:2cents:... Use a bottom tap when the tap can bottom out.

Use a tapered tap where the tap won't bottom out.

smcguyer
05-18-2015, 11:35 PM
Well, I got around to setting the studs, and noticed the threaded holes are much deeper than the studs. So the shoulder of the stud "bottoms" into the top of the threads in the head. Methinks this results in high stress concentration on the uppermost threads of the head; pulling up the aluminum and destroying some thread material in this area... which was visable upon inspection with a spotlight looking into the holes. There was more thread destruction than I realized, as there was not much aluminum material present on the studs when I took them out.

Still, the thread destruction didnt look too bad, so I used blue loctite and 14 ft lbs torque, put a rotation index mark on the studs, and relied on sight and "feel" when the wrench approached the torque limit to try to detect ongoing thread destruction. Everything "felt" good, but I imagine the top threads have no choice but to get further chewed up again.