Helicoil my Head?

[mplafleur]

Last night I installed the rockers on the head of my '89 190E 2.6. While tightening the bolts to the specified torque, one bolt gave that feeling that everyone has experienced, it was about to strip. This was as it was close to it's specified torque. Question, Should I tap and put a helicoil in for this bolt? Are all four needed or is three enough?

Another question: Should I put antiseize on these bolts? I didn't think about it when I put them in.

I would helicoil it, just to be safe.An engine has a lot of vibrations and forces.If 3 would be enough,why would they use 4 ?Anyway,it is little work now but if not done could end up in a load of work later.

Better to be safe then sorry.
Good luck

[mplafleur]

The block is, but the head is aluminium.

I guess I knew the answer before I asked it. It would be dumb not to helicoil the head while it is out of the engine.

Anti-sieze the bolts?

Michael,

I apologize that I did not warn you. when laying in the cam and rocker arms, you have to start all the bolts and tighten them down evenly all around. I would think that helicoiling would work fine. After the helicoil is in place lay everything in and tighten each just a little at a time all around. Keep moving around 'till you have pulled everything down.

I was warned about this before laying the cam and rockers on mine, and I forgot to pass this warning along.

Sorry,

[Kuan]

As far as I can remember, I don't recall putting antisieze on stud threads. This is based on aircooled engines. (Porsche and VW) OTOH, I don't see how antisieze could foul up the situation. Unless antisieze "migrates" you're pretty safe.

Kuan

[psfred]

After gettting a spark plug stuck in the head of my old Dodge Aries in Canada, I put anti-seize on any steel bolt screwed into aluminum. Saves much grief later, when the bolt head breaks off, etc.

Probably not really a necessity for the rocker arm bolts, since they are oil covered, but why risk it? Antiseize is cheap, and doesn't affect torque readings!

Peter

[mplafleur]

That's good enough for me. Anti-sieze it is. I guess I was asking if there was a reason NOT to use it.

Larry,

Don't blame yourself. I immediately saw that there are some rockers that are going to push down valves and that I would have to try to tighten them down evenly so they would go down straight and mate correctly with the surface. The particular bolt that stripped out was not one of these and was not pressing down a valve. It stripped on the last quarter turn to get it to the correct torque value.

[Benzmac]

I have seen this a number of times. When one fails, most of the time, more will follow. If so, just take out the cam and rockers and heli-coil them all. I have done this and when done, the threads are stronger than stock.

The problem is the iron or steel bolts and aluminum threads. Mercedes had the same problems with the blocks then went with all chromoly bolts to cure the problems.

[mplafleur]

I just may do that. That's 23 of them to do. I had the machine shop do one when they did the valve job. The threads came out with one of the bolts when I disassembled it.

When I took the "topic of our discussion" bolt out an hour ago, the threads came out with it also. At $17 a piece, (what the shop charged) I'll save a bit doing it myself.