stripped threads on head bolt model 470 mercruiser

jonespj

Cadet
Joined
May 11, 2012
Messages
20
Hello Guys,

I have a 1984 3.7 mercruiser. I stripped the threads from block while torqueing the head (new gasket). So I drilled
and tapped a new heli coil into the block. I had asked a local machinest if I should install 2 sets of the coil into the threaded hole but he said it wasn't needed. I torqued the head down in 3 stages to 130 ft. lbs.(found the info on that on this web site).
The re-worked threads held and felt just like the rest. Started the engine and warmed it up to operating temp. A few days later I took the valve cover off to re-torque and that same bolt didn't hold. It's at 90
ft. lbs. and I can turn it just enough to tell its not getting tighter. Will this hold up for a season? If not how can it be
repaired again. Also is there a way to repair this without removing the head. The stripped bolt is on exaust side and the
first one toward front of engine. Thanks for your advice.

Paul
 

RogersJetboat454

Commander
Joined
Jul 9, 2010
Messages
2,964
Re: stripped threads on head bolt model 470 mercruiser

With out the proper, even clamping force, it's a crap shoot if the gasket will hold. You have an open deck engine, with a head of dissimilar metal working against you too (expansion rates are different).

As far as repairing it with out pulling the head, I just don't see it happening.
 

jonespj

Cadet
Joined
May 11, 2012
Messages
20
Re: stripped threads on head bolt model 470 mercruiser

How do I get the heli coil threads out and should I use 2 sets of heli coil threads this time?
 

RogersJetboat454

Commander
Joined
Jul 9, 2010
Messages
2,964
Re: stripped threads on head bolt model 470 mercruiser

How do I get the heli coil threads out and should I use 2 sets of heli coil threads this time?

Point 1;
If you can get to the tip of the coil, you may be able to pry it up with a pick or very small slotted screw driver. Once you do, grab a hold of the raised section with some needle-nose pliers (vice grip version would work best if you have room for them), and carefully pull the insert out.

Point 2;
If the heli-coil your using isn't long enough, get a longer heli-coil. They come in all different lengths.
 

jonespj

Cadet
Joined
May 11, 2012
Messages
20
Re: stripped threads on head bolt model 470 mercruiser

Thank you for the info!

Paul
 
Top