3.7 Mercruiser, re-torquing head

[Live-liner]

Hello,
I just replaced head gasket on my 1986 3.7 190. I torqued the head in three stages according to the manual.
I know you have to re-torque the head bolts after engine gets up to temp. My question is, should it be allowed to cool completely, or should it be done while still warm?
I ran on the muffs for about an hour yesterday at around 1100 rpms, everything seems good, just need torque it now.
Thanks

 

[sti1471]

Re: 3.7 Mercruiser, re-torquing head

it needs to be cooled back down after the engine was warmed up.

torque head bolts.
start the engine
reach normal temp for about 5 minutes
shut off engine.
let it cool
retorque.

When the engine warms up and cools that is the slack you are getting out of the bolt. if you tried when the engine was hot, you might snap a bolt. Or get it so tight, that when the engine cools down it might crack the head or block as it expands.

Someone correct me if I am wrong.

 

[stonyloam]

Re: 3.7 Mercruiser, re-torquing head

Yeah the manual is pretty ambiguous about that "cylinder head bolts must be retorqued after engine has been brought to normal operating temperature." Taken literally that says do it hot, but could easily be interpreted as bring it up to temperature once and let it cool. Anyway I did mine hot, each bolt tightened a little. Not saying the way I did it was correct, just that I have had no problem.

 

[Live-liner]

Re: 3.7 Mercruiser, re-torquing head

Thanks,
Well, I retorqued after it cooled. I hope that's correct. I had two bolts that just barely moved and all the rest never budged.

 

[achris]

Re: 3.7 Mercruiser, re-torquing head

The 'old-school' system was... Iron block/iron head, re-torque with the engine warm. Iron block/Ali head, re-torque after the engine has cooled. So, with an iron head/Ali block, I would expect re-torque after the engine cools.

To correctly re-torque, you should back the bolt out, then torque it to spec, in the correct sequence.

All the manuals for that engine just say 're-torque after initial start-up'. As you stated, it's ambiguous.

Chris.....
EDIT: Found some info on the re-torque procedure...

This procedure is from a genuine factory manual. Yes it's a car engine, but then so are boat engines... http://www.fordscorpio.co.uk/manual/engines/tdi/TDICHBolts.pdf

This is where I found that link. The poster explained the reason clearly and concisely. http://www.3geez.com/forum/1geez-mechanical/70225-how-retorque-head.html#post974064

 

[Live-liner]

Re: 3.7 Mercruiser, re-torquing head

Great, thanks for the info!

 

[stonyloam]

Re: 3.7 Mercruiser, re-torquing head

40C is 104F so it is still warm. Yeah I think I did back them off a bit and retightened, all kinda hazy now. Guess the important thing is to retorque.

 

[sti1471]

Re: 3.7 Mercruiser, re-torquing head

I guess you can do it when it is warm. However I would think that if you back them off a bit and retorque, then that might be bad on the gasket. I always thought if you tighten to spec ft. lbs. you should never back off as this might hurt the seal with the head gasket.

With that said, I learn something new every day.

 

[achris]

Re: 3.7 Mercruiser, re-torquing head

I guess you can do it when it is warm. However I would think that if you back them off a bit and retorque, then that might be bad on the gasket. I always thought if you tighten to spec ft. lbs. you should never back off as this might hurt the seal with the head gasket.

With that said, I learn something new every day.

You only back them off and re-torque them one at a time, not all of them then re-torque. There will be no effect on the gasket if it's done one at a time.