PDA

View Full Version : GT6 Head Re-Torque - Mk1 GT6



dklawson
04-30-2012, 11:25 AM
I was finally able to restart our GT6's engine this weekend after its lengthy rebuild. Most guides I am familiar with typically call for a head to be retorqued after an initial running period.

I did not retorque the head yesterday mainly because I was feeling very lazy after getting the car assembled and started. Being a Mk1 GT6, the only way I can retorque the head is to remove the manifolds again to access the head's shorter studs.

Is retorquing really necessary? If so, should it be done hot or cold? An inquiring and lazy mind wants to know.

Thanks,
Doug L.

Simon TR4a
05-01-2012, 07:48 AM
I think the theory is that a composite head gasket (most head gaskets are two sheets of copper with a heat resistant layer of fibrous material, used to be asbestos, between them) will compress in initial use.
This changes the torque on the head and can cause the gasket to blow or can change valve clearances.

So, yes, the head should be retorqued unless a steel shim gasket is used.

Why this is not needed on modern cars I do not know...perhaps someone can explain?

TomMull
05-01-2012, 08:50 AM
So, yes, the head should be retorqued unless a steel shim gasket is used.

Why this is not needed on modern cars I do not know...perhaps someone can explain?

Here's some of it: TTY or stretch bolts (https://www.gomog.com/allmorgan/stretchbolts.html)
Note the third paragraph, "Forget what you've read about permanent torque head gaskets, as they don't really exists. Perhaps less torque LOSS gaskets would be a better term than permanent torque." That's my experience too, I re-torque them all, although my most modern car is a 2002.
Tom

dklawson
05-01-2012, 11:22 AM
Thanks for the comments.

I obviously was hoping to avoid having to pull the manifolds back off for re-torquing. However, as I mentioned in my engine rebuild thread I am dealing with some low vacuum readings that may indicate a significant vacuum leak. So... I guess taking the manifolds back off to torque the head isn't out of line anyway.

Any comments on torquing hot vs cold?

Thanks,

TomMull
05-01-2012, 01:42 PM
Cold. Tom

dklawson
05-01-2012, 07:34 PM
So far I have (1) hot, and (1) cold.

I am inclined to go for cold simply because I hate working on hot engines.

TR3driver
05-01-2012, 08:49 PM
No way to reach down under the manifolds without removing them? Maybe a crowfoot wrench?

I believe the main difference is gasket design; modern gaskets are not fully clad in copper and lose less of their tension through thermal cycles. They are also typically coated with something that fuses and effectively glues the engine together.

+1 on cold. Hot is OK too, but who wants to burn their fingers, especially when removing manifolds. The factory always did them cold.

dklawson
05-01-2012, 09:56 PM
I wish a crowsfoot could be used.

The Mk1 GT6 head is different than the later heads. There is a row of 7 short studs completely hidden under the manifolds. If that were not enough, Triumph put the nuts for those studs down into counterbored holes in the casting. That leaves no way to access them except to remove the manifolds and use a socket.

I'm actually using a NOS Payen gasket. It did not appear to have any special sealant on its surface like modern Payen composite gaskets. Regardless I am planning on re-torquing the head cold.

Thanks for your suggestion.

Simon TR4a
05-03-2012, 10:55 AM
Thanks for the link, Tom! Very interesting- I had always thought that if a bolt was stretched to the point of necking that it was weakened drastically and its behaviour in relation to stretching became non linear and unpredictable.
Shows (again!) how little I know about material science.