Jump to content

Re- torqueing cylinder head


Recommended Posts

Well it's goodbye from him and ...

 

Errr sorry second Ronnie ? but we haven't a name for you ?

 

Tom is correct about torqueing up the heads and to approach it in 3 stages to avoid warping the head or causing the gasket to "creep" across the surface of the block, however that's normally only possible when performing initial torqueing.

When retorquing the head you need to at first undo the fastenings by about 1 flat, that's to remove any "stiction" caused by the thread deformation when being torqued up and any surface induced torque caused by the clamping force between two opposing surfaces. That means you have very narrow parameters to complete the retorqueing process because the retorque will be completed within the angular change of about 1 flat of the fastening. Hence set your torque wrench and then apply the torque smoothly in one motion and the torque will be achieved very quickly and with only the smallest of movements.

 

I always drop enough coolant to reduce the level below the height of the engine deck before carrying it out, helps prevent any coolant creep between mating surfaces, and then after retorquing obviously retop the coolant up.

 

Mick Richards

Link to post
Share on other sites

Hello R Corbitt, welcome to the forum.

I have a different method from Mick, because I reckon the TR6 gasket sticks to both surfaces - its coated both sides with a heat-and-pressure sensitive 'varnish' that turns into a glue. The glue seals against water /gas creep. So initially I run the engine for an hour -at least - at tickover, up to full temperature and a bit more with carpet over rad. The heat both activates the 'varnish' and the head expands and compresses the gasket. Then I leave to cool overnight and retorque, in stages. Although Mick method of loosening the nuts is correct I dont loosen any nut for fear of breaking the glue seal. Then I drive it, and check the torques afterwards, cold.

I've never had a gasket let go. But am meticulous about cleaning every scrap of old gasket off the surfaces - I use WD40 as a reveal agent to show up the invisibly thin remnants of old gasket that go darker when wetted. Followed by thorough degreasing. To help that 'varnish' do its stuff.

Peter

Edited by Peter Cobbold
Link to post
Share on other sites

Hi All!

 

Nobody has mentioned the condition of the head studs/nuts. There is no point doing all this fancy torqueing up if the studs and nuts are 40+ years old, which will now be subject to stretching, as they are tighten up!

 

Bruce.

Link to post
Share on other sites

Peter mentions meticulous cleaning on the faces, to which I'd add, after removing the studs. Very hard to clean around a stud.

I use an old wood chisel, 1" across, too blunt for good woodwork, but sharp enough to get under the sliveriest old gasket fragment.

 

Old stud are old studs, and yes, if you will take them out, why not get a new set? They're not expensive.

But insert with a proper stud extractor, one with three offset rollers inside, not the brutal knurled-cam tool!

 

But will an old stud really get stretched in use, if never taken to its original yield point?

This article http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=392show me that strain-ageing of mild steel, as might be a head stud in use, will increase its yield strength. not weaken it.

Even if it does lengthen in the ageing.

But glad to be corrected!

 

John

Edited by john.r.davies
Link to post
Share on other sites

My studs are original 280k miles old, head refitted several times....reckon they're 'pre-stretched' :) ! Never had gasket let go. But they'll be changed soon. I have changed the hardened washers in the past - they soon go manky and 'warped'. Peter

Edited by Peter Cobbold
Link to post
Share on other sites

 

 

 

 

But will an old stud really get stretched in use, if never taken to its original yield point?

This article http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=392show me that strain-ageing of mild steel, as might be a head stud in use, will increase its yield strength. not weaken it.

Even if it does lengthen in the ageing.

 

Sounds about right to me - except they won't lengthen plastically ( vs. elastically ) unless they yield, and I don't think they're " mild " steel, but rather medium-high tensile stuff.

 

Cheers,

Tom

Edited by Tom Fremont
Link to post
Share on other sites

Hi John,

 

I have read your read your article, which I believe refers only to the building industry, but in their testing they do not mention vibration, this fact introduces metal fatigue which dramatically effects the life of any type of steel in tension. You would have a hard job convincing the likes of Rolls Royce that their fasteners do not need to be replaced after a certain number of flying hours.

 

Lastly when Beans Industries were in business in the 1960s to 1980's re-conning 100s of thousand of OEM automotive engines, why did the strip out all the fasteners and send them back to GKN for smelting down and remanufacture into new fasteners? If the Automotive Industry thought that they could save money here they certainly would re-use if possible.

 

Bruce.

Link to post
Share on other sites

Thank you, Bruce! Metallurgy is indeed an art and a science!

 

I dug that out because I didn't think that tightening head studs to less than their yield strength, and even heating them slightly compared to melting point, and allowing the parts they clamp to expand, would cause them to stretch beyond elastically. I am so ignorant that I didn't consider vibration, but that is more a fatigue matter, isn't it?

 

And Rolls Royce will have other considerations in an aero engine, in particular that failure jeopardises the mission - to keep the aircraft in the air! And a Triumph engine unless race modified is much less stressed than a high performance one.

 

John

Link to post
Share on other sites

Re-torqueing seems to be the way to go, thanks for all the advise. Re-used the studs and nuts with new washers as engine is low mileage. Engine is back together and running.

Good luck :rolleyes: It will leak if you do.

Link to post
Share on other sites

Nonsense, ntc!

Done that many times, for non-racing engines.

John

 

PS Good thought Roger!

12.29.10 is the section.

Line 15 Clean block and head faces (I paraphrase)

Line 16 Fit new gasket.

17 Fit head and tighten nuts in sequence.

 

That's it. J.

Edited by john.r.davies
Link to post
Share on other sites

Nonsense, ntc!

Done that many times, for non-racing engines.

John

 

PS Good thought Roger!

12.29.10 is the section.

Line 15 Clean block and head faces (I paraphrase)

Line 16 Fit new gasket.

17 Fit head and tighten nuts in sequence.

 

That's it. J.

Exactly and bullshit baffles brains.

Link to post
Share on other sites

I'm with Tom.

After my refurbishment I was waiting for 1000kms to retorque the head, when the gasket blew at several 100 K's

With the next one, I did a few 100K's, then retorqued it (tappets off to get to the head bolts).

It has been good as gold ever since. get in early.

Link to post
Share on other sites

" Would a garage get a customer back after 500 miles for a retorque? "

 

The garage I utilise would . . . . . they make it entirely clear to customers that without the torque check the work is not warranted, end of.

 

That ensures 19 of 20 customers do return on schedule to have the head checked . . . . .

 

Whether or not it is absolutely essential one could argue all day long, but the garage are not in the business of having failures - and prefer to cross the t's and dot the i's.

 

And, to be fair, it is very rarely that they do experience problems with their work - but like every garage, of course they have occasional come-backs, and deal with any such problems most efficiently.

 

Cheers

 

Alec

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.