tr4 TR4 Head re-Torque

[TRnorm]

Hi you helpful bunch!

I researched this on the forum and found I was still a little unsure as to whether to torque the head Hot, or to torque the head Cold - so forgive me if I raise the issue again. It was Mad Marx that got me wondering with this...

 

"I do it like this:

Installing everything, warming up the engine for about 10 minutes without driving the car.

Then torquing the head hot.
What know is that only aluminum head are torqued cold because of the heat expansion.

A full cast iron engine should be torqued hot."

 

So, my situation is...

Engine rebuilt and now coming up to the 500 mile mark.

• The head is iron (nothing fancy) - so do I re-torque Hot or Cold?
• Do I first back-off (half turn say) the nut being re-torqued and then torque up?
• I presume you wouldn't back them all off first (in one go) and then re-torque them(?)
• And I suppose, the WM value of 100-105 ft-lbs is (still) the figure?

And just to be sure, the WM says the tappet clearance is 10 thou cold - so presumably resetting at the 500 mile point is done cold.

 

And if I go for a supplementary question:

A little water seeps through the thread twix stud and nut on one of the studs, which I think might benefit from the application of a little loctite. Given that everything is (probably) cold and all the other studs are fully tightened, does anyone see any risk in fully slackening off this one nut to apply the loctite, and then re tighten it?

 

Thanks in no small measure to this forum my 4 is now looking good and going very nicely - and most importantly I'm starting to gain confidence in her. Thanks Guys.

Norman

 

 

 

 

 

 

 

 

 

[Chilliman]

Well Norman at the risk of going first and getting shot to pieces, I'll give you my view,

 

1) I re-torque when the engines hot (but I have no reference material to confirm any advantage - which I suspect to be minimal)

2) I don't, and I can't see why you would need to on a freshly built engine (it's the kind of action I associate with older connections that need to be 'broken' before the thread runs properly

3) No - I wouldn't

4) Depends on a number of things such as the gasket and head studs used - E.g. the gasket I'm using on my last built engine recommends a max of 105, the studs are ARP which I believe recommend 110. I opted for 105 and re-torqued after about 200 miles and was surprised at the amount of additional movement I got on the wrench - pretty much a further 90 degree of movement to re-set at 105 ft/lbs.

Can't help with your tappet clearances - mine are specific to the cam

As for your supplementary question - I have removed a single nut to enable work on some bits at the back of the head without any detrimental issues and I'd do it again without fear of warping/leaking/cracking etc - probably not the done thing in racing circles but it's a seriously solid block of metal.

 

..........let the floodgates open.......................!

 

[AlanT]

The torque value in the charts for a 1/2in UNC thread is not much more than 110 ft.lbs. Especially if the thread is lubricated.

 

This for for a top-grade HT bolt. This suggests to me that old threads in a cast block are somewhere near their limit.

 

So make sure your wrench is accurate and go easy if the threads are lubricated.

Realise that lubricating the thread raises the shear-force in the threads before the torque-value is generated.

 

We have had a few cases of block threads being pulled out and this is awkward to fix on the longer studs.

 

I'd suggest you google about torque values on UNF and UNC fasteners and then have a think.

[TRnorm]

Thanks John and Alan, that's all very insightful - really appreciate it.

I'll probably be doing it next weekend, so still time for a few more views.

Norman

[peter clarke]

I have replaced spring washers for the correct flat steel washers on each head stud in turn with no ill effects ......torqued to 105lbs. Water leaked at a couple of the washers under the nuts.

[BlueTR3A-5EKT]

I have replaced spring washers for the correct flat steel washers on each head stud in turn with no ill effects ......torqued to 105lbs. Water leaked at a couple of the washers under the nuts.

 

Hardened steel washers I hope. Regular ones chew up.

 

Peter W

[Graham Harris]

Do not back the nuts off, just set the torque wrench and go round in the correct order.

Personally i wouldn't bother, to do it properly you will have to take off the rocker gear and reset the tappets when you put it back together. I would just check one or two with it cold and if they are right ,just leave as is

Graham

[Motorsport Mickey]

Stop...you MUST back off the nuts a flat otherwise you are fooling yourself that the torque is ok.

 

The nuts develop a "stiction" ie the stud thread is deformed from it's initial setting which resists turning torque, and the surface area of the nut on the washer when not in "turning" mode also needs X number of lbs ft to break it. The torque to be correct needs to be achieved in a single smooth progressive turn which will overcome all these hindrances and then when the wrench clicks off or the needle on a beam torque wrench indicates 105 lb ft you stand a chance it is correct.

 

At about 500 miles (it's not ultra critical, I do it at 200 miles on race engines) these engines need pulling down, the gasket (especially any composite gasket) will have compressed and relaxed the head torque, you stand a chance of future head gasket failure if the head isn't retorqued.

 

I don't think the hours work of resetting any tappets can be compared with the considerable saving of labour helping to avoid head gasket problems.

 

As AlanT states unless studs are ARP or other make bolts which are sold and require lubrication (and likely lesser quoted torque requirement)do NOT lube the standard studs and nuts.

The reduction in the "stiction" of the thread (as mentioned above) by lubing, means that a higher clamping force is transferred through the threads and the stud, and it's entirely possible to strip a thread without achieving an indicated 105 lb ft, through the increased actual clamping force being transferred into a shear force through the thread. Remember there are 2 threads you are preserving, stud into block, and nut on thread.

 

Oh... and to confuse Chilliman the head "seriously solid block of metal" that it is, will flex at the front or the back of the block if the torque is released. In the centre of the block there are studs and clamping force either side ie outside it, at either end, after the end studs are released the next stud is inside only, allowing about 5" of cylinder head to flex upwards and releasing the torque on the extreme end of the engine. You will get away with it if releasing only one stud when cold and then retorquing, but if a Surform reading (stress reading) was shown of the head when torqued you'd see it flexes all over the place. As for the lovingly honed bores in the liners they also twist and move such as to make you wonder how the engine runs, but they do and very robustly too.

 

Mick Richards

Edited May 1, 2015 by Motorsport Mickey

[TRnorm]

Well, as expected some differing views - for which I thank everyone.

For me, I find it insightful, and comforting, to know what the "spread" of opinion and practice is - not just the clear cut advice that everyone agrees on. What's reasonable and what's not. I've now got a pretty good idea of what I'll be doing, and it'll certainly including calibrating the torque wrench before I start!

Thank you guys.

Norman

[2long]

I used an extra thick solid copper head gasket to compensate for head skims. I was told that the solid copper does not settle so no need to re torque. Does that sound right?

 

Dan

[Motorsport Mickey]

No.

 

Mick Richards

[Drewmotty]

My opinion based on non impirical intuitive engineering.........

 

I consider 105 ft lb a bit high for the standard studs so mine gets torqued to 90 - 95 ft lb in sequential 10 ft lb increments.

The threads get lubricated with thin 3 in One oil and wiped as dry as possible with a clean rag.

When re torquing I back them off just enough to get some movement when re torquing as the coefficient of static friction is greater than that of moving friction. Each one is backed and re torqued in the prescribed order before moving on to the next one.

 

..........I'm ducking below the parapet now so feel free to shoot away.

 

Andrew

[Motorsport Mickey]

Don't know why Andrew, you're entitled to your opinion as is everybody else.

 

Everything you said agreed with my comments with the exception of the final head torque figure, depending upon the tune of your engine and if your threads have been oil wiped (even if dried)the actual achieved torque is likely more than the 95 lb ft, especially if taken up in 10 lb ft increments. I use WD40 on the threads and wipe off, which cleans but has much less lubrication retention on the threads and helps maintain the original "dry thread" torque fitting.

 

Mick Richards

[AlanT]

I should think you come out about right.

 

Lubricating reduces the torque required by about 20-30% if you study the bolt charts.

Edited May 1, 2015 by AlanT