Potential error with Toyota/Haynes manual cylinder head bolt torque settings.

[spudgun]

Hi All,
As some of you may know last year I had a head gasket go on my car, all done and replaced.
However out on a trip to Germany again this year I had a depressing case of de ja vu. Head gasket number two up the swanny.
I have since discovered that Toyota changed their method for tightening their head bolts and the end results are a world apart.

I have an early Toyota 4age engine manual and also an american haynes. These state that the head should be tightened in three passes, with a final torque setting of between 42-47 lb/ft. I have always felt this seemed to little for a cylinder head, but as it came from official sources took it as accurate.

Having recently trawled the net and found a download version of a later mk1 manual in pdf the way of doing it is totally different.
This method involves tightening all the head studs to 22lb/ft and then another 90 degrees and then another 90 degrees.

Armed with this info I went out and compared the two types on my head. The net result is that to get the head bolts turned another 180 degrees after 22lb/ft setting requires over 80 lb/ft to do so. It also ends up tightening the bolts over 1/3 of a turn extra.

I feel there must have been a reason why they changed it from one method to the other in the first place. The addition of an extra 35 lb/ft or more is bound to be benifical to keeping the head sealed.

I guess some of you will know this info already, but I didn't, and they may be others out there who are using, what I now feel is, is the wrong method for the job. I wonder how many engines have been consigned to the scrap bin because the head bolt just weren't tight enough.

I hope this may help others and to not give up immediately on what you already have.

Cheers

Steve

[scomr2]

The reason for two different methods is because of two different types of head bolt. Early style were obviously not 'stretch' type bolts where the later ones are - the correct method with the correct bolts should give similar preload values but the stretch type are usually more accurate.

[spudgun]

You might be right, but to me, 47lb/ft for head bolts seems very light.

I do also wonder, if the head bolts changed, when they changed so you know the cut off point for conventional bolts to the stretch type was.

It strikes me that it could be a bit of a mine field of that was the case which engine, which bolt sort of thing.

[jimi]

According to MR T there's only one type available. The part numbers in the EPC for cylinder head bolts are the same for all AW11 MK1's (84-89).
The AW10 has a different part number.
EDIT
My 1987 Toyota 4AGE engine manual shows the second method of tightening as well i.e. 22lbs/ft, +90deg, +90deg

[dex]

The change from 44 lb ft to 22 ft lb, 90 deg, 90 deg is probably just a change Toyota instigated following investigations of failure, you see this quite a bit with all manufacturers.

Do not be concerned that 44 lb ft is particularly low, the head bolts on my old Peugeot TU24 engine were 15 ft lb plus 240 deg!

[spudgun]

The change from 44 lb ft to 22 ft lb, 90 deg, 90 deg is probably just a change Toyota instigated following investigations of failure, you see this quite a bit with all manufacturers.

Do not be concerned that 44 lb ft is particularly low, the head bolts on my old Peugeot TU24 engine were 15 ft lb plus 240 deg!

The thing is though, 44lb/ft is the finshed torque. If you add another 240° on to 15lb/ft I bet the torque you have to apply to get there will be the other side of 80lb/ft, if you see what I mean.

I was finding the difference, in rotation, between the 44lb/ft and the 22 was not very much at all. Its not until you start stretching the bolts that you get a good rotation of the stud to torque applied to it.

[Icsunonove]

Very useful post Steve.

As you say it was changed and there must have been a reason.

Therefore I wouldn't use the 40-47 ft-lbs finished torque figureand use the latter method.

For reference ARP stud nuts recommended finished torque is 60ftlbs (81Nm).

[dex]

As Icsunonove has said, I would go with the 22 ft lb, 90 deg, 90 deg method.

I've already marked up my Haynes manual to show this

[spudgun]

Without a doubt Dex I am going to use the 22+90+90 method on my head gasket replacement and see what happens. It has got to be worth a go and I haven't got much to lose.

Cheers for your input Tom, I had a word with Paul Woods as well and he seemed to feel something wasn't quite right either.

Like Jimi mentioned, they only list one type off stud now, so if they did change them, you can't get the older type anyway, making to old method null and void.
The threads in the block must be constant (M10x1.25 if anyones interested) as one stud wouldn't do all other wise and I can't imagine a head change would have an effect.

Dex, your haynes said 44lb/ft as well did it? I know it should but I beginning to wonder if I'm not been played on in some great big MR2 conspiracy

I guess at the end of the day you can use what you like but at least this post has made a few aware and in that respect it is doing its job.

[scomr2]

ok if the bolts stayed the same maybe the gasket design changed.

Applying a bit of maffs, 47lbft of torque gives about 36kN of tensile load in the stud. 22lbft + 180degrees is a bit more tricky but guessing the stud shank diameter and it's length I reckon about 47kN of tensile load which is about the top end of what you'd expect for an ally cylinder head.

If you want to know more about bolts and studs look here; http://www.boltscience.com/index.htm?

S.

[spudgun]

ok if the bolts stayed the same maybe the gasket design changed.

Applying a bit of maffs, 47lbft of torque gives about 36kN of tensile load in the stud. 22lbft + 180degrees is a bit more tricky but guessing the stud shank diameter and it's length I reckon about 47kN of tensile load which is about the top end of what you'd expect for an ally cylinder head.

If you want to know more about bolts and studs look here; http://www.boltscience.com/index.htm?

S.

Yeah, your probably right about the gasket design changing but that again would lead to there maybe being an issue in the first place. Very few companys do work for the sake of it, unless ,maybe, it had a material in it that was changed for some reason Asbestos banned or something like that.

The bolt software wouldn't work on my PC's vista. don't why.

All good stuff though.

[dex]

My Haynes manual (USA, no. 92065(1339), no print date but is copyrighted as 1987) gives the torque setting as 44 ft lbs.

My Toyota 4A-F, 4A-GE engine repair manual (pub no. RM-063E, dated May 1987) give the torque as being 22 ft lbs, 90 degrees, 90 degrees. The head bolts are to be lightly oiled with 'engine oil', both the threads and under the bolt heads.

Interestingly, the Toyota manual gives the 4A-F head bolts torque setting as 44 ft lbs, I wonder if this is the cause for the confusion/difference

[spudgun]

I reckon your right Dex, it sounds like they may have just carried the torque settings over from the "f" to he "g".

It makes a fair bit of sense that.