Torquing down 4A-GE head bolts.

[Sweetpea]

Hi all,

I need help.

I'm torquing down the head of my 4A-GE. I know the manuals show 2 methods for doing this.

1, The early manuals say you go to 43 ft-lb in several passes.
2, The later manuals say you go to 22 ft-lb. Add 90 degrees on the second pass. Then on the last pass add another 90 degrees. That's 180 degrees in total.

I hate choices so I went reasonably cautiously expecting that both methods would give about the same result. They don't seem to.

So I went to 22 ft-lb and moved on from there. I'm currently at about 45 ft-lb but by method 2 I've only got about 80 degrees of additional turn over the base 22 ft-lb. I took one bolt to 90 degrees and needed nearly 60 ft-lb to do it.
If I add the final 90 degrees the torque needed to do it is going to be huge. Certainly not anywhere close to the 43 ft-lb specified by method one.

What's going on? Which is the correct method? Did method 2 supersede method 1 or is it only for later engines?

For the record my engine is…

An early 'bluetop' with a 3 rib block.
Its a genuine Toyota head gasket and new genuine Toyota bolts.
And the bolt holes are all clean.

Thanks

James

[Phil H]

Did they change bolt spec at some point?

20-sh lb/ft and 2x90 degree pulls sounds in the right ball park for stretch bolts. By their nature you'll probably end up with something like 90-120lb/ft in reality as the bolts are now in the plastic zone. If you try it on non-stretch bolts, you'll break something trying to do the 2x90's

43lb/ft is maybe a bit low for non-stretch bolts in my mind - depends on the engine though. It's not a crazy low figure for an ally head.

[Sweetpea]

I don't believe they changed the bolts but I have no evidence of that at the moment.

More interestingly, the manual that suggests 22+90+90 does not say to use new bolts and goes on to say that if a bolt deforms or breaks you should replace it.

That sort of suggests they aren't stretch bolts. But then any bolt becomes a stretch bolt if you tighten it enough.

James

[iainw]

may not be much use but ARP quote 70ft-lbs

So i would suggest that the angle setting is more likely, given that arp settings are usually lower

arpinstructions.com/instructions/203-4304.pdf

[oukie]

Hi Sweetpea, I have a genuine Toyota dealer workshop 4age manual I will check what it says for the earlier spec engine, as I believe it covers a few incarnations Including torque settings, give mme abit of time I'm at work, manual is in garage at home

[gregg106]

For added confusion Autodata suggests the following;

Stage 1 25Nm
Stage 2 45Nm
Stage 3 60 (+ or - 4) Nm

And says no to using new bolts.

[Sweetpea]

Hi iainw, that's for a 20 valve which is probably different again. Thanks for looking it up though.

oukie, that would be great if you could look it up. If not don't worry, Toyota have parts for me so I'll ask them what their version of the '85 BGB says.

gregg106, converted to ft-lb that's basically version 1. A chap on the MR2 MK1 forum (where I've also asked this question) says that's what the Haynes manual says.

[oukie]

Hi, my Toyota book is saying your version 2. The three stages, of 22 then 90 degree, then 90 degree but in a certain bolt order and your meant to mark one of the bolts part way through, complicated? Yep.

I've taken photo's of the process shown in Toyota's own engine repair manual. Ps my book is a 1987 version.

[Sweetpea]

Hi all,

I posted this question over on the MR2 MK1 Forum too. The thread briefly came to life again recently which reminded me that I had written up what I actually did but forgot to post it. Well I found it and here it is...

-------------------------------

I've come to decision about torquing my cylinder head down. First of all, thank you all for your thoughts and information. No doubt whatever I've decided to do will upset somebody but that's life. The best I can do is explain my thoughts - right or wrong - and hope it's ok. And if it's not ok I'll admit my mistake and you'll all know what not to do.

To recap.

The 4A-GE manual written when my car was built says you should torque it to 43ft-lb over several passes.
After a couple of years Toyota redesigned the block slightly and the new manuals says you should torque to 22ft-lb, then add 90 degrees, then another 90 degrees. I don't know what torque this would actually give you but it'll be a big number. Massively more then 43ft-lb. I'd guess 75+ft-lb. Of course if the bolts start to stretch it'll limit the torque needed to tighten them.

The later manual does not differentiate between the two types of block. It just says 22ft-lb + 90 + 90. In all probability it's probably fine to use it on early engines too. Had the torque figures been 'reasonable' this would have been a no brainer.

The next debate is 'stretch bolts or not?' Most people say they aren't. A few say they are. At the end of the day if you tighten any bolt enough it'll deform. For me the most telling thing is that the manual does not say you have to replace them. That probably means they aren't being stretched even by the 22 + 90 + 90 method.

So where does this leave me? Torque figures from 43 to 75+? Mild possibility of stretched bolts. Plus different figures for other members of the Toyota A series engines or different manufacturers bolts. But all in the 45 to 75+ ft-lb range.

So I started going for the 22 + 90 + 90 method expecting to end up in the mid 40s. I torqued everything down to 22ft-lb and then added 90 degrees to the first bolt. The torque was up around 60 to do that and I got scared. So I backed it off to zero degrees and then went to 33 and 43ft-lb. Effectively the old school method. In new method terms this was about 22ft-lb + 80 degrees.

Now this is the spec it would have come out of the factory as. It kept the car running for 25 years and the gasket only failed when the cooling water escaped so it can't be that bad. Even though it's a little low compared with other head bolt torques of the day.

Then I stumbled into an old school mechanic who worked on these things at the time. He suggested 43ft-lb and then 'nip things down'. I'm not totally convinced by that plan either. But having pulled one bolt down to 22 + 90, squashed the gasket a bit, and backed it off again I wanted to 'make sure' it was all evenly tight. So after a few days sitting at 43ft-lb I set the wrench to 55ft-lb and tweaked it down a little more. That is 22ft-lb plus about 90 degrees.

So where does that leave me? Well tighter than the old method and not as tight as the new method. In fact I'm somewhere in the middle of range of values given in various places - but not actually on any of them.
But looking at the positive side, it's a bit tighter than the slightly loose old method, I haven't pulled the threads out of the block, the gasket hasn't been 'unclamped', and if it does leak oil into the water or visa versa I can always add the final 90 degrees to the bolts.

I've also been looking into the relationship between bolt torque and the joint clamping force it produces. Basically it's very random. There is a formula that allows you to calculate it but there is a 'fudge factor' to cope with friction under the bolt head and in the threads. And that's a massive unknown because it depends on how well the threads were cleaned and lubricated. Or even if they were cleaned at all.
Some people suggest you could be - I think it was - plus or minus 30% in error in the clamping force for a given torque. And that's with bolts installed at the same time with the same tool.
The problem is so bad at the extremes that it could lead you to vastly under tighten one bolt and break the one next to it. (This is bolts in general - not head bolts specifically.)
The 'snug it down and then add some degrees' method is more accurate (but still not brilliant) so that's likely to be why Toyota changed to it. What I haven't worked out it why they increased the torque (and presumably clamping force) so much. Or indeed if it pushes the bolts into their deformed state.

So there we are. I've done what nobody suggested and annoyed everybody! I like to be even handed.

Thanks again,

James

PS. I wrote that bit some time ago and forgot to post it. Since then the engine's had a few heat cycles and a road trip to the MOT station and back. Everything is fine. However, because the car failed the MOT it's not had a proper ragging yet. The jury is still out…