Hi All,

Slightly unanticipated problem regarding head bolts has arisen for me. I am about to fit H89 head to early A12 block. Oil passage has been drilled at angle from gasket surface through to centre bolt hole so should be all good.

However, are the torque specifications the same for the H89 head as for the original A12 head? Should I torque all head bolts to 72Nm (53lb/ft) as per manual for A12?

Also, can I torque the centre bolt to the same torque spec? It is marked with a single ‘T’ only and is from the original A12 motor and is 97mm long (presumably I can torque this to 72Nm). The remaining 9 original bolts are not marked at all.

I also have the head bolts that came with the H89 head that are marked with a '12'. Centre bolt marked with ‘12T’ and is the longer 111mm bolt. Should I be using the bolts that came with the H89 head? I can’t use the centre bolt from H89 head as it is too long for my block. I suppose I could drill and tap the block deeper. Prefer not too though if it can be helped.

Thanks guys

According to Tech Wiki, the unmarked bolts are to be torqued to 33-36 ft-lb. Quite a bit less than the 53 ft-lb stated in workshop manual. Even the bolts marked with '12' are listed as 40-43 ft-lb. Do I need new bolts marked with '13' to be able to torque to 53 ft-lb as per workshop manual? If that is even the spec for A14 heads.

According to this section in tech wiki, the A14/15 motors need the bolts marked with '13'. I guess this applies to my H89 head. Even if I buy some new bolts, the longer oil bolt will be too long for the thread in my block. Are there any shorter bolts available with the '13' specification or is the only option to drill and tap the block for a longer bolt? I sure hope not as I have only just reassembled the motor and don't want to tear it down to drill deeper hole.

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....Just thinking it through, provided the older style A12 block had sufficient material, you could possibly drill and tap deeper hole with engine in car (head off). I was thinking in previous post that I would intercept an oil passage by drilling deeper and therefor contaminate with swarf but that wouldn't be the case for my block.

No problem, use the '12' Head Bolts and torque to 43 ft lbs. The bolt marked 'T' is also a 43 ft lb bolt

Yes, the '13' bolts are slightly stronger, but the '12' bolts are good enough. Just retorque them every two years as per the Periodical Maintenance and Lubrication Schedule. The '13' bolts were introduced for the 10:1 compression A12GX Engine, but the 12 bolts were used for years afterward

As for workshop manual, that is for A14 engine. The B110 manual specifies the three different torque specs depending on which A12 engine

Thanks DD. I was starting to worry.

So I can torque the original centre bolt marked with 'T' (not '12T') beyond 33 ft-lb? Is this an exception to the table from tech wiki?

Also, is the rubber oil ring a redundant feature these days? Do modern head gaskets take care of things without the separate ring seal? Presumably it is for the older A12's like mine where the head lube passage crosses the gasket?

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Taking a closer look at my existing short (97mm) original centre bolt marked 'T', I am not thrilled about re using it due to the corrosion on shank. A small part of the thread is even missing that you can just make out in pictures.

What are my options if I want to use a different bolt? I do have the longer '12T' (111mm) centre bolt in good condition. However, the smooth shank of this bolt is 9mm diameter instead of the reduced 8mm. It is also too long obviously so not a feasible option at all.

Are original 97mm long centre bolts available? I can easily find a new set of bolts marked '13' but they all have the longer centre bolt.

Would it be ok to take a regular '12' or '13' bolt and turn the middle section down to 8mm?

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good questions

All A-series engine have a pressured oil passage through the gasket. Early ones have a dedicated passage, but in later ones pressurized oil goes though the center head bolt hole. As far as modern gasket goes, many new gaskets are made like the original. And it usually doesn't leak even without the o-ring. If your new head gasket comes with the special seal, use it. If not don't worry

Yes that bolt is corroded. Get a replacement

Yes they are all available at spares yards

I have torqued the 'T' bolt to 43 ft-lbs. It worked OK, never had a blown head gasket. The '13' bolts are everywhere, the Navara even uses 10 of them. But the center '13' bolt is rare, only used by the A12 GX for 3 years

I'm wondering if the late blocks have a larger center head bolt hole, to let oil flow around it. You can measure the old head and the H89 head, and see if the head bolt hole is slightly bigger where it meets the block

Thanks again! You're saving my sanity here at the moment

I just measured my original A12 head (can't see ID mark but it is the early type with factory oil passage drilled adjacent to centre head bolt) centre bolt hole and it is 11mm which is rthe same as H89 head.

Considering I am a little ways from the city (Melbourne) out in rural Victoria (..Australia..), it may be difficult finding a wrecked/used original head bolt. I'm under a little bit of time pressure to get vehicle back on road. Considering this, would it be ok to turn down the shank of a '12' or '13'? I know it's a bit of hassle too but I can order new set of bolts and get it machined all within a few days. Well hopefully...

I'd much rather just source a good condition original centre bolt but time might get the better of me.

Cheers again DD.

I don't know the answer to that, maybe it will work, or maybe the bolt is heat-treated