What sealant to use on head bolts?

[STEVE W]

I'm puttin the heads back on to my rover 3500 block. Can anybody tell me what thread sealant to use on the head bolts ?

[TINKA]

Hi Steve, when I rebuilt my Rover Engine I was advised to use the 4.6 bolts for 2 reasons.1, The washer is cast into the head which they think is a better Idea. 2, They are stretch bolts so you do them up to a ridiculous setting, most feel like they have in fact stripped the thread. When in actual fact it is the bolts stretching.

Anyway the point is to torque a bolt properly you actually lubricate the thread so the torque is not going to be affected by the friction of the threads. This is how I did mine anyway and It has so far run perfectly ok.

Martin :tu :tu :tu :tu :tu :tu

[russell_ram]

Steve,

Martin is absolutely correct in what he says.

The bolts he suggests were introduced in 95 with the serpentine belted engines (4.0 and 4.6) and with the Land Rover composite gasket. You can only do them up 'ridiculously' tight - actually 20Nm snug torque, then 90 deg angle, then a final further 90 deg angle - if you use the composite gasket. this is designed to take the bolt just into elastic yield, hence getting the maximum possible clamp load from the system. If you use a 'tin' shim gasket with these bolts you must use the standard 90Nm (10 long bolts) and 60Nm (4 short outer bolts) torques otherwise you will overtorque the bolts using the torque plus angle method. The composite gasket is obviously a much better gasket, and a straight swop for the tin one, although you will lose about 3/4 Comp ratio using them on a pre-95 engine, unless you skim the heads by 25 thou to recover it. If you're heads have only 10 head bolt holes, then they use the composite gasket as std, if 14 head bolt holes, then the tin ones are std.

If you're going to use the tin gaskets, then there is not too much wrong with the old seperate bolt and washers (except the washers sometime crack). Do not use 'standard' washers - the correct ones are thicker to spread the bolt load and ground flat. Threads should be cleaned on the bolts and in the block, then lightly oiled only. NO sealant on the threads or heads of the bolts at all - that will just cock up the torque readings - and serves no sealing application at all in a Rover engine.

Russ

[TINKA]

Hi Russ, just a quick question, the people who did the head and block work on my Engine ( who for got to tell me about skimming the head's for composite gasket ) were the ones who sold me the head bolts and told me how to tighten them up as you have stated. The thing is they knew that I was going to have to use tin gaskets. So far I have done over 2000 miles of trouble free motoring, do you think by what you have said earlier I might have got away with fastening in this manner or might I have some serious problems ahead??? x( x( x( x( x(

Martin

[russell_ram]

Martin,

I guess this is what comes of people (not you, you were just following 'expert' opinion) not understanding the full reasons and mechanics behind a change and just assuming that they're new, therefore must be better.

The reason for 'torque plus angle' tightening is that, by taking the bolts just into yield, you guarantee the clamp load much more (and you can vary it by varying the bolt diameter) than if you use the older 'torque wrench' method - which is highly dependant on thread condition and friction etc.

In your case, because your gasket has not compressed as much as a composite one would have, you have 'overstreched' the bolts from their design condition. Remember that, in theory at least, these, like most modern cyl head bolts, are 'single use' - use once and replace - to avoid them becoming progressively overstretched. Luckily for you, the bolts did not snap and you didn't strip any of the block threads.

If I were you, as there is no problem currently, I would leave well alone and perhaps think about changing to composite gaskets (and definately new bolts in your case) at a later date if need be.

Russ

[TINKA]

Thanks Russ I think when I can afford it I will get the heads skimmed as well so I don't loose too much Compression. Which is why they told me to use tin gaskets!!x( x( x( x( x(

Martin