The V8 Owners Forum -

Hi again all,
Today Sunday I read the manual that I am using PROPERLY.
It reads centre & inner row 90Nm - the outer small bolts at 60Nm are not used due to later block giving only 10 threaded holes.
Engines with suffix "B" .....
Stage 1 = 20Nm
stage 2 = then 90 degree`s
stage 3 = further 90 degree`s. I have to assume you stop at 90Nm `cause it doesn`t say so, the 90Nm comes from above centre & inner row reading.
The bolts I am using are the flanged head bolts - stretch type.
I can see where we`re going with a start set of 20Nm then a 90 degree, then a 90 degree then 1 hour 50 x 90 degree`s later we stop at 90Nm and every 90 degree kept in sequence.
On every sequence of that system the first bolt you 90 degree will be tighter than the other nine, you then go through the sequence and bring the other 9 bolts ( after a 90 degree ) to the same torque, surly all 10 bolts are now set at the same torque after ANY sequence.
What is the difference in starting at 20Nm - sequence - 30Nm - sequence - 40 Nm - sequence ( e.t.c ) by 10 Nm & sequence each time until we arrive at 90Nm?
All bolts have gone through the correct sequence each time and the bolts have been tightened down slowly and surely and arriving at the same 90Nm.
What is wrong with that? What is different apart from the method?
Here I am not saying anyone is wrong --- I just can`t see any difference, its the same result so whats different?
All answers are treated with respect .... even the rude one`s.
Cheers guys .... Mike-b

As a point of interest the manual I have been reading is at www.landroverresource.com/35_39_42_v8_overall.pdf

Engine designers have found from experience that a more accurate and even pressure will be put on the head gasket by applyimg an initial low torque (say 20 Nm) on the bolts and then rotating the bolts a set number of degrees after that.

The former method was less accurate because of varying friction in the threads when subjected to high loads.

Once you set the the initial low torque with the torque wrench, you then don't use it again but turn the bolts through the required number of degrees.

The sentence where you say "then 1 hour 50 x 90 degree's later",
has totally confused me.

Now you hav the correct info you only have 2 choices. Use the pre torque and then 90+90 or use non stretch bolts and do it the old way where you can nip down in several stages with bolts that dont stretch.

When you use stretch bolts you only use the torque wrench once, at the beginning. Then its 90+90 only. Once fitted they are scrap when removed.
You can of course use the torque wrench afterwardss to make sure it clicks at 90nm, bit all that tells you is that they are all at or above 90nm.

I think if you nip the stretch bolts down in sequence to 90nm that you may not have turned them as much as if you did 20nm then 90+90 ??
They may have some stretch left in them is what I'm thinking.

This is one of the reasons I dont like them (apart from the fact that my heads come off several times a year) because once used they are scrap and I prfer to use non stretch with lubricant and torque down in several stages.

Denis has explained the theory behind the stretchy bolts. Theoretically more accurate and repeatable setting with angular torquing.

The other benefit of stretch bolts is that they keep compression on the head gasket over time as the gasket compresses. The old non-stretch bolts should be retorqued as part of the service schedule to keep the head gasket under the right amount of compression.And that job is just about impossible on the later V8 installations.

Chris.

Hi all yet again,

Chris, I agree 100% on your last. I assume a stretch bolt will "Hold Down" a head to the block better because it is always trying to pull the head toward the block.

Denis, The "50 x 90" I was referring to was ..... first set at say 25Nm via sequence, then via sequence a further 90 degree, then via sequence a further 90 degree, then via sequence a further 90 degree. Hence after about 50 times through the sequence turning the bolt 90 degree each time I finally ( at last ) arrive at 90Nm. This being the correct method, hey I`m not disagreeing. How do you know you have arrived at the correct torque?
I assume you check with a torque wrench all bolts are at 90Nm, however there is a good probability that one or more bolts are over 90Nm and that would make ( in theory anyway ) the other 9 bolts being looser.
The method I wrote about earlier I know for sure ALL the bolts are at 90Nm - no higher or lower - in fact all exactly the same.......... are they not?
The 90 degree system may well be more accurate but it still arrives at the same result.

Can i leave that with you? Sorry guys but I am finding it hard the accept this 90 degree only on each and every bolt ( even if one or more is a little different ) changes the result.

Cheers for now ..... and thanks for your patience. Mike-b

I was taught that a `head MUST be bolted down in a sequence, the sequence being start in the middle and work outward in equal and opposite directions, that is obviously true with the Rover V8 and any other engine. In fact you should do that same sort of sequence when any two machined surfaces are bolted together.

Without a STRETCH bolt you do indeed need to go back and re-torque, the advantage of the stretch bolt is you don`t need to.

[quote="mike-b"]
How do you know you have arrived at the correct torque? (quote)

You don't need to check if you have used the 90 + 90 degree method.
The pitch of the bolt thread has done the thinking for you and loaded the bolt to the designed force equally.

All the bolt heads will have moved down the same amount and all bolts will have the same force in them.

If you want to argue that the head gasket could compress more at one point compared to the next then you are getting into watch making tolerances and trying to "reinvent the wheel" on this matter.

Hi all .... again .... and my final.
I have at last seen the light ( I know and about bloody time to ) sometimes it takes a while to sink through the thick skull ...... but then never lost.
The problem was I just could not see what EXACTLY was happening, surprise, surprise now I do.
You have all been kind with the answers given and I thank you all - however - most of all I thank you all for your patience.
I learned my "Car Mechanics" many years ago and still tend to do it the old and probably the harder way of doing a job. The RV8 is the first engine I have ever worked on that seems to demand a different approach to other engines I have repaired ( all my own ), so the idea of not using a torque wrench every time I tighten a bolt seemed totally wrong.
I see the 20Nm or 25Nm start point and then not using a torque wrench - there being no need - afterwards was completely alien to me.
Should you happen to answer a post of mine at a later date ( though you may not want to get involved ) please remember the guy this end will soon be 68 and is already "loosing it".
So again ... I thank you all for your help and patience. Mike.

Hi Mike,
Glad the penny dropped eventually. Glad to help in the process.
1945 was a good year. "Loosing it", I don't think so.