Cylinder Head Removal

[Doug_RS2]

Originally posted by Mihnea
I beg to differ Dave but I know of at least 8 people in germany running 400+ HP on ABY engines and 2 stacked head gaskets with no issues so far.

Need to know asap - should I put 2 RS2 head gaskets on Mihnea?

[audiman]

Head bolts have to slackened in the opposite sequence to tightening! Otherwise distortion can occur. So start from the outside and work inwards.

[audiman]

I know for a fact that Volvo used two gaskets to reduce compression ratio. But these were two paper gaskets and non turbo cars. Not sure Doug, but the man from delmonte he says yes, so it must be OK. Woth a try, worse thing it can do is blow out! A bit like this one

[SteveH]

Doug, If you'd like a copy of the 3B repair manual give me a shout. I'm sure all the basics, like torque settings and tigtening sequences will be similar.

[A6 AVANT]

Whilst head is away being sorted send a new Cam chain as well. No point in not changing that if everything else is being done. Not sure on P/N but it was about £15 from Stealership.

[Doug_RS2]

Originally posted by A6 AVANT
Whilst head is away being sorted send a new Cam chain as well. No point in not changing that if everything else is being done. Not sure on P/N but it was about £15 from Stealership.

It's on the list - the BIG fooking list.

It will have 2 RS2 gaskets At least if it doesn't work I will have reusable studs instead of the one-use head bolts. And it will be a shame not to stick in the 7A Exhaust Cam

[Doug_RS2]

I told some people at work what happened and got this back:


I'm not completely up to speed with your exact requirements, but do have a
little experience of threaded inserts.

You could try also looking at other types of threaded inserts, e.g.
keenserts or even the spiralock type of thread form (greater spread of load
across the thread form).

Typically in a thread form it's the first thread takes the majority of the
load, with progressively less load being seen on the other threads roughly
out to a minimum at about the fifth complete thread.

All inserts, correctly installed, should enable a high strength threadform
to be inserted into a lower strength body. If you are concerned about
over-torqueing use a graduated torque wrench, either that or remember that:-

Stripping Strength = basic shear area A x shear strength of material

Shear strength of the material can be approximated to .7 of the UTS.

Basic shear area = pi.Le.Ds 1/2 [1+{0.577 (Ds - En)/P}]

The above assumes that the thread strips at the by shearing along a
cylindrical surface containing the creast of the bolt thread. Use of inserts
raises the shear strength of the material (hardened thread engagement), but
relies on the bulk of the parent material not permitting thread dilation
(walls keep the thread from bulging out).

Just ensure that when you tighten you keep the values low enough to not
weaken the parent material.


Your concern is thread failure due to stripping the internal thread (the
weaker material). This can be thought of as removal of a cylinder (really a
helix) of material by shear. The outer diameter of this cylinder is the
outer diameter of the bolt (the external thread), and the cylinders length
is equivalent to the depth of engagement (thread length).

Previous overtightening will start to cause ductile failure of the thread,
usually as the thread loading on the first few threads start to stretch
beyond their elastic limit (exceeding the UTS of the material part way up
the thread crest). This can rapidly give rise to a catastrophic failure as
the crack propogates up the thread form, 'unzipping' the thread form.

Using a higher strength insert, it allows higher torque values to
resisted/utilised, by ensuring that the overloading of the first thread
crest does not occur (higher UTS). this is assuming that the parent material
does not allow the thread to 'bulge' outwards under torque loading - this
would then allow the forces to move to the outer part of the thread crest,
and possibly result in extrenal thread strippage (a bad thing TM).

Alternatively, utilising a different thread form (e.g. spiralock) allows a
more even distribution of the load across all the threads.

Either way, standing over the mechanic and making him use a graduated torque
wrench under pain of pain would be recommended!

[Mihnea]

@ Doug and whomever is interested in this:


here's what I've gathered regarding a twin head gasket install:


First off, a few people say that it's only necessary for 450+ HP upgrades and mostly only for people running at high speeds on the highway, like 5k+ RPM in 5th and 6th gears....

I for one, think it's not a bad idea to drop the CR a bit, just for the piece of mind that one can run more boost and more advance, and the engine will also rev happier due to that actually...


So, this involves having 2 new headgaskets, you have to drill the rivets off of them very carefully so you can separate all the layers that make each gasket.

I think the point is to reproduce the same layer pattern with the new gasket as with the old one, thus to add one more layer or something like that. Having not done this yet myself, I can't really tell more but if need be, I think I can ask a few germans who have already done it, in case more details are needed.

Apparently, 1more mm thickness drops the CR by 1 full point, thus to about 8.3:1 or thereabouts...


Cheers,

Mihnea

[Doug_RS2]

Originally posted by Mihnea
I think I can ask a few germans who have already done it, in case more details are needed.

Cheers Mihnea - definitely need more info - I was assuming you just chucked both in, one on top of the other. Might have parts and head back before xmas (probably not) so could do with this info.

Doug

[S2central.net]

@Doug - The manuals for all the ABY mechanicals are on Erwin if you need them.


Paul

[Mikes2]

Doug,

Contact me offline regarding the manuals.

Cheers,
Mike

[Vagsport]

There IS enough meat on stock S2 pistons to remove at least 1.5mm safely. I had a set of S2 pistons (4 for a Mk2 16V turbo conversion), the customer wants to run big boost later after running in. It cost me £25 to get them milled (-1.35mm) at my local engineering firm. This was even done while I waited. You can remove the pistons WITH the motor in situ. Don't take long at all.

Siena

[desmo888]

Originally posted by audiman
I know for a fact that Volvo used two gaskets to reduce compression ratio. But these were two paper gaskets and non turbo cars. Not sure Doug, but the man from delmonte he says yes, so it must be OK. Woth a try, worse thing it can do is blow out! A bit like this one

Pardon me but "paper gaskets"? I never heard of a paper head gasket!!!

[audiman]

Nearly all headgaskets are made from paper! Be it several layers compressed together. Only some turbo charged cars petrol and diesel use steel layered gaskets. I have done a few in my time, trust me!

[Mihnea]

Originally posted by audiman
Nearly all headgaskets are made from paper! Be it several layers compressed together. Only some turbo charged cars petrol and diesel use steel layered gaskets. I have done a few in my time, trust me!

Yep, this old and wise man has spoken right