composit head gasket

[punter]

quick question for you all...

I'm just finishing up a complete rebuild of my 3.5L aluminum v8...
bored out the cylinders, 10.25:1 pistons, new cam, and so on.

I'm just about to put the heads on, but I've got composite head gaskets and I've never used these things before. Is there anything special I should be doing to prep the gaskets or surfaces before I drop them in place and mount the heads?

thanks

[sidecar]

quick question for you all...

I'm just finishing up a complete rebuild of my 3.5L aluminum v8...
bored out the cylinders, 10.25:1 pistons, new cam, and so on.

I'm just about to put the heads on, but I've got composite head gaskets and I've never used these things before. Is there anything special I should be doing to prep the gaskets or surfaces before I drop them in place and mount the heads?

thanks

I fitted these to my 3.5 when I fitted my stage III V8 development heads.

They said just clean the gasket faces, use the correct lube on the bolts theads and under the washers and then torque up the bolts in stages in the correct order. (Don't use the outer bolts).

Ideally you should re-torque (if not stretch bolts) after 200 miles or so. I never bothered but did check them again after about 2000 miles (I was fitting some pushrods) and all the bolts were still at the correct torque.

10.25:1 is getting quite high for normal pump fuel, you'll need to be careful with your air:fuel ratio and ignition timing!

Pete

[chodjinn]

Yeah but with comp gaskets they'll drop the cr by about 0.5-0.7 right?

[ChrisJC]

They will, and also affect the alignment of the inlet manifold & gasket.

It's best to skim the heads by the height difference to get everything back into alignment.

Chris.

[sidecar]

Thats right, comp gaskets will drop the CR by about 0.5 This does mean that the heads can now not be skimmed too much or the CR will go quite high again.

The Edelbrock manifold that I use was such a sloppy fit that it would have fitted with or without the head skim. In fact you need to be careful when fitting a "Performer" to make sure that the bridge in the ports does line up with the bridge in the manifold. (You can do this by marking both parts then lining up the marks when you fit the manifold). This may not be too important with standard heads.

The other fly in the ointment is that the push rods will be too short if you don't skim the heads. You may end up with NO pre-load and this is very bad! Adjustable pushrods can sort this out. (127 quid inc vat from realsteel).

Personally I'd have gone for lower compression pistons, comp gaskets and a head skim. (The setup that you've can be made to work however!)

I'd be aiming for a CR of 9.75-10:1 for a road car that can use any pump gas. Others may say that you can run a higher CR and you probably can but you will end up retarding the ignition and only being able to use the higher octane fuels. An engine with lots of ignition advance and a lower CR will perform better than one with a high CR and not much advance.

Having said all that you might get away with 10.25:1 and say 30-32 degrees advance especially if you can keep the coolant down to 75-80 degrees C.


AJMHO,

Pete

[RoverP6B]

Composite head gaskets were introduced in 1994 when at the same time the combustion volume within the heads produced from that date onwards...10 bolt heads, was reduced from the prior nominal 36cc to 28cc.
The heads were skimmed by the factory to achieve this result.

Without the reduction in combustion chamber volume, the use of composite head gaskets reduces the compression ratio by 0.5 on average.

You could always just use the original pressed metal head gaskets, which were designed for using with the original 36cc heads, and the compression ratio will remain exactly as you intend,...ie 10.25 : 1.

Best of luck,
Ron.

[sidecar]

Composite head gaskets were introduced in 1994 when at the same time the combustion volume within the heads produced from that date onwards...10 bolt heads, was reduced from the prior nominal 36cc to 28cc.
The heads were skimmed by the factory to achieve this result.

Without the reduction in combustion chamber volume, the use of composite head gaskets reduces the compression ratio by 0.5 on average.

You could always just use the original pressed metal head gaskets, which were designed for using with the original 36cc heads, and the compression ratio will remain exactly as you intend,...ie 10.25 : 1.

Best of luck,
Ron.

Problem is...why did Rover drop the tin gaskets? well from my understanding and from what I've seen on my engine when it had them is that they are prone to leaking! (I know that others do use them so who knows!)

The other thing with all this talk about CR is that I would not trust any of the figures that are just quoted by piston manufacturers. (for starters the deck height my be out of spec). It is quite easy with a burette to actually find out the vol above the piston, the vol of the head then work out what the CR is actually "really" going to be. (You can calculate the gasket vol)

Regards,

Pete

[ChrisJC]

The tin gaskets leak. In conjunction with the asymmetric head bolt loading, the heads tilt and don't seal properly on the valley side. So combustion products get blasted into the valley area, and cause the 'black gunge' that gets everywhere. This is why you need to change your oil regularly, to get rid of all that muck before it gums up everywhere.

Rover probably knew this for a long time, but finally decided to fix it with the 4.0 / 4.6 engines. So they changed to composite gaskets, removed the outer row of head bolts, and fixed head sealing problems.

It's interesting to note that the original designers of that engine (Buick) had two versions, one with 6 head bolts per cyl, one with 4. Both gave symmetrical loading. Why Rover went for five, who knows!

And a leaky head gasket isn't a major issue on the RV8 as it doesn't have many coolant passages between block / head, so it's very unlikely to cause loss of coolant.

See http://www.v8engines.com/engine-4.htm#inside

Chris.

[punter]

agreed... 10.25:1 is a bit high, which is why I went with the composite gasket... to tone it down a little. I spec'd the engine out according to the recommendations of an engine builder who specializes in these old aluminum v8s. It'll be some time until the project is complete (this is just one step in an entire frame up rebuild), but I'll let you know how it works out when I get it built up to a point that I can fire it up.

This business about poor fit if the Performer intake, is news to me... I've never heard this before. Thanks for the heads up.

Any further advice/recommendations are always appreciated.

Thanks.

[sidecar]

agreed... 10.25:1 is a bit high, which is why I went with the composite gasket... to tone it down a little. I spec'd the engine out according to the recommendations of an engine builder who specializes in these old aluminum v8s. It'll be some time until the project is complete (this is just one step in an entire frame up rebuild), but I'll let you know how it works out when I get it built up to a point that I can fire it up.

This business about poor fit if the Performer intake, is news to me... I've never heard this before. Thanks for the heads up.

Any further advice/recommendations are always appreciated.

Thanks.

The Performer manifold is a good manifold and if your heads are standard then I'm sure that you can just plonk the manifold on without any problems. My heads are stage III and I opened up the manifold to suit the ports in the heads. At this point the inlet bridge is about 2mm wide in the heads and in the manifold. The manifold can be pushed forwards or backward maybe 3mm when fitting it so infact the two bridges could totally miss each other!.

If you are using the comp gaskets and not getting the heads skimmed so that the compression is lowered 0.5 of a ratio then I think that you will need to buy the adjustable pushrods. I know that its yet more money but they are the way to go if you wnat to get each and every pre-load spot on. (I doubt that you will get any of them right with the standard pushrods and shims will make it even worse!)

Pete