Head gasket

[LotusMini1975]

Just had a head gasket failure on my plus 2

The block has been recently re bored and the head re built by CTM engineering (Great job), its running forged Cosworth pistons and a compression of 11:1.. Engine temp is constant at 90 degrees but yet to strip the engine down to find out exactly what caused the failure. Lots of white smoke and oil emulsion in the oil filler cap.

Question is what type of gasket to replace with a Cometic or standard one?

Any thoughts

Steve

[promotor]

If you haven't stripped the engine down you can't be sure it's a head gasket failure just yet, it could be a cracked head or block.
If it is a failure of head gasket it may just be that the gasket wasn't centred over the bores accurately - there's not much margin for alignment with the original Payen head gasket on standard bores never mind oversize.

I like the Ajusa head gaskets on Twincams - they don't need any special fine machining etc and should work with a 84mm bore easily. The Cometic are expensive and not guaranteed to seal unless you have a nice smooth finish on both head and block and the surfaces are exceptionally clean to allow the coating to seal.

I'm not sure what the safe compression limit is on a Payen gasket but it isn't just related to static compression ratio - it is about the compression figure of the cylinders when running. A standard gasket may work with high static compression but low compression figures when running due to longer duration lower lift cams but a high static compression and short duration high lift cams may cause gasket issues in the same engine if a standard gasket is used.

[ericbushby]

Hi Steve and welcome to the forum. This is the place for solving problems.
I had the same symptoms, steam out of the exhaust, mayonnaise in the cam cover and the water level going down.
I believe my problem was caused by a leak from the water pump into the timing chain cover, but as I did a major strip and rebuild at the same time including the head gasket I cannot be sure. There was no evidence of failure of the head gasket when inspected. Just another suggestion.
Eric in Burnley
1967 S3SE DHC

[rgh0]

Some more details on the engine modifications would be useful in order to comment on potential cause of a head gasket failure and potential solutions or future head gasket recommendations.as many potential causes of a gasket failure in addition to other failure causes such as a cracked head

What size is your bore and what size and type of head gasket did you use and what height were the piston decks below the block deck. There is potential for the pistons to contact the fire ring causing failure or the fire ring to crack if its exposed due to overlap with the bore.

Did you retorque the head bolts and did you have the head harness tested to ensure the bolts would not just sink into the head. Was the head and block both check for flatness and if machined done to correct surface finish

What cams are you using and what ignition timing, what fuel are you using as 11;1 with short duration cams will be pushing it if using normal road fuels.

Assuming everything else is OK and its just a random head gasket failure then any good quality fibre composite head gasket from companies like Ajusa or Cometic with at least 1 mm bigger fire ring to bore diameter should be OK. I personally would not use a Cometic MLS gasket

cheers
Rohan

[2cams70]

Just lift the head and take a look.

[elans3]

+1 for the Ajusa. Not cheap, but I've used them several times on different engines, and never had a problem again.

[LotusMini1975]

Thanks for all of the responses and looks like the Ajusta gasket is the one fit and will strip the head off ASAP to see whats failed.

Cheers

Steve

[promotor]

Thanks for all of the responses and looks like the Ajusta gasket is the one fit and will strip the head off ASAP to see whats failed.

Cheers

Steve

Bear in mind that the Ajusa will drop your compression slightly as they are slightly thicker than the standard Payen one for Twincams.
You may also need to modify the gasket slightly to get it to clear the rubber tube that fits between head and block.

[rgh0]

depending on cams and fuel and ignition timing the 11:1 comp ratio may be part of the problem and dropping it a little may be part of a solution. Just speculation until the rest of data needed is understood

cheers
Rohan

[LotusMini1975]

Hi,

The block was bored to plus 40 and pressure tested, cams are Piper 285.

Deck height not to sure on and the timing was set when the new distributor was fitted last year and my fault but didn't check what is was set too but the company is highly specialised and familiar width the car and engine.

A slight lowering of the compression is not a problem, the engine has run very successfully for 18 months and all set up on a rolling road.

Steve

[rgh0]

Piper 285 and 11:1 and running on premium unleaded road fuel and standard ignition advance will probably result in low speed full throttle preignition which would not do your head gasket any good over time. Lots of other potential causes also as I have previously listed so need to see what it looks like when the heads off.

Just my opinion..... but I sometimes find lots of "highly experienced specialists" in twin cams are talking through where the sun don't shine when building modified engines...... to quote the Aussie vernacular

cheers
Rohan

[nmauduit]

Piper 285 and 11:1 and running on premium unleaded road fuel and standard ignition advance will probably result in low speed full throttle preignition which would not do your head gasket any good over time. Lots of other potential causes also as I have previously listed so need to see what it looks like when the heads off.

what about running a fuel with more ethanol (and rejetting accordingly) to counteract such an eventual pinging tendency? just thinking...

would a knock/ping detector be of use to assess the status of an uncommon build (I understand they are not obvious to fasten efficiently for maximum detection on all 4 barrels) ? at least during the tuning phase...

[pharriso]

You may also need to modify the gasket slightly to get it to clear the rubber tube that fits between head and block.

+1 for the AJUSA head gasket, what mod are you talking about? I didn't have to do anything...

[promotor]

You may also need to modify the gasket slightly to get it to clear the rubber tube that fits between head and block.

+1 for the AJUSA head gasket, what mod are you talking about? I didn't have to do anything...

The Ajusa gasket in the photo is laid underneath a normal profile gasket ie similar to the original Payen copper head gasket profile - note how the gasket edge runs straight on the Ajusa. The original profile gasket follows the line of the cylinder block. In my experience you can't get the rubber tube seated while keeping the head centralised over the bolts (ie without them pulling / binding). It's either that or trim the rubber tube.The tube is a leak point usually so I chose to trim the gasket.
Note how the Ajusa has red sealer on this edge which doesn't even follow the edge of the cylinder block and you can see how the Ajusa wasn't actually designed properly for any Ford-based pushrod engine even though it clearly wouldn't fit any other engines!!

[promotor]

This one highlights what I mentioned above a little better - for the photo I think the rubber tube was actually leaning away from the block and sat even closer to the block when the head was on :