Lotus Elan

Head gaskets

PostPost by: cadwell » Sat Sep 23, 2023 3:56 pm

I was just about to fit my new Cometic CFM 85mm head gasket when I realised that there were no rear water holes in it.
Photo shows comparison between the Cometic and an Ajusa 84mm gasket.

This surely cannot be correct. The two large triangular holes at the back are completely covered.

. I have emailed Cometic, so they are presumably contacting the USA for comments.

Has anyone come across this before, and if so what was the result? I am tempted to just punch circular holes through, in the location of the triangular holes but it seems a bit of a bodge on an expensive gasket.

Peter
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PostPost by: fatboyoz » Sat Sep 23, 2023 8:26 pm

Hi Peter,
Have recently fitted a Cometic CFM 84mm head gasket. Definitely had the two triangular holes that are missing on yours.
Cheers,
Colin.




cadwell wrote:I was just about to fit my new Cometic CFM 85mm head gasket when I realised that there were no rear water holes in it.
Photo shows comparison between the Cometic and an Ajusa 84mm gasket.

This surely cannot be correct. The two large triangular holes at the back are completely covered.

. I have emailed Cometic, so they are presumably contacting the USA for comments.

Has anyone come across this before, and if so what was the result? I am tempted to just punch circular holes through, in the location of the triangular holes but it seems a bit of a bodge on an expensive gasket.

Peter
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PostPost by: cadwell » Sun Sep 24, 2023 2:06 pm

Thanks Colin, that is very useful information, and seems to demonstrate that the 85mm gaskets have a manufacturing fault.

Petrr
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PostPost by: cadwell » Mon Sep 25, 2023 9:44 am

Colin,
Could you confirm that your 84mm gasket is a CFM version not an mls, multi layer steel version.

Cometic are telling me that closing off the the rear water ways is standard on these gaskets, which I have difficulty in believing.

Thanks

Peter
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PostPost by: promotor » Mon Sep 25, 2023 10:15 am

cadwell wrote:
Cometic are telling me that closing off the the rear water ways is standard on these gaskets, which I have difficulty in believing.

Thanks

Peter


Did they explain why? If you were to go from a Cometic MLS to a Cometic CFM on the same engine are they saying that not having the holes makes no difference to the engine? If so, why does the MLS have them?

Interesting thread, thanks for posting on here.
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PostPost by: 2cams70 » Mon Sep 25, 2023 1:32 pm

The gasket they have given you looks like it’s for an alloy block BD* engine. That triangle cut out for the waterway is a weak point on gaskets with larger bores. It should still have holes though even for a BD* (holes for the BD*, larger cutouts for the LTC)
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PostPost by: fatboyoz » Mon Sep 25, 2023 2:52 pm

Hi Peter,
Yes, definitely a CFM, and definitely had the triangular cutouts, as I was a little wary of the remaining thickness left to the edge of the gasket.
I think that 2cams70 has a point.
If it were me, and I was getting no joy from Cometic, I’d put the gasket on some steel or smooth concrete backing, and use a hole punch to make the two new holes the same size as the other cooling holes.
Cheers,
Colin.




quote="cadwell"]Colin,
Could you confirm that your 84mm gasket is a CFM version not an mls, multi layer steel version.

Cometic are telling me that closing off the the rear water ways is standard on these gaskets, which I have difficulty in believing.

Thanks

Peter[/quote]
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PostPost by: cadwell » Mon Sep 25, 2023 7:08 pm

The plot thickens
It turns out that the Cometic gasket which I have bought is a special, and not the standard Twincam version.
The part number of mine is C14098-043 whereas the standard gasket is C4134-043. According to Cometic standard gaskets have 4 numbers and specials have 5, it seems that I should have known this, despite no CFM Lotus gaskets appearing on their on line catalogue!
I obtained the part number from Burtons site, but they did not have stock. Cometic made no mention that the number I was ordering was a special.

It seems that this was all my fault according to Cometic.

I now have two choices.
1. Punch holes in the 95mm Cometic gasket

2. Use the 84mm Ajusa gasket I have in stock.

The engine is now 30 thou over, so 0.75mm making the bore 83.3mm, so the Ajusa will be 0.35mm from the edge of the bore. I think this is on border of acceptability, but having examined the fit, all the bores have the same clearance. So a touch of super glue in two opposite corners should do the trick to hold it firm.

The Ajusa appears to be of a much harder gherkin quality than the Cometic. It has sealant lines round holes and the whole gasket seems to have a sealant finish on it.

The Cometic however, is bare CFM with fire rings, nothing more.

So I am leaning towards the Ajusa unless any of you Twincam experts advise me not to.

Unfortunately I am now quite old so the car will not get any hard usage, ( until it is handed over to my sons and grandsons!). My pleasure has been in the rebuild. When I was young and penniless I bodged and made do with what I had, so it has been good to have reached that time in life when I can afford to spend what is necessary to make a great car.

Sorry I have probably bored you all to sleep now!

Peter
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PostPost by: Stevie-Heathie » Mon Sep 25, 2023 7:34 pm

Craig Beck Racing is the UK distributor for Cometic and Craig knows a thing or two about our twincams. I’d give him a bell.

https://www.craigbeckracing.co.uk/

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PostPost by: promotor » Mon Sep 25, 2023 8:30 pm

cadwell wrote:The plot thickens
It turns out that the Cometic gasket which I have bought is a special, and not the standard Twincam version.
The part number of mine is C14098-043 whereas the standard gasket is C4134-043. According to Cometic standard gaskets have 4 numbers and specials have 5, it seems that I should have known this, despite no CFM Lotus gaskets appearing on their on line catalogue!
I obtained the part number from Burtons site, but they did not have stock. Cometic made no mention that the number I was ordering was a special.

It seems that this was all my fault according to Cometic.

I now have two choices.
1. Punch holes in the 95mm Cometic gasket

2. Use the 84mm Ajusa gasket I have in stock.

The engine is now 30 thou over, so 0.75mm making the bore 83.3mm, so the Ajusa will be 0.35mm from the edge of the bore. I think this is on border of acceptability, but having examined the fit, all the bores have the same clearance. So a touch of super glue in two opposite corners should do the trick to hold it firm.

The Ajusa appears to be of a much harder gherkin quality than the Cometic. It has sealant lines round holes and the whole gasket seems to have a sealant finish on it.

The Cometic however, is bare CFM with fire rings, nothing more.

So I am leaning towards the Ajusa unless any of you Twincam experts advise me not to.

Unfortunately I am now quite old so the car will not get any hard usage, ( until it is handed over to my sons and grandsons!). My pleasure has been in the rebuild. When I was young and penniless I bodged and made do with what I had, so it has been good to have reached that time in life when I can afford to spend what is necessary to make a great car.

Sorry I have probably bored you all to sleep now!

Peter


There's one more fly in the ointment - neither of those gaskets has the profile / cutout for the rubber drain tube from cylinder head to block. I always have to trim the Ajusa. Compare those gaskets to an original copper head gasket that does have the relief for the tube.
The bore size of the Ajusa is just OK at your bore size - I did as you suggest in "setting" the gasket to the block to try to keep in in place while fitting the head.

I like the Ajusa gaskets - they seal so well they literally bond to the the head and block - taking the head off usually destroys the gasket!

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PostPost by: cadwell » Tue Sep 26, 2023 8:02 am

Many thanks for this, didn’t occur to me I’m afraid so will modify it today!

Peter
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PostPost by: promotor » Tue Sep 26, 2023 8:23 am

cadwell wrote:Many thanks for this, didn’t occur to me I’m afraid so will modify it today!

Peter


No problem.

I've been told this is unnecessary previously but I must be getting different Ajusa gaskets to other people! Can't hurt to double check before you fit yours.

Cheers.
Al
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