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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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 Posted: Sat Jul 07, 2012 5:16 pm Post subject: Cometic head gaskets |
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Has anyone used one of these Cometic gaskets on a larger than standard bore? Particularly on an 88mm bore?
Has anyone noticed any misalignment?
Has anyone measured the actual bore spacing?
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World`s quickest 924 2L slushbox
| Allan @ DTA wrote: | | I have no issue with superchargers, they are for guys who want to drive a car rather than talk about horsepower with their baseball cap on backwards |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Sun Jul 08, 2012 2:09 am Post subject: |
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I am using one on an 87mm bore on the 941. Did not notice an issue, and the car has been running quite strong for several thousand miles.
I would be somewhat surprised if there was a manufacturing/design defect, as we took Cometic a block, an NA head, and a 931 head, which were all scanned and used to create the original part. Of course, anything is possible...
I have 87.5mm and 88.0mm blocks on the bench, both of which I was planning to use with a Cometic gasket. When it cools down later this week, I'll see if I can get out to the garage and check the alignment with one of my unused Cometics.
I presume you are having some sort of alignment issue?
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daniel
Joined: 18 Jun 2009
Posts: 686
Location: Sydney, Australia
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| Posted: Sun Jul 08, 2012 10:33 am Post subject: |
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88mm bore, cometic gasket from dan, no probs at all
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet |
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Tue Jul 10, 2012 7:59 am Post subject: |
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Sure that you would recall if you noticed part of the head gasket over hanging the bore by 1mm? What about your engine builder?
To be fair though, its less obvious on a smaller bore, wasn`t to me first time round either, neither to a few pro engine builders now also.
No one has measured the gasket bore centres yet?
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World`s quickest 924 2L slushbox
| Allan @ DTA wrote: | | I have no issue with superchargers, they are for guys who want to drive a car rather than talk about horsepower with their baseball cap on backwards |
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daniel
Joined: 18 Jun 2009
Posts: 686
Location: Sydney, Australia
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| Posted: Tue Jul 10, 2012 8:48 am Post subject: |
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| Quote: | | Sure that you would recall if you noticed part of the head gasket over hanging the bore by 1mm? |
Yes without any question
| Quote: | | What about your engine builder? |
he is me
| Quote: | To be fair though, its less obvious on a smaller bore, wasn`t to me first time round either, neither to a few pro engine builders now also.
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I have an 88mm bore
If I had gasket hanging into the combustion chamber, I would have burnt it away and ruined the gasket by now. Had a motor a whil back that had valve relifes cut into the bore, the gasket overhung by less than a mm. The motor didnt even make it to the dyno, the gasket just got destroyed
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Tue Jul 10, 2012 4:00 pm Post subject: |
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Strange RC, even the stock gasket is still at least 1mm away from a 88mm bore out at 90mm diameter, would have thought it would essentially be the same as there is only one size in stock gasket size.
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Tue Jul 10, 2012 6:07 pm Post subject: |
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The VR and Goetze OE gaskets measure 88.6mm ID uncompressed. They have a bore spacing of 95mm. There is no issue with the stock gaskets.
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World`s quickest 924 2L slushbox
| Allan @ DTA wrote: | | I have no issue with superchargers, they are for guys who want to drive a car rather than talk about horsepower with their baseball cap on backwards |
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Thu Jul 12, 2012 3:57 am Post subject: |
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| ideola wrote: | | When it cools down later this week, I'll see if I can get out to the garage and check the alignment with one of my unused Cometics. |
Any chance you`ve been in the garage yet or corresponded with Cometic?
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World`s quickest 924 2L slushbox
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Thu Jul 12, 2012 4:28 am Post subject: |
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| RC wrote: | | ideola wrote: | | When it cools down later this week, I'll see if I can get out to the garage and check the alignment with one of my unused Cometics. |
Any chance you`ve been in the garage yet or corresponded with Cometic? |
I can't discern a problem on my 88mm block nor with my calipers, but I will send an email to Cometic and ask them to confirm what their drawing shows as the center-to-center distance on the bores.
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Thu Jul 12, 2012 5:24 am Post subject: |
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| ideola wrote: | | I can't discern a problem on my 88mm block nor with my calipers |
Really? Got your glasses on?
What bore spacing do you measure?
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World`s quickest 924 2L slushbox
| Allan @ DTA wrote: | | I have no issue with superchargers, they are for guys who want to drive a car rather than talk about horsepower with their baseball cap on backwards |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Thu Jul 12, 2012 5:50 am Post subject: |
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I don't wear glasses, although I am getting older, and perhaps need an eye test.
I did not pre-dispose Cometic to an answer by telling them what we expect the spacing to be. I asked them to refer to the drawing and confirm the center to center spacing. I'll report back when I have an answer.
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Thu Jul 12, 2012 6:01 am Post subject: |
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| my Cometic contact wrote: | Hi Dan,
I also just found out about this, I will be re-cutting the tooling and adjusting all of the parts to the 95mm bore centers next week.
Call and ask for are return goods department to set up any replacements. Tell them I send they are to be replaced no charge.
Thanks |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Thu Jul 12, 2012 7:31 am Post subject: |
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Ummm...and if the defective gasket was installed and then failed?
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- WeiBe (1987 924S 2.5t) - 931 S3
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Thu Jul 12, 2012 8:12 am Post subject: |
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I'm thinking the same thing.
I really don't want to pull the head again....
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Thu Jul 12, 2012 12:05 pm Post subject: |
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Personally am not worried for anything other than 88mm bores (I have one on the 941 @ 87.5mm bores and have driven many thousands of miles with absolutely no issue so far).
In any event, at present, I don't know what Cometic's approach is going to be for already-installed gaskets. But I when I talk to the returns department (hopefully tomorrow), I will find out.
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