Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Trigger on September 18, 2018, 09:49:12 PM
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CB750 head gaskets have always been a problem on the early engines and i have always got round this with upgraded 0'rings.
Today i was asked a question by a old time engineer that set me thinking. Why has no one ever done a copper head gasket for a CB750 ?
The most important part of any head gasket is the fire ring. The next is the sealing of any oil ways so, does anyone have any views on why a copper head gasket with insert 0'rings would or would not work ?
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I made a copper gasket in the eighties, after upgrading to 836cc. and putting in a sports cam and Kawa carbs.
The main idea was the re-useability, as the wiseco gaskets were quite expensive.
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I have seen them for sale at cycle x(https://uploads.tapatalk-cdn.com/20180918/2ecbb9fc8c59d4b9b8d0ff28af315fe2.jpg)
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I thought that you'd asked about them before Pete, I was trying to search about what came up.
They do go quite soft when annealed but they are routinely pulling drag race motors apart generally, be interesting to see if they do any other prep to use different gasket material.
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Cycle X have had them down as out of stock for years on there site and only did them in 65mm and 67mm, nothing std in copper. They do the MLS head gasket but you would have to skim both surfaces to require a much finer RA finish.
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Probably more realistic to get some laser/water jet cut nowadays if you wanted to get a supply line setup to specific requirements.
http://scegaskets.com/wp_super_faq/given-the-choices-why-would-one-use-a-copper-head-gasket/
Was looking through the above link for some more experience of using them. Interestingly they recommend coating the gasket to contain oil etc through the head joint.
As you say though, you're probably not going to get copper to take up surface imperfections in the same way as composite std types will.
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It used to be fairly common practice to go Copper and "O Ring" the head on very high compression engines as well as Turbo and Supercharged motors for competition.. not sure it is overly practical for daily running....
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Made my own copper head gasket for my 460 yoshi when I couldn't get the right one, just annealed it and gave it a smear of setting gasket compound before fitting, it performed well enough.
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Copper seems to be an out of favour head gasket material these days. More modern materials and manufacturing techniques have made other options more readily available for a lot of applications. I have an old pushrod Ford engine in a Westfield that required a head rebuild a few years back, and I was advised by a very well respected engine builder to avoid replacing the copper gasket that had failed with a composite item. Widely available for tunable car engines, but I'm guessing it would be more of a challenge to find similar for an old sohc honda as demand would be comparatively small.
There was a copper gasket on my 400 that was worked on by Dixon Racing back in the 80s, but it was no thicker than a std gasket, so a Cruzinimage gasket has gone back on - will see how that goes !
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We use copper MTC head gaskets with the 1428cc barrels on GSX based Funny Bike, it has turbo and 2 stage NOS injection, the head gasket is the only thing we don't wreck. I also use one on my XS1100 and re-use it after annealing.
I use instant gasket round the camchain tunnel, external oil way means no worries on that.
I recommend them.
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Dynoman in the USA has a whole range of copper gaskets, check out the SOHC page on the web site http://www.dynoman.net/bikepages/sohc/index.html
I use a copper gasket on my 998cc engine - billet JMR block with nikasil bores and a thin wire 'O' ring fitted around the top of each bore. A quick spray over with 'Copper Spay-a-Gasket' helps to seal the whole caboodle.
My CR750 also has a copper gasket fitted, no leaks there either.
Eric
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This guy appears to have one or two copper head gaskets. https://www.ebay.co.uk/itm/HONDA-CB750-COPPER-HEAD-GASKET-042-THICK-X-61MM-BORE/311395399538?hash=item48809cb772:g:fPUAAOSwu4BVlsXC
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I am going g to use a copper head gasket on one of my engines, I had one made a bit thicker into compensate the head been skimmed too much, I intend to use hylomar spray to seal it , having googled it that seems the way to go, does anyone see any problems, it's a 69, 750 head too expensive to waste so this is my option to salvage a very expensive head
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