The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: compressorman on 01.05. 2014 19:20
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Hi all
i am just wondering if anyone knows of were i can get a thicker than standard head gasket from?
i need to drop my compression a bit after probably too many head skims
thanks again to all you helpfu chaps out there
regards
ian
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Hi.
Not sure where in the Uk you will get them, but Copper Gaskets in the USA may help, they offer bespoke service
I,ve used them for copper rocket cover gaskets, and the price and carriage to the Uk was very reasonable.
I think they sell on Ebay
www.coppergaskets.us
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Ian,
Just curious. Have you calculated your compression ratio with the standard gasket and how much additional thickness you would need? Others should comment here, but perhaps it's OK to just use two standard versions. It seems to me that a copper-to-copper seal should be at least as good as one that is copper-to-steel (and/or aluminum).
Richard L.
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Yes, Lani is the man at Copper Gaskets. Very helpful and quick.
Two gaskets always leak eventually. The proper way is to use a thicker gasket or plate under the barrels.
0.010" extra thickness will give 1 cc extra volume. So to drop it from 9:1 to 8:1 you would need to increase the thickness by an extra 0.050" (a quick estimate at 5am).
Cheers
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Thanks all
My 58 is on plus 8o bores with 7 5 1 pistons as well as the
Many head skims that you would expect with this many
Re bores so I was thinking maybe a double thickness
Would be ok bearing in mind I have an iron head
I believe the standard gasket to be approx 1mm thick
Regards
Ian
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Have you calculated your compression ratio
#217 in http://www.a7a10.net/forum/index.php?topic=8306.0 (needs login)
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By my calcs, your 0.080" over equates to 19.16 cc. Seems you would have had to skim off an awful lot of head material to equal that difference, and then some, to end up with excessive compression.
Richard L.
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I wouldn't really expect there to have been all that many skims, unless you know for sure otherwise. It isn't done automatically with a rebore; it's not usually necessary, especially with an iron head.
I'd be inclined to measure the head & barrel thicknesses if you want to be sure. The unskimmed standard barrel is 4" from base flange to deck.
Are you experiencing detonation? If not, dont worry. 7.5:1 is super low, even if it has had .040" off and its now 8.5:1, that really isn't going to cause any concern.
You may be trying to fix something that isn't broken.
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Maybe this could be a solution? http://www.ebay.co.uk/itm/Compression-plate-for-BSA-A7-and-A10-/121330490578?pt=UK_Motorcycle_Parts_13&hash=item1c3fdc5cd2
John
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Why the hell you would make them out of stainless is beyound me.
However Lanai makes them as well from both copper or aluminium.
We had some done in aluminium for the A 75 as they disappear being aluminium.
On the A 75 you have to be careful with the head gasket thickness as they tend to spit them out.
On the A 10 this is not a problem so now you know you need .6mm