The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: UKlittleguns on 13.10. 2020 13:42

Title: Cylinder Head Gasket
Post by: UKlittleguns on 13.10. 2020 13:42
Hi Everybody,

Two questions and then the background.

Can an A10 copper cylinder head gasket be used on the A7.

Does the gasket need a sealant.

After the engine rebuild and the faf of setting the carb etc it ran a treat and started on the first or second kick.  First trip out and two miles down the road it spat its composite cylinder head gasket out of the right hand cylinder.  The only reason for using a composite was that my new copper gasket was for an A10 and the bore holes just looked too large.  Composite was the only thing available with the correct bore size.

The head and block surfaces were faced at the local reconditioners and the bolts were all torqued down.

Anyway, no damage done, just a bit of spannering.  Copper from now on, hence my initial questions *smile*

Regards to all.

Title: Re: Cylinder Head Gasket
Post by: RDfella on 13.10. 2020 16:09
Did you re-tighten the head bolts after the first run? If so, then either the bolts are thread-bound or you're not doing then up tight enough.
Title: Re: Cylinder Head Gasket
Post by: bsa-bill on 13.10. 2020 16:23
Quote
either the bolts are thread-bound

It's somtimes possible for the head bolt holes to have a layer of crud in the bottom of them which can prevent the head bolts from reaching full depth
Title: Re: Cylinder Head Gasket
Post by: UKlittleguns on 13.10. 2020 17:18
Hi,

Thanks for that but I don't think clamping force is the issue.  The block threads were tapped clean and blown out.  The bolts were tried without the head prior to assembly and the distance measured between block and bolt head.  There must have been some 5mm clearance down all the threaded holes.  I'll have to check my notes but I think the bolts were tightened to 24 ft lbs.

The key question remains.  Can an A10 copper gasket be used on an A7 engine.

Regards
Title: Re: Cylinder Head Gasket
Post by: Klaus on 13.10. 2020 17:57
To answer your question....   no.

For A7 are only the composit gaskets available and these are in my oppinion scrab.

Solid copper is best way, but you had to build your own gasket for your engine. I do it with 0,7mm copperplates I get from the roofer, cut it to a propper fit for every engine. Anneling and a light surface with sealant on both sides. Fit with correckt torque and thats all. Never retorque any head bolt on my bikes.

Cheers Klaus
Title: Re: Cylinder Head Gasket
Post by: Black Sheep on 13.10. 2020 19:39
Well, actually yes, not that I would recommend it. For a while you couldn't get any head gaskets for A7s so there was no choice but to use an A10 one. The exposed gap soon fills with carbon anyway.
If you spat out a composite gasket so quickly there was something wrong. Find out why and then try again. In my experience, solid copper gaskets need several re-torqueings and are still prone to oil weeps. I have reverted to composite gaskets and am happy with them. 
Title: Re: Cylinder Head Gasket
Post by: metalflake11 on 13.10. 2020 19:44
Did you re-tighten the head bolts after the first run? If so, then either the bolts are thread-bound or you're not doing then up tight enough.

First trip out, and two miles down the road.

35lbs is the S.R.M. recommendation, so they were a bit loose!

I'm not keen on composite and always use solid gaskets. I torque them, heat the head and barrels for hours, leave them to settle for 24 hrs, then re-torque.

So far I've got away with that.
Title: Re: Cylinder Head Gasket
Post by: chaterlea25 on 13.10. 2020 21:51
Hi All
Here is a link to a solid copper A7 head gasket

https://www.ebay.co.uk/itm/BSA-A7-A10-COPPER-HEAD-GASKET-1-06MM-THICK-X-67-3MM-BORE/312602264415

You need to tell him the exact bore size

Lani has supplied gaskets to quite a few of the members here and has done some specials for me including a 2mm thick A10 gasket I needed for a bike where the head had been skimmed to death

John
Title: Re: Cylinder Head Gasket
Post by: KiwiGF on 14.10. 2020 10:45
Hi,

Thanks for that but I don't think clamping force is the issue.  The block threads were tapped clean and blown out.  The bolts were tried without the head prior to assembly and the distance measured between block and bolt head.  There must have been some 5mm clearance down all the threaded holes.  I'll have to check my notes but I think the bolts were tightened to 24 ft lbs.

The key question remains.  Can an A10 copper gasket be used on an A7 engine.

Regards

From my bitter experience I would not trust a torque wrench unless it had been “callibrated” or at least checked against a known good one  *problem* - a duff wrench caused a head gasket failure on my A10.
Title: Re: Cylinder Head Gasket
Post by: Black Sheep on 14.10. 2020 10:46
Something to be said for the old fashioned arm and correct length spanner.
Title: Re: Cylinder Head Gasket
Post by: RDfella on 14.10. 2020 11:44
I presume it's common practise among members, but this is how I tighten heads down (all types of engine).
Just 'nip' the bolts / nuts to ensure head is seated level and evenly. Go around bolts / nuts again with a light tighten (always working opposite bolts), I then repeat the process at least twice more before giving the final tighten. And then re-check after a little running (unless it's an engine with stretch bolts etc). Never tighten a head by going from one end to the other or, in the case of motorcycles, around the cylinder.