Hi,
Has anyone every used an extra head gasket or made an extra thick one to lower compression?
Dave.
Yes,
It was on my B44 Victor special and lowered it nicely.
My the time I did my maths and cylinder calculations, I needed a .031 piece of copper sheet and traced round a base gasket.
Hi,
Is that .031"? how much did it lower the compression by. I want to lower 8.25:1 to about 7.25:1 on an A10.
Dave.
From memory, whatever the B44 Victor special was (I think mid 9s) it brought it down to mid high 7s.
I then had to make longer pushrod caps
Hi,
How much of an increase in thickness was the 0.031 from the standard gasket? I suppose a small increase in thickness can have quite an affect.
Dave.
I left the head gasket as std but elevated the barrel by this .031" thick copper base gasket.
It was easier to do that and leave the std head gasket and barrel to head spigot as std.
Worked well and reliably
Hi rhyatt,
That is useful. As I will not be replacing a base gasket I will knock a bit off the 0.031 to allow for it. So I will measure the thickness of the std. head gasket and make a new one at std. + 0.025 ish and see how it goes.
Dave.
On the B44 single , I had to extend the pushrod a shade to maintain the angle where they meet the rocker ball ends .
May not apply to your bike
Hi,
I will keep that in mind. I think that on an A10 it may not be a problem but worth checking. I will measure the existing gasket later today to see what thickness I need. Thanks.
Dave.
Can I ask why you want to do this?
Hi,
Of course. It is my wife's '51 Flash and it has +0.080" pistons giving about 680cc with a 8.25:1 compression. After many years of kick starting this bike her knee is starting to complain. The idea is to reduce the compression a bit to make it a bit easier to start.
Dave.
For what it's worth, when I bought my John hill big bore A65 barrel it came with two gasket sizes. A 1mm and a 2mm. I fitted the 2mm as I didn't want the high compression. That seems fine with no problems.
I can't remember the company but there is a guy who will make copper gaskets to any thickness and any quantity required. Might be the same person as TT John used for his A10 rocker box gaskets.
Unless you're going to hone the barrel and re-ring it. I wouldn't be so keen on lifting the barrel. That A10 has seen a lot of miles and the wear in the bore will suit what is setup now. Also if you raise it enough the can followers might not follow the full base of the cam circle (if they bottom out that is)
Hi Allan,
As you say a lot of miles covered and it still has good compression. The thicker head gasket is definitely the easier way to go. TTJohn may respond with info. on the people who do his gaskets.
Cutting one out of sheet copper by hand would be a bit arduous but doable but a spot on laser cut one would be even better - depending on cost.
The gasket I have just taken off is 1mm thick and a new one is 1.04mm, they do not squash much. I would think 2mm would be about right. Copper sheet is not cheap so i may end up tying two gaskets.
Dave.
Hi,
After a search only the British Cycle Supply Company (Canada) offer a thicker gasket at 0.080. Not cheap especially with postage added.
Dave.
Quote from: DAVE BRADY on 11 Feb, 2024, 16:45
Hi,
After a search only the British Cycle Supply Company (Canada) offer a thicker gasket at 0.080. Not cheap especially with postage added.
Dave.
That might be the way to go. Use FedEx if you get the option. If it suggests USPS it will take a LONG time before you get it and you'll pay more for customs charge than you would with FedEx.
Hi,
An 0.080 (2mm) gasket from British Cycle Supply is about £45 plus postage so I either buy a sheet of 2mm copper and cut one out myself or use two gaskets. The sheet would probably cost about the same as two gaskets or I use an annealed used one and a new one stuck together.
So stick them together with what? Copper gasket spray seems the best idea so has anyone used such a product?
Dave.
Wellseal maybe?
Just go to your local plumber or roofer for a piece of copper sheet 2 mm. Made one myself one evening in the mancave. The head of the A65 was to many times skimmed off. Just copied the original gasket.
For me it was easy to obtain a piece of copper sheet, as a plumber.
I always annealed it before reuse,
Gr gup
Hi Gup,
Which plumbing supplies companies have 2mm copper sheet?
Dave.
I understand your question, mostly you find thinner. We had some, left over from a work. I think, when you look for companies who work with sheet copper ,hopefully they got wat left overs .
You don't need much, maybe sheet metal companies who can sell by cm/inch?
Look for aliexpres, sold 200x200 mm 1,2,and 3 mm thick.
Gr gup
Quote from: Gup holland on 14 Feb, 2024, 17:08
Just go to your local plumber or roofer for a piece of copper sheet 2 mm. Made one myself one evening in the mancave. The head of the A65 was to many times skimmed off. Just copied the original gasket.
For me it was easy to obtain a piece of copper sheet, as a plumber.
I always annealed it before reuse,
Gr gup
Is this the one your tracing or the one you made?
The one on the picture you mean? This one made myself. 2mm thick.
Quote from: Gup holland on 15 Feb, 2024, 11:51
The one on the picture you mean? This one made myself. 2mm thick.
In the picture yes. You certainly have a talent there! it looks factory made!
If I end up making one I hope it turns pout as good. Although once it is on it will not be seen.
Dave
I made it about 25 years ago I think. Had lots of trouble with pinking when engine was hot. Mate of mine did compression test ( then had no tools for it). What the outcome was exactly I don't know anymore but remembered the number 13. He said looks like a diesel ;D
Took a sheet of 2 mm copper and copied the original one on the sheet precisely with a scribe. Then find back the center of every hole. The cilinder was drilled with a holecuttervoor steel. The smaller one start with a small dril and build it up.
When you see you moved out of center , drill max dia and correct it with a needle (small file), I had one hole i corrected this way.
When you've got a drill, a set off file small and big ones, caliper, scribe, steel drills and a bit of patience , you succeed.
Here in Holland you can order copper sheet online by the cm needed, possibly in the UK also. I found even on aliexpress.
At least I think it's cheaper as 45£ for one gasket, and is fun to do.
Good luck, cheers, gup
Hi,
Just a bit of an update. I have sourced a piece of 2mm copper about A5 size for £15.80 that will give me a gasket and a company that will cut it out for £20. So with a bit of postage it will be about £40 so a bit cheaper than two 1mm gaskets.
Dave.
Quote from: DAVE BRADY on 11 Feb, 2024, 16:45
Hi,
After a search only the British Cycle Supply Company (Canada) offer a thicker gasket at 0.080. Not cheap especially with postage added.
Dave.
If I can find an old gasket somewhere I'll check on how much it would cost to make a batch of ten or so at whatever thickness you want, it's just the initial cost of doing a cad drawing etc, lett me know the thickness you want and I'll do a check. The firm I use only do gaskets for me, once the cad is done, they are exclusive to me, so I could actually have some made thinner after yours have been done.
Regards John
Hi John,
As above I have ordered a piece of 2mm copper and found a gasket man who will cut it out for £20 so not too expensive. However, it may still be worth you making the enquiries. I do not know what the demand would be but that could be influenced by the cost.
If there are others out there who need a lower compression for easier starting, this is the easiest and cheapest way to go. Also, if a head has been skimmed one time too many then the risk of valves hitting pistons can be elevated by using a thick head gasket to get the clearance back.
Dave.
I think it would be worth doing, power loss will be negligible, yet starting would be easier and the thicker gasket should help improve sealing.
Hi,
Finally sorted the gasket. Sent the piece off for cutting but got it back unfinished and no charge. The extra thickness was a problem but at least the bores and bolt holes had been done.
I ordered some rotary files and while waiting for them I cut off as much surplus material as possible. So I fitted a 12mm rotary file in my drill press and set it to max speed. Rather rough probably because it was not rotating fast enough. A smaller 6mm seemed ok. Still not dead smooth but it managed to get it done. A bit of titivating needed so I put the rotary file in the Dremel and what a difference. The Dremel goes much faster and the file worked so much better at the higher speed. I did not over smooth the outer edges as they are not critical and I was getting fed up.
I did check the gasket on the barrels to ensure a good fit by putting a few head bolts in place. One edge did protrude in to the bore a bit so I dressed this back. It may not have been a problem but I thought that perhaps it may serve as heat spot or a weak spot so a few more minutes and I am now happy. I won't post an image as it just looks like a gasket.
Dave.