Author Topic: Old codger needs lower compression pistons  (Read 1517 times)

Online muskrat

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Re: Old codger needs lower compression pistons
« Reply #15 on: 08.11. 2017 11:53 »
G'day GB.
It is possible but very unlikely. For them to grind 1.5-2mm off the base circle the lobes must have had a very hard life. Add to that re-ground/worn followers, it could happen. The securing screws/pin would also be copping a flogging.
I think the only way to test is to lift the rocker box (oh no). With the left ex pushrod fully up test the right ex. Lift the follower (magnet), now with your left hand feeling the cam pinion/shaft, push the follower down quickly. You should feel the shock, Don't listen to the click, just feel for the shock. So on for the other three. If you don't feel a shock you may have a problem but I would think you'd hear it cold as well as hot.
Good luck.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online Greybeard

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Re: Old codger needs lower compression pistons
« Reply #16 on: 08.11. 2017 12:05 »
G'day GB.
It is possible but very unlikely. For them to grind 1.5-2mm off the base circle the lobes must have had a very hard life. Add to that re-ground/worn followers, it could happen. The securing screws/pin would also be copping a flogging.
I think the only way to test is to lift the rocker box (oh no). With the left ex pushrod fully up test the right ex. Lift the follower (magnet), now with your left hand feeling the cam pinion/shaft, push the follower down quickly. You should feel the shock, Don't listen to the click, just feel for the shock. So on for the other three. If you don't feel a shock you may have a problem but I would think you'd hear it cold as well as hot.
Good luck.
Cheers
Sorry, should have started a new thread for this. The followers were new ones. I have a new camshaft that I bought from Priory/Andrew Guttman two years ago but I haven't been enthusiastic enough about stripping the engine to fit it yet.

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Re: Old codger needs lower compression pistons
« Reply #17 on: 08.11. 2017 12:30 »
Aren't you guys lucky to have winter!
This fellow in the US   http://www.coppergaskets.us/contactpage.html  can do A7 head gaskets in .042, .050, .063, .093, .125".
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online Greybeard

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Re: Old codger needs lower compression pistons
« Reply #18 on: 08.11. 2017 12:54 »
Aren't you guys lucky to have winter!
Oh yes indeed, very lucky. Oh boy yes, I feel so very lucky. In fact I feel sorry for you guys having weather that allows you to ride your motobikes all year round.

Offline coater87

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Re: Old codger needs lower compression pistons
« Reply #19 on: 08.11. 2017 23:51 »
Aren't you guys lucky to have winter!
Oh yes indeed, very lucky. Oh boy yes, I feel so very lucky. In fact I feel sorry for you guys having weather that allows you to ride your motobikes all year round.

 This year we will average 4 feet of snow again, like every year. You would get to shovel snow over and over. Some days having a high temp of 8 degrees F, wind gusting to 40 mph, while you shovel snow.

 Getting to wake up 2 hours early so you can get the sidewalks shoveled for the school kids, and the driveway cleared so you can go to your real job. If your lucky, after work you can shovel snow. *smile*

 Lee



Central Wisconsin in the U.S.

Online chaterlea25

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Re: Old codger needs lower compression pistons
« Reply #20 on: 09.11. 2017 17:29 »
Hi All,
Quote
This fellow in the US   http://www.coppergaskets.us/contactpage.html  can do A7 head gaskets in .042, .050, .063, .093, .125".

The last A10 I built had the alloy head skimmed to excess  *eek*
I fitted a 0.093 ( I think) gasket from Lani at the link above
Great service and value  *smile*
You need to tell him the exact bore size required as the gaskets are made to suit this

John
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1963 RGS (ongoing)

Offline BSA Biker

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Re: Old codger needs lower compression pistons
« Reply #21 on: 05.12. 2017 21:15 »
Well last Saturday I finally fitted 7.25:1 compression pistons to my A7SS, plus the refurbished magneto. The pistons were "new" old BSA stock, still in the original boxes, sent to me by Brett at Mikes Classic Bikes in Australia, yes they were slightly pricey but as I hadn't found anyone with that compression ratio it the UK they were, to me, "priceless", thanks Brett. The magneto was rebuilt via Draganfly in the UK, and looks well done. I would also like to thank Greybeard for his help to get me set up with this forum, something that seemed rather difficult as a almost "computer literate".

My main reason for wanting to reduce the compression was the fact that as the engine is 57 years old, I didn't want to over stress it by using higher comp. (8.0:1) pistons than it was used to. The kicking over is and now always will be a problem for me using my right leg, oh the joys of getting old. Perhaps in the future it will be a case of an electric starter.

As always though, after a rebuild the tappets are set, start up the engine then they close up and require resetting when cold again, is this normal?

On a final note, the Catalan Government has brought in legislation to restrict the use of old vehicles in their main cities, mostly Barcelona, because of pollution/emissions etc. This is the thin end of the wedge and by the year 2024 will we be able to use our old bikes at all. Does anyone else in other countries have these problem.

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Re: Old codger needs lower compression pistons
« Reply #22 on: 06.12. 2017 09:29 »
G'day BSA Biker.
You'll have to move down here. We're about 20 years behind when it comes to things like chemicals/pollution/dangerous stuff!
Yes the tappets will need a reset after one or two heat cycles.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline JulianS

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Re: Old codger needs lower compression pistons
« Reply #23 on: 06.12. 2017 09:38 »
If you use  thick soft rocker box to head gaskets commonly supplied you will find that they tend to settle as the material compresses causing clearances to change. The copper gaskets are much more resistant to this.

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Re: Old codger needs lower compression pistons
« Reply #24 on: 06.12. 2017 12:46 »
The larger the engine sprocket the easier it is to kick the engine over. If a side -car gear is fitted it may be a part of your problem.

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Offline BSA Biker

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Re: Old codger needs lower compression pistons
« Reply #25 on: 06.12. 2017 21:13 »
Well thanks for the info on the gaskets causing the necessary tappet re- adjustment, in the old days we used to use paper ones without any problem,  the thicker ones moving makes sense. Re-adjusted this morning by the way, but because of salt now on the roads, it won't be used in anger for some time now.

On a different tack, I'd love to move to Australia, I have a brother who moved out there in 1972 with his family, one of the last £10.00 POHMS, probably still got the ball and chain marks on his ankles, lives somewhere outside Sydney (Barrack Heights). He had a 1959 Bonneville back in the early 1960's, wasn't a BSA person, after a Bantam and then a C15, understandable really. But the chances of selling up and moving now at my age are just not on.

As for the engine sprocket, its always been a solo machine and as far as I know its the same one that was fitted in the factory in late 1959 for the new year's model.

Thanks, for all your replies--- Morgan