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I am at the point of having my barrel "done" and am a bit undecided. Sloper is basically outside my knowledge so some advice if you would be so kind
I have two pistons of which neither is in super condition but as thats all I have its Hobsons choice.
One is High comp and the other is low comp: my question is what are the pros and cons of this situation what do I lose or gain with my choice.
I should be very interested in any possible input. Thanks
Mike 8) 8) 8)
How high is Hi-comp?
What are you going to be using the Sloper for, sidecars and general riding, then low-comp,
ringing at 70mph and fast touring, hi-comp
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As I said in my original post I have two pistons one each LC and HC.
The LC piston is unusable so my choices have "significantly diminished".
It has been pointed out that there is a thought that to run with the HC pistons leads to a level of unreliability. I dont have any other info on this aspect. I am told that it would be advisory to run it with a spacer under the cylinder 2/4mm??.
I would appreciate any input/advice on any of the points raised here. Does anyone run HC. does anyone run with shims??? etc
Thanks for your input
Mike 8) 8) 8)
My little B21 had been fitted with a high compression (Triumph) piston by a PO. You can see the results in my "Piston Broke" thread .....
https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=9467.0
As you will see, I managed to source a slightly lower compression, replacement piston and added an annular compression gasket made from copper and annealed before use. The resulting compression ratio was much more respectable but still higher than the original 6.2:1. I determined the actual CR by temporarily fixing the piston (no rings) at TDC having wrapped the piston with a layer of electrical tape to seal the piston in the bore with the top edge of the tape just covering the top ring slot. The head and copper gasket were then clamped in place on the barrel and the whole assembly was mounted in/on a Workmate with the spark plug hole uppermost. The volume of oil necessary to fill the combustion chamber to the point where the fluid got to where the end of spark plug thread would normally be was recorded in order to then calculate the CR knowing the swept volume of the cylinder.
Following a little nip-up and remedial action during running in I'm hopeful that it's settled down now having done something like 250 miles on it. Itching to get out on it again but of course that's off of the menu at the moment!
Alan
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Hi Alan
Thanks for that. As you will appreciate I'm pretty much clutching at straws, so your input is very valuable. As I said I do have an LC piston but it is poorly and we are not at all sure if it is machinable.
Mike 8) 8) 8)
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General Q. were sloper pistons originally cast oval and if so A--by how much and B--Assuming that they would eventually wear round would having a piston machined round be a serious problem.
Confused
Mike 8) 8) 8)
Mike this might help ....
http://blog.wiseco.com/pistons-arent-round-profile-and-ovality-explained
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Hi Thanks for that. I knew some pistons were forged oval and the general reasoning. But not in that detail so thats good. I know there are other methods used to combat the stresses present in the combustion chamber. For instance the piston goes from stationary to max speed to stationary every time it moves up and down the barrel. Totally unprovable of course.
I also know that a lot of pistons have other methods of heat/pressure control---split sides to allow expansion--it goes on.
Does anyone have knowledge of any company offering a ""re-ovaling""service by which I mean a machine shop that will/can resize pistons so that they keep their shape? Does such even exist?
In truth my pistons are so worn as to not be measureable for ovality. (at least by me)
So I ponder---what I really need is someone to call me and say that they have a brand new sloper piston added bonus Free to Collector. And I believe in santa claus--the check is in the post---and virgin birth.
Mike 8) 8) 8) 8)
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Just for further info there is a company in Germany Klaus Wahl engineering, who will rework vintage pistons. Obviously the piston has to be in a good enough state for the job to be completed. About £100 inc VAT rings and Gudgeon Pin.
They will produce a pattern piston (to fit bore) 8) 8) for about £275 inc etc
I'll keep you informed
Mike 8) 8) 8) 8)
Glad to hear that he could help.
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I have two or three books on the Sloper 500cc OHV earlyy 30's. One says the piston is 80mm the other says 82mm.
So which is it.
Mike 8) 8) 8) 8)
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Sent my piston to Wahl Engineering in Germany today. They are saying lead time 9 to 11 weeks. I'll let you know
Mike 8) 8) 8)
Hi Mike, 500cc BSA Sloper used an 80mm piston. The 557cc SV Sloper used an 85MM piston.
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Thanks for that. My mind is now at rest that I have sent the correct piston to be reprofiled.
Mike 8) 8) 8)
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I have just been offered a brand new Sloper piston at a very good price. I'm sure in my mind that there were two or maybe three different gudgeon pin diameters. 500cc OHV
I can't fine the detail in my books so would someone kindly advise/enlighten me
Mike 8) 8) 8)
Mike
From the Hepolite catalogue 5/8 inch for the side valve S29de luxe, S30-9 and S31-7.
3/4 inch for the OHV.
Got a number for the piston on offer?
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Hi Julian. Thanks again.
No I dont have a number but all the vital stats are correct, bore, Gudgeon pin to crown ht. I shall see if there is a No but I would imagine that its unlikely. The only unknown is the weight.
Marginally different pin dia is not a problem as the small end bush can easily be reamed.
Thanks again
Mike 8) 8) 8)
Hi Mike,
When I had my piston made, we set the pin at 19mm dia, which is just under 3/4". My Sloper is an S30-13, so OHV.
Cheers,
Gui
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Hi Gui Thanks for that info. I have not seen the piston on offer, but the price is such that I shall buy it anyway and we'll see what happens.
The piston that I sent to be re profiled mit Herr Wahl has not arrived at his workshop so maybe I am with a problem. Time will tell.
My Cylinder head came back gestern. New valve seats and guides acid bath and re paint. It looks good.
The bottom end is done and assembled-really smooth, so now just the piston and barrel.
Regards
Mike 8) 8) 8)
Hi Mike, the piston will get there. Unfortunately since Brexit, German customs are being a real bother causing huge delays on anything coming from the UK. Even a small parcel from Drags that I ordered was checked and rechecked and arrived at least a week later than usual. But it arrives eventually...
Cheers,
Gui
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Hi Gui
My piston arrived at the Wahl Factory yesterday and Herr Wahl confirmed today. We shall know soon whether it can be rescued without too much drama. I shall still buy the one on offer on the basis that they are extremely rare.
Mike 8) 8) 8)
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Greetings.
I have already posted this elsewhere so if you're reading it again ---sorry.
My Sloper piston is now finished,
It has been reprofiled and coated(Teflon???)
Total cost inc outward postage £149.20
Done by Wahl Engineering Frankfurt. Herr Claus Wahl is very approachable and speaks excellent English. Anyone wishes for the details just ask.
Sadly none of the UK firms that carry out this sort of work even answered my queries.
Thanks to Gui for putting me on the right track
Mike 8) 8) 8)
Mike
Hi Mike,
Glad it worked out!
Gui
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Regards.
Mike 8) 8) 8) 8)