Pistons

[tv175]

Hello there

I was wondering, if anyone could recommend, where I should order +060 pistons to Super Rocket?
British only Austria have only italians ones and the seller haven't informed me about kompression rations?
I was wondering also, if those italian ones are high quality, so if anyone has experiences, please inform me. 
And also if australian JP pistons are high quality?
Please, inform me where I should order these pistons? Preferably from Europe..
All information is welcome.

with kind regards,
Tapani

[trevinoz]

Tapani,
                     I have used Ialian GPM pistons with no problems but there are others that have not been so fortunate.
JP pistons have a reputation for high expansion but I haven't used them so can't comment.
I am running unbranded 7.25:1 pistons in my '55 Flash and they have given no trouble, in fact they look very well made.
  Trev.

[BSA_54A10]

And I have used JP's ( as they are local ) without much grief.
Some of them are a bit on the heavy side and as of late the rings are not the best but I went to gapless rings nearly 10 years ago.

[bikerboy]

Gapless rings ? Are they something I should know about ?

[0116harley]

Hi Tapani
i wasnt sure which pistons to use on my A10 myself. After asking around i went for Italian GMP pistons. Done over a 1000 miles and dont seem to be any problems.
cheers Neil

[beezermacc]

I am told, by an ex BSA employee, that BSA used GPM pistons as standard equipment just before they went bust.

[cyclobutch]

Not sure that's a good recommendation. Roger at Cake Street stocks Wiseco though I hear that they are not cheap.

[beezermacc]

The ex BSA employee reckons the GPM pistons are good, though I have heard other comments to the contrary. I know Wiseco are good because I used them in race bikes but that was in my motocross days on a Maico. The pistons were superb quality and were well matched and balanced to the engine. Are the Wiseco pistons available via Roger at Cake Street actually intended for A10's? I'm surprised they aren't more widely used if they're the answer to the current absence of good original or Hepolite. We need a recommendation from somebody who has done some miles with Wiseco pistons. The problem is we seem to be getting conflicting reports about all the pistons. I've used GPM's in my Super Rocket spec bike and it seems prone to vibration, whether this is because the pistons are poorly balanced or the compression is too high or anything else I don't know!

[Brian]

Bit of a difficult subject as there are so many variables to take into account.

I'm not going to recommend any particular piston so can only relate my experiences.

I have used genuine BSA pistons, GPM, Hepolite, JP, Wiseco, Polson and even have a A10 running on a cheap set of Tiawanese pistons and have never had a problem with any of them.

I think most piston problems come from incorrect clearances or other factors like a bike running lean and consequently at a higher temperature than desirable. At the end of the day a piston is simply a lump of aluminium that holds the rings in place, as long as the lump of aluminium doesnt get any bigger than the hole is slides up and down in then all is well.

Unfortunately a lot of mechanical devices get a bad reputation based purely on rumour and unfounded "experiences". How many times have we all heard the dont buy a BSA twin as they wear out or seize timing side bushes all the time. We all know a well set up timing side bush will do many miles.

[tv175]

Hi,

Thanks for the answers. After all I decide to use GPM pistons.

What clearance should be the best?

Thanks a lot in advance.

Best regards, Tapani

[Brian]

The BSA manual recommends .003"-.0045". Personally I would suggest .004", no less.

[BSA_54A10]

Gapless rings ? Are they something I should know about ?

Many moons ago I needed new rings for my Silver Shadow and the only people that could supply them apart from RR was Total Seal.
They recommended the gapless series so I fitted them and have been using them ever since.
Some times they are a right royal bugger to fit but worth it in the long run.
The second ring has an overlap thus no gap.
This takes all the pressure off the oil scrapers which can then do their job properly.
Oddly enough you oft end up burning a bit more oil than standard .
I buy a lot of rings from Total Seal as they will supply single rings in almost any size, very handy when ham fists here breaks the top ring. While a single ring is dearer than 1/6th the  price of a full set it is a lot cheaper than a full set.
They also supply oversize rings so you can delay boring a barrel that is not quite worn enough for a rebore or refit a piston that after cleaning up is a little smaller than it should be.
Both of these "bodges" assume that you ride a little more sedately than Musky.