Author Topic: What pistons !!!!  (Read 3116 times)

Offline Duncan R

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Re: What pistons !!!!
« Reply #15 on: 05.09. 2012 13:46 »
I also have the Taiwanese pistons, no issues so far. I weighed them before fitting and matched perfect(can't remember the weight) I used my old gudgeon pins as they were a slightly better fit. The price quoted on the site is for the pair.

Cheers

Duncan
Anglo - Indian A7SS (Actually is a 650)
Kawasaki ZZR 1100
BMW R80GS
BMW R1100GS

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
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Re: What pistons !!!!
« Reply #16 on: 06.09. 2012 08:09 »
Hi Chaterlea, yep I returned some pistons to BOA and got a full refund inc. the freight so no complaints there. I wish I had kept them now but the BOA rings and pins supplied were useless and the cost of buying those separately made the total price rather expensive. BOA could not replace just the duff rings and pins separately at the time.

The only reason I would not (now) give buying the pistons from BOA another go would be that they would not state the manufacturer of the pistons, so you cannot be sure you would get the same pistons as anyone else got!

I bought JP pistons instead, and at least for std bore flat tops I'm using I would say the JP's are not significantly heavier than the BOA pistons, but I am rather concerned about some of the comments made about JP's seizing and cracking etc - I just hope any quality issues JP have do not apply to std bore flat tops!
New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, project missing parts, mission impossible?

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife

Online chaterlea25

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Re: What pistons !!!!
« Reply #17 on: 06.09. 2012 22:31 »
Hi Kiwi,
I have only hearsay evidence on the JP pistons for the A series  ???? ????
However I have fitted one to a BSA B33 and its running very well.
The JP's need more clearance than "other" brands
I have a JP piston which was a special manufacture item for the Blackburne 350 engine for my Chater Lea
A batch was commissioned some years ago by Martyn Adams but these have all gone
I  aquired another cylinder and was looking for a plus 20 or 30 piston for it, mucho $$$$$  *eek*
gone off track now havn't I  ????

Cheers
John
1961 Super Rocket
1963 RGS (ongoing)

Online KiwiGF

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Re: What pistons !!!!
« Reply #18 on: 07.09. 2012 02:34 »
Hi Chaterlea, I've a friend with a 55 GF rebuilt with JP's and it's been fine for 30k miles. The need for extra clearance I've heard of before, I guess the JP's must expand a bit more than other pistons, in any event this suited me as my barrel was sleeved to std with some seizure scratches and after those were honed out it gave a clearance of a bit over 005 according to the engineering company. I'll be extra careful running it in.

Regarding the alleged heaviness of JP's compared to other brands I've heard that some brands of piston (maybe JP's?) are all machined on the O.D. from the same "blank" (which is a cast blank in the case of JP's, I think) - this approach is to keep manufactureing costs down, the result of tht is that the oversizes of piston are inevitably heavier, due to the thicker walls.

Do you think there is any truth in that?
New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, project missing parts, mission impossible?

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife

Offline gavinoz

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Re: What pistons !!!!
« Reply #19 on: 07.09. 2012 03:59 »
I've heard that some brands of piston (maybe JP's?) are all machined on the O.D. from the same "blank" (which is a cast blank in the case of JP's, I think)
This is the case, i was just speaking to JP r.e.8:1 pistons
gavinoz
Rigid A7S, 57 A10 in pieces
Australia

Offline MG

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Re: What pistons !!!!
« Reply #20 on: 07.09. 2012 19:46 »
Hi Kiwi!
I got JPs in the A7 SS, with no negative things to report whatsoever! I fitted them with a clearance of 3.15 thou (8/100mm), for the larger bore A10 you might want a tad more, around 4 to 4.5 thou I'd say.
The need for larger clearance is not necessarily a sign of inferior material or greater thermal expansion, the main reason is that the JPs don't have slotted skirts for expansion control. The larger clearance might cause some more noise when cold (although I could never notice any undue noise, unless the pistons and bores are REALLY worn). But otoh a solid skirt piston is substantially stronger than its slotted counterpart. Slotted pistons in Norton Commandos are known to fall apart at high revs regularly, owing to the high piston velocity of the larger capacity engines.
At the risk of repeating myself: If you want something really really good and can afford them, go for a set of forged Wisecos from Cake Street Classics!
Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

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