Author Topic: What pistons !!!!  (Read 3115 times)

Offline michael snellin

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What pistons !!!!
« on: 18.08. 2012 17:16 »
Hello,everyone, seem to have a problem now because iv,e bought this bike in bits, urgh, !! not a good idea,?? iv,e had or going to have the barrell,bored to +60 oversize, this is where it gets complicated, what do i fit low com,or high compression, and there seems to be a problem getting hold of flat top pistons,????? any help would be much appreciated, this what happens when you buy these things in bits, and have to source the parts.URGH !!. *sad2*

Offline Goldy

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Re: What pistons !!!!
« Reply #1 on: 18.08. 2012 18:55 »
Hi Michael. It depends what machine you have as there is no point fitting high compression pistons to a standard Gold Flash. Supreme list 60 thou pistons, have a word with them
http://www.suprememotorcycles.co.uk/product_details.php?ProdID=329
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Re: What pistons !!!!
« Reply #2 on: 19.08. 2012 20:45 »
In my view [and our racing friends / roadburners will disagree], is that with today's rubbish petrol, the way to make a sweet, tractable and long lasting "road motor" is to go with the low comp pistons, especially in a Golden Flash as Goldy states.
Regards

Andy

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Online K1100

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Re: What pistons !!!!
« Reply #3 on: 01.09. 2012 20:02 »
I'm thinly qualified to respond to this, but I have just bought a Golden Flash with a motor that was rebuilt in 2002 by SRM with 6.5:1 pistons. Acceleration is super up to 65 mph where there is the beginnings of a feeling of running out of energy although acceleration continues. I haven't been beyond 70. Between 45 and 65 the ability to maintain speed whatever the gradient is very enjoyable, and has made the 100 miles I have so far ridden very good fun. The previous owner toured Australia and NZ on the bike two-up so the low compression route gets my vote of support.

John

Offline t20racerman

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Re: What pistons !!!!
« Reply #4 on: 01.09. 2012 21:59 »
In my view [and our racing friends / roadburners will disagree], is that with today's rubbish petrol, the way to make a sweet, tractable and long lasting "road motor" is to go with the low comp pistons, especially in a Golden Flash as Goldy states.

Sort of..... If you have an iron head, or like to potter round at low revs, absolutely, without a doubt, fit low compression pistons.

If you are a petrol head speed freak with an ally head (on the bike, not you!) no, go for higher comp pistons. Mine is gas flowed, big cam, big carb, SRM conversion, polished rods, nitrided crank etc etc and goes like shit off a shovel with 9.1:1 pistons. However, the pinking is a real pain, and without a manual advance and retard, it would be unrideable. I've thought about the issue of pistons a lot lately and I reckon that 8.5:1 pistons would make a very good compromise, something I might change to in the future.
So really, the best advice is what kind lf rider are you? If you want speed and intend to thrash it, go for 8.5:1 or higher. If you are happy to keep it below 75mph and dont have the urge to beat that Ducati next to you from the lights, go for 7:1 pistons. Both routes have their merits - but only one route suits me!  *smile*

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Online KiwiGF

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Re: What pistons !!!!
« Reply #5 on: 02.09. 2012 01:39 »
JP Pistons in Australia also sell A10 pistons and I've bought flat tops from them, circa 7:1 comp.
New Zealand

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

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Offline duTch

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Re: What pistons !!!!
« Reply #6 on: 02.09. 2012 12:06 »
Simon, I guess by now you'll  have a weight on those JP pistons, which also can be discussed in the bf/dyhi??

cheers
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

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Re: What pistons !!!!
« Reply #7 on: 03.09. 2012 09:02 »
Hi Dutch, JP emailed me the weights at 351 gr for the 6.5:1 and 343 gr for 7.25:1. They did not say whether this included rings, pin clips.

Anyway, below are the results of some measuring using a cheap electronic kitchen scale. I checked the scale by measuring baked bean cans of water and calculating the volume hence weight (1 liter water weighs 1000 grams) and I think the scale is accurate to within 2%, but the comparison between piston weights is probably more relevant anyway.

Desc                                                            Weight (grams)             Comment
========                                               =========              ===========
Bare Piston JP brand 7.25:1                      256                                 Bare means no pin, rings, clips
JP Pin                                                          78                                   Not tapered ID, 0.475' ID
JP set 3 rings                                              25
JP clips x 2                                                 1.5                      
Bare BSA piston flat +060 bore               261                                   its "partner" weighed 258 grams
Bare piston 8.5:1 std bore                        241                                  unknown brand
Bare hepolite 9:1 std bore                        251
Pin, tapered ID                                          78
Pin  unknown brand                                   89                                     Not tapered, 0.43 ID, HEAVY!
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 duTch

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Re: What pistons !!!!
« Reply #8 on: 03.09. 2012 11:01 »
Ok Kiwi,
         
 I was surprised how accurate those cheap scales appear to be, having also done a few test weights. I bought a kitchen set from the 2$ shop(?) for $15, and two ebay gold weighing sets for 'bout the same total.
   
 My flat top +40 Hepolites are 359 & 361 grm, so that's about the same, pin I.D seems tapered,0.545 at ends.
 
I have 4 BSA 8.5 +20's (various pins),1@ 341g, 2@344g,1@355g(comp.w rings & pins).
 I'd been led to believe that JP's were 'heavy'(bit more than their guess 343<-360), but seems no more than what I'm using, funny thing with JP is domestic freight is same as international, so doesn't matter if I buy them from O/S.....?

 Anyway, Michael, I'd say if you just like to trek around and keep your license, the 7.25's sound the go, it's what I have and shall stick with. When it ran before, it got along just fine.

 Cheers for now, duTch
ps Kiwi am still working up to B/F
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Rocket Racer

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Re: What pistons !!!!
« Reply #9 on: 04.09. 2012 02:08 »
The nicest pistons I've come across are the early road rocket 8:1 but havent seen at +60

Personally have had too many issues with JP's -wouldnt fit them if someone paid me to. Nothing to do with their weight, didnt matter what clearances I ran they kept nipping up and one failed after  the shortest of test rides -suspect had a manufacturing fault as cracked.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline duTch

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Re: What pistons !!!!
« Reply #10 on: 04.09. 2012 11:38 »
Maybe tha's what my mate meant when he said "oih Geez, -they're heavy as buggery and....mmm...oih geeez...'...? basically wasn't encouraging, but I do like to support local industry....If it works.
 Had an email back from British Only Austria, re "Far-East Æ,'..?..they're 320 grms/ea,?109 ex vat
Any feedback on those??

 cheers
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Online chaterlea25

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Re: What pistons !!!!
« Reply #11 on: 04.09. 2012 20:04 »
HI Dutch,
Re, "Far East " or new AE pistons, these were/are the ones supplied by Wassel
I posted re these some time ago,
I fitted a set to a customer bike, pistons are fine BUT the rings are CRAP!!!!
I also received a set of ""AE"" rings  recently the oil rings had a 2mm end gap when fitted to the bore  *sad2*
The supplier sent a new set without question, but still its a PITA

I believe Kiwi had problems with pistons he bought from British only???
?109 sounds a lot per piston?????

HTH
John
1961 Super Rocket
1963 RGS (ongoing)

Offline duTch

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Re: What pistons !!!!
« Reply #12 on: 04.09. 2012 22:21 »
Thanks John,
                  I do remember reading posts about 'eastern' pistons and rings, it may have been Brian(?) who said he'd using some 'so far, so good'?
 At this stage i don't think I need some, but good to have advance research.

Cheers, duTch
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Rocket Racer

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Re: What pistons !!!!
« Reply #13 on: 04.09. 2012 22:45 »
after my (Norton - since sold) went through two sets of JP's, I put in some taiwanese pistons and they were fine. In my opinion far better!
Wiseco's from cake street classics are another option, could always fit a thicker head gasket or base gasket if compression higher than preferred.
I keep my eyes open for pistons at swap meets so have quietly built up a stash, but always need rings.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Re: What pistons !!!!
« Reply #14 on: 04.09. 2012 23:00 »
I have been using the Taiwanese 7.25:1 & GPM 8.3:1 pistons with no issues.

Trev.