The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: mrshells on 08.02. 2010 18:54
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Standard pistons for a 52 Startwin are 11288 at 7.25 CR
Ive heard a rumour that 11603 8.5 cr will fit
also bike has a 356 cam is there a quicker profile standard cam that will fit ?
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G'day mrshells, 357 is the sports cam that delivers more up top, have srrn them new on flebay for about 80 pounds. Pistons should fit if their for an A10.
Cheers
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I think you will need stronger valve springs for the 67-357 cam.
The pistons are A7 Shooting Star I suppose? Whats the bore and stroke dimensions of the 52 StarTwin? I think the SS is shorter stroke and larger bore, so I don't really believe they will fit.
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shooting star and star twin are the same bore and stroke 72.9x66 mm shooting star has higher compression
I have been told they will fit but just wanted a 2nd opinion *smile*
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you are right, it's just been the first star twins that had the different bore and stroke size.
So the A7 SS pistons should definitely work, and pistons for the std A7 should be fine too, although with lower CR. I made good experiences with JP Pistons from Australia for the SS. You could also contact Roger Shirman from Cake Street classics (just google). He sells forged Wisecos for A7 and A10 which are absolutely brilliant. But I can't remember what CR the A7 ones were...
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cant get hold of cake classics
but been on wiseco web site and they dont list anything ???? ???? ????
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Company: Cake Street Classics (A7/10 Parts and Rebuilding)
Address: Cake Street, Barnyard Screen
Laxfield
Woodbridge
Suffolk
IP13 8EW
Contact: Roger Shirman
Telephone: 01986 798504
The pistons are specially made for CSC, I also couldn't find them elsewhere. roger was very helpful, give him a phone call, I think he's not so much into computers and email...
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are you sure they were the real deal ?
I dont mean to insult anyone but wiseco are a bloody big company to make pistons for a little shop in the UK and not market them,themselves
In the mean time I got hold of some +40 good used pistons and put new rings and pins in them ,the barrels are in for rebore now
the crank is having a grind and the heads having a little skim !
couple of weeks and shell be running like new again *smile*
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They definitely are Wisecos. They came in the origianl box with factory documents and fitting instructions (and Wiseco decals *smile*). And having seen several forged Wiseco pistons before and knowing how they should look like, I dare to state that they are originals.
Wiseco also produces pistons made to specific orders, you just have to order a batch that is large enough. They also make pistons for Goldstars and Bonnevilles, sold by other smaller suppliers in the UK. I suppose it is not such a huge problem, if they have a suitable forging blank that can be machined to size.
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Ill have to keep trying him then
thanks *smile*
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Got hold of cake St he only has A10 pistons *sad2*
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Sorry to hear that, I thought CSC would have Wisecos for the A7 too, my memory has obviously fooled me here. I apologize for having mislead you.
But you might want to try JP in Down Under (http://www.jp.com.au/JPPistons.html).
They have listed A7 pistons with a CR of 6.6 on their website. I'm using JPs in the A7SS. Mine had a CR of 8.25 or 8.5, I can't remember exactly. Just write them an email, I think they haven't listed everything on the site.
They are cast and not forged like the Wisecos, but therefore they are a bit cheaper and look reasonably well manufactured. They work pretty well in the SS, I fitted them with a clearance of 4 thou. I think JP stated 3 thou if my memory serves me right, but I tried to stay on the safe side here.
Cheer, Markus
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Lyford Classics have them listed in their catalogue std,+20,+40 and +60 might be worth a call if you haven't already
tel 01773 768900
or http://lyford-bsa.co.uk/home.html (http://lyford-bsa.co.uk/home.html)
All the best - Bill
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mrshells,
I had trouble finding Hepolites for my A10, ended up ordering them from Draganfly, they sent me JP's, which I am thus far very happy with, as I am already in Australia, that makes my pistons very well travelled.
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Thanks to this topic, I now know what pistons I have. I wondered what 'JP 0624' on the piston crowns meant. Australian, 9:1.
Love this forum!
Alan
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Pleasing to hear the JP's work well on A7's, I had 9:1 comp JP's on a Norton Atlas motor and they caused me nothing but grief. They were also quite heavy. Both sets seized with the second set must have had a hairline crack in as one seized after a few minutes light running and had a visible crack in after disassembly. I ended up putting in Wiseco's and that sorted it. Perhaps in a road motor they might be ok. But I'd never use them myself given any sort of choice.
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Rocket Racer,
I agree, the JPs are ok for road use, but I would not use them for a racing engine. There's nothing better than a good FORGED piston for high performance use due to the higher material strength.
I had problems similar to yours with the Italian GPMs in the A10, I think I told the story in another thread already. Many others use them without any troubles.
I don't really know what the reasons for this discrepancy are, maybe its large manufacturing tolerances, insufficient quality assurance or finally just the riding style, no idea.
But like the crack in your JPs the problem with my GPMs definitely had been a mistake somewhere in the manufacturing process, the solution for me were the Wisecos, too.
But unless you are able to find a set of good Hepolites, there aren't any alternatives for the A7 I would know of. All the JPs I have fitted to several bikes so far actually never caused any sort of problems.
What I always do now before fitting new pistons is to temper them prior to fitting. I measure the diameter of the new pistons on several positions and directions and then slowly heat them up to 250°C (this is the maximum temp. the kitchen oven can deliver, but I suggest to wait 'til the better half is absent to avoid discussions similar to the one that occurs when you get caught cleaning cycle parts in the dish washer *eek* ;)) and let them cool down, I do this 3 or 4 times. When finally cooled down I measure again and check for any irregularities (residual deformations, visible cracks, etc.).
This way you have a chance of seeing the results of geometric irregularities or material imperfections and reduce residual stresses from the casting process.
Speaking of the piston weight: All pistons for the A7/A10 range I have seen so far are significantly heavier than the Hepolites, which in turn were slightly heavier than the original BSA pistons as well. The Wisecos I fitted to the A10 aren't really light-weight either, I think they they were around 4 or 5 grams heavier than the GPMs, if my memory serves me right.
Cheers, Markus
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Lyford Classics have them listed in their catalogue std,+20,+40 and +60 might be worth a call if you haven't already
tel 01773 768900
or http://lyford-bsa.co.uk/home.html (http://lyford-bsa.co.uk/home.html)
All the best - Bill
Lyfords A10 piston (at least the 8.5:1 cones) are the italian cast GPMs - according to PAt at Lyford (who swears by them) -know they have mixed reviews here....
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-know they have mixed reviews here...
I bought pistons from Lyford but they are A10 9.5 and IIRC made in Australia, can't say anything about them yet as they've yet to meet a spark *conf*.
I'm confused are we looking for A10 or A7 pistons now
All the best - Bill
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On the subject of piston weight, does anyone have the weights of Wiseco pistons compared to JPs on A10, standard size? If Wisecos are heavier by some relatively small amount I'd consider getting a pair from Cake Street and carefully take metal out of them in some unstressed area to match the weight of the JPs to avoid screwing up the dynamic balancing my crank assembly with JPs has had. I used a Wiseco piston in my Gold Star and was happy to rev it really hard.
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Im looking for A7 pistons
allthough I have got hold of some perfect used +40 hepolite
and the barrel is being bored to match them
I phoned Lyford and to be honest hes taking the P**S 110 for GPM pistons each !!!
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ouch, I didn't pay that much for mine, pretty sure it was around £130 or so, looks like his online catalogue is out of date as it is stating £110 for A7 and a bit more for A7 long stroke and clearly states for a set (2), even with postage and VAT it should not come anywhere near his quote.
Just been down the shed to check receipts ( not to be recommended ) but couldn't find one for the pistons so maybe I got them elsewhere, pretty sure I remember having a conversation with him though upshot of which was the Italian ones were heavier and the Aussie ones were good.
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I fit a lot of JP's and am generally happy with them.
They did have a problem with rings a while back but they seem to be on top of that now ( wrong rings supplied ).
This is not a problem for me as I buy them bare and fit Total Seals with a gapless second ring.