Author Topic: Piston questions  (Read 1377 times)

Offline Josh Cox

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Piston questions
« on: 30.04. 2009 12:02 »
Good evening,

Presently have my A10 engine being dismantled, the gentleman doing it says the pistons will need to be replaced, apparently standard size (spec) and will find out in the next few days whether the barrels are OK.

So pulled out the trusty parts manuals, came up with a few different part numbers.

The present pistons are apparently original concave head types, what are your recommendations for replacement items, higher compression, which provider presents best value etc etc.

Thanks in advance.
Black 1953 Golden Flash Plunger

Offline LJ.

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Re: Piston questions
« Reply #1 on: 30.04. 2009 12:16 »
Well Josh, I'm not an engineer or mechanic as such and more knowledgeable guys here will be able to tell you better, but with my simple thinking you'd not go wrong sticking with standard compression pistons, all my bikes are standard and run far happily than with higher compressions that can invite more stress and possibly later problems. I think those in the UK will likely recommend you to C&D autos if yourself is in the UK.
Ride Safely Lads! LJ.
**********************
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
1961 BSA A10  650cc Golden Flash-Blue
1961 BSA A10  650cc Golden Flash-Red

Online Brian

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Re: Piston questions
« Reply #2 on: 30.04. 2009 12:45 »
I guess it all depends on what you want from your bike Josh. Personally I would up the ante a little as I have done on my 53' A10. I went to 7.25 - 1 compression with the 356 cam which seems to work very well in the plunger models.

As yours had the standard pistons it probably has the standard cam 67-334 ( stamped on the end of the cam).

If you choose to go this way you need the cam with 67-356 stamped in the end plus the new pistons. I would try to find some pistons with a known reputation, like Hepolite. If you can find Hepolite ones you need SW11062 which are the 7.25-1 ones. If anyone offers you pistons from an unknown manafacturer or from Asia tell them no. With a bit of searching you should be able to find some Hepolite ones. I have used GPM pistons which are Italian and they are very good also. I think C@D's stock GPM pistons.

Here in Aus we also have JP pistons but I havent used them yet so cant give any feedback on them. I have not heard any bad reports about them so they should be ok. Maybe someone else has used them and can provide some feedback.

This combination will give you a very sweet running motor which will cruise all day at 65mph, easy to start etc.

The standard set up also works well but its nice to have just a bit more go and I am guessing that like me, you have larger distances to cope with so a lot of highway cruising will be in order.

Brian.

Online A10Boy

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Re: Piston questions
« Reply #3 on: 30.04. 2009 14:11 »
Josh
I think its a good idea to go for a hotter cam if you want a bit more power, if yours is a later engine then it will probably have the 356 cam anyway but you can check this.

I wouldn't advise going for higher compression pistons if you are using a cast head as this can cause it to run hot and pre-ignite, and by themselves they don't make much difference anyway.

Good luck
Regards

Andy

1958 Super Rocket
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1974 Kawasaki Z1a
Yam XJR 1300

Offline roadrocket

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Re: Piston questions
« Reply #4 on: 30.04. 2009 14:15 »
I also have the 356 and 7,25:1 combination, though in my SR-headed RR replica. It works well there without any temper. They are JP, and are doing fine.

Otto in Denmark
Otto in Denmark

Online A10Boy

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Re: Piston questions
« Reply #5 on: 30.04. 2009 14:26 »
Yes the alloy head has far better heat radiation capabilities and therefore can run much higher compression than the cast head.

Its a nice looking bike.
Regards

Andy

1958 Super Rocket
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline BSA_54A10

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Re: Piston questions
« Reply #6 on: 01.05. 2009 01:36 »
As a rule of thumb,
Lower compression pistons will put a lot less stress on the bottom end, run for longer and be far more tollerant of poor quality fuels , vibrate less harshly and of course deliver a lot less power.
As you go higher you get all the benefits  of more power but more vibrations, fussy about fuel & timing shorten bottom end life etc.
What is most important is what you want to do on your bike.
If it is going to be a daily transport bike in modern traffic or extended motorway riding then bigger pistons are a must.
If you are going to be doing a lot of long distance riding then bigger pistons are a maybe
If you do a couple of leisurely rides each month then leave it as is.

It is your bike make it suit you.
 
Bike Beesa
Trevor

Offline olev

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Re: Piston questions
« Reply #7 on: 01.05. 2009 13:06 »
Gday Josh,
JP pistons are very good. They are used by a lot by the racing boys.
They use modern high silicon alloys.
They are also quite expensive.
Give Mike Reilly a call  (07 38040055 - business hours)
He just might have some originals in the size you need.
cheers
ps: go original. get it running sweet. then when you start modifying the thing, you have a reference.