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Pistons

Submitted by kenwyn_smith on Mon, 19/10/2015
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Heavy Twins

Hi, I am restoring a 650ss and I require some new standard pistons. Could anyone avise me where I can purchase some from. Norvil ?

Thanks

Kenwyn.

Submitted by Xanna_jeannett… on Mon, 19/10/2015

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Previously kenwyn_smith wrote:

Hi, I am restoring a 650ss and I require some new standard pistons. Could anyone avise me where I can purchase some from. Norvil ?

Thanks

Kenwyn.

Hello No you need BHB pistons numbers 23270 and 23271 there the originals there was a set on Ebay the other day have a look and see if there still there other than this go to Thornton pistons there on the web they use JP pistons witch are a good copy of BHB pistons yours anna J

Submitted by kenwyn_smith on Mon, 19/10/2015

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Previously anna jeannette Dixon wrote:

Previously kenwyn_smith wrote:

Hi, I am restoring a 650ss and I require some new standard pistons. Could anyone avise me where I can purchase some from. Norvil ?

Thanks

Kenwyn.

Hello No you need BHB pistons numbers 23270 and 23271 there the originals there was a set on Ebay the other day have a look and see if there still there other than this go to Thornton pistons there on the web they use JP pistons witch are a good copy of BHB pistons yours anna J

Hi Anna, Thanks for the info I will have a look. Kenwyn.

Submitted by joe_seifert on Tue, 20/10/2015

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GPM pistons made in Europe to real AE Hepolite (not new Chinese Hepolite spec!) Andover Norton part##s 067081 through 067084 depending on the size.

Submitted by Xanna_jeannett… on Tue, 20/10/2015

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Previously joe_seifert wrote:

GPM pistons made in Europe to real AE Hepolite (not new Chinese Hepolite spec!) Andover Norton part##s 067081 through 067084 depending on the size.

well if you like bricks in your engine GPM are fine ! But finding the original BHB 23270 and 23271 would be a lot better has the a lot lighter to GPM' Bricks yours anna j

Submitted by dan_field on Tue, 20/10/2015

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I recently compared the weight of a GPM piston to a JP Piston (for an ES2) interestingly most of the difference was down to the weight of the GPM pin.

Submitted by kenwyn_smith on Thu, 22/10/2015

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Previously Dan Field wrote:

I recently compared the weight of a GPM piston to a JP Piston (for an ES2) interestingly most of the difference was down to the weight of the GPM pin.

Thanks everyone for information and advise. I contacted Duncan at FW Thornton and ordered JP Pistons yesterday which arrived this morning first thing. I spoke to my mate regarding these pistons because he will be carring out the machining for me. He said he has used these pistons on a number of occasions and you can get some fine tolerances with them.

Thanks again.

Submitted by chas_goupillot on Fri, 23/10/2015

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Previously kenwyn_smith wrote:

Previously Dan Field wrote:

I recently compared the weight of a GPM piston to a JP Piston (for an ES2) interestingly most of the difference was down to the weight of the GPM pin.

Thanks everyone for information and advise. I contacted Duncan at FW Thornton and ordered JP Pistons yesterday which arrived this morning first thing. I spoke to my mate regarding these pistons because he will be carring out the machining for me. He said he has used these pistons on a number of occasions and you can get some fine tolerances with them.

Thanks again.

Interesting subject! Just removed a set of standard GPM pistons from my Mercury this afternoon. I wonder whether the weight of these pistons is contributing to the considerable vibration I am experiencing?

Wt of bare piston = 209gm (7.37 oz)

Wt of G.pin = 49gm (1.73 oz)

Wt of rings = 21gm (0.74 oz)

Total = 279gm ( 9.84 oz)

Does anybody know the weight of the pistons used from the factory?

I would be interested to know if these pistons are significantly affecting the balance factor.

Best regards,

Chas

Submitted by phil_hannam on Fri, 23/10/2015

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GPM pistons must have improved. A weight of 279g for piston plus pin is very good. Are you sure that your scales are accurate? The first generation of replacement piston for Nortons, made by this company, were generally approaching 450g each and played havoc with the balance of any engine they were put inside.

Attached photo shows an original 99 piston weighing in at an acceptable 297g. Most of my re-balanced cranks have had pistons that weighed around 300g.

Attachments pistons-002-jpg

Submitted by Xanna_jeannett… on Sat, 24/10/2015

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Previously Phil Hannam wrote:

GPM pistons must have improved. A weight of 279g for piston plus pin is very good. Are you sure that your scales are accurate? The first generation of replacement piston for Nortons, made by this company, were generally approaching 450g each and played havoc with the balance of any engine they were put inside.

Attached photo shows an original 99 piston weighing in at an acceptable 297g. Most of my re-balanced cranks have had pistons that weighed around 300g.

well my BHB piston is a 10 + over size and it weights in at 7 oz or 200g on its own no pin or rings and I have two original model 88 pistons one 40+ over size complete weights in at 11oz the other one 60+ with pin No rings weights in at 10.3 oz So GPMs are 0.79grams heavier that the original BHB over size piston these are my findings and its not just about the weight of the piston there is the shape of the piston to most piston are narrower at the top than the bottom of the piston skirt and ovulated at the gudgen pins but you need a good digital micrometer to see this, Normal bare piston to bore tolerances should be 0.002 thou ,maximum tolerance would be 0.005 thou, Ring end gaps should be less than 0.008 thou and stage the ring at 120 degrees to each other before fitting also run some thick oil around the rings with you fingers and around the skirt too and in side your barrels this bit of oil lubes it all has you try to start the engine, please note BHB has fitted to Rolls Royce Motorcar engines only the very best parts fitted to Bracebridge Street built Norton's

Submitted by Xanna_jeannett… on Sat, 24/10/2015

Permalink

Previously kenwyn_smith wrote:

Previously Dan Field wrote:

I recently compared the weight of a GPM piston to a JP Piston (for an ES2) interestingly most of the difference was down to the weight of the GPM pin.

Thanks everyone for information and advise. I contacted Duncan at FW Thornton and ordered JP Pistons yesterday which arrived this morning first thing. I spoke to my mate regarding these pistons because he will be carring out the machining for me. He said he has used these pistons on a number of occasions and you can get some fine tolerances with them.

Thanks again.

Hello JP piston are just has good has the original BHB has fitted to Norton Machines but Wisco and MotoCovo are also available

Submitted by chas_goupillot on Sat, 24/10/2015

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Previously anna jeannette Dixon wrote:

Previously kenwyn_smith wrote:

Previously Dan Field wrote:

I recently compared the weight of a GPM piston to a JP Piston (for an ES2) interestingly most of the difference was down to the weight of the GPM pin.

Thanks everyone for information and advise. I contacted Duncan at FW Thornton and ordered JP Pistons yesterday which arrived this morning first thing. I spoke to my mate regarding these pistons because he will be carring out the machining for me. He said he has used these pistons on a number of occasions and you can get some fine tolerances with them.

Thanks again.

Hello JP piston are just has good has the original BHB has fitted to Norton Machines but Wisco and MotoCovo are also available
Hi all,
Thanks for the info on piston wts.
The set of electronic scales I used to weigh the componentshad a calibration check in August 2015, so I am happy wts are accurare enough to give a valid comparison.
From Phil's figures for his piston, minearelighter byabout 6 to7%. Can't imagine this would be all that significant (???). The 2 pistons weigh about the same, give or take a few gms.
Next question is where can I obtain new rings for GPM pistons?
Best regards,
Chas

Submitted by james_brierley on Sat, 24/10/2015

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I'm currently building a 99 engine with re-lined std cylinders and was thinking of using some new Hepolite hi comp pistons part No 13408, as I had them sat on the shelf for the last 30 odd years. I think they are from a Nomad.

Does anybody out there have any experience with these pistons and what's the best cam to use with them?

Submitted by robert_tuck on Sat, 24/10/2015

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I would check the CR and if its higher than 9 to one fit a compression plate under the barrel. Check the rocker/valve tip action and if necessry modify the pushrods to correct. A std (daytona) cam with flat followers will be an easy fit. Its an old motor ,why risk it?

 


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