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New Pistons?

Submitted by nicholas_clarke on Friday, 6 December, 2024 - 09:25
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Light Twins

Dear all, looking at future maintenance needs of my Electra I have spent some time looking for NOS pistons but with no luck from all the usual.sources.   The only pistons I can find are modern manufacturer JP Pistons and rings made in Australia.   I have heard very mixed reports on their quality from people using them on other classic bikes, particularly that they are much heavier than OEM pistons which causes excessive vibration and can lead to mechanical failure.   However, all of that is anecdotal and often contradicted!   Have any of you personal experience of using JP pistons and rings in an Electra or other Lightweight twin and if so what were the results?    Are there any alternatives out there apart from keeping a close eye out for NOS Hepolite pistons which seem to becoming incredibly rare?   My barrels are already at +30 tho - does anyone know of a trusted source of sleeves for the Electra?
Cheers.  Nick

Submitted by philip_hannam1 on Friday, 6 December, 2024 - 19:56

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I have recently purchased a set of Electra NOS pistons for my 500cc project.
They were half the price of Andover Norton and a third of a the cost of a set of JP sent from  Australia.
I got my pistons from  John Harding who advertises in OBM and elsewhere.

Submitted by nicholas_clarke on Friday, 6 December, 2024 - 21:02

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Thanks Philip, that's a great help, I always prefer NOS pistons.  I will contact John Harding and make some enquiries.   Cheers Nick

Submitted by ian_richtsteig on Friday, 6 December, 2024 - 22:21

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I can also recommend John Harding. A very helpful seller of hard to find items.

I have had to bite the bullet and buy a JP piston for my 1929 CS 1.  I had asked John but he didn't have one and Thornton's only had JP pistons available. 

My JP piston arrived in the post yesterday. Last night I weighed it to compare the weight to an original piston. The JP piston weighed in at 423g against 386g (9.6% heavier).

Much of the extra weight is in the gudgeon pin so I'll have to see how much lightening of the gudgeon pin can be done.

Submitted by nicholas_clarke on Saturday, 7 December, 2024 - 07:26

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Thanks Ian, that is very helpful feedback and confirms what I had heard about JP pistons.   A 9.6% increase in weight seems significant and I guess will effect the balance factor of the engine and therefore vibration and stress too.   Interesting that much of the extra weight is in the gudgeon pin.   As Michael says below gudgeon pins don't seem to wear but as a layman I would be venturing into unknown territory to mix and match between critical components from different manufacturers like that.   I wonder if machining the inside of the piston skirt to bring a JP piston to the correct weight would be a realistic proposition...?

Just to close this off for me, this is the completed job.
I reneged on using the std size JP piston. I showed it to my engine reborer and his comment was that the JP piston was too heavy to use without rebalancing. He also noted the very heavy gudgeon pin compared to the original pistons I have.
Enough weight could be taken from the gudgeon pin to bring the weight down to an acceptable number however this would take time.
We decided to bore out the standard bore to take a new Hepolite +0.040" I had and as I had have a batch of new barrels cast a few years ago I could always use one of these if a new standard piston turns up.
Barrel is back and ready to fit hopefully if time permits tomorrow.
 

Submitted by john_crocker on Saturday, 7 December, 2024 - 08:24

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I put a pair of JP pistons in my Navigator, after ~1300 miles, okay, so far.  Advice was to try to find NOS H&G pistons because of JP's poor reputation.

Couldn't find any so went with JP from Thornton's.

They needed work to get them to the same, near enough, weight as the originals.  Dimensionally, the JP's measured up well.  

I also looked at alternative pistons.  Triumph 5T might be suitable, certainly a better proportioned piston. 

I considered other pistons with a view to stretching the engines capacity, may be up to 500cc?  To do that properly a new crankshaft and cylinders might be needed, a project for another time.

 

 



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