GPM or "new" Hepolite pistons.

Reggie · Oct 26, 2019

My friend in Norway is wanting some new standard pistons in +0.020" for his 850 Commando.
I think as far as I can work out, that Andover Norton sell GPM pistons and RGM sell "new" Hepolite pistons.
Is one make known to be better than the other, or are they both considered to be of good quality? Obviously I am interested if anybody has had problems with either.
Thanks

Esmerela · Oct 27, 2019

Hi Reggie

I used EMGO , Cosmos emitted positive waves in their direction for a std tune motor. I threw away the round wire C clips and fitted OEM flat cut clips from AN,
combined with Harris rings. I had the barrel bored +.0200" to match the new pistons on assembly when I checked he ring gaps they came up bigger than expected but still within tolerance. All good so far. Do shop around I found massive variation in prices.

Triton Thrasher · Oct 27, 2019

EMGO, Harris, JCC and new Hepolite are the same Taiwanese piston and they have a good rep.

Some of the supplied wire circlips don’t look great.

Don’t put a flat section circlip into a groove meant for a wire clip, or vice versa.

Time Warp · Oct 27, 2019

For a stock type bike you would be hard pressed to find better than JCC pistons with Hastings rings.

kommando · Oct 27, 2019

To check the circlip groove profile press some plasticine or blue tack into the groove and then look closely at the impression shape. My JCC pistons came with wire circlips and square circlip grooves so bought and use the proper flat circlips.

Reggie · Oct 27, 2019

Esmerela said:
I threw away the round wire C clips and fitted OEM flat cut clips from AN,
combined with Harris rings.

Hi Kate, so you put a seeger circlip into a piston that came with a round wire "C" clip. I assume that's ok to do?

Esmerela said:
combined with Harris rings

Have the Emgo rings got a bad reputation for not bedding in?

Reggie · Oct 27, 2019

Triton Thrasher said:
EMGO, Harris, JCC and new Hepolite are the same Taiwanese piston and they have a good rep.

Time Warp said:
For a stock type bike you would be hard pressed to find better than JCC pistons with Hastings rings.

Ok, thanks for the info. It would seem then that all of the above makes are good to go. Is there a problem with the rings as Esmerela and Time Warp have fitted alternative rings?

kommando · Oct 27, 2019

Reggie said:
Hi Kate, so you put a seeger circlip into a piston that came with a round wire "C" clip. I assume that's ok to do?

Only if the circlip grooves in the piston are square shaped, if they are round then they need good quality wire circlips, where you get these from will be an issue.

Reggie · Oct 27, 2019

kommando said:
Only if the circlip grooves in the piston are square shaped, if they are round then they need good quality wire circlips, where you get these from will be an issue.

O.K. Thanks for clarifying that.

Esmerela · Oct 27, 2019

Reggie said:
Hi Kate, so you put a seeger circlip into a piston that came with a round wire "C" clip. I assume that's ok to do?

Have the Emgo rings got a bad reputation for not bedding in?

Hi Matrin

As you well know that would be a bloody daft thing to do, The C Clip grooves in my Emgo pistons were cut with flat bottom ( as Kommando ) hence throwing away the wire rings.

I don't believe the Emgo pistons are supplied with rings.
I bought my pistons and rings from the Bonneville Shop in Colorado for not much more than the cost of one piston in the UK . The company I work for has a US HQ in Atlanta had them shipped there and tucked them in to my suit case on the way home

Emgo USA is also in Atlanta those pistons had some journey before the started work in my bike.

Reggie · Oct 28, 2019

Esmerela said:
As you well know that would be a bloody daft thing to do

Ok. I suppose I did. You've caught me out.

Esmerela said; " I threw away the round wire C clips and fitted OEM flat cut clips from AN,"

I was just a bit confused with the reference to round wire being swapped for flat cut clips, but as the cut-outs in your pistons had flat bottoms (square essentially in profile), now I understand.

Esmerela said:
I bought my pistons and rings from the Bonneville Shop in Colorado for not much more than the cost of one piston in the UK .

Sounds as if you got a bargain.

Reggie · Oct 28, 2019

Thanks to all for the replies.

Chris Zet · Oct 30, 2019

Hi Reggie,

had GPM-pistons for the last ten years.
This year i had to replace them.

decided to take the pistons from RGM. The so called "New Hepolites".
these are JCC pistons with seagar type circlips and Hastings piston rings.

The price is about 100 Euros cheaper than the GPM-pistons!!!

My comparison:

piston construction: similar
piston weight: the JCC are 12 gramms lighter per piston than the GPM.
Both are non forged pistons
Piston-rings: i like the oil-scraper-type from the Hastings-rings [3-piece type] more than the oil-scraper-type from the GPM-pistons [2-piece type].

One thing i would recommend: take the lightweight gudgeon pins from RGM: another 10 - 12 gramms lighter per pin than standard.

Resume after one season with the new pistons: i am happy with them!

chris

Reggie · Oct 30, 2019

Thanks Chris for your informative and very comprehensive reply.

I'd not heard about the lightweight gudgeon pins. I might give them a go.

jseng1 · Oct 30, 2019

The problem with JCC, GPM, Hepolite, (AE) pistons is that the ring lands blow out prematurely. The rings are thick and heavy, they pound up and down in the slot causing the ring lands to loosen up and then you have blowby and smoking. Modern pistons use thinner rings to avoid this problem.

See this post "Why are my AE piston ring land clearances so large at .006"?"

https://www.accessnorton.com/Norton...n-ring-land-clearances-so-large-at-006.27291/

GPM or "new" Hepolite pistons.

Reggie

Esmerela

Triton Thrasher

Time Warp

.......back to the 70's.

kommando

Reggie

Reggie

kommando

Reggie

Esmerela

Reggie

Reggie

Chris Zet

Reggie

jseng1

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