Piston direction (10197)

uktom77 · Post by **uktom77** » Sat Oct 10, 2020 1:06 pm

Afternoon all.

I'll be fitting my new (to me at least) +40 Hepolite 10197 piston as soon as the rings arrive. I seem to remember the last time I did this it was clearly marked 'front' on the crown. All this one has is '+40' stamped into it. This is stamped north/south so may be an indication as long as I know which side of the bike it needs to be read from!

Any ideas good people? (Searching hasn't yet turned up the answer).

Tom

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Rob Harknett · Post by **Rob Harknett** » Sat Oct 10, 2020 1:28 pm

I would say you should read + 40 as typed here, sitting in the seat,piston manufacturers state, all pistons that should fit a particular way round are suitably marked.

uktom77 · Post by **uktom77** » Sat Oct 10, 2020 1:35 pm

Hi Rob, thanks for the reply. I probably didn't explain that very well.

By 'north to south' I meant south being the saddle and north being the headstock. So if sat on the saddle you'd either have to look down and turn your head either 90 degrees left or right to read it depending on which way round you have it.

Oh my lordy, have I just made that explanation worse. All I know is I'm now cross-eyed

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Rob Harknett · Post by **Rob Harknett** » Sat Oct 10, 2020 1:41 pm

I do not recall seeing piston markings that read sideways, those with an arrow are fitted with the arrow pointing to the front. Hench you read it marked pointing to the front from the saddle. That is why I said you should see +40 as typed here sitting in the saddle. But seems the book seems to imply no mark and it can go either way round.

Mick D · Post by **Mick D** » Sat Oct 10, 2020 1:49 pm

Hi

Look closely at the valve cut outs, if one is slightly larger it will be the inlet.

Regards Mick

uktom77 · Post by **uktom77** » Sat Oct 10, 2020 1:58 pm

Thanks both, when I am set free from 'other duties' I shall scrutinise the piston a bit more.

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1608 · Post by **1608** » Sat Oct 10, 2020 7:38 pm

As far as I know the piston is only marked as north and south or 'front' so if the piston is ever re-fitted for whatever reason it goes back as it came out. The only governing factor is as stated, if one valve cut out is larger than the other (usually the inlet) that goes rearward. North is toward the headlight and south would be toward the seat regardless of which way the bike was facing or the viewed whilst sitting on the bike.

SPRIDDLER · Post by **SPRIDDLER** » Sun Oct 11, 2020 11:30 am

If it's a split skirt piston there's ref in Christians Archive for Heplex pistons.....

http://archives.jampot.dk/technical/Gen ... ctions.tif

Piston fitting. Heplex.JPG

uktom77 · Post by **uktom77** » Sun Oct 11, 2020 2:03 pm

Great, thanks. So that about wraps it up. Totally symmetrical and not (directionally) marked.

And I thought I looked everywhere in the archives.

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