Split Skirt Piston Orientation

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James Hickman
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Split Skirt Piston Orientation

Postby James Hickman » Wed Mar 21, 2018 5:45 pm

Before removing the piston from my NH, I marked an arrow pointing to the BACK of the engine so that I could refit it the same way (unconventional I know)
IMG_2201.JPG

Having removed and cleaned further I can see it is marked FRONT - towards what I had marked as the back.
IMG_2202.JPG

Moreover it is a split skirt piston (Heplex 11210) and I am think I have read somewhere that the split should go at the front.

So, should I fit it the way it came out or, what would appear to be the correct way round, with "FRONT" marking and the split at the front?

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pappleton
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Re: Split Skirt Piston Orientation

Postby pappleton » Wed Mar 21, 2018 6:45 pm

Hi James,
I'd put the split to the front,as stamped. The rear of the piston is more stressed. the favorite place to crack is from the hole at the top of the split to the slot behind the oil ring. Pry the split apart gently with your hands, sometimes the crack is hard to see. Guess how I know...
BR,
Paul
Paul Appleton '53 VH plunger, '53 VHA rigid - in many boxes, '58 H.D. pan/shovel rigid

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robjameson
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Re: Split Skirt Piston Orientation

Postby robjameson » Wed Mar 21, 2018 10:21 pm

My brain struggles with things like this.

Why would you mark ‘front’ when it will read upside down when fitted?
Rob Jameson
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1957 Ariel VH
1956 Ariel KH (LARGE project!)
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Re: Split Skirt Piston Orientation

Postby keith wainwright » Wed Mar 21, 2018 10:48 pm

Hi James the split on the piston all ways fits to the none thrust side of piston. Keith

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Re: Split Skirt Piston Orientation

Postby Simon.Gardiner » Thu Mar 22, 2018 12:01 am

The clue is - the stamped 'front' marking.
Split to front (non-thrust face), thrust face is rear face...for a 'forward rotating' (which way does it rotate when the machine goes 'forward'?) engine....
Some numpty has put the piston in the wrong way round....either that or they've made some radical alterations to make the engine rotate in the opposite direction :D
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Re: Split Skirt Piston Orientation

Postby keith wainwright » Thu Mar 22, 2018 2:42 pm

Well done Simon very well explained. Keith

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alan.moore
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Re: Split Skirt Piston Orientation

Postby alan.moore » Thu Mar 22, 2018 3:26 pm

robjameson wrote:My brain struggles with things like this.

Why would you mark ‘front’ when it will read upside down when fitted?



Unless your standing in front of the engine looking back, then its the right way round :D
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Re: Split Skirt Piston Orientation

Postby paul.jameson » Thu Mar 22, 2018 8:41 pm

I'm sure that I taught Rob that the split in the skirt should be at the side - if the split is elsewhere she is no lady !
Paul Jameson
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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robjameson
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Re: Split Skirt Piston Orientation

Postby robjameson » Thu Mar 22, 2018 10:15 pm

Generational differences! These days the skirts are so short you almost never see a split in the skirt.

Not to mention the low friction coatings.

Are we still talking about Pistons?
Rob Jameson
AOMCC Member Number 4068
1957 Ariel VH
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