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#87389
Hi folks I have replaced my big end and reassembled the engine. Have decoke the piston and noticed an arrow on the crown which the workshop manual says has to face the timing side. As the arrow isn't in line with the piston pin can anyone advise which direction it should face. Cheers David
#87391
Somewhere in the dim and distant past I was told always point arrow on piston to exhaust
Seem to remember it's to do with the thrust side of the piston
I may be wrong but that's the way I have always done it
Hope this helps Dai
#87392
Sorry too late to edit

Gudgeon pin clips I allways fit with the gap at top or bottom (less chance for them to jump out of the grooves)
Hope this helps Dai
#87405
Hi Dia thanks so much for your advice it's very much appreciated. I never noticed the arrow when I removed the piston, wasn't till I started to decoke it that I noticed it. I will keep you posted on the rest of the rebuild. Thanks again.
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By Presto
#87486
This is a regular dilemma when refitting a piston.

Some pistons are marked ‘F’. The side of the piston marked ‘F’ is to be fitted with the ‘F’ to the front.

Some pistons have cut-outs for valves these must be fitted with the smaller cut-out to the front.

Some pistons have a split skirt. These must be fitted with the split to the front.

Some pistons have an arrow stamped on the piston crown these must be fitted with the arrow pointing forward.

Where a piston has none of these markings the piston may be fitted in either orientation.

The main thrust face of the piston is the side of the piston opposite the crank-pin as the engine rotates on a downward stroke.

On the downward stroke the piston skirt opposite the crankpin is forced against the cylinder wall. In a forward rotating engine (i.e. Bullet engine) this is the rear face of the piston.

The arrow on the piston does not in itself indicate that the piston should be fitted with the arrow pointing to the main thrust face. It simply indicates that the arrow should point forward.

In a forward rotating engine there is a tight seal created on the downward stroke between the piston and the cylinder wall at the rear of the cylinder. One effect is that oil is scraped more effectively from the rear cylinder wall.

Some forward rotating two-strokes placed the exhaust port at the rear of the cylinder. This would increase sealing on the downward stroke and help prevent the loss of incoming charge through the exhaust port.

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