Determining the correct piston alignment - 1098cc

[Fred_Maves]

I am installing 20 over pistons in my Spridget engine. There are no obvious markings to indicate front/back positioning. Two clues exist: a horizontal split below the ring grooves on one side and inside the piston there are two arrows that point to the side opposite the split side. Nothing is visible front or back.
Some of my research indicates that a split in the skirt would face the cam side of the block, yet the arrows inside conflict with this premise. I was thinking this should be more clear-cut.

 

[racingenglishcars]

The gudgeon pin is to the right side, away from the cam. It's only a very slight offset, but noticeable by the sizes of the space between the bosses inside the piston.

 

[Fred_Maves]

Donn,

Unfortunately the pistons in question (and the rods) are both symmetrical. This particular 1098cc does not have locking gudgeon pins nor any kind of offsets. The alignment of the rods on the crank is a non-issue. This is easily noted in the handbooks.

- Fred

 

[Hap Waldrop]

A series engines have centered pin bores, so if the piston does not list front, and most likely it does not, it does not matter, thats the exact case on the dished 1275 pistons. hope this helps.

 

[Roger]

Fred,
Some pistons are made with thrust and non-thrust sides. Generally, where this is so, any splits in the skirt will be on the non-thrust side. So your arrows point to the thrust side, which seems pretty logical to me.
The thrust side of a piston is the side pressed against the cylinder wall by the angle of the conrod on the ignition, or power stroke. In a clockwise-rotating engine, looked at from the front, it's the left-hand side, or the side away from the camshaft on an "A" series engine.

So yes, the split is on the same side as the camshaft.

 

[Fred_Maves]

Roger,

Good to hear from you! I just met with Peter Egan, editor at large for Road & Track Magazine. We researched this topic in several Brit. handbooks and concur with your statement. Good to have consensus. I'm good to go.

Thanks again,
Fred

 

[Roger]

I'm glad Peter Egan got it right, too!

I'd hate to think that a guy whose work in R&T I enjoy reading could be wrong, since I find I enjoy his writing, his wry humour and his taste in cars.

Roger,

Good to hear from you! I just met with Peter Egan, editor at large for Road & Track Magazine. We researched this topic in several Brit. handbooks and concur with your statement. Good to have consensus. I'm good to go.

Thanks again,
Fred

 

[glemon]

Peter Egan, way cool, loved his column for years.

Greg