Morris Minor Owners Club

hi has anyone fitted cp109 pistons in a 1098 ,i have a good set to fit but they don't have any fitment direction marks on the tops only two arrows inside the skirt which would point to the cam or distributor sides of the engine and the oversize markings are not forward either , the skirt has a slot just under the bottom ring on opposite side to arrows , any help appreciated

Don’t know, but I remember when a March Engineering fellow machined valve pockets on the wrong side of the split skirt pistons for my Escort engine. Advice from AE was simply to turn them round! Never gave it another thought and the engine ran OK for many thousands of miles.

Usually there is a very slight offset of the gudgeon pin towards the thrust side of the engine, which I think if memory serves me right is the spark plug side of the A series.

hi luckily they do have a slight offset so i can work it from there , cp pistons uk are very helpful but they don,t list the a series and they think they are from a limited production run, looking at the pistons with the offset to the plug side the internal arrows point to the thrust side

just found an original mowog piston and the offset /wider side is to the cam side

That seems to add up then, so the rod is slightly closer to to the plug side then ?, I cant remember now from when I rebuilt mine.

https://www.quora.com/What-is-a-piston- ... t-provided

https://www.bing.com/images/search?view ... ajaxhist=0

Transposing the diagram to the 'A' Series engine - it can be seen that the offset of the piston wrist pin is towards the distributer side of the engine with the clockwise rotation of the 'A' Series when looking from the front of the engine.

It should be noted that not all engines have the wrist pin offset.

Pistons without split skirts are more reliable in any modified or performance engine as cracking can start and radiate from the root of the split.

Phil