cp pistons fitting direction

Discuss mechanical problems here.
Forum rules
By using this site, you agree to our rules. Please see: Terms of Use
Post Reply
martin418
Minor Fan
Posts: 327
Joined: Tue Jun 24, 2014 9:54 pm
MMOC Member: No

cp pistons fitting direction

Post by martin418 »

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
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: cp pistons fitting direction

Post by oliver90owner »

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.
biomed32uk
Minor Addict
Posts: 630
Joined: Mon Feb 03, 2014 5:16 pm
Location: Gt Holland, Essex
MMOC Member: Yes

Re: cp pistons fitting direction

Post by biomed32uk »

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.
martin418
Minor Fan
Posts: 327
Joined: Tue Jun 24, 2014 9:54 pm
MMOC Member: No

Re: cp pistons fitting direction

Post by martin418 »

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
martin418
Minor Fan
Posts: 327
Joined: Tue Jun 24, 2014 9:54 pm
MMOC Member: No

Re: cp pistons fitting direction

Post by martin418 »

just found an original mowog piston and the offset /wider side is to the cam side
biomed32uk
Minor Addict
Posts: 630
Joined: Mon Feb 03, 2014 5:16 pm
Location: Gt Holland, Essex
MMOC Member: Yes

Re: cp pistons fitting direction

Post by biomed32uk »

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.
philthehill
Minor Maniac
Posts: 10767
Joined: Thu Jul 19, 2012 12:05 pm
Location: Hampshire
MMOC Member: Yes

Re: cp pistons fitting direction

Post by philthehill »

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

Post Reply