GPM rings

[1608]

A lot has been aired on GPM pistons recently and mostly to their detriment.However,My G12 is currently on +60,with a ring gap of 0.019.The bore is pretty good and so I intend using new 0.019 GPM rings from JSL and machining the AE (hepolite) pistons to suit.I will grudgingly have to resort to re-sleeving etc one day I know.
Any observations ( Horror stories)on GPM rings greatly appreciated.
John

[TommoT]

I don't know if GPM rings in particular are the culprit, more the whole piston assembly. They need extra running clearances in order not to nip up, this in turn causes piston slap even in fairly new bores. We have heard stories of whole piston crowns leaving the skirt and cracks in same. The machine shop I use, which rebuild engines for classic motocross, stopped using GPM years ago due to unsatisfied customers. Now I must stress that my own personal experience is based on only two GPM pistons fitted to my G1956 G80S. The first piston nipped up several times during running in, despite every pre-caustion taken. After 2000 miles I took the piston out for inspection. Serious contact spots all around the skirt, blowby past the compression rings and one gudgeon pin circlip gone, leaving the gudgeon to score the bore (this last could be my hamfisted efforts, but hard to imagine with all new parts and some experience in this area) The last piston covered over 10.000 miles, but increasing piston slap and loss of power caused me to rebore. An original Wellworthy replacement piston came along and made the decision easier. Engine has never run better or quiter, what a relief. Just my humble observations and opinion.Edited by - TommoT on 15 Mar 2010 9:40:32 PM

[SPRIDDLER]

Funny that TommoT - I too had a gudgeon pin circlip come adrift from a GPM piston and after it had been up and down like a bride's nightie a few thousand times it left a gouge akin to a two-stroke transfer port in the cylinder wall.
I too couldn't imagine how I'd fitted it so hamfistedly. Maybe I hadn't after all.

[bell]

There are better pistons you can use , but three times the price of GPM . You get what you pay for . Regards Richard .

[GOLDSTAR]

thats interesting Richard, I have not heard of GPM pistons before so can make no comment thereon, however with regards to skimping on a. quality b, price the old expression is 'you get what you pay for' and a further perhaps more sageful expression is ' if a jobs worth doing then it's worth doing well!' kind regards

[TommoT]

GPM is an Italian factory at Gandini in Italy. They have produced pistons for the home market for decades. The problem may be that their production line was initially for smaller two-strokes, or high revving Italian exotica. They may not have had experience with slow revving British singles and twins, that stress pistons differently. This is just my personal theory. Having lived with and loved Italian cars for decades I also have my own theories on Italian quality control. Their quality manual may very well be the thinnest book ever released

[Stan Palmer]

And yet they make the Ferrari, Lamborghini and Ducati. Always been a puzzle to me, I worked for a year in Rome, had a great time and they are lovely fun loving people, but I could never understand how they produced great cars and once ruled the world. At that time they relied heavily on a depreciating currency balancing costs out (at least they did in Oil and Gas, they could take on a job at a loss, get paid in dollars a year or two later and end with a healthy profit). Now they are in the binds of the EEC I can't see how they manage.
Stan

[paultbird]

quote: Funny that TommoT - I too had a gudgeon pin circlip come adrift from a GPM piston and after it had been up and down like a bride's nightie a few thousand times it left a gouge akin to a two-stroke transfer port in the cylinder wall.

Ditto - very annoyed to say the least

[bell]

Very difficult to say what the problems are with GPM . Ducati do not use them . Regards Richard .