26 replies to this topic

[Sprocket]

Well I run the STD 70.61mm Powermax pistons in my 16 valver with 11.5:1 compression ration and regularly take it to 8000rpm. However, thse pistons were new old stock. New stuff these days just is not that good.

While one piston make might survive longer than another, the engine could run through an area of detonation without any real signs untill its too late. One of the Turbo Minis guys run Mega pistons up to 9500rpm with 15psi+ of boost without any problems, while others running the same pistons break the ring lands in a matter of miles with 8psi boost. Some have had real bad luck and experienced the same damage twice in a row, then changed to another make of piston and the problem 'appears' to have gone away.

Its the engine set up which kills the pistons.

[Sprocket]

So do people think ive got a case, for gettin in touch with morspeed or contracting powermax,

Im going to change all 4 piston to Cast Omega Pistons people think they are going to be ok.?

No, you are on your own.

What is compression ratio, acurately calculated taking into consideration the head gasket and ring land. The fuel octane rating and how old the fuel was. The total ignition advance ( initial advance + dizzy advance)

Also which cam is used as this will also have a major bearing on the effects of the fuel octane and compression ratio.

Omegas are the better choice, but you have to find out what caused the detonation first or you might end up with the same. The Omegas might also survive through the area of detonation in the current engine configuration and set up. what you have to ask yourself is if you are a gambling man. Do you replace the pistons with Omegas and hope for the best, or do you get to the bottom of the cause of detonation first.

[minidaves]

Thats the set up not an engine building problem as i well know, engines need setting up on rolling roads and set up by people that know about dizzy,s because advance curves differ so much, and you can get an advance of like 37 degrees from some standard dizzys if set at 8degrees before tdc at 1000 rpm, with 10-1 comprestion this will cause detonation and piston failure

[jn1702]

All very interesting, for those of us that don't know how do you calc compression ratio? same for ignition advance? thanks

[the clarkster]

thanks for your reply's i dont know what the compression ratio is, and i dont know how you work it out, the fuel is new i use the car everyday for work it had a swifttune sw5 cam in it.

Edited by the clarkster, 06 September 2009 - 07:25 PM.

[minidaves]

the yellow bible as in vizards book is a good place to start.

dizzy advance curves for example using a electonic type from a mg metro etc, if you take the top part of the dizzy off it tells you the advance on the cams inside, typical issues are when using dizzys from sprite rios etc as they have typically 16 17 or 18 degrees of mechanical advance and if the springs are week this can come in at 2,000 rpm, causing big engine blow ups without mega comprestion

dave

[minimotor_JD]

Time to call morspeed?

LOL!!!!. Good one

Haven't they gone bust?

[bmcecosse]

My first impression was of pinking/detonation damage - but I would expect to see some crown damage - and problems on all 4 pistons, or at least more than just the one! But either way - i'm sure you now have no come-back on the engine supplier - so best to put it behind you and get the engine fixed! I would just renew that one piston - and see what happens. I'm still inclined to think it may have been damaged at gudgeon pin stage - or perhaps during assembly.

[bmcecosse]

Double post.

Edited by bmcecosse, 06 September 2009 - 09:26 PM.

[tog77]

looks like someone broke the piston rings when he fitted the piston on rebuild.....
tog77

Edited by tog77, 07 September 2009 - 06:02 AM.

[Lot]

So do people think ive got a case, for gettin in touch with morspeed

Yes, but I think you'd have no hope getting any co-operation.

Not without an independent examination and witnesses and the will to go to court should they find evidence.

See the link below where someone else had an independent examination done:
http://www.theminifo...x...t&p=1120360

You'd be better off getting a reliable engine builder to take a look at the whole engine and fixing the problem(s).

[Cooperman]

It amazes me that someone who claims to be an engine builder will supply a modified engine without both a full spec sheet and the compression ratio calculations. Especially when it's a 1380 lump. If the standard 21.4 cc head is simply fitted to a 1380, the comp ratio will be very high. How high will depend on how far down the bores the pistons are sitting.
A compression ratio calculation is vital on such an engine to enable the ignition to be matched to comp ratio, cam, head and induction/exhaust.
The bores will have to be re-honed/glaze-busted, so be sure to gap the piston rings before fitting new pistons. As a general rule, there should be between 0.003" and 0.004" of gap for every 1" of bore diameter, although a few thou too much gap is not a problem. I had a 1380 recently which had been bored too large at re-bore and the piston ring gap was 0.025". The result was a scored block and huge blow by of oil out of the breathers.