Oversized pistons

[wes]

OK, with zero availability of .5mm kit pistons, who are using .5/1mm Omega and what experience have you had and who are using J&E ?

I see that the Omega pistons looked very nice, and think they are lighter but have they been used in anger for a few races yet?
I also read the note about the small end (I think...), are there any special requirements about measuring or installing/running these apart from the normal compression and head matching work that may be required?

[toecutter]

An update on the pistons for you
sorry for being off the radar but had a bit of a health scare so forums etc were not my priority.

Well so far the bike has done 8 hrs back to back sessions at snetterton on the 30th of august (hottracks day there are probably photos ill look) ,Claire and a mate of mine smiffy (Ex Bains racing) were out all day to test the motor.Claire was on the 400 Mr smith on the BsB zxr750
the 400 didnt miss a beat ,all day none stop except for session change and fuel and the poor little thing (the 400 not claire) just kept on going ,its since done half a dozen track days ,been out on the road (tis road registered) and its fine .Oh and so far i have not had to top up the oil ,i know i know change the oil regularly but we are testing this thing properly to see what abuse it will take ,i hate doing it but its what you have to do .
Now Claire pushes the bike ,she is about 1.03 round mallory ,has hit 1.01 and is 1.03 ish on our mates yzf 750 sp,my bsb bike and on the zxr400 so its not dawdling but not the fastest .
The bike is going back on the dyno (hopefully next weekend ) to see how she is holding together .then we will pull the motor apart,see what has worn and then give it the full tune.

So with the Omega pistons 57.50mm
base gasket in
gas flow on inlet tract only
no skim on the head
large piston to valve clearence
standard carbs with out air box but jetted to suit
kent cams
she was producing 73 bhp with 33 ft torque (ill try post up the dyno sheet )If my memory serves me right
Now im sure the Je pistons are ok but they are machined from a large forging for another piston which means the piston is too heavy and needs machining inside the piston to lighten them up .Which if left un lightened really over stresses the crank
The Omega ones are specificly designed for the motor ,simple .
please dont think this is sales pitch as i just cover my fuel and a little for the running around that it takes to do these projects ,i just cant understand the logic in folk using inferior parts or secondhand parts in expensive motor rebuilds its bonkers ,in fact im surprised that motor tuners put second hand pistons and rings in but that all that was available at the time.
Anyway we now have the 58mm piston ring problem resolved ,which is a bonus and if anyone is free when i go to the dyno you are welcome to come and watch the bike and see the power/results for yourselves (oooo how exciting i hear you say ) but proof is in the pudding and im putting my money where my mouth is as it were .
I will take a vid of the dyno and try post it up
so ta for listening and i hope you are still awake
cheers rob

[wes]

Hi Rob,

Thanks for the update.
Don't mind reading at all, the more info the better.

I have heard about the JE pistons being machined down, but without .5mm or other 1mm oversize pistons available I guess there were no real alternatives.

When my engine threw a rod I ended up with stock pistons, in a stock barrel, so if I am correct the Omega pistons run higher compression as they are based on the kit piston, so will up the compression without any barrel or head skimming.

Would be interesting to see what bhp differences there are between the .5 and 1mm, quite tempted to go for the bigger bang!

Cheers
Wes

[BOLS99]

i have run je pistons for years and have no engine problems we use a 60.00 kit which gives 449cc cheapest power gain possible
if anyone wants the kit number let me know....std fzr600 rings fit straight in so no problem with ring replacement....we use lighter gudgeon pins...

[AFM327]

i have run je pistons for years and have no engine problems we use a 60.00 kit which gives 449cc cheapest power gain possible
if anyone wants the kit number let me know....std fzr600 rings fit straight in so no problem with ring replacement....we use lighter gudgeon pins...

How much do those pistons weigh? Are you racing with them or street riding? What kind of Hp?

[Max4music]

i have run je pistons for years and have no engine problems we use a 60.00 kit which gives 449cc cheapest power gain possible
if anyone wants the kit number let me know....std fzr600 rings fit straight in so no problem with ring replacement....we use lighter gudgeon pins...

Tell more, this sound interesting.