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Discussion Starter #1
as title .. anyone any experience with aftermarket pistons in ZX6's ?

asking as i have a F model engine that has been fitted with stock bore (66mm) je pistons, but which has dropped a valve.. and i'm in the middle of rebuilding it.. would stock pistons be ok to drop straight back in ? or do the JE ones hike compression compared to stock ?

ta :)

*nice site by the way, and HI!!*
 

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Most JE are better than stock as for compression there are many factors.

Do you plan to re-hone the cylinders before installing new pistons and rings?

If you want power now would be a good time to overbore and get some more CC's out of it.

Also while they cylinder is off some clean up and porting would also give you gains.

Also check the valve guide where the bent piston came from to make sure it is not damaged.
 

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Discussion Starter #3 (Edited)
hi,

the engine had "just been refreshed" according to the previous owner, and on stripping it i can see he was telling the truth, sadly whoever had done it was a twat, and had miss-timed the exhaust cam by a smidge (kent "race" cams with adjustable sprockets) so the pistons been ever so slightly kissing the exhaust valves across the board, cue 13500rpm and it ripped two exhaust valves apart, mangled the piston and lightly scored the bore right at the top (dead quick clutch hand me!)

so anyway, the head has been sorted with 3 new valve seats inserted, valve guides sorted, 4 new valves, all 16 valves/seats re-cut and lapped in nicely (head had already been ported and valve guides cut back)

cylinders have been *lightly* honed and hopefully my new piston arrives in the morning so i can put it all back together.

conrods are already lightened/balanced as is the crank

I'd love to bore it out to a 69mm bore (654cc) but cant afford too many £110+ vat pistons at present !! lol not on top of the head-work anyway, besides everything else in there is new, the other 3 pistons/bores/rings etc etc all look like new.. shame he got the cam timing wrong really..

what i was really wondering i guess is whether the JE pistons would be providing a higher CR than stock and if i'd notice a drop in performance by shoving stock pistons in across the board in the event that i couldnt either source or afford a matching replacement.

as it turns out they do increase compression to around 13.5:1 (depending on block height/head skim) so yeh, i'd have lost maybe 5-6 bhp across the range which, given that once upon a time before someone meddled with it it was pushing around 115rwbhp would not of been a *good* thing:) it would infact have been a complete waste of the rest of the nice bits in there.
 

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The JE's I ran were lighter and better machined than stock.

That being said stock are pretty dam good and very durable.

After reading your posts I would say see the price difference. If you are looking to keep compression and run OEM pistons just get a thinner head gasket as save some cash.

Anyway sounds like you have quite a nice setup.

Good luck and please post how it turns out.
 

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Discussion Starter #5
shiny new* JE piston should be winging its way towards me as i type so hopefully i'll have the engine back together by the weekend.

i'll probably double up on base gaskets to ease off the CR a bit as the squish was on the tight side before and i'll still be way over the stock compression ratio. Its a streetbike after all.

with a bit of luck i'll even have the chassis back in one piece and be able to ride the sodding thing :)

modified zxr400L frame
revalved/resprung forks
resprung zxr400 rear shock
EBC Prolite race discs
Renthal Alloy sprockets (16/42)
Custom Ram-Air intake.



not the best or most recent pic, but you get the idea :)
 

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I would keep all the pistions the same - defo wouldn't use one JE piston with 3 stockers:dowhat
 

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ZX400/ZX6RF hybrid?

How cool is that!?!?!

Talk about a wolf in sheeps clothing - nice one mate.
 

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I would keep all the pistions the same - defo wouldn't use one JE piston with 3 stockers:dowhat
x2 bc your compression on all 4 cylinders will not be the same, it's just like puttin bigger jets in 1 carb and the others havin smaller 1's it's not going to run right:confused
 

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Discussion Starter #9
never said i was going to fit mismatched pistons, it already had je pistons, im just getting one to replace the mangled one :)

was considering fitting 4 stockers if i couldnt get a replacement.

but yeh, could have been clearer i guess.
 

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Discussion Starter #10 (Edited)
ZX400/ZX6RF hybrid?

How cool is that!?!?!

Talk about a wolf in sheeps clothing - nice one mate.

cheers, :)

yeh, its good for confusing fireblade/r1/gixxer riders :)

although i must confess i didnt actually get the fabrication done it came to me with the engine aready in, and the rest of it kinda thrown together no airbox, stock running gear, shot bearings, warped discs, shagged forks, fucked plastics .. etc etc etc .. it did 165mph then tried to kill me so i took it apart, rebuilt it properly, got it MOT'd and it snapped the valves a day later having covered a total of 24 miles in 12 months :(
 
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