ZX9 pistons into slab 750

[HDTboy]

Hi guys,

I remember in the old forum there was some info around using a particular stock piston to over bore the 85-87 GSXR 750. Does anyone still have that info, I think it was some generation of Kawa ZX-9 that could be used. I've acquired a spare set of barrels and head, so am keen to give it a go, everything about my bike is sleeper modifications, looks stock, goes better.

Thanks,

Gav

[Swiss Toni]

I'd start by measuring from centre of Gudgeon  pin to highest point on Slabbie piston skirt/dome, then take it from there. Lots of choice and availability! You want to try getting hold of 63mm T100 pistons. Impossible to find at non-ridiculous prices. Toyota pistons can now be made to work. Poke in the eye for NOS  Tri  piston stockpilers!!!

Edited March 20, 2017 by Swiss Toni

[markfoggy]

Are you sure that you're not confusing this with ZXR750, made an 836 or some such. Having said that it's probably possible, but a known solution would probably cost a lot less.

[richyrich]

how about a 2007/8 zx10, 18mm (of top of my head) gudgeon pin.  Not very scientific but  look nice and squat, so should leave some room under valve heads.  I looked at this once to put in a b6 and took a punt on some inexpensive used pistons with rings and a barrel from someone who'd planned this.  The stroke with those pistons should work and give 9 hundred and something.  Im sorry i cant be more specific right now, mabe next week end i can dig them out and measure them again.  I think the b6 is a slingshot motor so dont know if the gudgeon pin is the same for you. 

[Blue]

RF900 pistons

[cregnybaa]

3 minutes ago, Blue said:

RF900 pistons

19mm pin and piston dished like busa  so no compression.

[dixiethedog]

I dont want to go off track, but does the above mean you could put RF900 piston's into a Bandit 600 motor with a lower than standard compression???

Im just asking as I have a blandit 600 engined chop with a partly made blow thru set up.

I also have a spare gsxr 750 slabby motor sitting here.

[turboguzzi]

i am building one with zx9 pistons, gives 850. regretfully it will not result in  as high compression as i'd like but considering pistons cost all of 50 euro (for the 4 of them ) nice return on investment. comp  height is lower by about 2mm, so gonna get it back from milling the block, no biggie. actually project is on hold exactly at that point: bigger sleeves are already installed and bored (off a 89-90 750), "just" need to do a dry build to nail the exact dim to mill down the block. project on hold due to vintage road racing duties   let me know if you need more info.

Edited March 22, 2017 by turboguzzi

[cregnybaa]

8 hours ago, turboguzzi said:

i am building one with zx9 pistons, gives 850. regretfully it will not result in  as high compression as i'd like but considering pistons cost all of 50 euro (for the 4 of them ) nice return on investment. comp  height is lower by about 2mm, so gonna get it back from milling the block, no biggie. actually project is on hold exactly at that point: bigger sleeves are already installed and bored (off a 89-90 750), "just" need to do a dry build to nail the exact dim to mill down the block. project on hold due to vintage road racing duties   let me know if you need more info.

Ask canamant on here as he has already done it.

[Oilyspanner]

Just wondering :

What sort of clearance is required for the pistons ? Our bikes are essentially air cooled, with some help , using water-cooled pistons that are designed for expansion of liners with a water jacket , I guess some sort of allowance has to be made ?  I know piston manufacturers use several alloys, which need different clearance.

[Gixer1460]

17 hours ago, Oilyspanner said:

Just wondering :

What sort of clearance is required for the pistons ? Our bikes are essentially air cooled, with some help , using water-cooled pistons that are designed for expansion of liners with a water jacket , I guess some sort of allowance has to be made ?  I know piston manufacturers use several alloys, which need different clearance.

General rule of thumb across most pistons is 0.003/0.004". Only if they use coated alloy barrels - eg. busa can the gaps be tightened as both will expand at similar rates.

Edited March 24, 2017 by Gixer1460
Corrected tolerence

[cregnybaa]

9 hours ago, Gixer1460 said:

General rule of thumb across most pistons is 0.003/0.004" per 1.0" of piston dia. Only if they use coated alloy barrels - eg. busa can the gaps be tightened as both will expand at similar rates.

Are you sure your not getting that mixed up with ring end gap.

[Gixer1460]

1 hour ago, cregnybaa said:

Are you sure your not getting that mixed up with ring end gap.

Yes I did - i've edited so now correct - good spot..............would have only rattled a little bit LOL!

[markfoggy]

On 3/23/2017 at 9:36 AM, Oilyspanner said:

Just wondering :

What sort of clearance is required for the pistons ? Our bikes are essentially air cooled, with some help , using water-cooled pistons that are designed for expansion of liners with a water jacket , I guess some sort of allowance has to be made ?  I know piston manufacturers use several alloys, which need different clearance.

Well that's got me thinking,

Ally Pistons, should in theory expand at a similar rate, almost regardless of actual material. So if you have accurate dimensions for standard piston and a standard bore, the gap should be what you are looking at, probably work on a percentage to do some maths for reassurance. But and a big But, the barrels need to be of the same sort of construction. 

This should all work for a piston working in an Iron liner, dry lined or wet lined, but.....

Get into Nikasil/plated barrels and it will all go horribly wrong.

 

[Oilyspanner]

I think the amount of silicon can alter the rate of expansion to suit use. I remember that Cosworth pistons needed more clearance because they expanded at quite a different rate than the cast liners, because of their compostition. I think Wiseco alloy doesn't expand as much, much closer to the liner's rate, so clearance could be tighter - so... I was thinking that our engines will run a little hotter than the better temperature controlled w/c unit and wondered what alloy differences would be -  there would only be fractions in it , but it made me wonder.

I just found a magazine article P.B. April 1994 - higher silicon content means lower expansion and Japanese pistons tend to use high silicon content alloys - that means both liner and piston should expand at similar rates, so even if the temp. is higher on O/C engine there shouldn't be a problem......thanks P.B. for answering my curiosity ! 

 

[canamant]

Yes - I've done it.  Twice. It isn't cheap in terms of time or materials.  The ZX9 pistons have a lower deck height than the standard ones and they do tend to very so you have to do lots of builds and tear downs.

The 70mm liners have to be pushed out and the barrel bored for the 73mm liners.  Then you have to get the liners bored to match the 75mm pistons. Then the first dirty build to compress the base gasket.  Strip down to determine the amount to skim off the cylinder face (they all vary so you need to measure it rather than go on someone else's numbers).  Skim to get the pistons flush.  Recut the recesses for the oilway O rings 

Next you need a head gasket.  The 76mm bore 1052 GSXR1100 won't do because of the camchain tunnel differences.  The head gasket thickness will determine what inlet cm timing you can run.  Remember you have already skimmed approximately 2mm off the cylinders which will retard both cams.  I had a bunch made from 1mm, 1.2mm and 1.5mm copper.  I used the 1.2mm one for my builds and it gave the (non standard) valve timing I wanted (well almost) just getting to the minimum valve to piston clearance.

The pistons are flat topped but the cutaways are not in the same plane as the valve heads because the ZX9 valve angle is narrower so the valves will get close to the pistons when you start playing with cam timing later.

Build it up again either using a gasket you have had made or shims to mimic the gasket.  Time up on the standard marks and using a degree wheel and dial gauge make a camgraph, checking and measuring valve to piston clearance before TDC on the exhaust and after TDC on the inlet when the exhaust is clsing and the inlet is opening.  You should have plenty of clearance at this time.  Then you need to advance the cams to get either standard timing (or your own timing).  You did remember to slot the camshaft sprockets didn't you ??  Do another camgraph and valve to piston clearance graph.  Measure the exhaust VTP Before TDC from anout 30 degrees BTDC in 5 degree intervals - 2 would be better.  Minimum clearance is 1.7mm or 70 thou.  For the inlet the minimum clearance is 0.8mm or 32 thou.  If you can't get these minimum clearances you are into a thicker gasket or pocketing the pistons although I got larger clearances on standard timing.  .  When I set the timing I wanted, The clearances were very tight so great care has to be taken with the revcounter.  All these worked with the standard camshafts from a slabby 750.  I don't know what would happen with the J/K cams. If the opening ramp is similar, no worries.  If it is a steeper ramp, then you have to start from scratch.  During all measurements, standard valve clearances were used.

The standard cam is actually vey good, but the timing is a bit odd on GSXRs.  Standard inlet timing is a bit retarded for serious power, but advancing it can cause valve to piston issues.

To do it properly you also need to repeat the measurements on each cylinder as well.  In short, to do it properly is a long slog of setting up but tat is always the case when doing the development yourself.  I reckon I must have done half a dozen builds and put 40 or 50 hours into doing the measurements and builds to get to the final position of a running engine, not including the machining time.  A good place to start for your settings would be the GSXR Hop Up manual which used to be on the site.

 

[HDTboy]

Thanks for the detailed description. From the sounds of it I may as well look at getting aftermarket pistons as either way I'll be doing liners, and that gives the option of going to 955cc.

I've spent a few years mucking about inside engines, and playing with compression and cam timing has got me over 100hp at the tyre so far.