Help Overboring an FZR/FZX. Options.

The different FZR compression heights are of course long and short rod pistons. Both use the same barrel height.
I was pretty cautious going bigger. I wanted around 3mm wall on the liners and a generous wall on what was left of the barrel.
What I made up is 53mm bore with 3mm wall so 59mm OD. This left around 3.5mm of barrel wall to support and seal the liners.
If you're a tad less cautious you could go a mm bigger in the liner OD and get to 54mm bore...
Bear in mind that the liners are pressed down to rest against the top of the barrel casting surrounding the liners. Sealing against water is purely the shrink fit of the liners in the alloy sleeve of the barrel. Too thin here and you could either crack it or get a leak due to insufficient stiffness/tightness of the fit.
Good find on the GSXR pistons too.

There is a way of using the rods with bigger pins...Very "colonial"...
TIG strengthening/stiffening webs around the smallend eye. I'd use two webs rather than one heavy one.
Once it's cooled, get the eye honed to the bigger size.
Bronze small end bushes are fine - but not as thin as .5mm.
If you have to use a bush this thin, I'd use mild steel - I've done this previously and it worked.

Oh - cutting the piston skirts shouldn't be needed, i had plenty of clearance with longer pistons.

Carry on...

 

hmm valve recesses for four valves, 14mm pin diameter, 52mm piston diameter...ticks all of the boxes has me wondering about the deck height and compression ratio with the fizzer cylinder head

http://www.ebay.com.au/itm/125cc-52...497474?hash=item2357d5fe82:g:dBEAAOSwd0BV415i

sleeve to match
https://www.lasleeve.com/cylinder-sleeves/l.a.sleeve-sleeve-h102

 

To check valve to piston clearance it's just time...Mock it all up with plasticine in the valve pockets. Pull it down after turning the engine over a couple of times and carefully section the plasticine to see what you've got. Only need one piston fitted to do it of course.
Yep, 53mm gives my twin 152cc. Class top limit is around 160 with over bores etc but this will do.
Bulletproof....well mine doesn't owe me a lot but as an old bugger ex the trade, I have my ways and contacts....
I've enough bits that if it blows, the second version can have corrections.
Carbs are actually my problem at present...no budget for FCR's.
I have some ideas. Nothing definite yet.

I can't open that link to LA Sleeve so don't know what you're looking at there. I'd point out that the std sleeves have a pretty thick top shoulder - and whatever goes in has to have that feature as the barrel doesn't go right to the top...
I'll get a pic of a std sleeve later to show what I mean.

 

As promised. The portion of the barrel which encloses the sleeve is 61.5OD. The lip on the sleeve is 4.5mm high.
As mentioned previously, it's the barrel casting which dictates how big a sleeve you can fit.
And no, you do not want a sleeve which is only located by the lower end...

 

this is a generic picture - the lip is there obviously we'd need to check the dimensions on the lip - they have a large selection of generic flanged sleeves also
https://www.lasleeve.com/tech/all-purpose-sleeves

huge salute to @gregt for sharing his work as this has opened up enormous possibilities for getting more out of the fizzers

I think the real trick here is getting suitable pistons in the 53mm - 54mm range with
the right pin diameter, compression height and the correct valve formations in the crown or sufficient material to machine the crown appropriately to suit the combustion chamber in the head

CBR400 pistons are perfect in most ways but I think 55mm diameter may be just too much - BTW 55mm pistons gives 327cc - time for some bigger carbs

https://www.aliexpress.com/item/Pis..._1&btsid=6c8afeef-f29d-463e-8297-54a3c2ab9964

piston dimensions in this listing

http://www.ebay.com.au/itm/Piston-R...130066?hash=item33adbc4992:g:EmUAAOSw6dNWTreL

 

Bigger carbs would be nice, yes, but you guys with better internet search capacity than me could also look for bigger valves...
1mm oversize would easily go onto the std seats, both inlet and exhaust. Std are a tad small.
BUT - 3.5mm dia stems are not common...
I could have used Suzuki Fxr150 exhausts on the inlet side on mine but it meant going up to 4.5mm dia stems.
I felt that although I could have reamed the guides to suit and done the rest to make them fit, they'd be too heavy.
Anyone have the dimensions of ZXR250 valves ?

 

Greg you're reading my mind, I was looking into that precise option last night

I don't know the specs of the CB400 valves - yet

https://www.aliexpress.com/item/8pa...-stem-for-Honda-CB400-CB-400/32324095499.html

ZXR250 valves
https://www.aliexpress.com/item/Gif...or-KAWASAKI-ZXR250-ZR250-ZXR/32326328441.html

What do you think about the feasibility of going to 55mm pistons - steal 1mm wall thickness from the liner (equivalent to 4th oversize piston on a standard liner) and keep the rest as per what you've done? or go .75mm less on the wall thickness and .5mm larger diameter on the sleeves or is that cutting it too close?

Those CBR400 pistons do look very appealing as the compression height on a search I found to be 13mm, leaving enough material to cut them down to appropriate height and check valve clearance etc.

 

edit on above - miscalculation 4th oversize (1mm) piston would take 0.5mm wall thickness - my bad

 

54.0mm is as big as I'd go using sleeves in the std barrel.

My internet is very basic - I can't open any of those links.
Next time I go to the local library I'll have a look.

 

Hey dude fit a 250 or 350LCD motor more bang for your buck

Sent from my ALE-L21 using Tapatalk

 

I'd do that in a heartbeat, however engines for RD/RZ 250/350 and Banshee 350 engines are incredibly rare in Aus

 

Honestly guys, Cool and all if it works, but by the time you did that and spent all the cash, you could take the thing down and get it dyno tuned and get similar gains

 

Realistically Gregt's pioneering work on re-sleeving has given a 25% capacity increase - that's substantial and he's done it with his own skills and ingenuity, so not expensive for him personally.

For a simple capacity increase - Lasleeve sleeves are $62 USD each, plus pistons and rings - depending on which ones are suitable for use with straight barrels not needing a spacer plate...machine shop costs on boring and fitting sleeves ?$

This isn't the sort of work you'd contract to a mechanic, too much $$, but this site emphasises DIY, shares skills and knowledge
Personally I really do like the idea of a fizzer with a little more zoom zoom

 

@gregt
Greg, whilst in search of CBR400 valve sizes/diameters and reading through the service manual for a CBR400 from here
http://service.tanga-moteurs.ro/data/Honda_CBR_400_Repair_Manual.pdf

- valve stem diameters are 3.8mm, I still haven't found the valve sizes yet though

 

FZR400 pins are 15mm vs the 250's 14mm.
Valve pockets are much more widely spaced and the crown shape would need much change....

Honda CBR400 valves - typical honda, odd size stems...

Aky141 - please supply the adress of your dyno man, I'm sure plenty here would use him if he's that good, LOL

 

CBR 400 pistons come in at 55mm - 1mm over the max Greg recommends - I've been trying to rationalise taking that extra 1mm over Greg's recommended figures - the guy very obviously really knows his stuff and I don't want to end up with a mea culpa

Correct pin diameter 14mm, piston crown shape with sufficient material to cut for correct deck height/squich band and valve clearance
very reasonably priced - https://www.aliexpress.com/item/Pis...3-29-CB400-92-98-STD-Standard/1939318855.html

I'm actually on the trail of some barrels and a cylinder head to begin the journey...

For carbs both FZR400 & YZF600R have the appropriate bore area increase ~30% to cope with increased flow requirements