Upgrade to Bigbore Pistons

No eBay APP ID and/or Cert ID defined in Kunena configurationWe have talken about these in another threat, but want to split it:
www.kzrider.com/forum/2-engine/607482-cy...ndition?limitstart=0

I have a bike with 81 KZ750-4 engine & VM24 (from 650 engine). The bike has worked fin with current carb setup.
These winter I`m overhaul the engine and I need to do a job with the cylinders. The question is shall I upgrade to
bigbore pistons, at the same time....

Will I got problem to make the engine rune find? with my VM24 carbs?

1. How much more power?
2. Negative side of doing it?

I have been given a link:


Cheap but they are maybe good quality?

Thank you all.

I went from 903 to 1015 in 78. I would only buy the Wiseco piston kit knowing the quality and performance over some cheap ones. From what I've seen, the cheap ones have stock compression while the Wiseco's are 10.25/1 and lasted 20 years. Can the cheapo's make that claim? All I had to do was minor jetting and RODE THE PISS OUT OF IT. :woohoo:
Steve

Wiseco Piston 69.00 4186M06900 for Kawasaki .... ebay. discounted. seems like a good buy.

Ape Racing --- main page

Ape Racing >>> Kaw KZ/GPz >>> KZ Zone

Ape Racing >>> Kaw KZ/GPz >>> KZ Zone >>> pistons

Inexpensive piston kits >>> piston & piston ring quality unknown. risky.
From what others have posted, you especially do not want to scrimp on the piston rings.

Inexpensive piston kits. Further reading. Related topics.
KZRider --- 750 810cc special coated pistons

KZRider --- New 810cc kit available from Japan ....Important note: Japanese distributor but not made in Japan.

KZRider --- kz750e Resto-Mod by daftrusty ... Inexpensive piston kits. see first post. if sharp edges. file down the sharp edges.
as a side note. and for curiosity's sake. if I bought them, I would figure out their density. just for the heck of it. probably can't deduce anything from that, but just for the heck of it.

I think the Cruzin Image kits are made in India or Pakistan - where labor is like 20 cents / day! That comp[ares to Japan's $35 / hour and up for tech labor....

If you can afford it, go with Wiseco or MTC big bore kits. Proven parts. If you can't, like I said, I haven't heard anything terribly bad about the Cruzin Image kits yet....just keep in mind that you will have to be extra careful to inspect the parts and you might have to do a little filing, de-burring, and corner smoothing, but that goes for any parts you are going to put in your engine anyway. In fact, I've heard more complaints about "Hot Cams" parts (ATV's and dirt bikes) quality and durability than the cheap "Cruzin Image" stuff....but I can't speak for myself, as I haven't had any of my rebuild engines F - up yet.....and I haven't personally installed a Cruzin Image kit yet, either. I might gamble on some Cruzin Image or other cheapo pistons next time some hipster CB550 SOHC Bobber / Cafe / Hacker owner calls looking for a $200 engine re-build, though. Gotta love those calls....

Big bore kits alone usually do not require major re-jetting or carb tuning, only minor tuning. With 24 mm carbs, you will not gain much peak power. You should notice a boost in low rpm and mid rpm torque.

Maybe my concern is unfounded but I've never been too thrilled with boring the liners out to the max limit. Less material means less stability in terms of roundness and taper, so unless you are looking for max power going +3mm isn't ideal in my mind. That said, the Wiseco big bore kits have an excellent reputation so maybe 3mm overbore is no worry. I'm not sure. Personally, I'd just go the conservative route and bore to the min possible to clean things up.

Thank you all, also your feedback Nessism, I like to look at both "sides" before I doing something

Is there not anybody other who has done the same as we talking about here many years ago ?
Some experience?

I will not run the bike hard all the time, so still if I have more power it will not be used all the time..

I will send a email to the workshop and ask about the stability.

It is typical for big bore engines to run hotter than stock. Even the old thick cylinder wall car V-8's (352 Ford "FE", for example) ran hotter with the typical 0.030" overbore so widely accepted in that industry. That, and heavy throttle hands, are really the only problems with reliability that I know of. If you don't abuse or overheat the engine, it should last nearly as long as a stock engine. The engineers that design the kits are very careful in determining what the maximum safe overbore is for normal street use. I've re-used Wiseco big bore pistons without concern, just a quick brush / ball hone, replace the rings, and thoroughly clean the pistons and re-install.....some Wiseco street kits I know of have over 30K miles on them and are still going on the 1st set of rings....I can't say the same for most of the stock KZ1000J's and GPz1100's I've seen....

....and this is an air cooled engine. More power, more heat,........in a liquid cooled engine, the thermostat would open longer and more often to compensate, but here....... this is what you get with the extra power.

I run a Wiseco 810 kit in my ZX750A1 motor and on the street or at the drag strip I've NEVER had an over heat issue
related to the big bore. I'm say this based on REAL WORLD I beat the dog shit out of this bike I am not nice to it when I ride it.

As for the cheap piston kit's hey it's your motor but you'll never find one in my shop.

I think have landed on +0.5mm piston instead of bigbore.
In Norway you are not allow to increase the power without get it approval.... and I think I`m happy with the performance for now.

So now my questions is what shall I choice of oversize +0.5mm pistons....

I started a fresh threat about it:
kzrider.com/forum/2-engine/607519-750cc-oversize-piston-0-5mm

I want to thank you all for sharing your experience and knowledge.
You can call me "chicken", but I take I go for the safe way at these point...

Again thank you all !

As to what size you need to take the cylinder block off the motor and take it to a machine shop and have it checked
before buying pistons.