larger cylinder and pistons on KZ500 B3

Hi!

I am thinking of boring out my Z500 cylinder, but before I do that, I thought I should at least ask if anyone knows if it is possible to fit a Z550 or even better, a Z650 cylinder and pistons on a Z500 engine?

I expect I would also have to get a new cylinder head as well if I find Z550 or Z650 cylinder that fits.

Thank you!

Using 550 parts should be doable. The 650 engine is completely different and wouldn't work.

Thank you Nessim!

What would be the main concerns if I'm heading for a Z550 cylinder and pistons?
Re-jetting the carbs?
New cylinder head and cams?

Only reason I'm thinking of doing this, is because the piston rings on my current setup probably needs to be changed, and I havn't been able to find new standard rings. (been searching for the past 6 months).
But there seems to be easier to find oversize rings for the Z500 as well as more options for the Z550.

I'm pretty sure the head and cams are the same between the 500 and 550. if you can find a parts fishe for your bike it may help if you checked the part numbers compared to those from the larger engine. Not sure about the carb jetting. You may need to do some minor tweaking, but that would be minimal if you keep the stock airbox.

The z500/550 engines (including the zr550 Zephyr) are based on the 400J and most parts are interchangeable within the crankcase.
The 500 is a bored and stroked 400 - From 52mm x 47mm to 55mm x 52.4mm.
The 550 is a 3mm stroked 500 - from 55mm x 52.4 to 58 mm x 52.4 mm
550 barrels fit the 500 but they are taller than the (shorter stroke) 500 so you can't simply drop a 550 block on the 500 for bigger capacity without using the 550 crank too or you just end up with a very low comp 500.
Heads are the same and interchangeable.

zed1015 wrote: The z500/550 engines (including the zr550 Zephyr) are based on the 400J and most parts are interchangeable within the crankcase.
The 500 is a bored and stroked 400 - From 52mm x 47mm to 55mm x 52.4mm.
The 550 is a 3mm stroked 500 - from 55mm x 52.4 to 58 mm x 52.4 mm
550 barrels fit the 500 but they are taller than the (shorter stroke) 500 so you can't simply drop a 550 block on the 500 for bigger capacity without using the 550 crank too or you just end up with a very low comp 500.
Heads are the same and interchangeable.

The FSM in my signature shows the 500 and 550 have the same stroke and different bore.
500 has 55.0 bore and 52.4 stroke.
550 has 58.0 bore and 52.4 stroke.
If that is correct, I think he can just convert to a 550 with block and pistons.
Compression is 9.5:1 on all models except GPZ's, which are bumped up to 10.0:1.

(Blocks would all have to be the same height otherwise cam timing would get altered.)

The carbs will probably need to be rejetted, but how much will depend on which carbs you are starting off with. Some KZ500/550's had TK21, and some had TK22. They are almost the same carb, but the minor differences might require a minor jet change.

zed1015 wrote: .........
The 550 is a 3mm stroked 500 - from 55mm x 52.4 to 58 mm x 52.4 mm
550 barrels fit the 500 but they are taller than the (shorter stroke) 500 so you can't simply drop a 550 block on the 500 for bigger capacity without using the 550 crank too or you just end up with a very low comp 500.
......

The statement above appears to show the stroke of the 500 and 550 to be the same at 52.4mm, so the statement that the 500 has a shorter stroke would appear to be incorrect. Is that an error? If not, please explain. Thanks, Ed

650ed wrote:

zed1015 wrote: .........
The 550 is a 3mm stroked 500 - from 55mm x 52.4 to 58 mm x 52.4 mm
550 barrels fit the 500 but they are taller than the (shorter stroke) 500 so you can't simply drop a 550 block on the 500 for bigger capacity without using the 550 crank too or you just end up with a very low comp 500.
......

The statement above appears to show the stroke of the 500 and 550 to be the same at 52.4mm, so the statement that the 500 has a shorter stroke would appear to be incorrect. Is that an error? If not, please explain. Thanks, Ed

The FSM suggests it's the bore that grew as displacement increased from 500 to 550. It's the 400 that has the shorter stroke.

650ed wrote:

zed1015 wrote: .........
The 550 is a 3mm stroked 500 - from 55mm x 52.4 to 58 mm x 52.4 mm
550 barrels fit the 500 but they are taller than the (shorter stroke) 500 so you can't simply drop a 550 block on the 500 for bigger capacity without using the 550 crank too or you just end up with a very low comp 500.
......

The statement above appears to show the stroke of the 500 and 550 to be the same at 52.4mm, so the statement that the 500 has a shorter stroke would appear to be incorrect. Is that an error? If not, please explain. Thanks, Ed

Sorry about that, my bad :blush:
550 is just a bored out 500. Same stroke so just swap the blocks.
Newer zephyr block will fit too.
Goes to show not to trust your memory after a heavy night at the bar. :laugh:
Had a few of these many moons ago and fitted 550 barrels to a 400 to make a rapid short stroke 500 ish.
Had to skim the barrels to correct the deck height but it did make a great little screamer.

Note to self.... Avoid the internet after drinking Captain Morgans and Cider

Had a few of these many moons ago and fitted 550 barrels to a 400 to make a rapid short stroke 500 ish.

Interesting, an idea that was floated many moons ago on the gpz550 forum but I don't think anyone did it. A good candidate as they are rpm happy motors with a really strong bottom end just in standard trim.

Using 3mm oversize 615 cc barrels would be a very oversquare engine, but limiting factor i guess is I don't think the 8 valve head would be able to breathe like a modern 16 valver.