Z1OwnersClub GB

I starting to look at rebuilding my old GPz550 and the engine will need a rebore. I fancied a bit more "go" from the engine so started looking at a big bore kit. Wiseco list a 615cc kit that is 3mm o/s but it seems to leave the liner wall very thin.

Std bore is 58mm, the 615cc kit is 3mm o/s, so a bore size of 61mm. The o/d of the liner at the bottom of the barrels is 63.5mm, which leaves a liner wall thickness of only 1.25mm

I'm no engineer, but surely that's way too thin ????? Any engineers out there who can comment, please - am I right or totally missing something ?

Kawasaki maximum o/s is 1mm (with good reason given the above calculations), so I'll probably try to find some NOS o/s pistons/rings or a good set of used barrels/pistons as an alternative

Mark.

I don't know about 550s but 1100s run 3mm oversize pistons with no problems (I hope)

You will be ok at 1.25mm liner thickness at the spigot.
The 3mm o's 1105cc kits leave the 1000 liners this same thickness at the spigot.

Thanks Zed1015,

Having looked a bit deeper, I've found that Cruzin Image do a 3mm o/s as do Scheuerlein in Germany. I know a lot of the Kawa triples boys have used the CI pistons with no issues and the price is very attractive I've not heard of Scheuerlein before so don't really know much about them, but they're still cheaper than Wiseco.

Decisions, decisions

Are they cast or forged pistons, some of the cheaper ones are cast which are not as strong as forged.

You get what you pay for.
Those Cruzin image kits are cast whereas the Wiseco's are forged .
Personally I think those Cruzin ones are false ecomomy and wouldn't touch them with a pointy stick.
Wiseco's reputation (along with MTC, Cosworth etc) for quality and performance on road and track is renowned worldwide.
There's a reason why you don't see any reputable engine builders using the Cruzin pistons in their builds.

Yes - I know the cheaper options are cast not forged and I take the point on WIseco's reputation. In the past, when I've had a big bore kit fitted in my engines, it's always been Wiseco - I was just exploring the options. However, if I'm rebuilding the bike totally, it's false economy to cut corners - the expression that springs to mind is - "spoiling the ship for a 'haporth of tar"

Thanks both for the comments & advice - much appreciated

Mark.

Never heard of Cruzin Image pistons until now, but £51 for set of 3 piston kits for a Kawasaki S3 doesn't fill me with confidence
The Scheuerlein sets aren't a great deal cheaper than Wiseco ones, £480 rather than £525 for a set of Unitrak piston kits, but again I hadn't heard of Scheuerlein until now.

i had a supply issue with wiseco. ordered a big bore kit and waited 3 months with no joy and finally canceling order. ended up getting a set of cosworth pistons from Roger Upperton who also done the rebore and head work for me.
maybe the situation has changed at wiseco now. i just thought i would share my experiance with you.

Just my views here....
With max bore (1105cc) I found that on my old Z1000 the liners could move if the engine got too hot (I used to drag race it).
Personally rather than go for max big bore kit, I would look at other ways of extracting power.
Head work, cams, raising the CR, all easily achievable.
If my memory is correct, you have a D1 don't you? If so ditching the TK carbs in favour of the ones fitted to the H model may help considerably?

Just my views here....
With max bore (1105cc) I found that on my old Z1000 the liners could move if the engine got too hot (I used to drag race it).
Personally rather than go for max big bore kit, I would look at other ways of extracting power.
Head work, cams, raising the CR, all easily achievable.
If my memory is correct, you have a D1 don't you? If so ditching the TK carbs in favour of the ones fitted to the H model may help considerably?

It's actually a H1 (first unitrack model) it has 26mm TK carbs, but my plan was to fit the larger 27mm TK carbs and better cams from the later "A" model unitrack, anyway. The head has already been flowed & lightly skimmed as I used to proddy race it back in the day

Obviously, It's only going to be a road bike, so not subjected to the abuse of drag racing, but I take your point ! As I said in my original post, a liner thickness of 1.25mm just sounded too thin to me - but then, I'm no engineer