BIG BORE Tech Advice needed

[Pigford]

If you go for a big bore job, have the cases milled out to suit, whats the score whith working the head. Daft question I know, but can't get my HEAD ( ) around it
Coz the bores will be bigger than the head combustion chambers, do they need to be machined, to increase diameter I know a large head gasket will be needed

Paully, Fred or Fitzer, don't bother to reply thanx

PS - Which engines had the 17mm or 18mm pins

[london calling]

The 1100R1 Lawson Rep and the ZX1100 motors have the 18mm pins.
The 1089cc blocks can be bored straight out to 75mm,which gives 1170 cc and you don't need to open the crankcase mouths.
This is probably the most cost effective power increase you can get.
Any bigger is really more use for racing,drag racing,etc.

[Pigford]

I fancy a 1260 for me Z1000A1 motor.
Seen a barrel & piston set, so wanna know the score wiv the head
My motors (77 & 78 thou's) are 17mm then
Should be cool for street use, Bigger is Better

[RALPHARAMA]

I was chatting to the man (Steve) from Piston Broke the other day and he had just had to open up the 'oles in the top crankcase cover for some fellow who had a serious big bore kit. Looking at the barrels, there didn't seem much meat between the bores. I understand that you can get 'em stroked as well. I have to say though if I want more power I would be tempted to start with a younger engine in the first place. 1000 EXUPs can be picked up for thrupence ha'penny these days and having had a one new one all those moons ago I can vouch for them going like the proverbial turd off a shiny shovel. I am sure the engines won't put out what they did when they were new, but that was excessive. I indicated a ton seventy five on a public road and it stiill had moer left ... but I never found a road long or clear enough to hit absolute max speed. I think performance bike got one though rader or timing lights at 172mph (true).

[london calling]

Piggy,in this case bigger means more heat,more ??? and possibly more grief.
You get it on with it my old china ,I'd never go over 1170 for the road

[debben1]

Hello Pigford, to answer your question you do not need to change the head, the pistons are machined to accomadate the stock combustion chamber shape and achieve the designed compression ratio. I would agree with Jack thay the 1260 is not a good size when used with the stock block as the large liners leave the casting to thin to support the liners properly, another problem is that the stock block bored right out and with the casting resess between the liners is that very little gasket purchase area is left, which leads to a real chalenge in obtaining an oil tight seal. The biggest problem with the 1260 conversion is the risk of a liner dropping, this is where the 1325 big block conversion wins, much more liner support, bigger and a more substantial gasket purchase area, so you really have a choice of 1170, which is straight forward, reliable with out many other modifications requied and so inexpensive or if you want more then skip the 1260 and go for 1325, but you will need to bore crankcases, fit heavy duty cylinder studs, weld the crank, fit higher lift camshafts, better valve springs and a shim under conversion as well as bigger carburretors, I have used my 1325 on the road for many years with out any issues, my 1260 engine before it did drop a liner though. Steve

[Pigford]

Thamx for the comments, and tech bit from Steve...
OK, gonna stick with 1075 for the moment.
Bit brassic anyhow, or I'd be tempted by Jacks GPZ mill

[london calling]

Be tempted Piggy,you know it makes sense and will be cheaper in the long run