Max bore size

[Johnnie]

Hello all, I'm contemplating a big bore kit as a winter project for my '96 bandit 12. Does any know the maximum safe bore size I can go on stock liners?

[370steve]

12 minutes ago, Johnnie said:

Hello all, I'm contemplating a big bore kit as a winter project for my '96 bandit 12. Does any know the maximum safe bore size I can go on stock liners?

I was told 82mm, i am fitting 1246cc,  82mm kit too mine

Edited October 30, 2019 by 370steve

[Gixer1460]

Not saying don't do it, but +30cc's makes two tenths of fuck all difference compared to a 1216 kit but the bores will be more flexible and with a 1216 kit you do have the option of another overbore if it all goes tits up?

[zedhead]

Echoing Flipper, I'd advise going for a 1216cc kit - it'll make for a physically stronger motor that will withstand heat and miles better than the more flexible sleeves resulting from a slightly larger bore. And remember,  the 1216cc kit makes for a feckin' awesome road engine ;-)

[Johnnie]

12 hours ago, 370steve said:

I was told 82mm, i am fitting 1246cc,  82mm kit too mine

Are you replacing the con rods as well?

[370steve]

8 hours ago, Johnnie said:

Are you replacing the con rods as well?

yes, going with Carrilo, dont know if there is a need, but doing it coz i could

[Gixer1460]

9 hours ago, Johnnie said:

Are you replacing the con rods as well?

Really not worth it until you are seeing over 250hp - makes more sense spending the money on a proper full engine balance job IMO!

[rdubandit]

Has anyone ever increased the stroke of a 1216?

[baldrick]

falicon stroker crank will increase the stroke.

[Gixer1460]

9 hours ago, rdubandit said:

Has anyone ever increased the stroke of a 1216?

Why stroke a baby one - bore it to 85mm and add a 5mm stroke - proppa!

[rdubandit]

2 hours ago, Gixer1460 said:

Why stroke a baby one - bore it to 85mm and add a 5mm stroke - proppa!

5mm more stroke with 81mm pistons would get you to 1319cc with bored stock sleeves.  Would that not be "streetable?"

Wouldn't 85mm that require case boring and new sleeves?

[Gixer1460]

8 hours ago, rdubandit said:

5mm more stroke with 81mm pistons would get you to 1319cc with bored stock sleeves.  Would that not be "streetable?"

Wouldn't 85mm that require case boring and new sleeves?

Stroked motors generally make better torque which is better for a street bike but that's not 'trendy' or 'on point' with those that like revs as your example would probably redline at about 8500 - 9000! With the extra stroke I think the thin sleeves may become a weak point. My 1460 took a bit more than just case boring and some sleeves!

[rdubandit]

2 hours ago, Gixer1460 said:

Stroked motors generally make better torque which is better for a street bike but that's not 'trendy' or 'on point' with those that like revs as your example would probably redline at about 8500 - 9000! With the extra stroke I think the thin sleeves may become a weak point. My 1460 took a bit more than just case boring and some sleeves!

1460cc - wow, I bet that was a lot of work!

I'm very much a novice at engine building as my experience is limited to installation of 1216 pistons and a Web 236 intake cam and performing cam timing.  I've never opened an engine up all the way, but I'm eager to learn.  I would not drag race any of the bikes, and while I've taken a few of them to a nearby roadrace course, they'd be used mostly for commuting and joy-rides -- both of which would benefit from big torque. 

So, related to this thread, it appears there may a benefit to not aiming for maximum bore, but perhaps increasing the stroke a bit?  The downside is paying for stroking the crank (and then probably choosing to have a little mass removed and knife-edging done as well).     Lots of fun variables!

[clivegto]

Just fit a turbo with a few engine mods. 

[rdubandit]

Just now, clivegto said:

Just fit a turbo with a few engine mods. 

I'm a "naturally-aspirated" kind of guy.  Turbos are cheating!  

[Gixer1460]

17 minutes ago, rdubandit said:

So, related to this thread, it appears there may a benefit to not aiming for maximum bore, but perhaps increasing the stroke a bit?  The downside is paying for stroking the crank (and then probably choosing to have a little mass removed and knife-edging done as well).     Lots of fun variables!

The real problem with stroking a bike engine is unlike auto engines where conrod alternatives are viable option to allow just resize the BE & regrinding the BE offset, with bikes the variations are small and often don't compliment the small ends so you have to either find a shop capable and competent to either use stick, TIG welding or spray metal build up, remachine an offset pin and then grind back to stock journal size - quite expensive or pony up for a new billet crank - very expensive. I'd guess the former to be at least the cost of a bore and piston job, possibly 50% more whilst the latter (in my case) was 3x the cost of bore and pistons (which was done bigger as well LOL!)

Psssst - turbo's give TORQUE and lots of power - makes a really good street bike LOL!

Edited November 1, 2019 by Gixer1460

[rdubandit]

16 minutes ago, Gixer1460 said:

The real problem with stroking a bike engine is unlike auto engines where conrod alternatives are viable option to allow just resize the BE & regrinding the BE offset, with bikes the variations are small and often don't compliment the small ends so you have to either find a shop capable and competent to either use stick, TIG welding or spray metal build up, remachine an offset pin and then grind back to stock journal size - quite expensive or pony up for a new billet crank - very expensive. I'd guess the former to be at least the cost of a bore and piston job, possibly 50% more whilst the latter (in my case) was 3x the cost of bore and pistons (which was done bigger as well LOL!)

Psssst - turbo's give TORQUE and lots of power - makes a really good street bike LOL!

Great info, thanks!  Hint received!! 

[Oilyspanner]

Our engines are limited by the head, if you increase the capacity and not do head-work you won't gain that much power, it'll develop more torque at lower revs and have more peak torque, but power will drop sharply after peak torque. Fitting a turbo will force the air into the engine getting around head design, larger valves and careful flow work will yield far more power than stroker crank or huge bore. The old high output engines did have large capacity, but they had very special heads too - along with machining to lower pumping losses and venting etc. A 1340 engine with little or no head-work will put out in the 140s hp , it'll make a load of bottom-end and mid-range power though (they feel very grunty) - it depends what you want. Some engines have heads that can easily feed a larger engine and you get big gains with less than a 100cc extra displacement - ours don't, the heads need some work to give big gains.

If you want a really grunty motor just increase the capacity, the more the better. If you want a really impressive motor spend most of your time on the head (and money !) ,plus a high comp. big bore - if you want to blow your socks off, fit a turbo …….it's a long winter, so the plenty of time to get work done.

[clivegto]

3 hours ago, Oilyspanner said:

Our engines are limited by the head, if you increase the capacity and not do head-work you won't gain that much power, it'll develop more torque at lower revs and have more peak torque, but power will drop sharply after peak torque. Fitting a turbo will force the air into the engine getting around head design, larger valves and careful flow work will yield far more power than stroker crank or huge bore. The old high output engines did have large capacity, but they had very special heads too - along with machining to lower pumping losses and venting etc. A 1340 engine with little or no head-work will put out in the 140s hp , it'll make a load of bottom-end and mid-range power though (they feel very grunty) - it depends what you want. Some engines have heads that can easily feed a larger engine and you get big gains with less than a 100cc extra displacement - ours don't, the heads need some work to give big gains.

If you want a really grunty motor just increase the capacity, the more the better. If you want a really impressive motor spend most of your time on the head (and money !) ,plus a high comp. big bore - if you want to blow your socks off, fit a turbo …….it's a long winter, so the plenty of time to get work done.

My turbo set up is 1216cc with tdo4 turbo usaly good for 180hp. I also fitted a big valve flowed head which made a massive difference. When first built it made 260hp on 2 different dynos in the same week.