peformance engine build question...or two.

[garyd]

I'm in the very fortunate position of having a MKII engine in bits, a complete 1260 Unitrak and a 1260 bigblock.

Sometime it would be easier if I just had an engine and stuck with that but as I now have a choice, I thought I'd try to make the best engine I can.

So it's looking like I'll be using the MKII cases, the Bigblock with the big valve Unitrak head with STD cams.

If I can, I'll be using the Unitrak crank and rods as that's what has the 1260 pistons attached

[garyd]

Oh, I have contacted the Guy with the P&Ms to see if he'll sell one of his spare engines....waiting to be told to 'clear off'

[Toyboy]

Oh, I have contacted the Guy with the P&Ms to see if he'll sell one of his spare engines....waiting to be told to 'clear off'

i know him well...hope you've got very deep pockets

unitrak stuff is better..that's why he uses it in all his engines

The only z thou bit is the crankcases.

If it's a road bike stick to 1170 lot less hassle

1260's get to hot and leak oil everywhere

[zed1015]

For a good simple bolt together road motor you want all the mk2 bottom end internals.
Mk2 big pin crank is the strongest so get that welded.
Mk2 Gearbox cluster has extra engagement dogs so use that.
Steel clutch basket on the kicker motors is the same for all z9 upwards so use your Mk2 one as it will have less wear being newer,
Unitrack head is factory ported and has the biggest valves BUT the valves are steeper in the head so you will have to watch piston/valve clearance as the piston may need the valve pockets re-machining to match.
Using a '1000J' head would be simpler as it uses the same valve angles as the earlier motors.
The 'J' head has slightly smaller valves than the UNI's but they are still bigger than the mk2's etc and you won't be restricted unless going really big on the CC's.
With either of the later heads you will lose compression and will need to compensate.
Unitrack cams will work well but ideally you should run under bucket shims with them.
As for CC's, I would go for 1075, it's the best compromise between power and reliability and will stay in one piece longer with no problems like overheating, oil leaks etc.
You should be good for 160 ish with the above and a decent pipe and carbs.

You could go for a Uni gearbox, Uni crank etc etc but it would a lot more work and a waste of time and money to be honest if you aren't racing.

I might have a 'J' head that's been drilled for the top idler, 8 plugged and modded for external oil feeds going spare if you want to swap for the uni one.