The old 750cc big bore kit trick

Has anyone done a 750 big bore Kit?? I hear a lot of bad stuff about it and can't deside if I wanna do it or just put the money into a full rebuild with port and polished heads maybe performance valves and springs etc, the 750 kit cost about $2000 Australian all up

If u have nothing to add to this topic other then it's been covered before or search it, then don't bother commenting on my topic!! This forum is about asking questions to a greater community of people with the same or similar experiences to help the people who haven't experienced it yet

don't know were you get 2000 from try geoffs xs hes got 1 listed 800 and hes local with good back up, if you mean 2000 for full rebuild a lot of that money would be spent on port/polishing springs etc etc anyway ,got the mikes750 kit in project motor and all looks good,dont know about bad reports but eveyone I know whos done it are happy ,would be intrested in hearing about any bad reports out of curiosity

The 750 big bore kits work pretty good and service life is about the same as for 650cc. One variable is if you buy the kit complete and ready to go (new block with bored and honed sleeves with pistons and rings) or buy the sleeves, pistons and rings and have the machine work done locally. The complete kit ready to go costs more but, unless you know a machinist who is accurate and reliable (or are one), the extra cost might be worth it.

Porting and polishing is not cheap and could actually make your motor run worse if it isn't done right. Again, proven skill is necessary to have the job done right.

One solution some have used to freshen up and add some power to their 650 is to bore it to 700cc. Installing a 750 kit means two new pistons and two new sleeves and two machine jobs (boring the block for the sleeves and then boring the sleeves to fit the pistons).The stock sleeves can be bored for pistons to give 700cc without sacrificing reliability, saving the cost of the sleeves and machining them. If the rest of the tuning (ignition timing and carburetor jetting and adjusting, exhaust pipes and mufflers) is done correctly, there isn't a whole bunch of practical difference between 700 and 750. (The loudest, "coolest looking" exhaust system does not necessarily make the most power or put the power in a RPM range where it is useful.)

One thing Mikes got right. Our club racer has one, And if you think its gonna be a pussy then read .....HERE......

New Barrels/Pistons/rings so the old ones can be rebuilt and /or go the 700 route but if the barrels are good a 4th over, leaves room for another re-bore to 700 later.

THIS THREAD will cover the XS650 Porting and Polishing question. Read all posts, couldn't get better advice, or much better experience on this subject.

But some will say, work the head to its best capabilities, and the gain will be better than a 750 swap. Get the 750 at a later date and have a rocket.

More HERE

I had heard that the 750 big bore kit needed rebuilding almost twice a year, that was my only consern, do u use ur stock cam?? I didn't know Geoff sold them! Thanx for that! Yeh port and polishing can be a tricky thing

Why would a 750 kit need rebuilding twice a year? it's still two pistons just bigger, not sure where the $2000 came from, you can pick up Wiseco pistons pretty cheap from the US, Australia uses the same crank and rods as the US so easy to get parts and no import duty on what a 750 kit costs, even the JE kit from Hoos wouldn't cost $2000,
The increase in power from the 750 kit transforms the 650 engine, makes it a real joy to ride.

Maybe this has been covered before or you might try searching the topic... HAHAHAHAHAHA! I am a DICK!!!

Jay my 750 kit with your cylinder bead blasted, bore and ready to install is only a low $800.00 But is done right. With the best piston available not the $120 as set P.O.S out there.

hooser said:

Jay my 750 kit with your cylinder bead blasted, bore and ready to install is only a low $800.00 But is done right. With the best piston available not the $120 as set P.O.S out there.

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I run your JE pistons in my engine, only mentioned them because they cost more than the Wiseco kit, I can highly recomend the JE pistons they have transformed my engine, had the Wiseco pistons in there before performance is much better with the JE.

Thanks Jay glad you like them.

jay760 said:

I run your JE pistons in my engine, only mentioned them because they cost more than the Wiseco kit, I can highly recomend the JE pistons they have transformed my engine, had the Wiseco pistons in there before performance is much better with the JE.

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The Wiseco pistons are great pistons,just to heavy. Dome shaving or hollowing underneath the dome or shorting the skirts would be beneficial lighting the load on the rods and engine vibes.

Chop089 said:

Has anyone done a 750 big bore Kit?? I hear a lot of bad stuff about it and can't deside if I wanna do it or just put the money into a full rebuild with port and polished heads maybe performance valves and springs etc, the 750 kit cost about $2000 Australian all up

If u have nothing to add to this topic other then it's been covered before or search it, then don't bother commenting on my topic!! This forum is about asking questions to a greater community of people with the same or similar experiences to help the people who haven't experienced it yet

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Ive built a few over the years, including a full race engine didn't have any problems, Geoffs kits ahve a great reputation

Chop089 said:

Has anyone done a 750 big bore Kit?? I hear a lot of bad stuff about it and can't deside if I wanna do it or just put the money into a full rebuild with port and polished heads maybe performance valves and springs etc, the 750 kit cost about $2000 Australian all up

If u have nothing to add to this topic other then it's been covered before or search it, then don't bother commenting on my topic!! This forum is about asking questions to a greater community of people with the same or similar experiences to help the people who haven't experienced it yet

Click to expand...

My son bought the 750 kit and installed it on a 1981 xs650 Heritage. We could never get it to stop smoking. I have sent it to a mechanic to rebuild. We thought it was smoked because the rings were not setting. The mechanic thinks that the 750 kit was ok problem was crankshaft connecting rods the head needed decking. I would say if you are putting the 750 kit in you better make sure ever the else it to spec.

I had a 1981 that I put a BBK into and I also put performance value springs in and it ran great.
A lot of torque. A lot faster.