650 Maxim to 750 conversion?????

Hello,

Just got my hands on a set of jugs, pistons, rods and crank from a 750 maxim...question is, will I be able to fit it onto my 650 case? And then, will the 650 head bolt on?


Thanks,

Jon

 

If my brain cells are working right- - yes.
Using a 750 head required 2 extra long studs.
using the 650 head might boost compression, and give you smaller valves, and might give you tuning headaches, also, you need to replace your wimpy 110 jets for some 120 ' s, and the air jets also.

I'd go with a 750 head just to be safe, anyone else????

 

Hey...Thanks for the reply.

My bike already has the 120 jets, and all the other jets were trashed so I need to replace them anyway...I am planning to port and polish the head and then slap it on a flowbench my buddy has, so I think the 650 head will flow fine...but we'll see.

I have broken the bike down to the point where I think I can just split the case and slap the new crank and all in, put the pistons and jugs on and see what happens...

I need to do a little more research about splitting the case but I will most likely be doing it shortly.


Thanks for the advice,

S/F,

Jon

 

Hold on !
There's a tricky bit about matching up bearings by color, and getting sealant in some spots, and not others, and replacing the starter guide, cam guide. You need a manual to re-assemble the motor, unless you want to build a "grenade" motor.

 

sounds nice, anytime you get your hands on a nice set of jugs... that's as far as i go so as to not get kicked off this site.

 

NICE!!!! didn't even think about that...well played sir, well played...

 

ok my question from dealing with motors is this, does the 750 just have a longer stroke then? if the piston bores are the same diameter then yes you can use the 650 head without too much problems you may run too high compression but a thicker or custom base gasket can help that. If the piston bores are not the same it won't be right as the head combustion chamber will have two things wrong you will have a ledge around the cylinder which will give you a messed up squish band. Then of course the chamber will still be too small. You can in theory recut the head to suit your needs but way tooooo much math for me to consider doing that.

 

I was wondering if a whole 750 engine would fit. There seems to be some around when people part out bikes the engine seems like the last thing to sell. I have a 81 650 and under the work bench I have a 82 750. It looks like it might fit but I didn't want to go through all the work if someone here has tryed it and it doesn't work. Since the 650 has a slightly smaller frame and lighter than the 750 it would be alot of fun to get thatr extra HP into the 650 frame. I think would be a fun ride. Besides there is a lot of money to be spent on rebuilding and modifying an engine like that. Gaskets, bearings, machine work and all the other stuff you run into when you take something apart like that.

 

In this thread:

http://www.xjbikes.com/Forums/viewtopic ... html#91567

there's a 650 Maxim with a 750 motor, and one problem is the "reverse pattern shifter", which I think would be kinda neat. Didn't old Bultaco dirt bikes have you downshift thru the gears?

750 ' s are bored and stroked 650 ' s

I think an awesome "sleeper" would be put my turbo stuff on my 750 Maxim, with a double head gasket, blocked waste gate, almost hidden turbo, quiet exhaust, and a stock overall look.

 

Alright...so here is the deal...

I am looking to put a 750 CRANK, PISTONS, CYLINDERS onto my 650 CASE...and then put the original 650 HEAD on top of the whole mess...

The stroke issue would not be a concern as the 750 cylinders should be set up for a 750 stroke...like wise with the bore...

from what I have researched and read on this board, the 750 is stroked and bored 650, as was mentioned in one of the earlier posts. My question remains, will the 750 Crank and Cylinders fit in/onto the 650 Case.

If that is the case, then bammm, we get us a regular pony show... I think the Cylinders are going to fit. (will see this monday) but my concern lies with the crank and case fitment... I figure worst case, I slap some 750 pistons onto the 650 crank and rods, throw the 750 cylinder on and use an old saab turbo I have in mygarage and turbo the beast becuase I know that the compression will be plenty low with that setup...


ANY Ideas? Thoughts? Suggestions?


Thanks,

Jon

 

I don't think it's going to happen.

The 750 and 900 share the same bottom end.
The 650 is different from those two.

I have never heard of anyone doing that Mod ... I guess you are breaking ground giving it a shot.

I was going to try and put a 900 engine in my 750 Max. After doing a few measurements I don't think that's going to happen anytime soon.

Good luck, though.
If you are going to do all that work ... I hope it come-out nice!

 

Alright...so here is an update on the project...

Got the bike put back together. Didn't switch out the crank, just put the 750 pistons and cylinders on and everything fits just fine. will be finishing the assembly and posting pics and such later this weekend.


Thanks for the info everyone!!!!

Semper Fi,

Jon