putting a 750 or 900 into a 650 seca?

hey guys does a 750 or 900 fit into the frame of a 650 seca?
cheers brenton

 

750 will fit, not sure about the 900.

 

Let me rephrase that, I know that a Seca 750 will fit onto a Maxim 650 frame (yes, bought the engine and tried to stuff it in, forgot the tach issues and yanked it, haven't gotten back to it yet). Good luck, sounds interesting, wish I had a 900.

 

what sort of tach issues ?
cheers brenton

 

I know that the 750 will fit into the 650.

 

650 Maxim has a mechanical tach, the 750 Seca has an electronic pick up on the coils. I expect that there are some models of 750's that have the mechanical hook up, but I failed to source the correct head for that application. I could have stuck with the 750, the mod is really no big deal except I haven't a spare eletronic tach for a Yamaha laying about. How's life down yonder? That storm cause you any grief?

 

nah theh storm was up qld , im down in sydney so i was allgood. but yeah we wont be havein bananna's for a while.
so you just need a electric tacho , that doesnt seem that hard.
has anyone got any ideas on the 900. i can get on cheap to rebuild?
cheers brenton

 

Engine Swapping

 

i couldnt seem to find out if a whole 900 motor and gearbox would bolt straight in ?, but it seems like the 750 will ?
cheers brenton

 

i'm pretty sure that the seca 750 and and the 900 share the same bottom end.The top end is where it takes up a little more room.Hence if you can shoe horn a 750 in a 650 chassis I would almost bet the 900 would go in. The biggest problem would be height.You'd have to modify those top frame tubes.Sounds like an in depth project to me.How deep do you want to dive in?

 

One guy stated that he had both the 750 and 900 engines in his bike at one time, so it should fit just fine. Consider that the turbo probably has less space to work with than the NA Seca, and you should be good to go. The 1984 XJ750R (not Seca) was virtually bolt for bolt a 900 Seca with a smaller bore and stroke. The engines are identical. The owners manual for the 84 750R was the 900 Seca manual with a small addendum included for the different 750 parts (carbs mostly).

 

cool well if i do it ill prob just go to a 750 then, the 900 that i found needs a rebuild anyway.

 

how much would the swap benefit you?

Is there that much difference in power between the 650 and 750 or is it just a better platform to build on?

 

Hi everybody... :wink:

I'm new here..

I had in a german forum xj650.de read that a 900 fits ok.

regards molgaard

 

hey thanks molgaard, ill keep that in mind.
the 750 is supposed to make 80hp over the 70hp from the 650, and the 900 is supposed to make 100hp :lol:
cheers brenton

 

The 900 also has a better flowing head and bigger cams. Would love to find a 900 around here, they're total beasts! But it's rare enough to find a complete XJ900, much less one that is being parted out. :cry:

What I'm doing is putting the 750 rotating assembly in a 650 motor. Why you ask? Well, mostly because all I have is 650's, and one of them needs to be rebuilt anyway. That with a set of 900 cams and some mild port work should make a pretty decent motor...

 

What is the advantage of the 900 cams? lift and duration? Won't you need to port to take advantage of that? Where is the restriction in the 650/750 engine? Are you trying to bolt the entire 900 head onto the 750 jugs?

 

Welcome Molgaard, hope you join us often. Thanks for the link, keep them comming!

 

The 900 cams have more lift and duration. Some port work is planned on the 750 motor that I am in the process of building. As far as where the restriction is, I'd guess the first restriction would be the small intake and exhaust ports, followed by the small cams. I'm not going wild with this setup, the 900 cams are only slightly larger than 650/750's, just trying to squeeze out a bit more performance without spending a bundle on custom cams/oversize valves/high comp. pistons, etc. If I were to find a 900, I'd use the complete motor.

 

Ok Now I got my head thinking. I'm tempted about the 900 engine in my 83 750 seca. Do I gotta change the carbs, coils, exaust? What other "accessories" besides the engine have to be swapped out as well?