xj900 engine into 750 Maxim Frame

You guys might call me crazy, but I'd like to find a 900cc engine to transplant into my 750 Maxim. I'd love to have the challenge and the extra power...

Any thoughts... ?



Paul S
Barrie, ON

 

Everything I've seen says it'll bolt right in. The 650/750/900 externally are the same. Might have some differences as far as electric tach/mechanical tach, etc., but should bolt right in. Now, the real trick is finding a 900 motor. I've been keeping my eyes peeled for a while to no avail. Unfortunately the 900 never really caught on here in the US. Don't know why though, awesome bikes.

 

The new 750 Interceptor made it look decidedly old-tech. Too bad.

 

I have a 900 motor. It is currently awaiting shipping to me here in AZ. They are hard to find without the bike.

 

Oh, yeah, it is basically a bolt-in upgrade.

 

Swapping the engines might be a bolt-in affair, sure. But, there's a few things to consider after you have the 900 mil in the frame. What are you going to use to feed the heavy-breather. You'll definately want the 35mm's Mic's std on the 900. This factor will require some creative fabrication from the carb intakes to the 750's airbox. If you are planning-on putting the 900 mil in a 750 Max ... (as I am - someday - got the motor and everything else) ... you need to take in to account that the stock Max fuel tank is either going to have to be replaced with one "Less deep" or the std tank requiring some tailoring. According to my measurements. last winter, the bottom seams on left and right ... precisely where the intake side of the cam-cover will sit, will prevent an unaltered tank from proper fitment. I raised the front of the tank to where there was sufficient clearances and the problems just got worse. The look was a hundred-percent Mickey-Moused and the handlebar clearances L & R get into the act. My personal opinion, right now, is to leave my low-miles 750 motor in ... until I have all the skills needed to be on "American Chopper" and "Monster Garage." (( After I take the Welding Class offered in a nearby Technical Highschool ... and can MiG and TiG without coloring outside the lines ... I might give it a shot. ))
Rick Massey
XJ900
XJ750 Max
900 Spare engine.

 

Hi all, just reading the forums before i post my rebuild of a XJ 750.
Had a guy on eBay/OZ a few mths ago selling a XJ 900 with sidecar and leading link froks, which was made up of a XJ 650 turbo case [more internal bracing than standard] XJ 900 crank and top end, which was apparently built 15 years ago, and survived by frequent oil changes @ 3000km.
Looked a bit ratty, bike did not sell and he threatened to rebuild it to a cafe racer or something, but someone did buy his sidecar when he re listed them separately. Darn, i forgot to save a pic of it.

But yes, the 650, 750 and 900 are the same externally, i suspect the gearing is the same, but the use of the matching crankshaft, rods and barrels are for the stroke length which is different to each one.
Cheaply you could grab the XJ 900 internals and upgrade your case, this bike was the first one i have seen mashed like that, but i do own a XJ 750P where the police mechanic apparently installed 900 cams into the Australian XJ 750 police bikes.
Only the West Australian police used the XJ 750 im told.

RickCoMatic- So you are saying the 900 motor is taller? Longer stroke in the pistons makes it taller, thanks.

 

can you say, "yamaha only exported them to the U.S. one year"?

i dont understand Ric. if the engine is the same dimensionally, why would the 750 tank not fit properly? shouldnt everything on the 900 be in the same place as the 750?

 

The 900 Block is different.
The Head is much larger.
The Intake Manifolds Larger.
Huge Mikuni 4-Pack.
The Frames are all-together different.

The only 900 Engine I have seen stuffed into a 750 Frame had a Gas Tank Mod that looked absolutely ridiculous.

 

oh i was confused after reading this:

 

I'll check my friends XJ. He has a 900 engine in the XJ650 SECA frame and it just bolted straight in. From what i remember he just used a different airbox and did something with the carbs.
Next time i see him i'll take a few pics.
(BTW, it was done by the local Yamaha mechanic)
Nick

 

Sorry, was just referring to the cases and i thought [rightly] the top end is taller for the 900.

Oh.
Time to get the rulers out yet?. I don't have access to the 900 block.
How did old m8 get the 900 crank [maybe he just used 900 rods], into the 650 cases?
I usually save XJ photos and im sorry i cant show you the bike, his setup looked ok but im not sure of the frame he used.

 

Good old Google, and eBay still have the listing up

I forgot how ugly it looked, whats that tank look like Kawasaki?
Did the army build it? Bulletproof, like out of mad max..

Description:
I have had bike for over 15 years and set it up as an outfit to transport my kids, they are now to cool to go in it being teenagers.
The bike was originaly an XJ650 Turbo but has had 900 crank barrels heads carbs etc fitted into original cases
This Outfit has been a regular winner over the years of both Longest distance and Rat bike a great combination in my opinion.
You can either restore it with the huge quantity of spare parts, or register it keep up the oil changes (every 3000km) and ride it forever.

Q: G`day, Is the turbo still on it & working. Doug 04-Mar-09
A: No Turbo removed, 900 crank bareels head carbs etc produce more power and torque than turbo ever did, much less complex also. I got the bike cheap in the 80's because it had no turbo. I have since riden and owned turbo Xj's and this is faster (without chair of course) Dave

Q: What condition is the :-1)motor 2)Gearbox 3)Transmission 26-Feb-09
A: All good, Oil changed very regularly (if you know XJ's as soon as the gearshift starts to get stiff it is oil change time regardless of milage) Clutch gearchange no noise apart from normal final drive is good and has had new oil within last 2 years. I would check tyre pressure and ride bike anywhere without hesitation. (actually i would check sidecar wheel bearings as i just noticed dust cap is missing) 900 crank/rods were balanced before being put in turbo cases (turbo cases massive internal bracing and oil pump moves double oil to standard XJ), barrels pistons etc were new (ex Qld police) head was flowed all this happened about 9 years ago and bike has done approx 70,000 since, it uses about 500ml of oil per 1000kn which is good for aircooled bike pulling chair. hope this helps Dave


I know this is way off the original post now, but you can see what has been achieved using the XJ motor.
He converted the case 9 years ago, not 15 like i thought.





To answer the question, a xj900 will fit in the frame [his is XJ650T], 2nd photo shows top of cam cover to be VERY close to the frame bracing and you will need to look for a fuel tank that looks better.

 

That's the standard turbo tank without the side panels to cover it up.

 

Has anyone attempted to bolt an xj900 motor into an xj650 Seca frame?

 

I have measured a 900 against a 750 Seca, and the head and jug come out the same fin-for-fin starting from the top of the engine side covers.

I don't see that a 900 engine is any taller, although the carbs and intakes could be bigger, as Rick Co said. I think it's a bolt-in with some intake tweaking. And they are geared taller, not the same.