900 Engine in 750 Frame?

Hi,
Looking at the mountings on the XJ900 compared to the XJ750 they look to be in the same sort of area but... the XJ900 has a longer stroke so... taller?

I don't have an XJ900 engine to physically measure so I thought I'd ask this question as after a bit of research via the XJCD and the search function I can't seem to find any engine height specs or mount distances.

Is it possible to fit an XJ900 engine into a XJ750 Seca type frame?

If anyone knows the
1. distance between the mount points
2. height to the top of the valve cover from the top/front mounting hole on the engine.
3. distance from the top/front mounting hole on the engine to the rear of the engine.
That'd be great too!

Thanks.

 

Don't have the measurements you need, but I know it will be close. I know the 750 engine has been swapped into the Seca 650, and the 900 interferes with the fuel petcock. I'm still planning on swapping the 900 into my Seca, and will do whatever is needed to the tank to make it work. I'm pretty sure the mounts are the same, but the height of the engine and the exhaust and induction will be your sticking points. The 900 engine is also geared taller, IIRC.

 

Chacal has a summary of engine-swap options in his "Information Overload Hour" http://xjbikes.com/Forums/viewtopic/t=27544.html , about 1/4 of the way down the page...

 

A brief musical interlude to be sure, thanks Fitz.

I'm left with the feeling that it 'might' fit so I'll have to persue it further.

Thanks for the info and Cooter... Good luck to you... We may both need it.

 

The 4 MM extra stroke would need just 2 MM extra deck height. I've measured my 750 against the 900 and can't find any extra height.
The valve cover seems a little bigger, and the carbs are more bulky.

People have put the 900 innards in a 650 TURBO.
I think it's a "go".

 

Just did one of these transplant. Put XJ 900 in 82 XJ 650 Maxim frame. Fit right in. Had to build oil plate to hold oil cooler. Had to change choke cable position. No issues with fuel tank. Even hooked up stock to air box. Still finishing the fine tune. Runs like scared rabbit!

 

[quote="
People have put the 900 innards in a 650 TURBO.
I think it's a "go".[/quote]

Is there a thread or info on this conversion ?
Cheers
Andrew B

 

Thats good to know. Altho the 900 engine is getting kind of hard to find. Did you swap the harness or did the tci plug into the harness on the 650

 

Thanks, Fitz!


And a big shout out to Chacal- great to see all the work you put into not just parts, but also gathering info for all of us and archiving it. It is very much appreciated!

 

I can't find the picture of the 750 Maxium with a 900 Engine in it.

The Bike looked very strange.
In order to get the Fuel Tank on without cutting-up the Tank, ... they built a "Riser" and elevated the Tank above the Main Center Frame Tube.

The job didn't look right. Everything looked too forced rather than designed.
But, it proved a 900 Mill could be snuggled into the 750 Max Frame and be a runner.

 

Sounds like a real "go" now.
So I've taken the plunge and have the motor(s) in place for fitti... no! wait I mean, I have the motor(s) ready to be looked at for repair after I weld up the holes in the frame and attend to another hundred odd things... you know the story!
I'm looking forward to the process, although without studying the manual first, looking at the innards of the gearbox is a bit overwhelming at this point.

This is my parts bike frame (XJ750P 1984 37H) and 2 * XJ900 Motors (one with a good top end and one with a good gear box)

 

Is this Bike going to have a 750 Rear-end or are you going to fab-up the 900 Rear-end for it?

Either way, ... you should consider fabricating the SwingArm to accommodate a WIDER Tyre.

Both the 750 & 900's Swings could possibly be modified to run a wider tire.

1.) The Shaft Tunnel's Inside Convex curvature can be removed and replaced with a Flat-sided piece of Billet, ... as close to the Drive Shaft as possible, ... leaving merely a very close tolerance to the Drive Shave, ... or Machined down it's Center Line to provide for relief to the Drive Shaft.

2.) The "Horse Shoe" at the Pivot will need to have the Convex Inside Surface "Cut, Squared, and Reinforced with Solid Alloy or Steel (depending).

It's a lot of work to do, ... just to gain a little bit more rubber ... But,, if you get that 900 in there, ... you are going to be happy with however many mm's of width you can get on-the-road, at the back-end.

 

The 900 swingarm is longer (by 1 1/2" ?, 40 MM)
This would help control wheelies,
And you got the 891 CC engines, not the 853 ??

 

Rick, I was going to use the 750 swing(because of the brake torsion bar) and the 900 diff as I have the 750 wheel which is drum brake and don't have either the 900 wheel or disc brake assembly/bits to suit the 900 wheel.
I don't feel overly confident with re-engineering the swing-arm but that being said... this is going to be a long build.

Do you think a few extra millimetres of rubber would actually make that much of a difference? Cornering?

Time, aah well I won't be doing wheelies! I swear!
They are both 853cc engines.

 

Another question in the same sort of vein...
I have the,
XJ750 carbs - Hitachi HSC32 - rebuilt.
XJ900 carbs - Mikuni BS35 - need major overhaul, water damage, holes in diaphragms, etc.
FJ1200 carbs - Mikuni BS36 - look new! except holes in diaphragms.

I can see that the XJ750 Hitachi carbs are a much smaller venturi ID of 32mm compared to 35mm/36mm ID of the Mikunis. They are spaced differently also, so the Hitachis are not suitable I'm thinking for more than one reason.

I can see that my stock 750 airbox is going to need some sort of boot modification to suit the larger OD on the airbox side of the Mikuni (about 4mm) which is one problem but...

The main question is based on that I'm looking at these FJ1200 carbs and since they look so good, age-wise and cosmetically, compared to the ones that came with the XJ900 motor... what sort of difference could I expect if I swapped all the jets/needles into the BS36 from the BS35 Mikunis? or would it be a complete farce to even attempt the alteration?
Any opinion or advice welcome of course!

Mikuni BS35 condition





Mikuni BS36 condition





and, just for laughs, where I'm up to so far with assembly and rebuilding...

 

Make sure your police wheel fits the 900 diff. My police wheel would not fit my Seca diff. XJ750 and XJ750p diffs were different (the one time I tried it)

 

It's got cop tires, cop suspension, cop shocks, a 900 plant. It's a model made before catalytic converters so it'll run good on regular gas. . .

Oh Yeah ! :twisted:

 

Darkfibre, the XJ750P wheel fit the diff no prob... except the XJ900 Diff has a different shock mount point so, although the diff fits the XJ750P swingarm and the shaft fits the diff the mount points are offset for the shocks!
So no go on using the XJ900 diff but it looks like the gearing is exactly the same between the 3 diffs I checked.
XJ750Seca
XJ750P
XJ900RK
and the gearing difference is in the transmission, all in all no loss so I'm sticking to using the XJ750P diff and swingarm.

Latest pic with Swingarm, Diff and rear wheel fitted.


So a quick question. I have these two 900 motors...
One that was working till it blew second gear and the other with a good gear box and with the parts for replacing the gears in the first motor.

After spending a bit of time splitting the gearbox(2nd motor) and looking at the "oil spray nozzle" I suspect the HYVO chain is stretched but in looking at the same components in the other motor the HYVO chain has caused just as much damage to the "oil spray nozzle".

2nd Motor oil spray nozzle


Main Motor oil spray nozzle


The 2nd motor has an intact HYVO chain guide, although worn, and the Main motor has a broken HYVO chain guide...

I thought these HYVO chains didn't stretch?
They only start the bike and run the generator, don't they?

I'm a bit puzzled but I can see Rockerto had the same worn down "oil spray nozzle" also, so is it a common problem and perhaps the source of the low idle knock, like the XJ550s even though it isn't a primary drive chain in the 750 or 900?


On a side-note,
I guess it does pay to have engine guards, I wonder if this had anything to do with the second motor being scrapped... Try getting that to idle!

 

Houston we have a problem... that dowel hole in the crank is probably not worth trying to fix

As for the drive chain, on my rebuild I decided to replace it anyway along with the guide.

When assessing the pistons and bores for reuse, be critical of ring land wear.
Evidently in hot climates bikes left idling (police bikes especially) had some extreme temp cycles leading to ring groove wear. Too much and you may get high oil consumption.

 

I decided to shuffle the good chain guide to the main 900 motor and give the oil spray nozzle a bit of a tweak to make it actually squirt oil at the starter clutch again (filing and drilling was undertaken.)

I was told the top end of the main motor was worked on just before the 2nd gear started playing up and I plan to find out what that means.

The 2nd gear fault seams to be shift fork 2 and 3 being either bent or mis-aligned but the gear dogs looks like there in good shape, for both the motors, and I have a spare set of good looking shift forks in the 2nd motor so it's looking good.

I figure no harm in giving it a shot, if I have to pull the motor again, then I'll just do it! So far it will cost me some sealant, a whole bunch of kerosene, some WD40, and time but I believe I have a better understanding of what is going on now inside these motors and am glad I took the time to strip the 2nd motor's lower end completely before going further.

FYI: (The lower case on the XJ900 has 4H7 stamped on it. I'm starting to see a pattern here.)

 

Update:
Fitting the XJ900 motor into the XJ750 frame was no problem at all size wise and mount wise.
In saying that I've seen the codes 4H7(650) and 5G2(750) stamped into quite a few of the parts on the XJ900(31A) motor also.

The Mikuni 36mm carbs, on the other hand, are much larger physically than the Hitachi 32mm and definitely take up more space. Even still with a bit of finagling and a possible hernia, because of the bloody hard intake boots, it all fits together.

The Carbs required XJ900 carb to airbox boots and some 'judicious' holesaw work on the airbox to alter the spacing and size of the holes.

TIPFJ1200 carbs are the same as the XJ900 carbs at the core level but... they have a push/pull cable setup and a big spikey bit hanging off the bowls so unless you have a throttle shaft from a 36mm carb you're gonna have to do some cutting and modifications to make it work with the XJ throttle assembly plus some bowl modifications unless you have parts. Something I definitely will steer away from doing again. Although they do look shinier than the XJ900 carbs that came with the motor, so there is that!)

Here is what the motor looks like fitted. (no clamps on the carbs - must buy some)


A bit of a close up of the installed motor.


and with the tank(pre-repair) on to check the clearances.


Nothing is any tighter than the XJ750 setup, as far as I can tell either.

In case you were wondering, that is the XJ750P generator installed also. More AMPs the better I say.

 

Fundamental XJ900RK -> XJ750p differences so far,
- Oil filter cover bigger(same filter?). 750 cover fits still.



- Oil cooler lines shorter with support mount in different place. 750 lines and cooler fit.
- Gear lever longer than XJ750p and made out of alloy instead of iron. 750 lever fits.

Only FYI. We shall see once the hybrid system is in completion, if it works.

 

Some pics of the physical difference of the XJ750P rotor and the XJ900RK rotors.
Also a good view of the taper fit and the bolt used to pop it off.

The larger one is the XJ750P.
Side

Top

Bottom

 

Some pics of the XJ900 Diff.
The reason it is apart is before I realised the shock mount points were further forward as compared to the 750 Diff I decided to wet blast it...
Now that in itself would have been fine except where I'd blocked off the shaft component wasn't so blocked off and unfortunately I ended up with a whole bunch of fine grade glass inside the diff.

After a week of rinsing the diff out with kerosene over and over and filtering the kerosene over and over I ended up with one very de-oiled diff with no glass.

Then, I realised I couldn't use it! lol. Good times!

Nice to have a look inside at any rate. Looks like the shim was punched to increase the thickness which seems like a good workaround.

 

I had a dream about doing this Mod, myself. But, my health deteriorated and I can't do the work ... anymore.

If there is any among you wanting to give it a try, ... i have a Complete 900 Engine, on the floor, next to my toolbox that can be yours for $325.00

You'll have to make all the arrangements to have it. I'm under Doctor's orders not to lift anything heavier than a full cup of coffee, ... forever.

The Engine's on my Creeper.
In Massachusetts. 01821

 

Rick, could you tell me a little more about the 900 engine? Condition, how much is included, etc. PM would be fine, as I don't want to hijack this thread any more than I have.


Great thread, BTW. I have it bookmarked.

 

A bit more info on the difference between the XJ750(5G2) and XJ900(31A).

The 5G2 TCI and 31A TCI have the same plugs in different places...
On comparison of the XJ900 harness and the XJ750 harness ... now wait for it...

The 5G2 4Pin plug wires actually get moved to the 6Pin plug for the 31A and the 5G2 6Pin wires get moved to the 31A 4Pin wires... Now you can see why plugging a 31A TCI into a 5G2 would probably not end well and likewise a 5G2 TCI into a 31A.

One of the reasons for the design change/plug switch actually seems to be the inclusion of the 'over revolution' circuit and so the 6pin plug is utilised for the, normally empty on the 5G2 TCI, extra pins.

5G2 TCI with XJ750P harness.


31A TCI with modified XJ750P harness.


In saying this I noticed that the impedance for the XJ700 and XJ900 ignition coils is different compared to the 650+, according to chacal's info, and so I'm wondering about the affect of using the existing 5G2 ignition coils which seem to be fairly standard for 650 up as they are stamped with 4H7, which is the base for most of the XJ motors.

Slowly, slowly...

 

Hi,
Just had to get this thing to run...
After a bumpy start and tracking down a corroded main fuse holder and a broken positive supply to the TCI it started turning over.

I hooked up the coils in reverse (2 and 3 were using 1 and 4s output, etc) so fixing that made a big change, although I couldn't find a good reference to which output went to which cylinders originally, must have too look harder.

Of course after the original pull the rack apart and engineer a part to support the 750P throttle cable everything was way out of sync and the mixture was all over the place so, needless to say... 1 flat battery later, a lot of misfires, a carbtune and a colourtune.

It runs! And now I am really looking forward to riding it... which is cosmetically a long way down the line but now some more enthusiasm has crept back in!

Short 'proof' video XJ750P(900) Cold Start 1.

 

Is it just me or is it damn easy to flood these damn mikunis?

 

Very cool! Congratulations!

Orange is 1/4, Gray is 2/3, but, as long as the Orange pickup wire leads to the TCI circuit that's running the 1/4 ignition coil, it really doesn't matter which circuit is used for which pair.

 

Well it's taken awhile but its eventually been drilled into my skull that low voltage equals all sorts of symptoms when trying to get these things to run.
I know it's been said before and over and over but... sometimes it takes a whole bunch of hands on experiences to make it stick.

At any rate I purchased a 900A starter battery thingemie and... oh boy does it make things easier when tuning and fiddling about.


and here is where the bike is up to now, new paint and seat re-upholstered, sounding fantastic but a still a few cosmetic bits and pieces before it hits the road.

 

I can't tell if it has the Oil Cooler mounted.
Does it?
How did it fit?

Looks like a Police Bike.

When you get it all finished-up and want to add a personal "Custom" touch; MAINLY METALS in Bristol, VT ... could add a CNC-cut design or Lettering to the Rear Case Risers.

http://mainlymetals.com/cnc_cad_waterje ... _steel.jpg

 

I like the "curtain" on the front wheel.
Doesn't that screw up the balance? :lol:

Looking good

 

Rick,
The original 750 oil cooler, pipes and oil filter housing are in place. I would have liked to find a 900 cooler but until then the 750 cooler ought to suffice.
I'll post a couple of close up pics when the sun comes out again.

Mike,
, the bike is undercover but the afternoon sun hits the tyre and since it's been sitting for so long... well 'the curtain' is in place!

 

Oil cooler pics of the 750 cooler and pipes on the 900 engine.

The 900 has shorter hoses and the 900 bracket is lower to lock them into place.

I guess this is because the 900 cooler is larger? I don't have a 900 cooler to compare(keeping my eye on ebay for one) but it would make sense I'm thinking.

 

An Update,

After trying all sorts of semi-successful alterations with the BS36s installed (dropping the needles lower, removing the airbox lid to increase airflow) and getting to the point where no matter how i go, low and high power is flooding and fouling the plugs...

I have cleaned up the original BS35 carbs and put all the jets and needles back in there rightful position and placement...

Guess what! Yamaha really did know what they were doing and now it runs BEAUTIFUL!

Should have known better to question engineering, but those BS36s just looked so shiney on the day.

 

nice work man!! that seat looks like it will be fun to keep clean, lol.

nice bike!

 

You should see the light reflection from the white bike on a clear summer day. it definitely is hard to miss.

The seat gets a bit grubby but the main thing is that it never gets hot. I can leave the bike in full sun without getting a burnt backside when i ride off.

The other thing I've worked out is the scuff marks from swinging your foot over and hitting the seat(the ones you can't see on a black seat) can be removed with methylated spirits. It takes a little bit of agitation and then magically it comes off.

I don't think I'd get another black seat again in this climate and I'll be getting my pushbike seat done in white too!

Call me a white seat convert!

 

Some of the "design variations" between models make no apparent sense; trying to figure them all out will drive you crazy.

Have I got a deal for you:

I have a set of "normal" sized, "loop" 650/750 case guards in decent shape (sombody drilled small holes in each for footpeg mounting) that I will GIVE you and ship to Australia AND even SPLIT THE COST if you promise to lose that giant loopy thing you have now.

Sorry but it's just too... too...

Interested? They're a tad scuffed from the aforementioned footpegs, but the chrome is in otherwise nice shape.

 

I appreciate the offer but... The look has grown on me and after taking a closer look I realise that these are crash bars and not engine guards.

I was hit once when i was turning a corner by a car which smashed straight into my leg, only thing I broke was the bone the car hit, I think these woulda saved that... plus if the bike falls over it just sits, perched, on the guards and the back rack guards which is pretty cool... It fell of its side stand the other day when i parked on a downward slope and nothing was damaged.

It is the original guard for the WA version of the XJ750P also and was donated by another member locally to my project.

So thanks again but i'll keep me loopy guards!

 

Hi
Just came across this thread....
The oil coolers I have are off the XJ750RL & the XJ900 & they are the same, I just did an engine swap myself, putting a 900 mtr into the 750RL frame. :?

 

ol_750 what are the model numbers of your bikes?

If your XJ750RL is a 45T it came to Australia factory built with a 750 engine in a 900 frame so the 900 engine is a straight bolt in.

My 750 45T and 900 1FX oil coolers are the same as are the frames (except for the fairing brackets). I'm not sure if the US models were like this.

 

ol_750 thanks for the info about the cooler sizes.
I can stop looking for a 900 oil cooler now.

 

None of our 750s (or 650s or 550s) came with oil coolers. The 900 was the only early-series XJ that came here with an oil cooler.

 

8) Both my 750's are 45T's & the 900's are 31's & 58's.
Yes it was an easy swap over , done in 2 days. Then I rode to QLD & back 2500ks in 4 days & it didnt miss a beat. 8)

 

We must get more hot rideing weather here 8) I've been stuck in Sydney traffic jams in the middle of summer & you could smell the motor overheating.

 

I don't think Yamaha ever realized that a few of us actually use our bikes as transportation. Or maybe there were so few of us they didn't care.

The MAJORITY of bikes sold in the US, especially in those days, were just "toys." (Still are, actually.) That's why there are so many low-mileage bikes here that suffer from fossilization.

Yamaha knew that and didn't waste money including bits that were largely (because of how they would be used) unnecessary.

 

I think my oil cooler should be about 50 percent bigger and have a thermofan in front for the sort of weather we had in Brisbane last week, gads 41 deg C out my way !

 

I have several oil coolers... The 900 has 2 different ones that are about the same size which are longer and skinnier than the one you have on this bike... I've removed one of those from a 900 but I'm sure they're 650 and 750 ones.

From the look of them they're a straight swap

 

Hi Alive,
After doing a bit of a search I now know what you mean.
Looks like the 900 cooler is 7 row while mine is 5 row and deeper.

Here is a pic of the 900 cooler I found from another thread.
http://s611.photobucket.com/albums/tt195/mighost63/Bikes/Lucille%20-%2083%20XJ900%20Seca/Oil%20Cooler/?action=view¤t=2011-10-29154737.jpg