650 engine mods

I know, I need to get the XJ CD. I do plan on getting it, just haven't gotten a chance yet.

Anyway, if what I've read is correct, the 650 can be turned into a 750 with 750 rods/crank/pistons. Now, I read somewhere else that the 900 is simply a 750 with a big bore kit. So, here's the big question. Can I safely take my 650 up to a 900? Or will I have to find a set of 900 jugs (if they have thicker sleeves or something). I've done a big bore kit on a GSX-R 1100, and I believe I took about .100" or so out to make it a 1297 (I run a machine shop). I just don't have any of the specs on the bore and stroke of the three motors. Can someone enlighten me please?

Also, where can I get pistons for these motors? I've seen several sets of 750 rotating assemblys go for cheap on ebay, but they don't include the pistons, and I've been having trouble sourcing new ones. Guess I could go to Yamaha as a last resort.

 

I have no idea, but the 650-750 is the only one I've heard. I don't think the 750 and 900 are upgradable that way. Pretty sure the bottom part of the engine block is different.

 

... and if they were it would probably be cheaper just to bolt a complete 750 or 900 into the 650s frame. ( See if you assume the bottom ends are the same then why not just use the bottom of the larger displacement engine in the first place)

650 to 750 might be possible... of course it's the subtle differences that will be the problem you'll get into when you do it.

 

All I have been able to find is for the 650 and 900.
650 bore and stroke 63mmx52.4mm
900 68.5mmx60.5mm
I could not find the 750 specs right now.Might want to check out the link section. It has a technical site that lists the bore, stroke, hp and torque values for a lot of the xj series.
Hope this helps.

 

Bore and stroke on a 1981 750 Seca is 65.0 x 56.4 mm
Compression ratio 9.2 : 1

 

Thanks for the help guys, I'll do some more research. The reason I'd rather build it myself is because I want to get some more experience working on motorcycle engines. I have a full machine shop at my disposal, and I have a hard time bringing myself to swap junkyard motors into any of my vehicles.

Sick, I know...

So anyone know a good place to get new internal engine parts? Bearings, rings, pistons, etc...

 

Where would I find the upgrade kit for this improvement? I have a 1981 XJ650H. Sounds like wintertime fun!

 

650 turbo bottom end will take a 900 crank with no modifications, but the rods will have to be bolted up with the bolts reversed to clear the cases. I would think the cases for the non-turbo 650 would have the same clearances. 650 turbo cases are the strongest of all the Secas (lots of extra webbing). 900 barrels will fit with some relieving with a dremel tool for the larger barrels. Anecdotal stories have mentioned 130 rwhp with a 650 turbo and 900 top end. Personally, if I was wanting more power I'd just drop in a complete 900 Seca engine and be done with it. Don't know what a turbo 900 would do. Still dreaming of a turbo Maxim X.

If you need XJ specs in a hurry, go to the German XJ riders group board XJ-IG site mentioned in the links section.

 

Thanks, that's definetly some food for thought!

130 whp! 8O 8O

If I happen to find a 750 or 900 motor for a decent price, I probably will pick it up, but they seem to be somewhat hard to come by. I have however seen the 750 rotating assemblys on ebay, which is why I asked. The 900 was only made for a few years in the US, right?

 

The thing is - if you seriously only wanted the horsepower - it would be cheaper to buy an early 90's sportbike. Even the mid to late 90's are getting to be dirt cheap.

Ok - I'm not suggesting that as the solution, as a higher powered maxim would be fun - however - if the goal is simply power (and not to create a sleeper) then I'd suggest a newer bike

That being said - I did go up to a bigger horsepower bike and I just got bored. ( This is where I can understand the more power in a maxim being of interest)

If I cruised the backroads on a sportbike I'd be bored. They handle so well that the speed limit is a snooze. So I did what any young male would do - ride until it felt fast again - ride until it felt as fast as it did on my maxim. Now I never got a speeding ticket doing this - but I came to realize that this lifestyle wasn't going to work in the long run. I wouldn't say I was a true calamari - but I would say that at the speeds I went to have fun that I didn't have a chance in stopping and that I would certainly be loosing my licence if I was ever seen.

So - my solution - keep the maxim and enjoy the lack of power ( not really a lack as we're still talking better than average car power ) and enjoy the weight of it's handling. Now I ride the maxim at sane speeds, feel like I'm flying and am proud that I'm riding this '24 year old dog' with the big boys... and having more fun than they are humping their gas tanks.

Oh sure - I'd love a TL1000R or a VTR for some fun twisty riding once in awhile - but if I owned one of those bikes again it would be a track only vehicle.

A tangential rant - but sometimes bigger isn't better... Hell - I'm considering going back to the 250 because really - only a real man can flog a 250 at race speeds... Seriously - that bike is a hoot because you really do have to ride it... and that's fun.

Woot.

 

I've ridden a Ninja 250 on several occasions - fun, fun bike!

In fact, we have several in our fleet where I teach. I have to be careful not to do stoppies in front of the students! :twisted:

 

lol - Dean you're an under cover squid

Anyone seriously considering a long distance ride -- I mean AZ is a long haul from here but if we're talking half way???

Maybe we can all ride some 250's...

Cheers,
woot.

 

The 900 was a one year only model here in Canada, probably in the US as well, but they soldiered on in Europe up until 93, when they were replaced by the 900 Diversion. They eventually got the larger fairing of the XJ750RL in Europe, as well as a slightly bigger motor than the 853cc engine we got over here.

I guess they didn't sell too well, as they came out the same year as the 750 Interceptor, which would certainly clean its clock performance wise (although the 900 didn't eat its top end, but that's another story...)

 

I have to agree with woot, I think you can only do so much before it's just not practical anymore. From what i've found out, puttinf a 750 into a 650 is not that difficult but the amount of proformance you will gain is not a whole hell of a lot. I personally would just go with a differnt bike

 

I think what you guys aren't understanding though, is I can't AFFORD to buy a newer bike, as much as I'd like to. I can do all the motor and machine work myself, and plan on doing all the rest of the work to the bike myself as well. Even if I have to rebuild most of the entire bike, I'll still have a basically brand new machine for less than I could even get a heap of a newer one. And as far as the engine mods go, I'm a hot rodder at heart, and figure as long as I'm going to be doing internals, why not upgrade? Won't cost much more.

And, just as an update, I bought an entire 750 rotating assembly and XJ900 cams to go in it when I rebuild. The 750 rotating assembly I bought for less than a new set of oversize 650 pistons would have cost, so I still get to start out with a nice fresh bore, and increase displacement for less than the cost of a stock rebuild.

 

sounds good... keep us up to date with this project...

as for myself? I found a zx7r for < $2000 US that is tempting me to no end... with a bit of paint I could flip it, or keep it as a second bike. Not at all the bike I'm looking for for a primary bike (hence the hesitation to buy it)

 

And what is wrong with squids Woot? Hummm? (you'd never notice me).

 

I like calamari, if that counts for anything? The sportier the bike you ride the harder it is to have 'fun' legally.

The 7r is a fun bike.... but it's not really a touring bike. I think everyone should ride one when they're ready... closed track and just get a feel for it at low track speeds.

 

Got good calamari down here at a place called Neptunes Net, just down the road on the Pacific Coast Highway. It's a little seafood (really?!) on the shore just above Santa Monica. Great fresh stuff, little pricey, but good eats. Perfect place to stop after comming down off of Muholand Drive (half a mile south of there). I understand you like to drag a peg or two through the twisties, yes? Do drop in!