Is there a "big bore" kit for the XJ650

Well, the title pretty much says it all. Is there such a thing as a big bore kit for an XJ650. Or, is it possible to swap out pistons and everything necessary from a XJ750 engine onto a XJ650 engine and make it a 750. And, one last question, barring the other two options, is it possible to swap out a complete 750 engine into a 650 frame without any major hassle?

 

900 will swap straight into a turbo, I don't see why the same wouldn't work for the Maxim. 750 should bolt right up as well.

 

Good question. I know my kz 750 had different jugs, but the bottom end was the same. (I think I have that right...) I assue the 700's tarrif bikes were sleeved 750's so there should be some micing and matching available.

XS650 has big bore kit, XJ650 does not here. It looks as though you have to bore out the original sleeve and then resleeve it, so I am not sure if there is room or not. Scroll way down almost to bottom for yamaha for this dealer.

http://cyclewareables

 

Here is the same question asked. I found it with google but not the xj search.

XJ Bikes Linky

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There are larger pistons availabe, (Wiseco, Mahle, etc), but it'll cost you close to $1K to buy and properly install a set.

Yes, a 750 Seca engine plugs right in. The 900 will fit also, but you'll have some airbox issues, and the 900 exhaust isn't a direct bolt on into the smaller bike's chassis. I think you'd need to pull the engine in order to get the valve cover off to peek at the valves.

My Seca is a 650 with a 750 engine, using my 650's stock airbox and exhaust. It's a nice improvement. After warming up, it pulls from 25 mph in 5th gear, and will actually pull well at freeway speeds.

While this transplant is an easy one, there are a few minor things to be aware of...

The 750 Seca is a die-cast top end, with a slightly different bolt count from the head gasket upwards. It's 2mm larger in bore size, and has a 4 mm longer stroke. The cams are different, but the valve sizes are the same. The carbs are the same, aside from jets and needles. The cam chain tensioner is auto on the 750. My 750 engine weighs about 5 pounds less than the 650's did. Your results may vary.

A 750 and 650 Seca can not play musical top end parts...it's all or nothing. Putting a complete 750 top end on a 650 lower end will only give you a 696 cc engine...not worth the cost of gaskets, and you get to jet the carbs all over again. :cry:

Externally it's just enough difference to notice a bit less finger room when switching the petcock to reserve.

The 750 tach is electric, so you lose a drool area as well as your tach. An electric tach from an XS 1100 is supposed to work. I haven't bothered to yet, as the engine's in the powerband if it's anywhere over ~1500 rpm. I never have to buzz the rpm up...just whack it in 5th gear.

The oil level senders are the same but different- the 750's will have your 650's oil light on all the time. Swap senders before swapping powerplants.

Be sure to install the 750's ignitor unit. It's a different part # from the 650's, and probably has a different ignition curve.

Everything else is plug and play, zero surprises.

The 750 engine vibrates a bit more, and makes the 85 mph speedometer into a joke. I'm going to install a 900's secondary gearset to drop the cruise revs.

This is last year before the engine swap-

 

Great writeup, thanks for taking the time to do this.

 

Dang bosozoku, that's the exact kind of information that I needed. So, in essence, my best bet would probably find a decent donor 750 motor, clean it up, and then swap it out (switching the oil sender and probably getting a different speedo) correct?

 

Yes-get a whole bike if you can, as enough parts are the same to be worth it. It's also a lot easier to move a roller than it is to drag a 175# engine around.

While the engine's out, check the valve clearances, and pull the bottom pan and clean out any debris. Swap the oil senders and you're done with engine tinkering. You'll need to re-jet the 650 carbs, or rebuild and install the carbs that came with the rest of the bike if you bought a roller.

The speedo "upgrade" presumes you're clipping right along, dancing in handcuff territory.

I've found that the St. Joan Claybrook 85 mph speedo is just fine, although mine seems to read about 5% low. If it's pegged my attention should be on the road ahead, not the instruments.

This summer I rode about 1500 miles in Northern California without either a tach or a speedo (the drive died), and still had fun.

 

How would an engine swap affect the speedo?

 

... So that you can tell how fast you are going when you are taking advantage of the more powerful engine, not that the stock speedo is up to the power of the 650 in the first place ...

That's why he said "speedo 'upgrade' presumes you're clipping right along, dancing in handcuff territory ..." You only need to upgrade the speedometer if you are going to go fast enough that they won't just ticket you, the cops are going to take you away and confiscate your bike ... Unless, of course, you are on certain parts of the autobahn ...


Mike

 

That was a year and 1/2 ago- - but what is this 900 final drive gear reduction swap? and how much RPM does that save, in a 750?
and how much more using a Maxim motor in a Seca, with this gear reduction? This would be the "missing" 6 th gear or overdrive we've all been craving!
(BTW Maxim motors are geared one tooth taller to make up for the smaller tire)

 

There is a Big Bore Kit for the XJ-650.
Yamaha called it the:

XJ-750

The Big Bore Kit for the XJ-750 is the revered:

XJ900RK

 

You told your wife you're going to sell it, but you know you're not going to ever sell it. So all you have to do is hide it. I can help you out there.

But seriously, what is the 900 final drive difference, in gear ratio?
How much taller is it? Than a 750 ? In 1985 I've gone an indicated 135 MPH and had throttle left !
I got skeered ! but it felt good.

 

You don't want to take a 83 900 much past 120.

The front fairing is not anchored to the frame,
It becomes aerodynamically unstable when wind forces on it exceed 120mph.

It goes "Hunting" for a slipstream.
Left and right.
Very, very un-nerving!

 

I know there is one for the XS, but I've not seen one for an XJ.
http://www.650motorcycles.com/PartsPricing.html