XJ700X ? sleeved cylinders

Everything else being equal, a 750 imported into the U.S. market would cost 45 percent more than a 700. So, what did the Japanese producers do? Sleeve 750's to make them 700's. That explains why you and your friends up north had 750's and we poor souls south of the border only had 700's.

I am wondering if the above statement is correct then by owning a 86 XJ700X I should be able to remove the sleeves and replace with the either new or lightly used.

Any comments greatly appreciated

 

I'm not sure that it was quite that simple.......

 

Xj700x 68 mm bore 48 mm stroke
Xj750x 68 mm bore 51.6 mm stroke

 

They figured we could handle the extra power

 

To deal with the shorter stroke Yamaha made a taller piston for the 700, unfortunately taller also meant heavier so they also lowered red-line 1000 rpms.
700X 10,000 red-line
750X 11,000

back to the original post, even if a bigger piston was available to you, keep in mind anytime larger pistons are installed, compression ratio also goes up. Unless you carve out the head to accept all that additional squished charge or install a thicker base gasket you would go beyond the OEM 11:1 ratio. A proper aftermarket big bore kit with nicely forged pistons will take this into account and state what your CR will be.

 

Well, this is going to requires some more research
My original thought was that I could re-sleeve the jug I have as a spare being as the bore was out of round in one cylinder.
That's was all
I do appreciate the other information though

 

the jug can be resleeved in a machine shop

 

Luckily I still have access to the local community college and all their tools
Now I just to need to find a sleeve, guess I will have to buy another used jug and remove the sleeve.
Ah the choices

 

find a sleeve just ask chacal

HCP12460 Aftermarket standard-bore CYLINDER LINER for all XJ700-X water-cooled engines, each:
$ 119.95

HCP12460SET4 Aftermarket standard-bore CYLINDER LINERS, set of 4:
$ 399.95

 

I am glad that these are still available, now I just hope that my rebuild last me as long as possible.

 

the height of the piston has nothing to do with the stroke

 

Note that sleeves for the 750X are not listed

 

In this case it does. When Yamaha modified the 750X into a 700 the pistons didn't reach the top because the stroke was too short. If it wasn't a parts bin special you'd make a shorter cylinder block to match the stroke. Yamaha just made a taller piston instead.

 

Also realize when installing a shorter throw crank your compression ratio will also decrease. The 700 piston top surface will need to go even higher (or have a hemi-shape bulge, not much real estate available with 5-valves) since the 700 will need a smaller combustion chamber than the 750.

 

the stroke of a engine is the distance from the center of the main journal to the center of the crankpin journal times two
compression ratio is the volume of the bore plus the volume of the head at BDC vs TDC
piston height and shape or head shape has nothing to do with it

 

Polock, I said they used a taller piston to deal with the shorter stroke, I didn't say they used a taller piston to change the stroke. We all agree only a change of crankshaft can accomplish that.

Let me expand further on the Maxim-X. When Yamaha built the 5-valve FZ they had a hot-rod XJ in mind which is why the FZ by more than coincidence has the same bore centres as the XJ's. The XJ750X was a concept intended primarily for the US market. I think Yamaha had all the tooling ready to go when they got blind-sided by Ronald Reagan's import tariff for 1985.
This measure was intended to save Harley-Davidson by taxing any bike imported larger than a 700. At this time Harley re-tooled and brought in the Evolution engine which brought them enormous market success anyway, but that's topic for another discussion.
So the Yamaha designers quickly looked over their new 5-valve XJ and decided a shorter throw crankshaft would be the easiest approach to downsizing their new 750 to 700.
They did this as I stated in my previous posts, new crankshaft with a 48mm stroke in place of the 51.6mm stroke originally intended.
The logical next step would be to tool up a shorter cylinder block. The problem with that I'm guessing is that would position the head 3.6mm lower. The head exhaust pipes would now be too long, the rubber parts connecting the carbs to the head and airbox would be misaligned. Being the shade tree mechanic that I am I think I could make all that fit but Yamaha doesn't do things like that. And this late in the game the tooling was already too far along. What to do? Aha, draw up new pistons with taller crowns, this way the external dimensions of the motor are the same as all their design prints.
Design this piston to take up this gap created by the shorter stroke and add in a little more to account for the lowered compression the shorter stroke creates. Nothing external to the motor need change.
To play it safe with the heavier pistons they installed a TCI with a shorter red-line.
So, new crank, new pistons and a TCI and they're back in production. Take that Ronny Ray-Gun!
I remember reading a post a while back which stated the connecting rods are different also. I'm not sure why this would be but it would be another way get the piston to the top of the cylinder. They might even be stronger to deal with heavier pistons but the shorter stroke puts less force on them to. It would be interesting to compare them.
Now what to do with those 750's they intended in the 1st place? Oh ya, Canada is just like the US market but no silly tariff, we'll finish the initial batch and send them there. The Canadian market is much too small to get our own model here but again, I think the tooling and parts were already being spit out so lucky for us we Canucks we got the real deal, the real Maxim-X!

 

ok, deal with. i was thinking compensate or congregate or constipate or conjugate or something like that....never mind

 

the strangest part in this whole caper is that once the US lifted the tariff and 700's faded into their history, we here in Canada continued to be offered the XJ700N. Just shows that good things sometimes come from bureaucratic red tape. Too funny!

 

Back to dowski's original post, he made the logical assumption that Yamaha simply sleeved the bore down. The main reason that was not considered is that the Maxim-X was to showcase Yamaha's new 5 valve combustion chamber. Yamaha had invested a lot of R&D into it, deciding on a 68mm bore as best to locate all those valves into a 750 four. At that time this was the only 5 valve combustion chamber in existence. The FZR1000 would not appear for another 2 years. There would be no budget to engineer a new size combustion chamber for the Maxim-X. The Maxim-X was a true parts bin special.

 

With all that information I as a XJ700X owner am very glad that I own one!
Being as this is my first bike I feel as though I scored a performance bike in sheep's clothing and I am grateful.
This will be my 5th season riding, 3rd set of tires and 20,000 miles give or take a few hundred miles that I have put on her.
The lessons that I have learned from choosing to rebuild the engine myself are priceless.
I truly would like to thank all the fellow members for their contribution to this forum.

 

The argument about the 700/750 is a longer rod and smaller crank throw is how they got it down to 700cc. Shortening the cylinders would require a shorter cam chain or bigger sprockets.

 

I thought about that to, the shorter barrel with same cam chain would put premature wear on guides, chain and tensioner

 

And what's interesting on this side of the decade, is that (as I understand it) there were more X's built than airheads. Yet now, the X is the more desirable one. Funny the one they built many more of are more desirable than the one that had less production. Why?!?! People didn't quite know how to respect the X, and burned 'em/wrecked 'em/blew 'em up/etc...... Now there's many less than the airheads! So either way, if you have any 85-86 xj700/750/airhead/X, you gotta a good piece of history.

Maxim X - more made, less now still exist
Airhead- less made, but more still exist

Dfox

 

I agreed with Hogfiddles statement about demise of X bikes.Have seen a few X models with burnt or blown valve/pistons. I believe this was due to higher cost of maintenance that was skipped and also due to them being quite a bit faster leading to more wrecked ones. The recession of the early 80's cut production of midsize Yamaha bikes from 83-85. We had new 1983 bikes in the store until fall 85-spring 86. Same with new hondas. in 1989 we received a shipment of new 1986 vfr750's and ch250 elite scooters. About a dozen of each.

 

I have to agree with Hogfiddles as well and I can account for a few. So here's my list just for reference:

#1 85 700x Revived and sold locally (I think it's still on the road)
#2 85 700x Parts lot from 4K mile wrecked bike
#3 85 700x Wrecked parts bike with fairly low but unknown mileage. (Have the engine as a spare)
#4 85 700n (Air-head) Neglected non-running bike that donated a lot of parts to the cause
#5 86 700x No title bike with 16K (Another member bought the engine as a spare)
#6 85 750x Current ride that I imported and built around the original frame and engine

You used to be able to see the X models pop up on Craigslist all the time. Now it's more common to see the Air-heads.

A fun fact: The 85 and 86 X models are the only Yamaha's powered by the 5-valve Genesis engine combined with shaft drive.

Tony

 

Ok, so I may as well toss mine in,

#1 '86 700x - on the road
#2 '85 700x - on the road Needs carbs cleaned though
#3 '85 700x - being built from scratch
#4 '85 700x - parts bike, missing a lot, no title
#5 '85 700n - daily ride, is shown in gallery
#6 '85 700n - rough bike, needs work, may try to get title through Vermont sometime

 

Hmmmmm......maybe they're harder to find because Tony and have them all........

 

But, I only have one....

 

You two have at least two more bikes that can be built out of spare bits.

 

But I only ride one (one airhead......oh, and one X). ok, I only ride one at a time.

 

That's probably true......

 

You guys are a hoot-
I live in Southern Oregon and in the five years I have been riding I have only seen one other and that was when I took a trip down Hwy 101 along the coast stop to get fuel and one happened to pull up. Started a conversation with the owner and he stated that he got his X from his boss. He paid the price for scrap metal cause that was where the bike was going. Only had 2,400 miles on it. appeared as though the bike had been garaged it whole life. Sure hope the owner still has it in one piece.
On that note that is when I seen my first sissy bar/back rest for the X.

 

That's a rare-option part, too--

 

Yes it took me awhile to find one and then it was 150.00. which I gladly paid.
My wife has been much more confident when riding with me. She said she always felt as though she may fall off.

 

It is always a good idea to keep the wife happy on the back. When I had my standard sport bike ZRX1200R, I had a Corbin seat with the backrest option. That really made the wife happy. For some reason the front tire on that bike just loved to hover a little off the ground from time to time.

 

Yea they are rare in the rest of the world, because you have them ALL!