Holy Grail of XS400 Big Bore Pistons

[Greasey Fingers]

the xs250 cam is exactly the same as the 400, except Germany who have a power limit so its not as "lumpy"

.

oops my bad, I meant crank. I did just pul the cam out so I mixed it up lol. Anyway ill have a spare crank too, but im yet to see is condition. Is good to know the cams are the same anyway, means i have a good spare

 

[Greasey Fingers]

anyone in germany after a lumpy cam?

 

[hjennings]

This was started in another thread and we were directed to continue it here as it was getting lost.

The discussion is how to modify a stock XS400 to accept a slightly larger piston and ring set that is commonly available. Not for a performance gain so much (though that could be worked into the equation), but just so we have repair parts (since pistions/rings are about impossible to find for the XS400).

As I explained in the other thread, I’m a car guy and just now getting into these bikes. I have technical data sheets for all kinds of cars that lists rod length, piston diameter, piston height, etc, etc, etc. I do not have this information for bikes and am having trouble just Googling such info. That said, here is my thought.

If I am correct, the bore of the XS400 sleeve is 69mm. I do not know how thick the sleeve is, nor do I know if the jug itself has any room to be bored. So without knowing all that information, I’m thinking there are two options.

First, if the sleeve could be slightly bored, bump up the bore to 70mm (depends on how much it can be bored, if any, and what pistons you could possibly use) and find pistons that fit that bore. There are lots of 70mm pistons. Now you’d have to go through all of the pistons that are 70mm and find one that has the same height from the wrist pin center to the top of the piston. Otherwise compression would be nil (if too short) or it’d smack the head (if too tall). The overall length of the piston isn’t a problem. If the skirt were too long and were to hit the crank (very unlikely) it could be easily ground down to fit.

The other route would be to pop out the stock sleeve, bore out the jug (if that is at all possible) and press in another slightly bigger stock sleeve and again use those pistons/rings.

Or… along that same route, but if another parts combo had a sleeve with the same outside diameter as the XS400 but had a larger inside diameter (thinner sleeve… ) then it’d be same result as if you were able to bore out the stock sleeve.

So find the parts that fit the bore and piston wrist pin to piston top height, press the Frankenstein piston onto the stock XS400 crank, and continue as normal. If the piston had a slightly different size wrist pin, it could be bored to accept the new pin/piston combo. No modifications of the head or crank would be needed.

With a search of inside bores, here are some possible candidates:

A 1984-1985 Kawasaki KXT-250 sleeve/piston combo looks like it'd fit 70.00 Bore

70.00mm Bore, for use on Honda®, ATV, Each
Part Number: LAS-FL106

Cylinder Sleeve, Chromoly, 70.00mm Bore, Arctic Cat, Snowmobile, Each
Part Number: LAS-FL1094

Cylinder Sleeve, Chromoly, 70.00mm Bore, Arctic Cat, Snowmobile, Each
Part Number: LAS-FL1095

Cylinder Sleeve, Chromoly, 69.50mm Bore, Ski-Doo, Snowmobile, Each
Part Number: LAS-FL1149

Cylinder Sleeve, Chromoly, 70.00mm Bore, Arctic Cat, Snowmobile, Each
Part Number: LAS-FL1159

Cylinder Sleeve, Chromoly, 69.72mm Bore, Polaris, Snowmobile, Each
Part Number: LAS-FL1189

Cylinder Sleeve, Chromoly, 70.50mm Bore, Ski-Doo, Snowmobile, Each
Part Number: LAS-FL1222

Cylinder Sleeve, Chromoly, 69.50mm Bore, Ski-Doo, Snowmobile, Each
Part Number: LAS-FL1224

Cylinder Sleeve, Chromoly, 69.75mm Bore, Ski-Doo, Snowmobile, Each
Part Number: LAS-FL1225

Cylinder Sleeve, Chromoly, 70.50mm Bore, Yamaha, Snowmobile, Each
Part Number: LAS-FL1226

Cylinder Sleeve, Chromoly, 71.00mm Bore, Arctic Cat, Snowmobile, Each
Part Number: LAS-FL1234

Cylinder Sleeve, Chromoly, 70.50mm Bore, Polaris, Snowmobile, Each
Part Number: LAS-FL1254

Cylinder Sleeve, Chromoly, 70.50mm Bore, Polaris, Snowmobile, Each
Part Number: LAS-FL1261

Cylinder Sleeve, Chromoly, 71.00mm Bore, Arctic Cat, Snowmobile, Each
Part Number: LAS-FL1272

Cylinder Sleeve, Chromoly, 71.00mm Bore, Yamaha, Motorcycle, Each
Part Number: LAS-FL510

Cylinder Sleeve, Powersports, Chromoly, 70.250mm Bore, Each
Part Number: LAS-FL5239

Cylinder Sleeve, Powersports, Chromoly, 70.000mm Bore, Each
Part Number: LAS-FL812

Cylinder Sleeve, Powersports, Chromoly, 70.000mm Bore, Each
Part Number: LAS-FL845B

Cylinder Sleeve, Powersports, Chromoly, 70.000mm Bore, Each
Part Number: LAS-FL88

Cylinder Sleeve, Powersports, Chromoly, 70.000mm Bore, Each
Part Number: LAS-FL942

Cylinder Sleeve, Powersports, Chromoly, 70.000mm Bore, Each
Part Number: LAS-FL949

Cylinder Sleeve, Powersports, Chromoly, 70.000mm Bore, Each
Part Number: LAS-FL988

 

[krzsiek]

I'll tried to do it with piston from yamaha xt225. Nominal diameter is 70mm, 16mm piston pin and is only about 1mm lower than the original piston.

 

[drewpy]

throwing this our there again'

450cc

off ebay Germany

 

[xschris]

When has anyone seen one of theses kits for sale tho?

 

[drewpy]

When has anyone seen one of theses kits for sale tho?

who said they were kits?

wiseco pistons and new cylinder liners

 

[xschris]

Not sure where to get new liners? As far as I can remember someone asked wiseco to make pistons and they said yes but you would have to order 5 sets at least and they where standard size.

 

[Scorpio1963]

I remember when that was brought up it would have to be group buy if you could get them.At the prices that was put out there a lot of people lost interest real quick

 

[Vincent_Vega]

interesting ... could use pistons GPZ900 unmodified and original rod? Thanks!

 

[BBS360]

interesting ... could use pistons GPZ900 unmodified and original rod? Thanks!

No, not unmodified.

See the original post and a few following for more information and pictures:

I use Yamaha XJR1300 rods and modified Kawasaki GPZ900R pistons (diameter 72.5mm).
The stock sleeve allow max. 73mm pistons.
You can also use FJ1100/FJ1200 rods, but the better way are XJR1300 rods which are lighter and stronger.

In the original photos you'll see that he had to completely reshape the piston crown. Unmodified, they protrude above the head at TDC and appear to be designed for quad valve heads.
You'll destroy your engine if you try to run it with unmodified GPZ900 pistons, if you can even close the case.

 

[FarmBoy72]

Could always go to LA Sleeve and have new liners made based off the old ones, pretty sure they make custom pistons too, all for a price of course.

 

[xschris]

It's always for a price

 

[CDNTX650]

Take a lesson from 1970 to 1973 xs650. The 256 engines had bigger small ends on the rods. Stretch and ovaling was a problem. 74 to 83 447 engines went to a smaller diameter hole. Apparantly far more of a problem under hard use all the time...obviously.

 

[Vincent_Vega]

No, not unmodified.

See the original post and a few following for more information and pictures:

In the original photos you'll see that he had to completely reshape the piston crown. Unmodified, they protrude above the head at TDC and appear to be designed for quad valve heads.
You'll destroy your engine if you try to run it with unmodified GPZ900 pistons, if you can even close the case.

Ok! thanks!

 

[montechoate]

What the hell is a 4V 4 stroke?

 

[BBS360]

I'm not sure what you're referencing but I imagine it's a four-valve four-stroke motorcycle, like all of our bikes.

 

[montechoate]

I'm talking about OP's picture

 

[BBS360]

In that case it's 4 valves per cylinder.

 

[salisride]

So I thought Id comment to bring this thing back up we to find over sized pistons for the sohc xs400. Doesn't have to be big bore just so we can rebuild it