xs650-4-me
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Curious, anyone, ex-racers, ever do this ?
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Anyone Ever Stroke a XS650 ?
- Thread starter xs650-4-me
- Start date
Didn't do it myself yet, but own several stroked cranks.
In the 80's stroking was common practice in sidecar motocross.
84mm stroke was a popular value, because it could be done with standard diameter flywheels without opening up the crankcases.
In conjunction with 87mm bore, using XT500 pistons, that would result in 998cc IIRC.
There's a thread about a similar motor here:
https://www.xs650.com/threads/1010cc-cafe-racer.32481/
In the 80's stroking was common practice in sidecar motocross.
84mm stroke was a popular value, because it could be done with standard diameter flywheels without opening up the crankcases.
In conjunction with 87mm bore, using XT500 pistons, that would result in 998cc IIRC.
There's a thread about a similar motor here:
https://www.xs650.com/threads/1010cc-cafe-racer.32481/
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Thanks for the link. I am going with the 80mm basik 750 big bore big fin. I would like to get more stroke. What is stock stroke? 70mm bore 74mm stroke I believe on a 447 American? Any input on rod and piston combination to increase stroke with plate and plus one or two links of cam chain?
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Old thread brought back to life . . .
There are many variables. First you will need a modified crank with longer stroke. If you have the knowledge and tools to do that yourself, maybe you wouldn't ask these questions. So you'll have to buy one new, or try to score a second hand one and rebuild it. Either way, finding a supplier won't be very easy. Cranks that were used in motocross often have a turned down left taper because the charging system was swapped out for a total loss ignition like a Kröber. Then you'll have to repair the taper as well.
The big end pin diameter on your crank must match your conrod (either 256, 447 or 533 type). However, the larger 533 big end only allows very limited stroke increase, so you will most certainly end up with a 256/447 type pin.
There are 3 different length conrods for the XS, of which the 256 rod is almost unobtanium now and the 533.. see above. Apart from the remaining 447 rod, there are some additional 'long rod' options from other engines as well, but probably your pistons of choice will call for shorter ones if you don't want to end up with a very tall engine. Of course, if you have deep pockets, you can have your rods custom made by Carrillo or such.
Then you must determine deck height for available pistons in your targeted bore size, or decide to have custom pistons made.
Your stroke/con rod length/piston deck height will determine the thickness of an eventual foot plate. If its thickness does not end up being an integer multiple of the cam chain pitch, you'll need to rephase the camshaft by moving the sprocket.
At this point, you have a good mechanical fit, but an increased swept volume. You will have to adapt combustion chamber volume, either by modiying the cylinder head or piston dome volume, to achieve an acceptable compression ratio.
With all that said, the 'standard' recipe is an 84mm stroked crank, 256 rods, XT500 pistons, no additional foot plate. Which gives you the aforementioned 998cc and a decent compression ratio. You'll end up with an engine like in the 1010cc racer thread.
If you want to modify stroke based on the 80mm BBK, do the above homework and maybe you'll find something that works.
Make sure to let us know the outcome.
The big end pin diameter on your crank must match your conrod (either 256, 447 or 533 type). However, the larger 533 big end only allows very limited stroke increase, so you will most certainly end up with a 256/447 type pin.
There are 3 different length conrods for the XS, of which the 256 rod is almost unobtanium now and the 533.. see above. Apart from the remaining 447 rod, there are some additional 'long rod' options from other engines as well, but probably your pistons of choice will call for shorter ones if you don't want to end up with a very tall engine. Of course, if you have deep pockets, you can have your rods custom made by Carrillo or such.
Then you must determine deck height for available pistons in your targeted bore size, or decide to have custom pistons made.
Your stroke/con rod length/piston deck height will determine the thickness of an eventual foot plate. If its thickness does not end up being an integer multiple of the cam chain pitch, you'll need to rephase the camshaft by moving the sprocket.
At this point, you have a good mechanical fit, but an increased swept volume. You will have to adapt combustion chamber volume, either by modiying the cylinder head or piston dome volume, to achieve an acceptable compression ratio.
With all that said, the 'standard' recipe is an 84mm stroked crank, 256 rods, XT500 pistons, no additional foot plate. Which gives you the aforementioned 998cc and a decent compression ratio. You'll end up with an engine like in the 1010cc racer thread.
If you want to modify stroke based on the 80mm BBK, do the above homework and maybe you'll find something that works.
Make sure to let us know the outcome.
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No, but I used to give it a little pat on the seat occasionally...
You ever tried talking dirty to it during warmup?
Oh, I've talked dirty to it all right. Usually while pushing it...
The guy in South Africa @JohnGoodenough had a Halco? 1010cc stroker he ran and talked about a bunch.
Here: https://www.xs650.com/threads/1010cc-cafe-racer.32481/
Here: https://www.xs650.com/threads/1010cc-cafe-racer.32481/
Ooh, naughty!
Yup.. see post #3 above.
So with a 256 rod and xt500 pistons, that would give me 998cc with the standard 70mm bore? I guess the xt500 is a piston for 87mm bore. Got it thanks for this information.
Edit: I see in an earlier post 87mm bore. So the xt500 is 84mm piston. Thanks for the information.
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I would like to try the 80mm bore of the big fin 750 kit with the 84mm stroke of the TX rods and pistons. So I'd have to come up w a 447 crank fit xt 500 rods to it? and piston possibly custom piston. Or a 253 crank and rods and 87mm 500 pistons. I'd really like the bore to stay at 80mm I want the stroke to be more than piston over square. I believe its called.
From your response I'm not sure if you have a full grasp of stroke.
The center distance between the crankshaft main journal and the big end pin determines the stroke.
In a standard crank with 74mm stroke, this distance is 74/2=37mm.
In a crank with 84mm stroke this is 84/2=42mm.
So the big end pins need to be moved outward by 5mm, which requires serious modification of the crankshaft flywheels.
You won't get there by just mixing and matching standard crankshaft parts and rods.
The center distance between the crankshaft main journal and the big end pin determines the stroke.
In a standard crank with 74mm stroke, this distance is 74/2=37mm.
In a crank with 84mm stroke this is 84/2=42mm.
So the big end pins need to be moved outward by 5mm, which requires serious modification of the crankshaft flywheels.
You won't get there by just mixing and matching standard crankshaft parts and rods.
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Ok I have a better understanding now that you explained it. Thanks.
was thinking a piston with the small end of the rod closer to the dome? I see now I missed the "84mm stroked crank".no foot plate.
If the added foot plate direction was done I'd have to add 2 links to cam chain and again not prepared for that. Cam and ignition timing etc. I have a better understanding. Not to a level where I'd mess w it tho.
Thanks for the replies and the explanation. Ya it's not worth me messing with all that. The reason I thought about it is because after some research, I found the added cc in the stroke would give the power at a lower "streetable" range. I wasn't looking for anything like an 880 or 1010.
[/QUOTE]
Ok I have a better understanding now that you explained it. Thanks.
was thinking a piston with the small end of the rod closer to the dome? I see now I missed the "84mm stroked crank".no foot plate.
If the added foot plate direction was done I'd have to add 2 links to cam chain and again not prepared for that. Cam and ignition timing etc. I have a better understanding. Not to a level where I'd mess w it tho.
Thanks for the replies and the explanation. Ya it's not worth me messing with all that. The reason I thought about it is because after some research, I found the added cc in the stroke would give the power at a lower "streetable" range. I wasn't looking for anything like an 880 or 1010.
