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On most oversize pistons the marking on the piston is just the over size. as .25 mm over the marking is 25, the .50 over is marked 50.
If it has a three digit marking then it's a stock size. I have two sets of stock pistons. One set marked 956 the other set 963. these pistons when new measured 74.956 and 74.963.
If it has a three digit marking then it's a stock size. I have two sets of stock pistons. One set marked 956 the other set 963. these pistons when new measured 74.956 and 74.963.
Thanks Guys
I also see after removing the barrels that on the right side of the crank is stamped with the number 2, what does that mean???
the piston tops have 050 stamped on them but i dont think there xs pistons this is the second engine I picked at the same time & the first had TX750 pistons in it these pistons look the same but are not 750 pistons but the same style pistons Im shore
I also see after removing the barrels that on the right side of the crank is stamped with the number 2, what does that mean???
the piston tops have 050 stamped on them but i dont think there xs pistons this is the second engine I picked at the same time & the first had TX750 pistons in it these pistons look the same but are not 750 pistons but the same style pistons Im shore
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That looks like 0.50 to me, so those are second over pistons.If you measure them and the bores they came out of you can determine the clearance, if its ok then a second over set of rings and it should be good to go. Or if they are to worn then reboreing a to small set of cylinders to match those pistons should work.
The #2 on the crank, I don't know.
The #2 on the crank, I don't know.
If one of the engines is a 750, that would be my first choise on getting together. Especially if you use forged pistons. I think Mike's sells replacements for his 750 kit, they might work with your cylinders.
I read somewhere that after going to a 750, people think that the 650 should have been a 750 from the start. After doing Mike's kit I have to agree. It runs much stronger, and much smoother. Even with a stock cam. I think my 82 may get a rephased 750. The rephase is smoother yet.
I read somewhere that after going to a 750, people think that the 650 should have been a 750 from the start. After doing Mike's kit I have to agree. It runs much stronger, and much smoother. Even with a stock cam. I think my 82 may get a rephased 750. The rephase is smoother yet.
Mike's sells two 750 pistons. One is the stock size for his kit, 80 mm. The other is a first over at 81 mm. I think using a set of these will make it run smooth and strong.
I went and checked, I remembered wrong. Mike's sells just the 81 mm piston. This with the stock stroke makes 762 cc's. His 80 mm piston is 743 cc's.
You might find good pistons other places too.
I went and checked, I remembered wrong. Mike's sells just the 81 mm piston. This with the stock stroke makes 762 cc's. His 80 mm piston is 743 cc's.
You might find good pistons other places too.
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A few possibilities: Some performance/race builders preferred the 256 due to longer its rods (but usually avoided stock rods, as they tended to be weak at the small end). The PO may have blown the crank in his 447 and swapped in the 256 crank, cam, and pistons because they were available. Finally, The PO may have wanted the livelier 256 cam and had the misguided idea that installing 256 crank and pistons was a better way to go than pressing a 447 sprocket onto the 256 camshaft.
Thanks
This & another engine Im shore were in some kind of race bike
It has a 36 tooth cam in it as well.
Are the pistons in this engine 256 or from something else you think
The other engine had tx 750 pistons which look the same as these but these are standard size pistons
Oh & no 447 stamped on the cam
www.xs650.com/forum/showthread.php?t=462
This & another engine Im shore were in some kind of race bike
It has a 36 tooth cam in it as well.
Are the pistons in this engine 256 or from something else you think
The other engine had tx 750 pistons which look the same as these but these are standard size pistons
Oh & no 447 stamped on the cam
www.xs650.com/forum/showthread.php?t=462
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Sounds like 256 rods were pressed onto a 447 crank--I can understand doing that using performance rods, but that's a very odd thing to do using OEM bits.
Stroke is the same, rod length is compensated for by location of the wristpin holes in the pistons. Barrels from XS2 through end of production are the same; XS1 and XS1B barrels had different head gasket surfaces. Wristpin diameter is 22 mm. in 256 engines, 20 mm. in 447's. Sure, 447 rods can be installed, but why do that if what's there already is in good shape?
