Talked to an acquaintance who tends to be a better mechanic in story telling than in real life. He told me he rebuilt a xs400 using pistons from a 200cc Yamaha 1985 moto 4 atv. Anyone have any history or theories on this? I kind of have my doubts.
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replacement piston
- Thread starter ksrebel
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kshansen
XS400 Addict
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Any chance this guy has a part number for the piston he used? Or an exact model number for the ATV?
Not hard to believe that a 200 cc single could use the same piston as a 400 cc twin.
I know some XS650's are running around with rings out of I believe a Nisson or is it a
Toyota?
Main thing would be finding a piston with the correct wrist pin diameter and height from center of wrist pin bore to top of piston. Also the crown of the pistons would have to be pretty close or compression ratio could be way off. Either high or low.
Not hard to believe that a 200 cc single could use the same piston as a 400 cc twin.
I know some XS650's are running around with rings out of I believe a Nisson or is it a
Toyota?
Main thing would be finding a piston with the correct wrist pin diameter and height from center of wrist pin bore to top of piston. Also the crown of the pistons would have to be pretty close or compression ratio could be way off. Either high or low.
They share the same wrist pin as the 77-78 XS360, so I wonder if they would in fact work. Would have to do a bit more digging to find out why the 360 used a different wrist pin on those 2 years. Then it would just be a matter of finding out if the piston height is usable without machining, and making sure all the clearances with the valves are correct. If they would work, that's a pretty cheap option for stock pistons-
http://www.ghdiscountatvsupply.com/1985-1989-yamaha-yfm200-moto-4-piston-kit/
http://www.ghdiscountatvsupply.com/1985-1989-yamaha-yfm200-moto-4-piston-kit/
ah, that explains it. Did a little more digging. Looks like these will work for a 360. They are too small of a bore for the 400s. The Moto4 200 uses smaller bore and longer stroke than our crank/motor. The moto4 uses 67x54 standard, we use 69x52
Damn chris beat me on the submit button 
Looks like the 225 piston 'could' work for the 400. But the squish band looks all wrong.
Why not use the a stock replacement piston??
http://www.yamahapartshouse.com/oemparts/a/yam/50041ea7f8700209bc7868fe/crankshaft-piston
This is just one place; I imagine there are more . . . you can probably get them from Yamaha.
Why make things difficult.... just my thought on it.... Nad
http://www.yamahapartshouse.com/oemparts/a/yam/50041ea7f8700209bc7868fe/crankshaft-piston
This is just one place; I imagine there are more . . . you can probably get them from Yamaha.
Why make things difficult.... just my thought on it.... Nad
Following that link, only the .25 oversize piston is available and only the standard piston rings are available.
A quick look on ebay brings up a couple NOS oversize pistons and a few used pistons.
Pistons are quite rare.
A quick look on ebay brings up a couple NOS oversize pistons and a few used pistons.
Pistons are quite rare.
My bad.... I have never really searched for pistons much... where I came from if a motor was bad enough to need pistons it was scrapped for aluminum (except two-strokes). Too much work to pull a motor apart when you could buy another bike for the price of parts ..... times have changed though....
Wiseco also makes 225 pistons. Different crown, much more expensive.
Did anyone determine whether the wrist pin-crown height matches?
I don't think you'll find that info anywhere online. Someone would need to grab an Ebay piston and measure.
I think they would work just by looking, but even with those wiseco pistons, you won't get anywhere near stock compression.
I think they would work just by looking, but even with those wiseco pistons, you won't get anywhere near stock compression.
On a slightly related subject then, any thoughts on "gapless" piston rings?
Total Seal makes top rings that look like they'd fit. Their gapless second rings are 1.2mm, .3 too small.
Total Seal makes top rings that look like they'd fit. Their gapless second rings are 1.2mm, .3 too small.
While looking up something else I found Wossner's aftermarket pistons for the yfm225. They list the compression height at 22.2mm which might be the same as stock yfm225 pistons.
I'll post the direct link when I'm on a pc. For some reason my phone can't handle copying and pasting urls.
The Wossner 73mm would increase capacity nicely to around 439cc but with a 22.2mm compression height (to center of the pin?) I think they're a fair bit shorter there than our pistons. It'd drop compression a lot.
Wossner does have some 73mm pistons with higher crowns. Might be workable with a significantly thicker base gasket but could run into issues with the length of the timing chain.
I'll post the direct link when I'm on a pc. For some reason my phone can't handle copying and pasting urls.
The Wossner 73mm would increase capacity nicely to around 439cc but with a 22.2mm compression height (to center of the pin?) I think they're a fair bit shorter there than our pistons. It'd drop compression a lot.
Wossner does have some 73mm pistons with higher crowns. Might be workable with a significantly thicker base gasket but could run into issues with the length of the timing chain.
The big bore thread went over some aspects of the YFM250 pistons already. I think it fizzled out as an option before anyone even got to the compression height issue.
This is the Wossner 73mm piston:
http://www.wossnerpistons.com/produ.../name/wossner-piston-yamaha-yfm250-73-mm-bore
They also have a 71, 72, and 74mm version.
OEM compression heights would likely be the same and at 22.2-23.5mm they would not work out very well in our motors without significant other modifications.
Maybe worth the work in a big bore or forced induction project but hardly worthwhile as close-to-stock replacement for our pistons.
This is the Wossner 73mm piston:
http://www.wossnerpistons.com/produ.../name/wossner-piston-yamaha-yfm250-73-mm-bore
They also have a 71, 72, and 74mm version.
OEM compression heights would likely be the same and at 22.2-23.5mm they would not work out very well in our motors without significant other modifications.
Maybe worth the work in a big bore or forced induction project but hardly worthwhile as close-to-stock replacement for our pistons.
Could someone please tell me the stock pin to deck height on an XS400 or 360 ? I'm assuming they are the same ? I don't have a piston out so I can't get the measurements without pulling the engine down .
Thanks in advance for any help .
Thanks in advance for any help .
