Need Help With Piston ID

gene xs

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In my new to me '78 XS650. Inside the piston it says Yamaha and 80. I need to know what piston it is so that I can get new rings.

full


Thanks!
 
That piston looks to be cast.
First, measure the diameter of the wristpin.
Then, measure the thicknesses of the rings, top, middle, bottom.

If wristpin is 22mm, and rings are 1.5mm, 1.5mm, 2.8mm, then that would be the old '70's 256 factory racing piston, hard to find rings for those.

If wristpin is 20mm, and rings are 1.2mm, 1.5mm, 2.8mm, then that would be later 447 aftermarket piston, easier to find rings.
 
Doubt this'll help, but here's a pic of a stock 959 piston pulled from my '77 447 with 20mm pin.(EDIT piston is from 533 crank/rod assembly in 447 engine with 447 cam)
Posting because it looks like your pin connects further down from the piston crown than mine, it's certainly a fair bit further down from the rings. Not sure what that means though.
MykL0k9.jpg

see if these guys can help:
I've bought from this guy before and I know they're not 20mm pins etc but might be worth shooting a message see what he has.
http://www.ebay.com/itm/NOS-Yamaha-...650-22mm-Pin-Hole-Pair-Big-Bore-/360671088905

or this guy in Japan might have something or access to it.
maybe tx750 will fit?
http://www.ebay.com/itm/YAMAHA-TX75...ded-/131366729529?vxp=mtr&hash=item1e96113739
 
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I'd like to keep this thread alive for awhile, as I'm also pursuing early style 80mm ringsets.

TLCbobber has a point about the deck height. Here's a pic of 447 piston dimensions. You'll want to confirm dimension "E". Also, confirm the diameter of your pistons. Are they 80mm?
 

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Here's the 80mm early 256 pistons (22mm wristpins) from that eBay dealer in Lockhart.
These are what I ran back in the '70s, and use the thicker top ring.
 

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The dome shape of your piston looks familiar, triggers old memories that are still buried in cobwebs. Can't place it right now. I've found some potential alternatives for sourcing those thick-top rings, and ordered a set a few months ago, but my notes are misplaced, gotta dig them out. So, more on that later...
 
Finally found the listing for the Toyota 1587cc rings I ordered back then. Haven't unboxed them yet to see if they're useable though. Alfa-Romeo 1750 rings are another option to investigate.
 

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Hope you finally went to bed toomany!

watching I think the OP may need to double check rod lengths crank stroke etc. Once you find ONE item is custom............. Is it a Verified running engine? There are more than a couple guys that would assemble a bunch of random parts into a "it was running good yesterday" motor. and peddle it.
 
It runs. Before I took apart the top end I cleaned the carbs and started it up. It seems to run pretty well. I ran it long enough to verify that the left cylinder was burning some oil. I tore down the engine to replace the valve seals, but while I was in there took a look at the cylinders. They have very light scoring, so I plan on doing a hone and rering.
 
Gene, if you can, measure the widths of your old rings, and post here.
See if they set deeply into the piston grooves. If they set too deeply, wider rings may be needed.

I'll dig out my Toyota rings and report their widths...
 
Here's one of the vintage XS1 (256) 80.25mm pistons from that eBayer in Lockhart:

Piston-XS1-750.jpg


And, here's the Toyota 1587cc 4AC 81.00mm rings:

Rings-Toyota-4AC.jpg


I haven't feeler-gauged the ring/land clearances yet. The only concern I have right now is the width of that 2nd ring, at 3.5mm, which is the same as the piston's groove depth. Since the ringlands of that piston are recessed a few thou from the bore, it may be okay, but need to research this some more...
 
I'd like to keep this thread alive for awhile, as I'm also pursuing early style 80mm ringsets.

TLCbobber has a point about the deck height. Here's a pic of 447 piston dimensions. You'll want to confirm dimension "E". Also, confirm the diameter of your pistons. Are they 80mm?

TwoMany, you've got me wondering about my piston now. I've looked at that chart you posted with 447 dimensions on it E=38.2 whereas on mine E=29 as near as I can measure with this rule. How come the image shows different dimensions to what I have? My piston isn't marked 447 but the cam shaft and engine cases are.

Just been to check the rods on my old crank, they're marked 533:yikes: I never checked that before, I just assumed it would be 447 like everything else. So correction to my earlier post, that piston is a 533 piston for 533 crank/rod hence the location of pin hole in the piston.

Thanks for posting that TwoMany, you may have saved me confusion later when I come to rebuild. Although I do have a rephased 447 unit to go in I won't be wondering why the new pistons don't quite look the same when I buy them.
 
OK, so here's what I have:

Top two rings are identical. 1.5 mm thick and 3.6 mm wide (as measured with my verniers).

Oil ring is 2.8 mm thick and 2.5 mm wide

20 mm wristpin.

Measurement from the CL of the wristpin to the edge of the cylindrical part of the piston 38 mm

The rods are 447

The stroke is stock: 74 mm
 
Ok, so far, so good. Can you measure your piston's groove depths, and are they equally deep?

Edit: Also need to confirm piston diameter, measured about 1/2" above the skirt buttom...
 
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