Topic: 812 piston Pop Y versus ART photos / new Q?

[Don R]

It appears close to 64mm with my cheap caliper, the cylinders look good, The oil ring is one piece thinking 68 and newer honda 350 correct?

[754]

 Looks like 12 to1 compression !!

[Don R]

I ran out of space on the camera but it says ART on the inset near the pin. I googled ART, they seem to be a Piston co in Japan. Largest supplier if oem pistons to motocycle manufacturers. Sudco carries their product. They don't currently list these though.

The dome might be a deal breaker, the guy that owned it rode it to school but that was the days of leaded premium too.  I'm pulling a piston and taking it to my favorite vintage bike shop in the AM.

[HondaMan]

Those look like the Yoshimura racing pistons from about 1977 or so, for the F2/3 engines. It takes some work to make them fit in the earlier engines.

[Don R]

Really, hmm maybe I should look at this old motor a little closer before I just rob the pistons and run. I might know the guy that sold the parts, this bike was a clone of a bike shop owners own K0.

[Jerry Rxman Griffin aka MuthaF'er]

Don,

My 812 Yoshi does not look like those but then again it is not the 77/78 F engine either and does not have a dome close in height to those. More like stock pistons in appearance. Mine have "812" and "PopY" on the inset by the wrist pin on one side too. No ART either. It does use the 350 rings. 1.5mm ; 1.5mm ; 2.5mm rings. 3 piece oil rings last time I bought and installed. If that is from your "bored" K0 engine I'd like to think that added compression along with the 64mm pistons would make it run like a 67mm+/- 900'ish engine. You have a self serve pump at an airport nearby?? 

[Don R]

These were out of a K4 engine I knew to be bored, my supposed big bore (also K4)engine turned out to be stock. I compression tested the 812 but it had carboned valves leaking. I didn't get any high numbers to get my attention. I already tossed the head gasket, I wonder how thick it was?

I am close to the airport but there is also a new 54 gallon barrel of Q16 VP race gas  in the shop. Approx 116 octane and bearing it's own supply of oxygen. When you're not racing it's supposed to go back in the barrel. the oxygen tries to escape. I'd need some really big jets for that stuff and boy does it stink. At $14 a gallon I don't even want to put in a bike.  Good for 182 in the quarter mile though.

[jaguar]

These are what I have.
small dome but nothing like what yours are

[Don R]

I may have a clue who made Pops pistons, pretty close. There are some significant valve dents in 1 and 4, two has slight ones and 3 looks fine. That strikes me as wierd.
 The offset of the valve marks tend me to think Hondaman is correct about these being for a 77-78F. If you look close there is a corresponding mark on the left side of the compression bump. The intake side doesn't have any contact marks at all.

[Don R]

Those look like the Yoshimura racing pistons from about 1977 or so, for the F2/3 engines. It takes some work to make them fit in the earlier engines.

Not true, apparently they will clearance themselves.  LOL.

[Don R]

I'm wondering if the F2-3 engines have the same intake angle but a relocated exhaust valve location and angle. That would explain the lack of damage on the larger side intake valve and the obvious contact on the exhaust side.

I might have access to a very used F2 head, probably the worst reason to use it though.

[seanbarney41]

Here are what my ART 64mm pistons look like...anybody got any help with finding oil rings?  Last pic shows piston dome compared to stocker...what compression ratio are these looking like?  Am I gonna need race gas to run these?  Is there a cam with enough overlap to bleed off cranking compression for pump gas?

[Don R]

I read in tips and tricks, on most 750 big bore pistons the exhaust valve reliefs are bigger than the intake reliefs. Is this the reason these pistons have hit the exhaust valves? These pistons were installed with the small relief  under the exhaust valve. 

[754]

 Piston are made in left and rights sometimes..may have got mixxed..
 I think I have a 812 piston marked ART on one side, and the yosh logo on the other (Japanese charachters)

[Hinomaru]

Here’s what a Yosh 812 piston looks like from this article dated 1/73:

http://www.hondachopper.com/garage/articles/yoshi_750/page1.html

[Don R]

Piston are made in left and rights sometimes..may have got mixxed..
 I think I have a 812 piston marked ART on one side, and the yosh logo on the other (Japanese charachters)

That's what I'm wondering. They look correct if the small relief is for the exhaust but if the big relief is for the exhaust they are all upside down.

[Don R]

http://www.dynoman.net/engine/pistons/piston-install/65mmSOHC.pdf

This is for a different piston but the installation diagram here looks the same as the valve reliefs used on this 812. Only conclusion I come up with is these are intended for F2-3 like Hondaman thought. Thanks for the shared info.

[jaguar]

These are the markings on the other side of my pistons if it helps