I posted this on the /2 forum...I think everyone over there was out riding! I got a start on cleaning the piston crowns today from my R69S. I found the following on the top of the pistons - 7192, 1/68, the letter H, and a triangle with unreadable info in the middle of it. If I understand things, the 7192 means it's 71.92mm in diameter also indicating that the cylinder bore is most likely the standard size at 72mm (+/-) (only 30K miles on the bike). The 1/68 is the manufacture month and year. What about the letter H? Is the triangle like a Quality Assurance mark or something? I expected to see the word "zorn" to identify which is the front for installation. I got to reading my workshop manual and see that is says that the R69S pistons are not offset but they should be installed with the lettering readable. Sound correct?? Thanks...
Kurt in S.A.
Yeah Kurt, I see what you mean they are really close. From your Pic the right recess looks a tad bigger but that could be shadowing. The best way would be to grab the calipers and measure but I think I"d have to agree they are probably the same.
Just curious are those the stock pistons or are they oversize. I see there stamped but did you mike them and your bore to verify dimensions. I know curiosity killed the kitty but am interested in why you tore it down to begin with did you have a problem?
I'm just assuming that maybe it was in pieces when you got it or forgot to notice piston orientation when you took it apart [Thats where the digital camera has it"s place in the tool box}
Either way I think Vech is right on with the fact that it probaby doesn"t matter and if thats the case you could always scribe the crown with your own arrow for the next person who tears into it down the road.
Keep me posted I'm interested in how it turns out. You never know I might own a 69s someday. CUL JIM
Hi Kurt. I would imagine that if they both measure the same and the r69s is not an offset piston than it wouldn"t matter which way it goes . It would be nice to put them back in the way they came out for wear purposes { are you going to hone cylinders before reinstalling? }. I Will continue to research piston marks for pistons made by Nural or any aftermarket pistons just for my own curiosity. But I got to tell you I don"t find alot of specifics on such things as that. The good thing is the next time you will take a razor or wire wheel and clean the crown first before taking it out. Just a little tidbit I learned from workin with small engines is gumout carb cleaner will dissolve carbon on piston crowns very efficiently, you can just about wipe it clean depending on thickness of buildup. But I can"t imagine yours was that thick other wise it would have boosted your compression ratio and you said you got 125psi both sides.
125 - 147 is normal compression and you had no appreciable difference between cylinders. [Did you take your readings at operating temp? Was your throttle open so it could draw air into cyl? How"d your plugs look ?they will tell you more than anything whats going on in there.
Good luck on your project i"ll keep lookin for info CUL JIM
Sounds correct Kurt. Don"t know what the H stands for but there usually is a directional arrow or the word "vorn" {german for front} or both together. If theres no directional marks and your crown has valve recesses the larger recess is the inlet and the smaller recess is the exhaust. Hope that helps in some small way. Good Luck Jim