Piston rings

[gwynfryn]

Hi all,
Guidance needed in fitting piston rings to my kitaco piston 75cc Honda c50 1974.
The piston kit included detailed instructions but all in Japanese.
My dilemma is with the two compression rings, one is dark grey and marked RN on one side(the top?). It appears to have 4 square edges.
The other is lighter grey with no markings(either way up?) and the edges are possibly slightly chamfered.
Any idea which ring goes where?
Thanks
Paul

[Grumph]

Conventionally, the lighter colour ring - silver? - would be a chrome top ring and the darker one the second ring.
RN is a common makers mark and the ring would usually be fitted with this mark upwards.

[F5 Dave]

.
. . .
Any idea which ring goes where?
Thanks
Paul
Yeah, in the piston grooves near the top.

Check piston side on and look for angle as precaution.

But first also check there is some ring end gap when you fit a ring a cm down the bore pushed with piston so square.

Look up clearance for C50 but heck 0.3mm should be ok. If it's too tight search ewe-tube or somewhere on how to file ring ends safely.

[Katman]

A general rule of thumb for ring end gap is 3 thou per inch of piston diameter.

And if there is a chamfer on the piston ring the rule is, if the chamfered edge is on the inside of the ring it goes to the top and if it's on the outside of the ring it goes to the bottom.

[gwynfryn]

Cheers all sorted, now lets see how the 45yr old circlips
go.

[F5 Dave]

No replace those, every time.

[jellywrestler]

No replace those, every time.

why is that??

[sidecar bob]

why is that??

Because bores are a lot more expensive than circlips.

[jellywrestler]

Because bores are a lot more expensive than circlips.

tell me about it, my vincent dropped one, it was brand new, i supplied a new piston kit to the guy who rebuilt the motor and he must have dropped one, it was a wire one so he went to his spares and grabbed another, the wire diamter on the correct one was 2.3mm, the wire size on the replacement was 2.6mm and of course it went walking.
cost me a lot of time and hassle and money.... only motor i've ever got someone else to rebuild too
there are some flat steel ones too, some of the two strokes are getting regular pistons and while it's wise to change them some don't think it's imperative....

[F5 Dave]

Well yes they are just a bent piece of wire and I wouldn't advocate replacement of the undisturbed side. But they can get distorted more getting them out than just springing them in.

[jellywrestler]

Well yes they are just a bent piece of wire and I wouldn't advocate replacement of the undisturbed side. But they can get distorted more getting them out than just springing them in.

my question was more about the flat steel ones that don't wear out as much

[F5 Dave]

Never seen those in an engine. Maybe they can cope in a slow revver?

Actually that's not fully true. I once bought a TS engine that was supposedly rebuilt by a Wellington motorcycle dealer. It had internal circlips fitted. And no crankcase seals fitted. But the mains had their dust seals, maybe those were supposed to be the seal? And they weren't C3. And there's no way it went through scooter centre.

[Grumph]

I'm assuming you both mean Seeger style circlips which are stamped out of flat steel.
The only engine I've seen them used in was a big Guzzi. I believe they're standard on them. Maybe some BMW's too ?

The thing to avoid of course is putting the square edged Seeger clips in a round bottomed groove made for a wire circlip.

If the end of the pin has a correct 45 degree chamfer on it, any end movement of the pin simply seats a wire circlip deeper.

[F5 Dave]

It just common sense .

That said I once ran a piston which didn't restrain the small-end from segwaying sideways. (Yamaha piston with Honda small end.) It grabbed the gungeon pin and pushed it sideways into the bore through piston, circlip or not.


I repeated that trick before I realised what was happening. Slow learner. Guess I was cruising on my looks.