SOHC.co.uk Forums > CB500/550
CB125 Pistons/rings suitable for 500/4 ?
AshimotoK0:
The oracle 'Hondaman' replied with this:-
Those --323-- pistons are interchangeable, just as the CB750DOHC oversize pistons fir the CBX 1000 Six, or the many other permutations Honda did with these engines. They technically only built about 5 different engines, modifying the bores and strokes, but re-using the pistons where applicable, rings where they fit, and wristpins almost everywhere were the same but for length. This all changed after the SOHC4 "era", for sure, but in the days when I started working on them (1965) thru now, I have interchanged lots of these parts successfully.
Here's the thing to watch for when swapping in the rings: make sure they have the same piston-to-ring clearance on the ring lands as is spec'd in their books. Of course, they must match the bore size and pistons you have, and IF they have a (trade)mark on them, that side goes UP. I have seen on honda engines the "stepped" rings and non-stepped rings in the very same year of production on the 750, 500, and 550 bikes (the Baby Fours I have done are all stepless, so far), with markings from RK, Riken, someone with a "T", and also a "C", "M", and others I have forgotten, but ALWAYS the mark goes UP.
The oil-control rings on the 500 were all 1-piece in the engines I have seen. They came both ways (1-piece and 3-piece) in the 550 engines, though. In the pre-1974 versions of the 125 I have been inside, the oil ring was 1 piece, but in the post-1974 it was 3-piece. Somewhere about that time, the 750 went to 3-piece oil rings, too.
An observation, for what it is worth, when you have the option: if you are NOT boring the engine, use 3-piece oil rings if possible, since these seat in odd-shaped bores better than 1-piece types. If you have used bores, the outer 2 (#1 and #4) are not round, and you can prove this with careful measuring: it is ALWAYS true. And, this non-roundness will cause the rings to not rotate in operation, so they will have shorter life by quite a bit, compared to boring round and straight. The latter will also ensure a very long life and more power, if you have the option, as the bores are now cured and will no longer continue to warp.
BTW: the "warp" in the 2 outer cylinders is rather shaped like an egg, with the blunt end toward the outside front corner of the fins, and the inside corner nearest the #2 or #3 cylinder will have the least of the wear.
;)
Trigger:
--- Quote from: Oddjob on August 03, 2016, 01:58:38 PM ---Very interesting about the warping. I wonder if that is caused on the outside bores because they get unevenly cooled, the inner bores are essentially surrounded by heat and so I surmise they cool/heat evenly, whereas the outside bores are getting cooled on the outside edges by the fins and so cool unevenly. It matches the warp as well as the front outside where it would get the most cooling is where the most warp occurs.
Clever and very observant fellow that Hondaman
--- End quote ---
It is normal on any air cooled engine.
AshimotoK0:
Got this reply to a further question from Hondaman.
Quote from: AshimotoK0 on Today at 12:51:27 AM
Have you seen that style of oil ring spring before in my pics (bottom picture) ?
Yep, I have! But, they were in my car's engine. They spaced the thin oil rings away from the piston body slightly, with just the ripple ring actually resting against the piston and the thin rings were "riding" on the ripple ring. Their outer surfaces were such that the ripple ring didn't touch the cylinder walls, apparently the thin rings are pushing the ripple-ly one in toward the ring lands. I can't complain about the design: I rolled over 300,000 miles on those rings last month and the car still doesn't use any more oil than it ever has, about 1 quart in every 4k miles or so. It did that since I rebuilt it, never got any worse, although using 15w40 instead of 10w40 oils in it will make it go further one the quart. When it reaches "almost 1 quart gone", I change the oil, that's my timer. :)
Trigger:
--- Quote from: Oddjob on August 03, 2016, 02:48:37 PM ---What about a single pot then Graham, like say the CB100 or CB125. All areas are cooled but the front 2 would get more cooling, would this result in a double egg shape?
--- End quote ---
All piston's are oval shape when cold, with the narrowest area in the area of the gudgeon pin as this area is the hottest and expands more during running. You will always get uneven wear with a object that is not round moving that fast and hot in a round bore. All this with outside temperatures cooling it unevenly leads to uneven shaped bores.
Kawasaki got it all wrong with the KH 250 as the piston to bore clearance was the same on all three cylinders. This caused the centre pot to over heat and seize due to uneven heat displacement. Give the centre pot a tad more clearance and the problem was resolved.
AshimotoK0:
--- Quote from: Trigger on August 04, 2016, 08:04:28 AM ---
--- Quote from: Oddjob on August 03, 2016, 02:48:37 PM ---What about a single pot then Graham, like say the CB100 or CB125. All areas are cooled but the front 2 would get more cooling, would this result in a double egg shape?
--- End quote ---
All piston's are oval shape when cold, with the narrowest area in the area of the gudgeon pin as this area is the hottest and expands more during running. You will always get uneven wear with a object that is not round moving that fast and hot in a round bore. All this with outside temperatures cooling it unevenly leads to uneven shaped bores.
Kawasaki got it all wrong with the KH 250 as the piston to bore clearance was the same on all three cylinders. This caused the centre pot to over heat and seize due to uneven heat displacement. Give the centre pot a tad more clearance and the problem was resolved.
--- End quote ---
Any comments on the two types of oil 'spring' in my piccies from you Graham? Think I am going to use the CB125T rings on my 500K0 (3-piece oil control ring version).
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