Kawi2strokes.com Forum

The H1 piston part number is 13001-031. Why do some have suffix like 1A, 2A or 2B on the end: 13001-031 2A?

Thanks

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Bikes I drive/own

Kawasaki
1973 H1-D (New Project)
Suzuki
1974 GT250 (T350 upgrade)
1976 GT250 (T350 upgrade)
1971 T350
1970 T350 (New Project)
1974 GT380
1975 T500
1973 GT550
1975 GT750
Yamaha
1972 DS7 (R5 upgrade)
1977 RD400

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Bad decisions make the best stories.

This is testing the old memory bank, (which is neuronally challenged daily), but it goes something like this. On a production line, they might fit the piston to hand which is marked closest to the actual size of the hole in the cylinder, and an A, B or C fit may be marginally different........ They are a lot fussier with internal components for a 13,000 rpm/200HP 4-stroke engine for instance, than the old Triples, but they did try and match a fit. I think it is as simple as that, really.

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"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.

III

Thanks, But I could not find answer at that link.


RODH2. I think you are saying it defines the diameter of the piston. Maybe no suffix means nominal diameter. My guess suffix go 1A, 1B, 2A, 2B, and piston diameter gets larger as they go?

Or, did they go +/- about nominal... 1s are smaller than nominal, 2s are larger?

Sure would be cool to know this
.

_________________
Bikes I drive/own

Kawasaki
1973 H1-D (New Project)
Suzuki
1974 GT250 (T350 upgrade)
1976 GT250 (T350 upgrade)
1971 T350
1970 T350 (New Project)
1974 GT380
1975 T500
1973 GT550
1975 GT750
Yamaha
1972 DS7 (R5 upgrade)
1977 RD400

I think the A B C indication was only on the 400 pistons, and were actually stamped on the pistons themselves, not on the part number. They did change the cut out design, so that might be one of the variations on the 500.

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

I see the suffix at the end of the part# on the Kawasaki 500 piston box label. I also see it stamped in ink on top of the piston crown.
The cut out change to piston drove a base part# change if I recall. I only see this for STD size piston not on oversize pistons. But, I have seen a few OEM pistons and not many around.

I think ROH2 hypothesis is best so far, just don't know what the coding means for size ... if that's what it means.

If you could get slightly larder STD piston, it could take up what is removed when homing. I wish wiseco's or wossner's STD piston allowed a little extra diameter for honing. I am sure they are nervous about seizing, but most everyone hones and then takes off too much material is my experience. Not too many NOS cylinders around.

_________________
Bikes I drive/own

Kawasaki
1973 H1-D (New Project)
Suzuki
1974 GT250 (T350 upgrade)
1976 GT250 (T350 upgrade)
1971 T350
1970 T350 (New Project)
1974 GT380
1975 T500
1973 GT550
1975 GT750
Yamaha
1972 DS7 (R5 upgrade)
1977 RD400

It is called a "magic number". Only one triple used a letter/number code, the rest were numbers. When an engine builder was to the point of selecting pistons for final machined cylinders for mounting on the cases, a magic number was used, such as a "36" for that series of engines.

Lets assume the cylinder and piston needed a m/n of 32, and the cylinder had a finish of 15, the builder would select a piston that had a 17, which added up to the magic number of 32. This gave a piston clearance of the prescribed .0015, perfect clearance.

All this was done because not all cylinders finish honed the same, and not all pistons finish sized the same, either. It is a way to fit the clearance correctly while production doesn't get bogged down with constant measurements needing done to fit assemblies together.

H2 was 36, H1 was 32, as I remember. Soime dealers tried to order the biggest pistons they could by m/n, so when they had an engine with some miles on it, but not needing a bore, they could fit the largest piston to a very slightly worn bore, didn't work, Kawasaki just sent pistons, some off the line with numbers, most with no numbers. The m'n was only used at the factory, dealers didn't have that fitting luxury.

I wish i knew if for example the 2A marking is a larger piston than one with no marking. Short of buying both and measuring.

_________________
Bikes I drive/own

Kawasaki
1973 H1-D (New Project)
Suzuki
1974 GT250 (T350 upgrade)
1976 GT250 (T350 upgrade)
1971 T350
1970 T350 (New Project)
1974 GT380
1975 T500
1973 GT550
1975 GT750
Yamaha
1972 DS7 (R5 upgrade)
1977 RD400

What is stopping you buying pistons and having cylinders bored and honed to spec. , maybe I'm missing something, lots of forums and groups out there!?

_________________
"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.

I have one new cylinder and the other two have less than 6000 miles and look it, but of course have some normal wear and light hone will take off a little. Having the piston clearance be correct makes an engine run and sound so well and makes street riding/touring experience perfect.

The two with 6000 miles I would like to buy larger std (2B?). The new one I don't want a piston too large and seize when I do want to get frisky when driving. I have calibrated tools to measure the bore/piston, so I can check fit. It seams like I won't know suffix size unless I buy one. I was hoping someone still new, but I am a hypocrite for probably won't take time to find answer: NOS stock on STD pistons is almost nil I think.

Please don't throw hate at me for what I say. I say too much is my problem. I have had hundreds of cylinders bored for me in my life. I have used various business to do them. Even today I have not found one that can "repeatedly" hold to tolerance. It is kind of like going to Deli and asking for a 1.0 pound of Ham. The person, if in a hurry, cuts thick pieces and does not measure often when close to done. By the time he is done you are significantly over your request of 1.0 Pound. One needs to slow down and be careful. It is also the tools.

I see that Sunnen, for example, the past few fears has introduced some new honing and boring equipment where its is now harder to fail and can achieve tight tolerance repeatedly. Not sure who has such equipment for motorcycle work, Those who purchase are usually for the auto engines. They seem to have had a hard time jigging up these old air cooled cycls and I have seen some weird mistakes. Here I am not a hypocrite. I will pay extra for those who provide me their final measurements for me to verify against. I want it perfect , to tolerance and as I request. I will pay extra if needed to ensure quality.

I think I will go 0.050" OS on all three cyls, and asked for size to be .00025" less, then I will final hone fit it myself when they hold to tolerance.... if they overshoot my request maybe wont be as bad.

_________________
Bikes I drive/own

Kawasaki
1973 H1-D (New Project)
Suzuki
1974 GT250 (T350 upgrade)
1976 GT250 (T350 upgrade)
1971 T350
1970 T350 (New Project)
1974 GT380
1975 T500
1973 GT550
1975 GT750
Yamaha
1972 DS7 (R5 upgrade)
1977 RD400