2hp 2001 piston ring size

[abuonocoreca]

How can I understand which is the right choice for my 2001 outboard between
646-11601-01-00 PISTON RING SET (STD)
646-11601-11-00 PISTON RING SET (0.25MM O/S)
646-11601-21-00 PISTON RING SET (0.50MM O/S)

I have the old rings in my hands but I don't know the meaning of the measure indicated in the part listing.

Help would be very much appreciated !!!!

Thanks in advance

[boscoe99]

The size of the piston rings correlate to the size of the piston which correlates to the size (diameter) of the cylinder wall.

If the cylinder is within original service limits then a standard size piston and standard size rings are used. As the cylinder becomes worn and is honed/bored its diameter increases which necessitates the use of an over sized piston and rings.

You need a service manual to give you the clearances (minimum/ maximum) between the piston and the cylinder walls. Depending upon the measurement you either install the original piston, the first over size piston or the second over size piston.

[robert graham]

Unless your cylinder has been bored to an oversize for some reason then the standard size should be the set you need. Why do you have the rings out? If they're not warn or broken then maybe just put them back on the piston and run it.....

[abuonocoreca]

Many thanks both for the prompt reply !
I had to disassemble every piece because the motor has been submerged, forgotten and then thrown away as a waste, but it seems to me it can be repaired. Unfortunately I have broken one of the rings .

THe 0,25-0,5 mm is the extra in cylinder diameter ? I will make another measurement, but I think I will go for the standard ones then.

[boscoe99]

What is the complete model of the motor please?

[abuonocoreca]

The sticker reads
2BMH 6A1-A0 model 02 year 2001 1,5 KW

[robert graham]

Most likely all lower end bearings should be replaced also....

[TownsendsFJR1300]

Should be either 2MSHKZ, 2MSHZ, 2MSHA if a US model (reverse look up of piston rings).

[TownsendsFJR1300]

Most likely all lower end bearings should be replaced also....

The crank / rod assembly is "one piece":

2001 2MSHKZ Yamaha Outboard CYLINDER CRANKCASE Diagram and Parts

Short of sending out the assembly to a shop for pressing out the crank pin and having replacement parts available (their not available from Yamaha, but the crank bearings are.

[abuonocoreca]

many thanks everybody.
I'm in europe, I will double check the cylinder diameter and then go for the right rings, but I believe the standard should be fine.

All of the lower end bearing are fine, they were still in the oil, eve inf I will replace all of the seals and O rings

A lot of fun !

[abuonocoreca]

thanks
I have to bring the cylinder to a shop because with a standard caliper I cannot appreciate these small measurements .....

[TownsendsFJR1300]

Put one of your good rings in the cylinder at say the top, middle and lower area's of the stroke/bore AND MEASURE the ring end gap.

If it's the same thru out the bore, the bore is pretty consistent(not egg shaped).

Checking against ring end spec's should give you an idea what your dealing with as well as how worn the rings are (or aren't).

Of course a micrometer (as noted above) is the most accurate and can also confirm if the cylinder' been bored out already...

If no boring is required, a light hone before installing new rings is required..

[abuonocoreca]

Wonderful trick !
Thanks !
I'll do that

[99yam40]

use one of the pistons to push the ring so it is squared up properly in the cylinder

[TownsendsFJR1300]

Wonderful trick !
Thanks !
I'll do that

Yepper and plus 1 using the piston to make sure the ring is square in the bore...