Johnson MD-38 Piston Rings

[Buccaneer]

I have the powerhead apart on the subject motor, and curious if
anyone knows the most current part number for the piston
rings might be?
I have no parts manual for this motor, but did find an Evinrude
piston ring chart of the correct era, that shows 1-3/8″ x .093 wide
rings for one of their models.
My MD-38 has the 1-3/8″ bore, but no idea if the rings are
the same. Will measure the width of mine today.
The little, single cylinder motor has 70 psi compression
spinning it over with a drill. The crankcase seems tight.
I didn’t rope pull to check for compression initially, as the
lower unit was binding up.
Thanks.

Prepare to be boarded!

[Buccaneer]

Found out the rings for these MS & MD , single, Johnsons are 378410.

Same as the Johnson HD, HS, HA models, but you need two
sets for those.

Prepare to be boarded!

[kiawahman]

The 378410 piston rings also fit the single cylinder 1hp Sea King motors from 1937-40, the ones with the ‘chipmunk cheek’ side covers.

[Buccaneer]

kiawahman wrote:

The 378410 piston rings also fit the single cylinder 1hp Sea King motors from 1937-40, the ones with the ‘chipmunk cheek’ side covers.

Good to know, I added it to my notes!

Prepare to be boarded!

[Tubs]

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

• This reply was modified 4 years, 7 months ago by Tubs.
• This reply was modified 4 years, 7 months ago by Tubs.
• This reply was modified 4 years, 7 months ago by Tubs.

[Buccaneer]

I have five Zephyrs, so good to know about those rings. One of them, I actually
used back in the early 70’s to power my dad’s old leaky 16′ cedar strip boat.
Oars and a bailing bucket were required.

Prepare to be boarded!

[lloyd]

I have had several MD’s and found that they needed unusually high compression to run well. 100-110 PSI

[Mumbles]

Just a note to the previous post, the Zephyrs have a 1 1/2″ bore, but their stroke is 1 3/8″.

• This reply was modified 4 years, 7 months ago by Mumbles.

[Tubs]

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

• This reply was modified 4 years, 7 months ago by Tubs.
• This reply was modified 4 years, 5 months ago by Tubs.

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