cylinder head identification please rd-17

[The red boat]

I have a red-primer OMC cylinder head that looks to be in very good condition.
It has a part number cast into the combustion chamber of 302575. It came off a 1955 RD-17 25hp but it isn’t original to the motor

when I try to look up examples of the part number, the images I’m seeing look nothing like this head.

can someone help me identify it please.

[frankr]

302575 is the casting number of the mold it was cast in. It is possible that it may have been finished to fit various motors, 30hp and 28hp for “maybe” examples. Other than that, I have no documentation.

[The red boat]

thanks for the reply Frankr.
I’ll look closer to see if there is a part number on it somewhere. I didn’t see one last night but I was in a hurry.

[frankr]

If there is some unique or “different” about the head, how about a picture?

[frankr]

A bit of research shows that the RD-17 used a 376336 cylinder head, superseded by 592984.

[The red boat]

thanks for the info.
I’ll have to inspect the head when I get home later and see if i can find a part number that matches one of those.

I have an RD-17 that is in good running order but I swapped spark plugs this weekend and stupidly stripped one of the plug holes. The NGK plugs seemed to thread a bit differently than the Champions I removed and i somehow over-tightened the bottom one. The top plug installed perfectly so maybe the NGK plug was at fault? i don’t know but I’ve never had that happen before.

Anyway – I also have a second RD-motor that runs but the compression was not as good so I’ve had it in storage. That’s the one with the red-primer cylinder head.
I removed the head and it looked pristine in the combustion chambers. But since it is not green, it is obviously a replacement from a different motor.

I was just trying to find out what it may have come from because I was going to install it on the better-running motor to replace the stripped head.
just trying to find out as much as i can so I don’t mess up the good motor.

do 25hp heads form different years interchange?

[frankr]

The book sez 592984 fits RD 16 & 17 and Gale-built 25 hp motors.

[The red boat]

i wonder why Johnson changed the number from 376336 to 592984 if they are the same part.
Is it just because it was manufactured at a different time or did they make some sort of improvement with the later version?

thanks again for all the info!

[frankr]

Generally speaking, some sort of a change in the part. Could be as minor as a screw hole. or ?????

[retiredoz]

If the part in play can be referred to as an ‘assembly’, it will have a part no in the parts lists that doesn’t match up to the casting number. And it doesn’t take much, a Welch plug would be enough. The casting # and the part # would generally be the same on a ‘simple’ part (us old Boeing folk referred to those as ‘detail’ parts).

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