1958 Johnson 7.5hp

[pro-crastinator]

Hi guys. Hope everyone is well.
I am wondering if the old babbit bearing rods are upgradable.
Specifically on a Johnson AD-12
Could a machine shop "install" a better bearing?
- or even a new bronze bearing surface?
I don't recall anybody trying to do this on an AD (7.5). I know about the QD upgrades (10hp)

 

[racerone]

I know that the newer 6 hp crankshaft with needle bearings can be retrofitted into the older 5.5 motors.---Hope to finish one next winter.-----Do not know of any tricks to do that with the 7.5 models.----Why the question.----------There should be lots of good used rods and cranks around for the AD models.

 

[pro-crastinator]

Well I may be in the market soon.....
DO you know about any new ones?
- is why I was interested in an upgrade.......

 

[Chinewalker]

You might want to pick up some other small OMC junkers - 1970s 6hp, 1980s 6-8, 9.5, 9.9, etc. and take them apart. Start measuring rod clearances and dimensions. Might have to have the 7.5 crankshaft journals turned down to a different spec, then case hardened to whatever Rockwell hardness required, as the journals are likely harder surface on motors with steel bearings than ones that only deal with bronze bearings. If you know a good machinist, you might be able to have some custom rods made out of billet aluminum, then use the bearing sleeves like those used on later motors. Would be a lot of work, but if you have time and money, I suppose anything is possible.