Reply To: 1950 Speeditwin 6039 Rods

[Buccaneer]

JAY T. WALLS wrote:

Here is the real answer, On a Speeditwin that just gets run as a fishing motor and has the clearances it was set up at the factory to run on gasoline/oil it was determined that the hole was no problem. If you wanted to race the Speeditwin at 6500 RPM you would need to set it up with the modern V4 rods and do the modifications to those rods tp be able to run them. In the early days of “C” Service builders got away with working with these stock rods but as RPM’s went up the stock rods would break. When OMC came out with the 75 HP V4 Starflight most all racers got rid of the stock rods and went to the 75 HP rod as it could be modified to run and could stand the RPM. Racers of today run any of the rods up to the 100HP V4 rod. When your building one you do the machining so that the oil holes are up on both rods and the clearances are right for running lots of RPM’s.
Jay

Jay, as I was looking for my Oct. 2019 Outboarder and
calendar, I ran across the Jan 2019 issur with an
article regarding Johnson V-4 Rod conversion.
Guessing that this was your article?

Reference was made to a July 1989 on the same subject.
I don’t have that issue to refer to.

The prior mentioned article says Johnson V-4 rods from 75 to 125 hp
could be used on the Speeditwin. No year range of usable rods was given,
so I don’t know if that matters.

I was hoping the article would mention the V-4 roller bearings, but it did not.
It did mention that the crank and wrist pin ends of the rods would have to
be machined down thinner.
Q. Does that affect the cages and rollers?

I looked on MarineEngine.com, but of course it doesn’t mention the crank journal
or wrist pin diameters.
are the bearings from the V-4 a direct fit in the Speeditwins?

Also, I was curious if Johnson ever offered “over sized” crank rollers / cages
so one could have the crankshaft turned down, but I didn’t find any indication.
Did they?

I put my “less than optimal” crankcase back together today, so I’m no longer
able to measure my crank or wrist pins for diameter.
Are “Specs” on the V-4 cranks available online somewhere?
I don’t have any manuals that new.

Thanks!

Prepare to be boarded!