Home › Forum › Ask A Member › 1950 Speeditwin 6039 Rods
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December 27, 2019 at 2:26 pm #190103
What is 6039 Speeditwin backfiring through the carburetor…😂 They are infamous for that🤭
Rotary valve Johnson’s Rule!
December 27, 2019 at 4:21 pm #190115P500 water pump is cool. I have NOS military spark plugs for those. Very interesting “foul proof” electrode arrangement.
Wayne
Upper Canada Chapteruccaomci.com
December 27, 2019 at 4:23 pm #190116Here 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.
JayJay, 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!
December 27, 2019 at 10:46 pm #190123The “Specs” are in the Service Manuals for the motors. OMC started that in the ’60s –
December 27, 2019 at 11:06 pm #190124The newest Johnson manual I have is the 10th edition. It shows bore x stroke, torque specs, etc.,
but I didn’t see any crankshaft specs.Prepare to be boarded!
December 27, 2019 at 11:22 pm #190125The larger rollers used in Speeditwins are more tolerant of imperfections than the needle bearings used in Mercuries. The bearing surfaces may be reground and yes – oversize rollers were available.
December 28, 2019 at 9:42 am #190136The larger rollers used in Speeditwins are more tolerant of imperfections than the needle bearings used in Mercuries. The bearing surfaces may be reground and yes – oversize rollers were available.
Good to know that oversize rollers were an option…… at least “back in the day”.
I wonder if the same cages were able to be used with the oversize rollers?Thanks!
Prepare to be boarded!
January 4, 2020 at 8:25 pm #190022{size=23]In the early 1940s the Navy saw a need for a high pressure portable firefighting pump. The highest power outboard at that time was the Evinrude Racing 460. Evinrude modified it to become the Storm Boat Motor, Johnson modified it to become the P500 Pumper. Being portable, it may not have a good source of water. Bubbles in the input caused periods of over the red line engine speed. Johnson designed a shorter heavy duty connecting rod for the pumper. After the war these Army Surplus pumps were snapped up and rebuilt to be used as racers. At one time Clyde Weisman (Wisco Piston Co.) furnished a high dome racing piston for the Speeditwin that used these shorter pumper rods. [/size]
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