Testing compression on a 1958 Evinrude Bit Twin

[58CorrySuburban]

I'm new to outboards, so when I went to check the compression on my cheaply aquired 35hp Big Twin I expected the worst.

First test upper cylider = 30lbs?
Secons Test (same cylinder) = 30lbs?

I stepped back and took a breath. There was no way I was sold a parts motor.

Being new to these enginse, I reexamined it. Ahah!

The Pin conected to the SS flat bar was relieving the compresion (making it easier to start under normal conditions.

I disconected the arm from the release vaulves.

Second test w/out presure release valves in effect:90+ psi, the second cylider read 100+

All tests were run cold and I lubed the interiors with Blast.

Any insight would be apreciated.

Thanks

 

[jonesg]

Re: Testing compression on a 1958 Evinrude Bit Twin

Seafoam the cylinders, it'll help remove carbon from piston rings and could very well increase compression, mine jumped +25psi.
I used the spraycan type, removed sparkplugs and gave it a good blast all around the walls, then let it soak a while and ran it on a water hose.

If the water pump has not been replaced in 2 yrs do that

then put it in the water and see if it goes, running it on a hose with muffs will tell you if it starts but not much else.

 

[55'Fleetwin7.5]

Re: Testing compression on a 1958 Evinrude Bit Twin

Hey Jones... I did not think you could run that motor on muffs... how do you do it? better still, can you show me a picture? I know lots of guys that would really like to know.

 

[tmcalavy]

Re: Testing compression on a 1958 Evinrude Bit Twin

There is an attachment for the old Johnnyrudes, but they are scarce. Best bet is to submerge the leg in a tub/barrel or just take it to the lake/ramp on a boat and run it there.

 

[58CorrySuburban]

Re: Testing compression on a 1958 Evinrude Bit Twin

Thanks Jonesg,
I'll do that. And I am replacing the impeller for sure. I have to pick up my driveshaft from the machinest.

(back story: I'm changing the motor from a long to a short shaft. The guy that sold me the motor gave me the shorter shaft. When I disconnected the impeller from the longer one, I noticed that the long one used a short pin to secure the impeller, and the short shaft replacement had no pin, but a half moon.)

Thinking that the guy gave me a bum shaft I checked the replacement by putting both ends in their respective places (one at a time). The upper, slid in nicely, and any flywheel movement corresopned perfectly (no lag) with shaft movement. Same story with the lower unit.

To make sure the length was correct. I set the housing spacer on a flat surface, stood the short shaft on it, and the long on the ground next to it. Perfect match for length. So I droped the short and long ones off at the machinest, and asked him to slap a pin in the same place as the long one. He's a marine machinest, so i'm sure he'll know what end to measure from.