1973 40 HP Compression

[little40]

This is my first post, so please forgive me if this is posted incorrectly.

Model: 40354D
1973 40hp Evinrude Norseman.

What kind of compression is acceptable for this motor? I measured 80 psi on both cylinders. Motor has been sitting for at least 5 years.

I have seen answers ranging from 75 psi up to 120 psi. Others have said as long as both cylinders are within 10% of each other it is good.

If the compression is too low, could I hone the cylinders and replace rings or do these motors typically need to be bored? This is the first boat motor I have ever attempted to work on.

Any advice is welcomed, thanks!

 

[racerone]

Rebuilt a 74 model this winter.-----Had the new pistons / rings on hand.-----That is LOW----Needs 120 PSI or so.----IT is so easy to inspect pistons and rings.-----Remove the 2 bypass covers on the side of the block.----Look at pistons.----Will cost you $8 on gaskets.----It is a mistake to put new rings on used pistons !

 

[little40]

Rebuilt a 74 model this winter.-----Had the new pistons / rings on hand.-----That is LOW----Needs 120 PSI or so.----IT is so easy to inspect pistons and rings.-----Remove the 2 bypass covers on the side of the block.----Look at pistons.----Will cost you $8 on gaskets.----It is a mistake to put new rings on used pistons !

I will take a look at the piston and rings and give an update. Thank you.

Where would I look to get new pistons? The only place I can find them is on ebay. Are these still manufactured?

 

[racerone]

Many places might have NOS on hand.-----Internet is a wonderful tool to find parts for these wonderful / simple motors.

 

[little40]

Rebuilt a 74 model this winter.-----Had the new pistons / rings on hand.-----That is LOW----Needs 120 PSI or so.----IT is so easy to inspect pistons and rings.-----Remove the 2 bypass covers on the side of the block.----Look at pistons.----Will cost you $8 on gaskets.----It is a mistake to put new rings on used pistons !

Here are some pictures from the bypass covers. Not sure how clean these are supposed to be but the crank appears to have a good amount of rust on it.

 

[racerone]

You are looking at the " cool side " of the motor.------I suspect scoring / wear to be worse on other side.-----Time to take the cylinder head off this motor.------Post pictures of cylinder walls.

 

[F_R]

That rusty crank is all I needed to see. That powerhead has to come apart for further inspection (bearings). It might not be worth repairing.

 

[little40]

You are looking at the " cool side " of the motor.------I suspect scoring / wear to be worse on other side.-----Time to take the cylinder head off this motor.------Post pictures of cylinder walls.

Here are some pictures of the cylinders. I will work on getting the bottom end apart sometime this week. I didn't notice any scoring on the cylinder walls, but I will take a closer look tomorrow. I did notice I was able to wiggle both pistons very little when it was TDC, is this normal? I figured the pistons would be super tight. Does it look like I could just hone the cylinders and install new pistons and rings? Sorry my last pictures were so big, I uploaded them from my phone and didn't realize.

 

[racerone]

Those cylinder walls are in AWFUL condition.----Take this motor apart or shop for another motor.

 

[little40]

Those cylinder walls are in AWFUL condition.----Take this motor apart or shop for another motor.

Do you think the cylinder walls are too far gone for honing to fix? How would I tell if they need to be bored out? What looks so bad about these? Just trying to learn, thanks!

 

[F_R]

In reply to your previous question,, pistons are tapered by design, meaning they have side to side movement. at the head end.

But you have water damage, which is your major problem.

EDIT: Just for kicks, I'll make a prediction. Missing or broken lower crankshaft seal has been letting water enter the crankcase.