1978 140HP Evinrude with seized lower unit - other damage? - Which lower units fit?

[colpaz]

Hello all,
I'm looking at purchasing an 18' fibreglass boat with a 1978 Evinrude 140 HP motor - dirt cheap, because the lower unit is seized - from talking to the current owner, here's what I know about the motor:

-rebuilt by previous owner in last 5 years
-lower unit does NOT look original, it's a different colour, but not sure what year it's from
-ran well with use a few times over last 2 summers until last outing in fall - stumbled at cruise power, stalled when power reduced, had trouble cranking
-with lower unit removed, engine starts and runs perfectly - compression checked and good in all 4 cylinders
-water pump housing removed and impeller and housing partially melted
-driveshaft to lower unit needs wrench on it to turn, and is very difficult

Current owner thinks it just needs a water pump kit and a bearing.

Questions;
-how likely is it that the powerhead was damaged by lack of adequate water flow for cooling?
-what are the chances that all the lower unit needs is a water pump kit and bearing, and how difficult is it to pull apart (any special tools needed?) - also, how can I tell the specific year of the lower unit as it's not original?
-what lower units will swap directly? From what I can see on the parts pages, 1978-1991 V4s look interchangeable.... Is this correct? I have a line on a good unit from a 1987 Johnson 90 HP - should this just bolt up? Anything special to know when swapping lower units? New gaskets, sealants, etc? Should water pump be done or inspected before installing the replacement lower unit?

Anything else I need to know?


Thanks in advance.


Cheers,
Colin

 

[iwombat]

Re: 1978 140HP Evinrude with seized lower unit - other damage? - Which lower units

-how likely is it that the powerhead was damaged by lack of adequate water flow for cooling?

Very, but if your compression checks out you're probably ok.

-what are the chances that all the lower unit needs is a water pump kit and bearing, and how difficult is it to pull apart (any special tools needed?) - also, how can I tell the specific year of the lower unit as it's not original?

I'd say that's unlikely if you need a wrench to pull it through. Pull out the lower fill plug and check the magnet for metal chunks. Worst case - you can buy complete used LUs for around $500.

-what lower units will swap directly? From what I can see on the parts pages, 1978-1991 V4s look interchangeable.... Is this correct? I have a line on a good unit from a 1987 Johnson 90 HP - should this just bolt up? Anything special to know when swapping lower units? New gaskets, sealants, etc? Should water pump be done or inspected before installing the replacement lower unit?
I'm not entirely sure, but that does sound right. Gear ratios might not be the same though, and you may need to use your existing shift rod and measure the length when you put it back in. You'll have to check that out. I'd put in a new water pump w/o batting an eyelash if it were me.


One more question - the owner didn't run it w/o coolant with the LU removed did he?

 

[colpaz]

Re: 1978 140HP Evinrude with seized lower unit - other damage? - Which lower units

Thanks for the detailed response!

As to your question - I understand that he started it up after removing the lower unit, but ran it for a few seconds only.... I can confirm with him. How much of a no-no is this? Is there a safe way to run a powerhead to test with no lower unit installed?

And, is there a definitive test to determine if the thing was damaged by overheating? Is compression the best indicator? And, what is a good range for the compression on these motors? I've worked with plenty of engines in the past, but really haven't worked on outboards....


Cheers,
Colin

 

[iwombat]

Re: 1978 140HP Evinrude with seized lower unit - other damage? - Which lower units

Generally when you run the powerhead w/o coolant the biggest problem is toasting the water pump. I suppose w/o a water pump a few seconds isn't so bad. Normally you just clamp a hose up to the water tube and use water pressure as your pump.

Compression is probably the best indicator - you want to see even numbers primarily, and anything over 100 is considered good. Below 100 and you need to consider your gauge as a problem and temperature of the engine etc. Anyway, even numbers is the key idea. Also, look at the head for any discolored paint and look at the sparkplugs (the firing end) for any melted electrodes etc. Usually, a bad overheat will warp a head and blow a head gasket, this is why compression is the best test.

 

[colpaz]

Re: 1978 140HP Evinrude with seized lower unit - other damage? - Which lower units

OK - so I just talked to the current owner again, and he did a quick compression test - numbers are:

-Looking at back of engine-

130 140

130 135

Does this look reasonable for that motor? Sounds tight to me, and max difference between highest and lowest cylinders is 8%

Cheers,
Colin