1970's mercury 1150 concerns rusted plug

[chris0061]

just picked up this 1979 bass boat that has that tower of power on it. All the wiring looked like new, manual jack plate, shifted smooth exc, exc. It hadn't been run in 4 years sitting outside all that time but the price was right so took a chance. Anyway, took all the plugs out and sprayed the cylinders with fogging oil. when I got to the number 6 plug it was loose and the nkg plug was very rusty so bad that it is pitted real bad. Before I start on this motor I was wondering if anyone out there can give me a starting point on figuring out why this happened. I did a compression test and ranged from 122 to 126 cold. When I pulled that last plug I thought for sure it would have little compression but it was good. any advice would be appreciated.

 

[GA_Boater]

The gasket for the cover is probably bad. Get the motor running and see if water weeps around the #6 plug - That's the sign the gasket needs replaced.

 

[chris0061]

I will look at that this weekend. I had it running but just for a minute and didn't look for nothing just wanted to see if it would run. After fresh gas got to it the thing fired and idled like it was new unbelievable..

 

[Faztbullet]

Could have bottom crank seal bad. It will allow water in cylinder when submerged...wont do it on muffs.

 

[Chris1956]

If the outside of the plug is rusty, the water jacket cover is likely leaking. I use a bit of silicone to seal it, as the water jacket cover bolts break easily upon removal, if they are rusted.

If the inside of the plug is rusty, you have water infiltration, as Fazt suggested.

 

[chris0061]

yea it's the inside of the plug. is the motor worth having it fixed or is it a job I can do myself?

 

[Chris1956]

You need to remove the gearcase and powerhead, loosen some of the crankcase screws and pull the three bolts holding the bottom end cap. Replace the seals in the bottom end cap and reinstall and torque the screws. Now install the powerhead and finally the gearcase.

 

[chris0061]

sounds doable. I have a guy wanting to buy it and when I told him about the rusted plug he suggested a leakdown test so ordered a gauge set for that will be hear Friday. he said that would tell us if there is a problem and where the problem is if so. is this true??

 

[Faztbullet]

Leak down wont show this....and checkthe lower bearing as they get damaged too.

 

[racerone]

Agreed-----And if motor sat for any length of time with water on bearings it may run but come to a dynamic halt at any time.-----Best approach on 40 year old motors is a teardown / inspection.

 

[chris0061]

ok, thanks for all the advice, tear down it is.....