Found some rust in spark plug bore

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Hey there, long time reader, first time poster!

So I'm working on a 1974ish mercuiser 165 with the GM 250 in it. It's been parked for a few years now and I've just pulled it out to tackle the rebuild / restore. I've been fighting trying to get the motor to turn over and I'm not having much luck. The starter is getting 12.75 volts. When you put power directly to the starter, it makes a whirling noise like it's free spinning. But when the engaged with the solenoid it will make a loud clunk like it trying to turn over the motor, and you can see the pulleys twitch. I can't figure out for the life of me why the starter is acting differently when the power is received directly or through the solenoid. So thinking my motor was piled up or the starter was weak, I pulled my spark plugs to try to reduce the compression (with no change in the starter's behavior) I noticed what looks like rust when you peer though the spark plug bores. I'm not certain if the boat was winterized properly so it could be a cracked block which has seized the motor, or if my starter is the issue.

Thanks for the help.
 

Scott Danforth

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welcome aboard

your motor may be rusted and locked up. there is always a valve open somewhere and the natural rusting happens unless you took precautions for long storage before letting the motor sit. if you see rust, good chance the rings and the bore have fused together from rust and you may need to tear the motor down to rebuild.

pull the drive off to make sure the drive isnt locked up
 

Bondo

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The starter is getting 12.75 volts. When you put power directly to the starter, it makes a whirling noise like it's free spinning. But when the engaged with the solenoid it will make a loud clunk like it trying to turn over the motor, and you can see the pulleys twitch. I can't figure out for the life of me why the starter is acting differently when the power is received directly or through the solenoid.

Ayuh,... Welcome Aboard,..... That's how starters are supposed to work,....

The solenoid drive the bendix out to engage the starter motor into the ring gear,.......

Like Scott says, pull the drive off, as it turns with the crankshaft, 'n Could be the problem,....
 
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Sorry I should of mentioned that the drive is off. I thought of that possibly being the issue. Now that you guys mention it, there was a drain petcock that I removed to drain the water. I left it off figuring it would be better for long term storage, rookie mistake I guess! Think the motor is worth saving or just replacing the whole thing with a 250 out of a truck?
 

Scott Danforth

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up to you.

drain petcock wouldnt have gotten moisture in the combustion chambers. that would have been from an intake or exhaust valve open. Normally for long-term storage, you pull the plugs, fill the cylinders with ATF or SAE-30, return the plugs, then back off all the rockers so the springs dont take a set and the valves are closed.

since you already have the drive off and it still wont turn, maybe pull the head and look

if you pull a 250 out of a truck, you still need to change the core plugs to brass and use a marine head gasket.

if I was rebuilding an inline 6, I would look for a 292 and fabricate new motor mount brackets.
 
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Which 292 do you mean? I'm pretty new. What do you mean by the core plugs? Would the drivetrain handle the extra power?
 

Bondo

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Which 292 do you mean? I'm pretty new. What do you mean by the core plugs? Would the drivetrain handle the extra power?

Ayuh,.... Welcome Aboard,... The 292 is Chevy's Big brother of the 250 I-6,.... longer stroke, bigger bore,...
Only came in trucks, 'n fairly hard to find now a days,....

Core plugs are otherwise, 'n wrongly known as Freeze-plugs,...

'n yes, the drive will take the added horsepower, though you'd most likely need a bigger pitched prop,...
 
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So turns out the 292 is pretty easy to find here. Found a blown up one for free! Just need a rebuild kit and off I go. So a couple questions if you guys don't mind;

-will the 292 bolt right up to the drive? No mods needed besides the motor mounts to actually get it in the boat?

-what do you guys think about going to high compression pistons and heads while I'm rebuilding the new motor?

- changing over to an electric fuel pump over the mechanical? What about an electric choke?

-do you need a marine head gasket for fresh water?

Thanks for all the help guys! Really appreciate it!
 

Scott Danforth

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find a runner and add a rebuild kit if you want

same Chevy pattern on it

you can increase compression just a tad, however your going to want to do some head work if you want higher RPM. the 292 is a torque monster the way it is

no reason to change over to electric fuel pump or choke unless you want to

I would run a 4 barrel carb

you always need a marine head gasket unless you run a closed cooled system (heat exchanger). Automotive gaskets are designed to be in contact with coolant, not water.
 
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