WHAT IS IT? Engine has no serial number plate. Either a Mercruiser 120 or 140

[jwestjr]

The original Mercruiser 120 was shot and I needed to replace it. A parts store/engine rebuild center owner said he didn't have a 120 but he did have a 140 and all components would interchange with my old engine to the rebuilt one. (Wrong) but the problem I have now is I'm now not sure that it is a 140. The timing on the 120s,
according to specs is 8 degrees before top dead center. The specs for the 140s is 6 degrees before TDC. This engine will not perform at 6 degrees TDC but smooths out fine or at least a lot better at 8 degrees TDC. Without tearing down the engine and measuring the pistons is there a way to be sure which I have. There is no serial number plate on it, just casting numbers. Is there a cross reference from the GM factory to the Mercruiser completion? I don't want to ruin the engine by trial and error with the timing.
Thanks for any and all replys.

 

[Scott Danforth]

you can look up the GM industrial engines by the casting number. the bore and stroke of the 3 liter (181 cubic inch) is different than the 2.5 liter (153 cubic inch)

deck height is also different

additionally the casting marks on the side of the block will tell you if its a 153 cubic inch or 181 cubic inch. if it says made in mexico, its the 181 / 3.0

 

[jwestjr]

you can look up the GM industrial engines by the casting number. the bore and stroke of the 3 liter (181 cubic inch) is different than the 2.5 liter (153 cubic inch)

deck height is also different

additionally the casting marks on the side of the block will tell you if its a 153 cubic inch or 181 cubic inch. if it says made in mexico, its the 181 / 3.0

I sure thank you Scott, That sounds like a great lead. Working midnights and it's my bedtime now. I'll research this tomorrow.
Thanks.

 

[Bondo]

A parts store/engine rebuild center owner said he didn't have a 120 but he did have a 140 and all components would interchange with my old engine to the rebuilt one. (Wrong) but the problem I have now is I'm now not sure that it is a 140.

Ayuh,..... Is this a long block swap,..?? What parts don't fit,..??

One way to tell is, the 3.0l has a harmonic balancer, 'n the 2.5l has just a pulley, no balancer,.....

 

[jwestjr]

Ayuh,..... Is this a long block swap,..?? What parts don't fit,..??

One way to tell is, the 3.0l has a harmonic balancer, 'n the 2.5l has just a pulley, no balancer,.....

Hi Bondo,
The exhaust/intake manifold wouldn't fit. I got one to fit and therefore I had to go to a larger carburetor.

I sure thank you Scott, That sounds like a great lead. Working midnights and it's my bedtime now. I'll research this tomorrow.
Thanks.

 

[jwestjr]

I sure thank you Scott, That sounds like a great lead. Working midnights and it's my bedtime now. I'll research this tomorrow.
Thanks.

Scott I got up early today/this evening and proceeded on the research. It is a 140 or 3.0L. Thanks greatly for your help.

 

[jwestjr]

Ayuh,..... Is this a long block swap,..?? What parts don't fit,..??

One way to tell is, the 3.0l has a harmonic balancer, 'n the 2.5l has just a pulley, no balancer,.....

Thanks Bondo for your replies. Yes it was a long block swap. The exhaust/intake manifold would not match up and consequently I had to buy another (larger) carburator. I have to regroup on the timing issue now. I have also have installed the pertronix 1146a in place of the points. What really had me baffled was the resistance wire. I have two manuals from different companies. The one I was relying on showed the resistance wire that was purple. There is no purple wires on this ignition system and they all looked original. Then I later, very recently rather, looked at the diagrams in the other book and there it was. A white resistance wire.
I was using a 3 ohm coil so therefore it was double resistance which resulted in a yellow spark. I'll try again soon to tune the engine with some good info found here. Timing, idle mixture and idle rpm adjustment. Maybe I can harmonize everything.
Thanks again.

 

[Scott Danforth]

your intake should fit unless the motor is a 1991 or later 3.0.

then all sorts of things wont fit.

in 1990 the 3.0 was re-designed for the 1991 model year. (they also dropped the 2.5)