Mercury Block / HP Identification

Hi all, I have (per the ID tag on transom mount) a 1973 1500. However, I suspect the block has been changed out because the two ground wires at the cylinder head that bolt to the lower pan have a smaller loop than the factory bolts. The loops were just "pinched" in under the bolt heads to hold them in. So...I suspect a different block was put in at some point. The serial number on the block itself is S762437, but I can not find anything on block serial numbers on the net. Anyone know how to figure out what this thing is?

Also, top cylinder compression is 130 psi while the rest are about 150. Looks like the top cylinder got hot on last run and actually started to blow off aluminum "Dust" on to bottom of sparkplug, top of piston etc... Is this a case of needing a rebuild or can I check/replace reeds, rebuild carb and fuel pumps (remove problem of lean condition) and run it as is?

Thanks to all who contribute to this great site!

Tim

Re: Mercury Block / HP Identification

1973 1500 is a 6 in-line, 150hp.

The only way to tell if the engine is really a 150 is to open it up and look at the piston skirts and the cylinder block in the area of the transfer ports.These are called 'power ports'. The piston will have transfer hole in the skirt on the non-thrust side, and the block will have a 'scallop' in the cylinder wall, lower and on the transfer side. If the engine has both of these features, then it is a 150hp.

Chris..........

Re: Mercury Block / HP Identification

achris said:

1973 1500 is a 6 in-line, 150hp.

The only way to tell if the engine is really a 150 is to open it up and look at the piston skirts and the cylinder block in the area of the transfer ports.These are called 'power ports'. The piston will have transfer hole in the skirt on the non-thrust side, and the block will have a 'scallop' in the cylinder wall, lower and on the transfer side. If the engine has both of these features, then it is a 150hp.

Chris..........

Click to expand...

Chris,

Thanks for the info. Can these features be seen through the intake side inspection covers or are you saying I would have to split the case? I have the upper intake side inspection cover off, but do not see any holes in the piston skirt - though I realize these holes may be below the area of the piston that can be viewed through the cover.

Curios, too, still weather or not the 130psi on the top cylinder will cause any issues or if a rebuild is 100% necessary. Bottom 5 cylinders are 150 - 155psi.

Further inspection revealed that the tell-tale holewas plugged, which may have contributed to the top cylinder getting hot...not sure though.

Thanks again to anyone chiming in... Tim

Re: Mercury Block / HP Identification

Blocked telltale with NOT make the engine run hot...

I believe the power port in the piston skirt should be seen through the transfer port cover....


130 on the top is ok. With 150/155 on the others, it's borderline. If you have metal on the plug, definitely needs to be stripped and that piston replaced. If it was just the top hole getting hot, I would be servicing the water pump too... and fitting a water pressure gauge to the engine when you're done....

Chris.......

Re: Mercury Block / HP Identification

Chris,

Thanks for the great info! A picture is worth a thousand words. I will be looking at it closer this weekend.

Tim