Replace Aq125a with aq125b or will Aq131d

So I have bad block and need to replace my Aq125a, my choices are getting a rebuilt block which is fairly expensive or drop another motor in. I have two in state I have found, a aq125b and an aq131d... will either of these motors drop right in? It appears they both have the different b230 block where the 125a has the other... will both of these still work withought modifications? The aq131d appears to be in better shape.

Go with the 131d it has the better crank and main journals yes it is plug and play!

Thank you, going to check it out tommorrow morning... the guy said frost plug was out but he had replacement, I assume he was talking casting plug besides checking obvious oil, cracks and hoping to do compression check anything additional a guy can do? This motor is on pallet right now so no history or anything besides “it ran”... hoping it slips right in where the Aq125a was and runs!

If he will not allow a compression for any reason whatever do not give him a dime unless you can pull the head and check the cylinder walls. In that case consider it a core. It is not a running engine if you do not hear it run period.

"frost plug" pop out is not an "independent failure", i.e. IT did not fail, something bad happened elsewhere in the engine (likely a freeze from improperly winterized engine) that cause the plug to pop out. Its not a freeze plug, its a manufacturing work around to allow removal of casting core material after casting. The fact that they SOMETIMES pop out when the block freezes is coincidental. The only failures of a freeze out plug I've seen was back in the day (early 1960s on a 1957 Studebaker Golden Hawk) was when a "freeze out" plug would rust and pop out because back in those days, antifreeze was a winter only thing and engines ran on tap water the rest of the year WITHOUT any rust inhibitors. Marine "freeze out" plugs don't rust. BE VERY WARY!!!!

The 131 motor looked decent, one block casting plug out in front, ran camera in and didn’t see metal buldged, all other plugs were in and still concave, oil looked good, cilinder compression was 150 in front two and 125 in rear two... leakdown check everything looked ok... sprayed cylinders down and hoping it was just rings or something...

for those reading this the 131 does indeed plug and play into the 125 with 270 outdrive and it appears they share some of same parts including exhaust manifold, water impeller ect... got the old one out this morning and new one should be in tonight, crossing fingers I don’t have more mess on my hands when I fill full of coolant and turn her on!

Im a little concerned with the compression it is over 10% between the high and low numbers it could be just a carbon issue. Make sure you adjust the points with a dwell meter preset them at .016”. Are you running the solex single downdraftcarb 44PAI?

Yes I have the single down draft solec which was same on both motors(actually swapped them ) also the starters are same on both and had to swap that as well.. got the 131 installed and it now purrs nicely, must have been carbon buildup as compression on all four after sitting all day with the spray is now 170-175.... the antifreeze is running orange as it is picking up rust from inside block as that had been sitting dry, I plan on trying to drain that oa couple times in next few days to try and prevent a clogged exchanger. Any suggestions on cleaning exchange unit?... sea trials tommorrow!

i had a rust issue with my 2.8 litre ford p/u and the only way to remove the rust in the block was ny pulling the circ pump and blast the block with the garden hose thoroughly. Then fill it half and half with a good antifreeze/bottle water. Its been 6 years nor and the coolant is still nice and green. I also filled the radiator with bleach water overnight and backflushed it both ways a few times.