4.3 Starter mount area cracked

[Boatdreams]

I’m new to the I/O world and have been searching for a while unsuccessfully for a decent project boat that wasn’t way overpriced. I believe I’ve found a worthy candidate but the price may be low because it probably needs a new block. It’s a ‘96 4.3 Mercruiser Thunderbolt ignition with obvious crack and missing piece where starter sits against bell housing. I’m assuming previous bolts were loose or overtorqued. I’ve heard opinions on this matter to the extreme in both directions, “you can weld it in layers and grind the new metal to the shape of the old block”, “the block is junk”, etc. opinions galore but before I buy it, I’m open to more suggestions.

 

[Rick Stephens]

4.3L blocks being as common as they are, I'd most likely plan to find one and swap over my external bits and pieces after marinizing it. Your's being a '96 makes it dead easy to find replacements.

 

[achris]

Agree. That block (in the picture) is beyond repair.

Chris...

 

[Bondo]

Ayuh,..... Looks like it took out 2 bolt holes,.....
Nothin' there to work with for any kinda "Repair",.....
Replacement is 'bout the only option,.....

 

[achris]

I've seen EXACTLY that damage before. It's caused by an attempt to start a hydrauliced engine. You'll find the starter motor bolts are also bent.

In the case of the one I saw, the owner still had the broken out piece, and I did manage to weld it in place successfully. In fact, 8 years later he did the same thing, but it didn't break my weld.

Chris....

 

[Boatdreams]

I've seen EXACTLY that damage before. It's caused by an attempt to start a hydrauliced engine. You'll find the starter motor bolts are also bent.

In the case of the one I saw, the owner still had the broken out piece, and I did manage to weld it in place successfully. In fact, 8 years later he did the same thing, but it didn't break my weld.

Chris....

Thanks everyone for your feedback. Given the fact that there is a crack in addition to the missing piece, I’m leaning in the direction of swapping blocks but saving some cash by using my external parts. Chris, apparently I need you to repair this one. Maybe you could save it? . I’m unfamiliar with Hydrolock but I know from my research this damage is very common on this motor. What causes hydro locking ?

 

[Rick Stephens]

Most common cause of hydro-locking is a crack in the exhaust manifold letting water in on top of your exhaust valves and into the cylinder. Need to inspect the manifolds carefully to be certain they don't have cracks.

 

[Scott Danforth]

or a salt water motor that was neglected.

either way, that motor is coming out

I would swap over your accessory drive, electrics, etc. however buy new manifolds/elbows

 

[Lou C]

maintaining your exhaust is your #1 top maintenance job in salt water. My old engine is on its 4th exhaust system since I've owned it (bought in 2002). Replaced orignals in 2004, again in 2011 and again in 2017. No hydrolocks due to bad exhaust. Even with 3 sets of batwings!

 

[achris]

Thanks everyone for your feedback. Given the fact that there is a crack in addition to the missing piece, I’m leaning in the direction of swapping blocks but saving some cash by using my external parts.

That's the normal way of doing it. Good ex-truck 4.3 engines are easy to come by. Just change the head gaskets to 'marine' and the core plugs to brass or stainless and you have a fully marinized 4.3 long block. make sure you get the same block casting number as the current engine.

Chris, apparently I need you to repair this one. Maybe you could save it? .

(I do know you're kidding)... But.....
Cast iron can be tricky to weld. By the book there is only one way to do it. You'd have to strip the engine block right down, including removing the camshaft bearings! Then place the block in an oven and preheat it. Once it's fully heated up, you pull it out and do the weld, with special welding rods, and then put it back in the oven and allow it to cool over a period of 3 to 4 days.
The owner of said block wasn't willing to go that far, and asked me to perform a 'cold weld' procedure he'd found on the internet. I agreed only on the condition that he sign a wavier acknowledging that my recommendation was a block replacement and there was no warranty or guarantee on any repair I performed at his request. He agreed and I got to preparing the block. I veed out a line to be welded, about 3/4 of the crack depth, I then used a MIG on about 19V and touched it for about 10-15 seconds. I walked away from it for about 15 minutes, then repeated the process until the veed out part was fully filled. Coat of paint and it was all good. In fact, better than new (as he sadly found out 8 years later)...

I’m unfamiliar with Hydrolock but I know from my research this damage is very common on this motor. What causes hydro locking ?

In the case of the engine I repaired, he was stopped and anchored up and having a party. Him and 5 mates (in a 6m boat ) all sat at the back and pushed it down far enough for the exhaust elbows to be below water level... Fill 3 cylinders with salt water. We got that cleaned out quick enough, but the second time it happened it was his son who did it, but he waited 3 months before calling me. We fixed it that time by putting a brand new 4.3MPI in (with 75mm risers this time)...

Chris.........