Mercruiser 140 Rebuild

[smiles16]

So I originally had a used 120 to replace my blown 140, but it had low compression and blow by. So now I am back to square one. I am now considering just rebuilding my 140.

For background, the engine had water in cylinder 1. Low compression in cylinders 1 and 3. No water in the oil, motor runs fine at 2000+ RPM. Motor was missing the freeze plug from the side of the block when I got it.

Any ideas on where to start? Can I save this with a new head? Just curious to see if I would be better off just replacing engine.

Any advice would be greatly appreciated.

 

[Scott Danforth]

I personally would replace the 3.0 with a 4.3. however you may want to price a rebuild for a 3.0. they can be a costly motor to rebuild compared to V6's and V8's costing nearly the same at the end of the day.

a missing core plug usually means that the block was not winterized, froze, cracked and the core plug fell out. the crack would be your source of water. if the block is cracked, you can get $0.30/# for it or about $20 as scrap, or chain a few of them together to make a mooring anchor.

 

[Bondo]

Motor was missing the freeze plug from the side of the block when I got it.

Ayuh,.... The block will need to be pressure tested to be sure it ain't cracked from freezin',......

If a core plug got pushed out, God only knows how much more freeze damage there is,....

 

[smiles16]

You guys are confirming my thoughts on this. How much goes into swapping the 3.0 for the 4.3? I know the alpha one will bolt up, but what about the mounts and exhaust connects?

 

[Rick Stephens]

I would recommend pressure testing the block before deciding. Not that hard to install a new core plug, block off the exhaust and pressurize the input line.

If you go with a V6 you probably should find a donor boat so you get all the marine parts that go with - exhaust, starter, ignition, alternator and so on. It also would be better to have a V6 gear ratio in an outdrive.Yes, you can most likely prop up to compensate if you use the 1.98 gear ratio Alpha 1 you already own. Just know it may not be as efficient. If you find a donor boat you'll have all the parts you need.

Making motor mounts is not incredibly difficult. End result can be worth the effort. I went through that not too long ago.
3.0L to 4.3L mtr mounts and 25 yo transom

Rick

 

[smiles16]

Yeah I don't think I want to deal with the hassle of a power upgrade for this boat. It's a mid-80's Sea Sprite 17' Bow rider.

So how do you pressure test with motor still in boat? do I just block off intake and exhaust and shoot compressed air in? I know how to pressure test in a machine shop setting, never done it on an assembled engine

 

[Bondo]

do I just block off intake and exhaust and shoot compressed air in?

Ayuh,.... Yer testin' the coolin' passages, so ya isolate the coolin' passages of the block, say at the t-stat housin', block off the port comin' from the drive, 'n the exit to the manifold, 'n pressurize to 'bout 15 psi, 'n listen,....

 

[Rick Stephens]

Pull the elbow off the top of the manifold and make a plate to cover that hole. Seal it on good so the water passages cannot leak into exhaust. Then pull the hose coming from the transom off the thermostat and use a short piece of hose and a fitting from it to an air source. Pressurize like Bondo said and listen.

 

[Scott Danforth]

I use this for small things like gear boxes, manifolds, etc. https://www.amazon.com/Mityvac-MITMV8500-Silverline-Automotive-Vacuum/dp/B0002SQYUA

And something like this for cylinder lean down testing and coolant side testing. https://m.summitracing.com/parts/pr...roform-parts&gclid=CMjAxLbFlM4CFQtZhgodCZAFiA

 

[smiles16]

Ok thanks guys lots of good info here I will try my best.