Inline 6 rebuild

[redmen62]

Hi all,

Picked up a 1968 Mark Twain as a project boat; it's cosmetically pretty solid but has a few known mechanical problems (250ci 160hp MerCruiser)...

We know that the engine has been submerged in water (previous owner forgot to put the plug in), he wasn't sure how high the water got, but immediately changed the oil... I think it got pretty high and was probably over the dipstick. The next time they took it out, it overheated on them and that was the last time they started it. They didn't know much of anything about boats, and when asked if they winterized it, they responded "Uhhhhh, what's that?"... so now there's a nice crack in the block (about 3/4" below the head and running ~7" from the front edge of the first freeze plug)

Got it brought home, and it started right up and runs pretty well. Misses a little, and seems to run a little hot to me. Did a compression test (both cold and at operating temp):
1: 50, 115
2: 110, 135
3: 115, 135
4: 140, 145
5: 125, 140
6: 115, 140

also noticed that we're getting some water into the oil

So here's where I'm at:
Cracked block, bad compression in #1, and oil in the water

I also have a 230ci 150hp Merc that came out of a mid 1960's runabout that hasn't been run in 30+ yrs (ran great when my uncle pulled it), it still turns .

I have both motors broken down to the block and am trying to decide where to go from here...
Do I rebuild the 150 or the 160? Do they use the same block? Any cool stuff I can do to it to get some extra hp out of it?

Since it's out and broken down, we're going to do a new oil pump, head job, ring job, and replace the aluminum divider in the manifold (heard that there's a history of issues there), gimble bearing and boots on the outdrive too.

 

[Silvertip]

Re: Inline 6 rebuild

If the block is cracked how do you expect to rebuild it?

 

[HT32BSX115]

Re: Inline 6 rebuild

Hi all,

Picked up a 1968 Mark Twain as a project boat; it's cosmetically pretty solid but has a few known mechanical problems (250ci 160hp MerCruiser)...

...............
So here's where I'm at:
Cracked block, bad compression in #1, and oil in the water

I also have a 230ci 150hp Merc that came out of a mid 1960's runabout that hasn't been run in 30+ yrs (ran great when my uncle pulled it), it still turns .

I have both motors broken down to the block and am trying to decide where to go from here...
Do I rebuild the 150 or the 160? Do they use the same block? Any cool stuff I can do to it to get some extra hp out of it?

Since it's out and broken down, we're going to do a new oil pump, head job, ring job, and replace the aluminum divider in the manifold (heard that there's a history of issues there), gimble bearing and boots on the outdrive too.

Howdy,

Welcome aboard!

I had one of those..... (A 66 Mark Twain, 150 Mercruiser) Sold it in 2006. The engine had unknown hours on it (39 years old, Dad bought it new and the hr meter quit in the mid 80's) But ran great.

I was going to either rebuild the engine or get a 250 cu-in 6 at the local truck wrecking yard etc. They had about 12 of them there.

Yes, there's some issues with the old manifolds. if you get the newer ones it's solved, but they are quite expensive. I wouldn't use a questionable manifold unless I knew it was ok. You can easily make a new aluminum plate. You may not be able to buy one.

You can do a lot with the old 6cyl engines. The heads are pretty much interchangeable. The 292 engine is a bit taller and mounts differently.

Your best bet would be to find a running 250 cu-in engine.

Inliners will have all sorts of rebuild info. Inliners International Bulletin Board - Powered by UBB.threads?

Old and obsolete. But the inline 6 engine is the smoothest thing around!


Regards,


Rick