OMC 4.3L HO with cracked block

[Travis71]

Well, I bought a project boat and got to looking around and noticed a crack in the engine block. You can see the crack in this picture. It's right at the top of the block on the front port side of the motor.

Is it possible to tell from the location if this was from freezing or a thrown rod or some other failure?

Here's the specs on the engine, title says its a 1991 model:
Model #: 434APRPWS
Serial #: 1203850

I am also looking for guidance with regard to the best way to move forward on this or whether I should completely abandon the idea of restoring this old boat and move on. How available is a block for this engine? Can I just get a comparable automotive block/motor?

 

[alldodge]

Have not heard of an actual 4.3 "HO" but that said, you can still find a 4.3 truck motor in a salvage yard, and reman long blocks.

Looked at the pic and can find some rust but unable to say that what I'm looking at is a crack. Close ups are good, but for me I need a reference from further back to determine what I'm looking at

 

[Big Gee]

What's the condition of the rest of the boat?

Everyone has their own personal preference, mine is to take on a project that needs either major hull work or a re power..

It would have to be something really special for me to do both.

Whatever you decide, good luck with it. iBoats is the place to be for assistance.

 

[Scott Danforth]

99.999999999990% of cracked vlocks are from impropper winterization

You will need a long block and manifolds. Usually the intake cracks too, and the exhaust manifolds can be pressure tested, however i would replace them

 

[tpenfield]

At this point would it matter if it was from frozen water or a thrown rod :noidea: . . . still needs a new block.

 

[Travis71]

Have not heard of an actual 4.3 "HO" but that said, you can still find a 4.3 truck motor in a salvage yard, and reman long blocks.

Looked at the pic and can find some rust but unable to say that what I'm looking at is a crack. Close ups are good, but for me I need a reference from further back to determine what I'm looking at

Here's a picture from further away to give better perspective.

 

[Travis71]

At this point would it matter if it was from frozen water or a thrown rod :noidea: . . . still needs a new block.

No sir, it wouldn't affect my next step, but it might affect my anxiety level until I get it pulled and torn down though.

I guess I was just curious if it was possible to tell what may have caused it based on the location and type/appearance of the crack.

 

[Travis71]

So, this is my first foray into the boat restoration world, or boat ownership period for that matter. Am I correct in thinking that the first step to pulling the motor is to remove the out drive?

Is there an existing thread that provides guidance and steps to follow to pull the motor out of the boat?

 

[tpenfield]

Yes, pulling the outdrive would be your next step. You can do a search for threads showing an engine pull. Many of the restoration threads involve pulling the engine.

 

[alldodge]

Here's a picture from further away to give better perspective.

Have not seen one crack there but does appear to be from freezing

Yes pull drive first.

 

[Lou C]

WELLL....before you get too deep into this....do you have any shops who are still willing to work on an OMC Cobra system, because these have been out of production for a long time and many shops either never worked on them (younger techs) or won't work on something that old, with limited parts availability. I've had one myself for about 17 years and have been able to find the parts I need but there are only 2 mechanics around here who will work on them. I can do the shift cable adjustment myself, once properly set up they shift well.

If you are going to go for it then keep in mind that if you need new exhaust manifolds you aren't going to find those OMC one piece units any more, they have been NLA for like 10+ years. I converted mine over to the two piece system used by OMC from '91 on and also used by Volvo Penta, by getting the V/P 90* aluminum exhaust pipes and hoses, + Barr aftermarket manifolds and elbows. Those fit perfect BTW. The V/P parts are expensive but no problems with fit or leaks. That's one issue. The other is that you have what looks like a Splitfire electronic ignition system and parts for that are NLA as well. Might have to convert to a Delco EST if it's not working, if it is then just run it. Probably has a Holley 4160 4-bbl for which parts are easily available. You will want to get back to the starboard side of the engine and get the casting # off the rear of the block, for a range of years that will work. The other thing that takes searching is finding a 4bbl cast iron marine intake. They do turn up on ebay now and then.

 

[Lou C]

this is the one piece to two piece conversion, done with V/P exhaust pipes and hoses, and Barr aftermarket manifolds and elbows....

 

[Lou C]

https://www.crowleymarine.com/johnso...cfm?mdl=MFZYE5

This is a link to a parts catalog, it looks like the "HO" differences are:
4bbl carb (Holley 4160)
Split fire electronic ignition (you would have been better off with the simple Prestolite points distributor!)
Remote oil filter mount (good to have)

I'm not familiar with the Split fire models but what it looks like by studying the parts manuals is that they integrated the ESA module into the ignition system rather than using a separate ESA module as the ones that used the points distributor had. They also appear to have added a knock sensor. So if you have to replace this system with a Delco EST you would need to find out how to make the ESA system work, might have to add the ESA module that works with electronic distributors (CDI electronics in Alabama will know about this). On the Cobra drive just like a Merc Alpha, you need a functioning shift assist system to lower the idle speed in order for the gear case to shift easily into neutral. On the points models the ESA switches and module performed this function. If it does not function you will have trouble shifting to neutral on the water....

 

[Travis71]

WELLL....before you get too deep into this....do you have any shops who are still willing to work on an OMC Cobra system,

My plan currently is to pull the motor and tear it down to the block myself. My idea after that is to try to find a block to rebuild on. I don't know exactly what all will be involved at that point, but I figured I will post questions about next steps and "cross that bridge when I come to it" so to speak. I figure I need to tear it down to see what parts are able to be used in the rebuild process.
:clock:

Big disclaimer: I AM A NOOB!! I am treating this as a project to tinker with and learn on. I currently only have $600 invested in the whole shebang and I feel confident that worse case scenario I can recoup that amount by selling spare parts and the trailer if I get to the point where further progress is deemed unwise or impractical. I am going to go as far as I can with my free labor and asking for guidance on this forum and then see where I am.

 

[PITBoat]

Don't skim over Lou C's info - you don't want to come out with a pristinely rebuilt engine and then realize there's one or more other critical items about the whole system that renders it unusable. I guess you can't know what works and what doesn't w/o the boat running though.

I got into this also without knowing much, but I had to pay for a lakeable, if obsolete, boat. I'm just hoping now that with a little attention, it all holds together long enough to recoup my investment.

 

[Travis71]

It was a good day!!

A friend came over this afternoon with a snorkel to circulate water through the system and we actually got the motor to run! I was super excited and encouraged that at least it runs. All six cylinders were getting fire so the ignition system seems to be intact.

I did notice the exhaust manifolds were dripping water, so I may have to go Lou C's route on retrofitting new ones. Thanks for the lead on that BTW!!

I am getting water in the oil, so I am looking at a bad head gasket if I am fortunate, or a cracked head if not.

I already knew I needed a new block. I checked casting number as Lou C said (10105867). After a quick search on eBay I found two bare blocks for around $500 delivered. Since my motor doesn't seem to have any major mechanical issues I am hoping to get a new (to me) block and move all my stuff over into it.

Here's a video of the motor running and prop spinning!

 

[Scott Danforth]

You cant move your stuff over. Each block is slightly different, and once run, all the parts are then specific to that motor

Youre getting water in your oil because your block is busted and your motor is junk

If your starting with a bare block, you have to bore, hone, then go with new pistons, rings, etc. Estimate $1500 to rebuild

Or buy a running motor for $300 from a truck, drop in brass core plugs and marine head gaskets, then get a marine circulating pump, new intake manifold (yours is most likely cracked) and new exhaust.

 

[Lou C]

If the block is cracked, then the intake, and both cyl heads are likely cracked as well. Same with the exhaust manifolds. If you really want to make this thing work, you are going to need a whole new (or used, rebuilt etc) engine including a 4bbl marine intake and the Volvo style exhaust I referenced earlier.
Also, your impeller is probably bad, this is the raw water pump in the upper gear housing of the Cobra outdrive, I say this because I did not seem much water getting exhausted under the drive, it should look like this:

https://www.dropbox.com/s/otc4vr4081vulhy/IMG_0481.MOV?dl=0

fortunately the OMC Cobra impeller is very easy to change.
You will really want to re-think this project, the boat needs a total refit in terms of the wood/fiberglass composites and you need a new engine as well. Unknowns are the outdrive, transom mount (tilt n trim and steering).
Having partially rebuilt one boat already (my current one) that's the last project like that I ever intend to do. Any boat I have in the future will be either new or near new.

 

[Scott Danforth]

You will really want to re-think this project, the boat needs a total refit in terms of the wood/fiberglass composites and you need a new engine as well. Unknowns are the outdrive, transom mount (tilt n trim and steering).
Having partially rebuilt one boat already (my current one) that's the last project like that I ever intend to do. Any boat I have in the future will be either new or near new.

Boat rehabs are a labor of love and a way to liquidate all money you may have.

 

[Travis71]

You will really want to re-think this project, the boat needs a total refit in terms of the wood/fiberglass composites and you need a new engine as well. Unknowns are the outdrive, transom mount (tilt n trim and steering).

Given my lack of experience I don't have any idea of a ballpark dollar figure that I am looking at here. I don't mind putting in some sweat equity, but I am trying to do this project the best I can without going broke.

How much to rehab the hull?

How much for a rebuilt long block?

How much for exhaust and all the other stuff that completes a rebuilt long block or that will marinize (?) a used truck motor?

I know there are lots of unknowns...I am just looking for a ball park...