1988 OMC 4.3 new block?

[Mattrick2oo3]

1988 4.3 OMC with Cobra outdrive - pulled the boat out to get it ready for some lake time, put it on muffs and started her up. The motor was idling nice and smooth for about 10-15 minutes and then it started spraying water out of the carb! Oh no... it doesn't stop there - shut it off immediately, checked the dipstick and saw my very own chocolate milkshake coating it about 7 inches up from Max. Same thing in the heads, creamy milkshake. Pulled the exhaust manifolds yesterday and will be removing the intake manifold and heads after work today (hopefully) to inspect.

So my questions start here:

-Should I be expecting to find a cracked block or a cracked intake manifold?

-Where can I find a decently priced replacement motor?

-I believe I can go to the local u-pick and pull the motor from a '87-91' Chevy 1500 and use the block from it - what are all the components that need to be swaped from my current motor to the new block.

Thanks in advance!

 

[Scott Danforth]

my guess is that you will be finding a crack somewhere or you have the failure prone bat-wing manifolds

if your block and heads are cracked and you go the salvage yard route, you need to get a complete Long Block (block and heads) from a truck (S-10's are filled with 4.3's). then change out the core plugs for brass and the head gaskets for marine. Just the long-block will be used (block, crank, rods, pistons and heads). water pump, oil pan, dipstick tube and all accessories will be migrated over from your marine motor.

LKQ has pull-a-part motor prices for $300

I would pressure test your exhaust manifolds. and if you have the batwing manifolds, I would not bother with testing, and simply replace them.

 

[Mattrick2oo3]

No Title

Thanks for the reply, I'm definitely expecting to find some damage once I get it tore down tonight.

Is this the "batwing" style manifold? They both look to be in very good condition and will bring them into the shop to have them pressure tested. What is the major issue with this style?

I was already planning on changing out the core blugs to the brass style, I will also need to use my old fuel pump and distributor, correct?

Does anyone know of a thread where the same thing was done that has all the necessary gaskets listed (not part numbers necessarily but just the required ones).

Thanks

 

[Scott Danforth]

yes, that is the motor killing batwing

batwing manifolds have a tendancy to leak internally and fill the motor up with water the best you can do is assume it junk and replace it

go to summit racing and order a felpro marine gasket set

yes, you need to use everything from your marine motor except the block and heads.

 

[Mattrick2oo3]

Okay so I couldnt get the manifold off yesterday because of weather but was able to today. Theres a freaking grand canyon size crack in the block on the port side under the intake manifold. Can someone please confirm what year automotive blocks I can use to swap out with?

Thanks!

 

[Scott Danforth]

stick with 1986-1991 for your vintage.

or if you want some reading http://forums.iboats.com/forum/engi...history-of-the-4-3-liter-with-casting-numbers

 

[Mattrick2oo3]

Just an update, found a donor motor on CL that I tore down to the block. Waiting on gaskets to arive hopefully tomorrow and will be installing all of the bolt ons.

Wednesday I have it arranged to use a buddies Bobcat to pull the motor out of the boat to take the final parts off for migration and drop the new (to me) motor in.

I'll update the post after I get it running, fingers crossed!

 

[Mattrick2oo3]

One more question, do I NEED to change the camshaft or will the existing camshaft in the donor motor from a Astro Van work fine?

Thanks!

 

[Lou C]

Thanks for the reply, I'm definitely expecting to find some damage once I get it tore down tonight.

Is this the "batwing" style manifold? They both look to be in very good condition and will bring them into the shop to have them pressure tested. What is the major issue with this style?

I was already planning on changing out the core blugs to the brass style, I will also need to use my old fuel pump and distributor, correct?

Does anyone know of a thread where the same thing was done that has all the necessary gaskets listed (not part numbers necessarily but just the required ones).

Thanks

Weird.
​I have heard this but thought people are talking more about the Merc version. As I've said before I have had 3 different sets of these, on my '88 over 15 years of salt water boating and never had water in the cyls, that happened only because of the blown head gaskets. I re-tested them with acetone and no leaks ever. Maybe certain runs of them were cast poorly.....

 

[Scott Danforth]

Just an update, found a donor motor on CL that I tore down to the block. Waiting on gaskets to arive hopefully tomorrow and will be installing all of the bolt ons.

Wednesday I have it arranged to use a buddies Bobcat to pull the motor out of the boat to take the final parts off for migration and drop the new (to me) motor in.

I'll update the post after I get it running, fingers crossed!

Do not forget to change the core plugs

 

[Mattrick2oo3]

Scott,

Yep, already got new core plugs. Can you give me any advice on the question I asked about the Camshaft?

Thanks!

 

[Scott Danforth]

the stock astro cam should be fine, however I would be pulling the timing set and replacing it. cheap insurance. then again, I would probably change cams to a custom grind with 268 degrees of duration, however that is me.

 

[Mattrick2oo3]

So one more question has turned into yet again, one more question.

The new motor has a very obvious different crankshaft pulley on it. Can I just swap the pulley from my old motor to the new one or do I need to swap the entire harmonic balancer assembly? If I CAN just swap the pulley, is it as simple as removing the 3 bolts going through it's face and changing or do I have to remove the crankshaft center bolt as well?

Thanks!

 

[Scott Danforth]

just swap pulleys, and yes, you have to remove the crank bolt as well.

 

[Mattrick2oo3]

No Title

Okay so I got both the pulleys off but the old one won't mate up with the new harmonic balancer correctly.

See the attached crudely drawn images. The harmonic balancer on the astro motor has a flange that is protruding from the face of the HB interfering with mounting the pulley. Are these dampers nuetrally balanced with weighted flywheels? If so, can I just swap the harmonic balancer along with the pulley?

Thanks,

 

[Mattrick2oo3]

Also, the boat one is 6.75" and the astro is 6.25".... lost as to where to go from here

 

[Scott Danforth]

4.3 dampers are specific to the crank and pistons you are running, with and without balance shaft. if both are the same vintage, same block casting numbers, then you can swap the dampers.

 

[Mattrick2oo3]

Update: Got the motor installed in the boat last night and ran it for a few seconds. Looks like all is going as planned. Tonight Ill be aligning the motor, installing the outdrive and tidying up all my wires.

Fuel pump comes in tomorrow and ill be installing it with my oil pressure safety switch and hopefully be on the water by Saturday.

While Im no expert, if anyone has questions regarding the process of swapping the van motor into my boat please feel free to ask. I noticed there are many posts asking questions about the process on the interwebs but I havent found an actual log of someone doing the project so maybe Ill write one up.

Scott you were a big help answering all my questions so far, big thanks to you.