1990 OMC 4.3L Equivalent and Swap Complexity???

[genuinegemini]

Hello Fellow iboaters,

So, I have this 1990 Chris Craft that I am rebuilding (with some great advice and instruction from oops and company). It currently has an OMC 4.3L that turns over and has compression, but I couldn't get it to fire off. After doing a mild amount of investigating, I'm not sure that it would be practical for my budget to rebuild the engine properly, and I don't want to half-a** it. My idea is this; take the old engine and sell the parts for a somewhat smaller fortune than everyone else is asking, and then apply that money toward a new power source. I saw a 12 bolt intake manifold, USED, going for $800.00. Insane! However, I have no idea what the best fit would be for a replacement to the 4.3L OMC. Nor do I know the details involved in making a change-over like that. From what little I was able to find in these discussions and others, is that lot's of things have to be changed in order to put in a different engine and outdrive in, and to properly align them. It's said to be a real "bear". Can anyone shed some difinitive light on the the complexity of this process, and whether a Merc 4.3L is the best and easiest choice for replacement? Any and all insight will be well received and much appreciated.

 

[RogersJetboat454]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Sound's like you may be prepared to throw the baby out with the bath water....

While I wouldn't recommend someone purchase a boat with an OMC, it sounds like you already crossed that threshold, so let's move on... Before you go ripping anything out, you should know that what you are proposing is going to basically require you getting your hands on a complete running, pulleys to prop donor setup. With an engine that may not be better or worse then yours, and a drive that would certainly suck allot less to get parts for, but still, consider this carefully.

You say the current engine turns over, and has compression... OK, so core of the engine you have sounds like its in serviceable shape, why not dig a little deeper to see if you can find out exactly what's wrong with it? Even if you don't keep the OMC power, it's allot better to try to be selling a complete running engine, then one part by part. And BTW, I don't know where you saw an intake manifold for sale for that much, but who ever was selling it was likely off their medication along with who ever would consider buying it.

Cover the basics check for spark. Check for fuel. Heck, you may even find it's a problem with the boats fuel system or fuel its self which would have undoubtedly haunted the next engine you installed.

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Thanks for the info, Roger. I would love to rebuild the engine and keep it in the boat, truthfully. I'm just concerned about finding the parts I need to make it right. Parts like the engine mounts are going for $200 used and new ones seem non-existant. Even the nuts and bolts are 2, 3, 4 and five dollars each. The intake manifold I found was here; http://www.michiganmotorz.com/12bolt-intake-manifold-1995earlier-remanufactured-p-991.html, and I agree with you. They are definitely off their rocker! But it's really the same no matter where I look. Parts prices are just high for this engine and I don't know if I can fit an extensive overhaul into my budget. However, I am prepared to pull the engine and overhaul it with a new gasket set, timing set and things of that nature, so I guess it just depends on whether it just looks worse than it really is. I sprayed the whole engine down with WD-40... twice, emptying two 24oz. cans, and the top themostat housing bolt still broke off. Luckily it left me a nice stud sticking up out of the intake. I suppose your suggestion is right on the money. It doesn't make much sense to part it out before seeing how much it will actually cost to rebuild. Worst case, the motor can't be repaired, but the parts would be off. As far as finding a donor setup, there are tons on craigslist. Whole boats with complete engines for a few hundred dollars. I paid $300 for my boat and it has the whole kit and kaboodle w/ a trailer. So, they are out there. Of course, it's a "seat of your pants" purchase in hopes that you can use the parts, but it is a viable option where value for the money is concerned.

So, deciding now to go ahead with the overhaul of the OMC 4.3L, I have a question. When I put power to the solenoid and kicked the engine over, it spun fine with no odd noises other than the compression of the air. The engine spun over seemingly without much effort. Initially I used a 3/8 drive socket and ratchet to spin the engine, and it spun around with minimal effort. However, now, when I put power to the starter, it won't spin the engine. It's like there is someting binding or snagging. I even took the plugs out to eliminate the compression and still it won't spin. I used a pry bar to move it past the sticking point and then put power to the starter again. The engine spun around several revolutions before I released the starter. Again, there were no odd noises or clunking sounds. No squeals or grinding, but the engine won't spin again. A friend said that perhaps there is something with the outdrive that is preventing it from spinning over, but the shifter is most definitely in nuetral. Any ideas, or is it just a tear it out and see type of deal? Thanks for the great info and insight, Roger.

 

[Bondo]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Worst case, the motor can't be repaired, but the parts would be off. As far as finding a donor setup, there are tons on craigslist. Whole boats with complete engines for a few hundred dollars.

Ayuh,.... It sounds like you Need a donor boat,...

Ya need to swap Everything, Pulleys to Prop.....

The hole in the transom of that vintage is the same as for Mercs,...

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Ayuh,....

The hole in the transom of that vintage is the same as for Mercs,...

Hmmff, well that's a gloden piece of information to have in the shoebox. Thanks for that tid bit, Bond-o. What about the engine mounting hieght and depth? Are they relative as well or is that where it gets tricky? I'm replacing the stringers, engine mount blocks and transom wood, so that would be the time to make any changes in the mounting location, I assume. I like to try and be as prepared as possible in the event of alternate outcomes, so finding out the details and complexity of a swap "just in case", is kind of an important part of the process. I am definitely going to tear the OMC down and see what's what before I make any rash commitments, but I also need to have a back-up plan. I will be keeping my eye open for a donor boat, "just in case", and I appreciate any and all pointers, tips, insight, experience and help regarding the swap procedure from an OMC to a Merc. Many thanks to the iboat community!

 

[RogersJetboat454]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Thanks for the info, Roger. I would love to rebuild the engine and keep it in the boat, truthfully. I'm just concerned about finding the parts I need to make it right. Parts like the engine mounts are going for $200 used and new ones seem non-existant. Even the nuts and bolts are 2, 3, 4 and five dollars each.
The intake manifold I found was here; http://www.michiganmotorz.com/12bolt-intake-manifold-1995earlier-remanufactured-p-991.html, and I agree with you. They are definitely off their rocker! But it's really the same no matter where I look. Parts prices are just high for this engine and I don't know if I can fit an extensive overhaul into my budget. However, I am prepared to pull the engine and overhaul it with a new gasket set, timing set and things of that nature, so I guess it just depends on whether it just looks worse than it really is. I sprayed the whole engine down with WD-40... twice, emptying two 24oz. cans, and the top themostat housing bolt still broke off. Luckily it left me a nice stud sticking up out of the intake. I suppose your suggestion is right on the money. It doesn't make much sense to part it out before seeing how much it will actually cost to rebuild. Worst case, the motor can't be repaired, but the parts would be off. As far as finding a donor setup, there are tons on craigslist. Whole boats with complete engines for a few hundred dollars. I paid $300 for my boat and it has the whole kit and kaboodle w/ a trailer. So, they are out there. Of course, it's a "seat of your pants" purchase in hopes that you can use the parts, but it is a viable option where value for the money is concerned.

So, deciding now to go ahead with the overhaul of the OMC 4.3L, I have a question. When I put power to the solenoid and kicked the engine over, it spun fine with no odd noises other than the compression of the air. The engine spun over seemingly without much effort. Initially I used a 3/8 drive socket and ratchet to spin the engine, and it spun around with minimal effort. However, now, when I put power to the starter, it won't spin the engine. It's like there is someting binding or snagging. I even took the plugs out to eliminate the compression and still it won't spin. I used a pry bar to move it past the sticking point and then put power to the starter again. The engine spun around several revolutions before I released the starter. Again, there were no odd noises or clunking sounds. No squeals or grinding, but the engine won't spin again. A friend said that perhaps there is something with the outdrive that is preventing it from spinning over, but the shifter is most definitely in nuetral. Any ideas, or is it just a tear it out and see type of deal? Thanks for the great info and insight, Roger.

Could be as simple as a weak battery, or corroded battery connection. A little more problematic like a starter checking out, or there could be an internal issue with the engine or drive. When you go to start the engine, is there just a click then nothing, or is there a click and you can hear the starter humming, but the engine isn't spinning over? If it's the second (starter clicks and hums) then chances are the teeth on your flywheel are shot. If it's the first, clean up your battery connections, and make sure you are using a fully charged battery. If it persists, remove the outdrive and try again. It all comes down to how much effort you want to put into this. Initially, it sounded like everything was all set, it just wouldn't start. But the more you type my friend, the more it sounds like it's time to think about other options.

Granted, if you wanted to rebuild this engine, it is possible. But I suspect your parts prices that you are getting is directly out of an OMC/BRP parts list, such as the 4 and 5 dollar nuts and bolts that are no different then the 40 and 50 cent nuts and bolts at the hardware store.

As far as fitting a new engine from a Merc or a later model Volvo; if you get a 4.3 engine from either of them, it's not like you are trying to stuff a Rolls Royce Merlin into a Vega. The 4.3 that Merc and Volvo offered is the same GM 4.3L V6 thats in your boat with OMC written all over it. It's dangly bits and pieces may be different. But they are all still essentially the same engine that should use relatively the same mounting locations.

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Personally, I woudl try to get your present engine running to at least see if the drive works and then go from there.

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Initially, it sounded like everything was all set, it just wouldn't start. But the more you type my friend, the more it sounds like it's time to think about other options.

Granted, if you wanted to rebuild this engine, it is possible. But I suspect your parts prices that you are getting is directly out of an OMC/BRP parts list, such as the 4 and 5 dollar nuts and bolts that are no different then the 40 and 50 cent nuts and bolts at the hardware store.

As far as fitting a new engine from a Merc or a later model Volvo; if you get a 4.3 engine from either of them, it's not like you are trying to stuff a Rolls Royce Merlin into a Vega. The 4.3 that Merc and Volvo offered is the same GM 4.3L V6 thats in your boat with OMC written all over it. It's dangly bits and pieces may be different. But they are all still essentially the same engine that should use relatively the same mounting locations.

When I started kicking it over, the battery was fully charged. I only let it go about 5 or 6 revs before I let off the starter. I went and got some fuel and put a lil in the carb and bumped it again to see if it would fire. It would not, but it did turn over and it did make compression. The next day, I pulled the plugs to check 'em out and clean them if possible. Before I put them back in, I tried to turn the motor over without the plugs. The bendix kicked out and that was it. No humm or whining of a spinning bendix. Just click. Dead battery? Possible, but I can't imagine spinning the motor those couple times killing a fully charged batt. Even if it's weak it should spin a motor that isn't under compression, shouldn't it? I mean, I can't even spin it with a ratchet now, so.... a donor hunt may be in the plans, but I am still going to tear it down and see. If I can strip it, clean it up, I may find it's not so terrible, but I am putting my backup plan on-deck in case the OMC is an out.

If I do end up putting in a Merc, is anything I have usable with it. Shift cables, brackets, trim pump, steering system or anything like that?

Also, how can I find out specifics about my engine? I see a lot about balanced shaft and no balanced shaft, split rear seal and solid rear seal. How can I make sure I get the right gasket kit if I do end up overhauling the OMC?

I have the following numbers:
Engine- Model# 432APRMED Serial# T1148792
Model# 985685 Serial# T0677597

Steering- Model# 986028 Serial# T00265336

Outdrive- Model# 986032 Serial# T0702979

Please enlighten me!

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Assuming your battery is good and assuming your starter is good, of course you haven't noted that you checked the battery voltage after you tried these tests, you may want to pull the drive to make sure it isn't causing the engine to not turn with the starter.

You have a few troubleshooting steps to go here. First step is to check your battery voltage after you run the starter to see where its at. Second is to determine if your postive and negative cables are all making good connection. Its also possible that you need a new starter.

Have you even done a compression check on this engine?

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Assuming your battery is good and assuming your starter is good, of course you haven't noted that you checked the battery voltage after you tried these tests, you may want to pull the drive to make sure it isn't causing the engine to not turn with the starter.

You have a few troubleshooting steps to go here. First step is to check your battery voltage after you run the starter to see where its at. Second is to determine if your postive and negative cables are all making good connection. Its also possible that you need a new starter.

Have you even done a compression check on this engine?

Hi Bruce. Thanks for the advice and suggestions. I just tested the batt and it's reading 12.7v. I would think that's more than enough to spin an engine with no plugs in it. As far as the ground wires and pos wires, I by-passed the original wiring with jumper cables to avoid the corrosion factor. Your comment about taking the outdrive off seems the next logical step, to avoid further damage, if that happens to be the case. I haven't tested the compression with a guage to get actual numbers. I'm just going by the sound of the air when I turned it over the first time, and I know that doesn't mean anything. Once I get the outdrive off, I will see if it turns by hand. If so, then maybe I will try to fire it up again to get a little more info on her. I don't have my service manual yet, but I plan on getting a real service manual, and not one of those "one book does all" manuals. I thought that I read somewhere that the shifter needs to be in gear when pulling the outdrive, which doesn't seem right to me. Did I just misunderstand or is that the deal? I also read that the shift bracket and cable position is important to remember. This is my first I/O so I apologize for the remedial questioning, but your help is sincerely appreciated.

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

OMC Cobra needs to be in neutral.

12.7V is a fully charged battery.

While you are waiting for your manual, it would be a good idea to read this site:
http://www.hastings.org/~stuart/cobra/

 

[Four Winns Erie]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

You can download the OMC Factory Manual here: http://www.mediafire.com/?j74z0nib459gh

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

OMC Cobra needs to be in neutral.

12.7V is a fully charged battery.

While you are waiting for your manual, it would be a good idea to read this site:
http://www.hastings.org/~stuart/cobra/

Thanks for the link, Bruce. Very good info on the shifting details. And thank you for the clarification of the shifter position when removing the outdrive. I don't know what the deal is with the engine not wanting to turn now, despite the batt. Either way, the future forecast is cloudy at the moment. I'll definitely keep ya updated on the progress and what I find.

You can download the OMC Factory Manual here: http://www.mediafire.com/?j74z0nib459gh

Thanks for the link Four Winns. That manual will be very useful in getting me underway with the tear down. I thought I could take the outdrive apart a section at a time, but I saw a video that proved otherwise. It was a neat little jig he had too for mounting the drive unit after it's off. I have a better than average knowledge of engines, but this is my first I/O and the outdrive stuff is all new to me. Apparently, I have to build a craddle before I can remove it. I'm sure I will get it all figured out eventually. Right now I am trying to absorb as much information as I can before I really get into the "meat" of this project. I have the boat gutted and the motor is coming out next week, and then, here we goooo!

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

It could very well be the starter. If that starter has EVER been under water, even once, it could be toast.

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

It could very well be the starter. If that starter has EVER been under water, even once, it could be toast.

It's hard to say Bruce. I'm pretty sure the guy I bought it from was not revealing everything. Of course, I bought the boat knowing it needed to be restored, and knowing it had been sitting under a tree uncovered for the better part of two years. However, when I looked at the tag on the trailer and the decal on the boat, it was clear this boat hadn't moved in six years. Still, I love the way the boat looks and after I modify the interior a bit, it will be absolutely practical for all of my needs. After I cleaned the boat, I found a repair in the side if the hull. It looks as though someone hit a pylon or rock or something. Needless to say, I am sure the boat took on some water. As to whether it was actually sunk or flodded out the engine, who knows. There is a lot of rust and corrosion all over the boats engine, components, outdrive and so on. The starter is really rusted too. The back plate on it is just a rusty disc. I should have the motor out by the end of next week, so I will have a better idea of what kind of shape it's really in. Thank you for the suggestion bruce. I'll post an update as soon as I get it figured out.

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Why are you taking out the motor?

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Why are you taking out the motor?

Because I have to replace the transom wood and stringers. All the wood is saturated, every where.

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

I see. I would still try to see if the drive is ok before you do this although the true test is running in the water under load whch sounds like can't happen.

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

I see. I would still try to see if the drive is ok before you do this although the true test is running in the water under load whch sounds like can't happen.

Yeah, I wish I could run it on the water (smile). Since the motor won't even spin with a ratchet anymore, I don't want to take a chance on messing anything up anymore than it might already be. Something has definitely got to be binding up somewhere since the initial cranking. Without plugs and a good batt, there isn't much else to figure for why it wont spin, even by hand. It was totally effortless the first couple times. Now it won't budge without serious force. Better to just see what's stopping it I think.

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Just so you know, the drive needs to come off to take out the engine.