4.3 Marine to Auto Block Swap

[zealer]

Hey all, I've got a 4.3 ('01 vintage) Mercruiser with a cracked block. My plan is to swap it with a block from a Blazer or Jimmy of the same year. I'd pick up one of those SUVs, remove motor, scrap car. I will leave the internals in the auto block, and swap everything else. Cam, heads, accessories, timing cover, pumps, block plugs, risers... So on and so forth. I think I can get this done for $500 (say if the block costs me $100), including gaskets. I suppose I may have to get the block and heads machined such that they are flat and will mate nicely. The only thing that deters me somewhat is this seems like a lot of work! And on top, I'll have to build a jig to lift the old motor out of the boat, because it is too high for a standard auto cherry picker. I was thinking a big saw horse with a chain hoist. That will cost some $$ as well. Say $200 for wood and hoist. Unless I build a raised platform to operate then engine lift from. This i could do with materials already at home. Am I crazy? Reman or even used motors cost several thousand in my area (quebec). Any and all suggestions, tips, criticism is welcome.

 

[thumpar]

You might also look at Astro/Safari vans for you donor motor. They are a dime a dozen. Really the only thing on the block you would need to change is the core plugs and probably intake to fit your injection. The cam and heads are fine for use in a boat as long as it doesn't come from a car.

 

[zealer]

Hey thanks for the info and suggestion, I wasn't even aware astro/safaris came with 4.3's. I thought they were all V8's.

 

[thumpar]

Hey thanks for the info and suggestion, I wasn't even aware astro/safaris came with 4.3's. I thought they were all V8's.

They are all 4.3l except for a few very early ones that had a 4 in them. I have owned 3 of them. The 4.3l is also in some of the trucks but they are harder to find. Just make sure you get one of the same vintage.

 

[zealer]

Here's all of the vehicles that I think would make a suitable donor car: Astro, Blazer, Sonoma, S10, C10, Jimmy, Envoy They all come with a 4.3 and are easy to find and cheap (particularly the SUV's). They are abundant in junk yards too, but I'd prefer to start and test drive it to verify it is in running condition. Thumpar, you really think I can just drop a truck motor straight in? (Change accessories, ignition stuff, risers etc). That would be a lot simpler than stripping the truck motor to block and swapping all parts. IMO, I don't think a Mercruiser 4.3 is built any tougher than a regular GM 4.3, but I have read rumours of different camshaft profiles, which could make sense. Also something about engine rotation, that is another favorite quip of the naysayers. Any thoughts on this matter?

 

[m_steiger]

Check out your local rental places... a company by me near to me used to rent out a trailer mounted cherry picker that had plenty of reach for pulling out an I/O. As far as the rotating assembly goes on replacing your block the ONLY thing that has to be marine spec is the cam.

 

[pureinsanity]

I've heard of people using automotive engines with no problems. But I have been told by a machine shop guy I know who builds marine engines that the cams are a little different and the head gaskets have a stainless compression ring. As for the hoist I used a standard cherry picker to pull the motor out of my 77 Mark Twain (302 Ford) with no problem. My picker has 3 settings for the lift arm and I just put it on the last one. Then I cranked the tongue of the trailer up to lower the stern of the boat. Had good clearance.

 

[Walt T]

Keep in mind if you take a motor out of a junk car or truck and install in your boat you now have a junk motor in your boat with 200,000+ miles on it. Then you are gonna make that puppy work harder than it ever has when it was in a vehicle. I'd say that makes you worse off for all the time, work, and money you invest in that.
Think about pulling or buying a motor and overhauling it yourself and sending out machine work. Buy your parts online maybe it's not as expensive as you think. I do understand the shipping costs and all, but if you end up with a motor going bad in your boat after all that work, then consider total costs of doing it twice or even three times. I personally have bought and rejected motors out of trucks that I had bought for rebuilding when I found cracks and damage not forseen inside. Valley cracks are not uncommon in aging Chevys. They can lead to damaged camshafts which then can lead to catastrophic damage with the marine type of hard use.

 

[zealer]

Thanks all for the good tips. The motors I'm looking at have nowhere near 200,000 mi, but rather 75,000 (120,000 km, I'm in Canada). I do have faith that 1) these motors can last a long time when properly maintained and; 2) I feel comfortable enough mechanically to find one of these motors. But with any used item, there is always a larger associated risk. On a side note, I work at a speed shop, so any parts I need will come through there. The selection I have is the same as what's on the net. Anyway, I'm still not 100% decided I'm going to do it yet. Part of me really wants to (I'm a sucker for projects), and the other half says these types of projects can get out of hand real fast. I need to dwell on it some more. Again, thanks for all the input so far. As previously mentioned, it is all greatly appreciated.

 

[thumpar]

As long as it is a truck motor the cam will be so close to the marine spec you would never notice. It is true that marine run stainless head gaskets but the motor will probably fail first. Unless you have twins the rotation will be the same. Internals are the same otherwise. Make sure you replace the core plugs with brass plugs and use the marine externals.

 

[zealer]

I thought of a way to (hopefully) to use a regular engine hoist. I can just back my truck up to the stern of the boat, and operate the boom from the bed of the truck. I should be able to lift the motor high enough without issue. Can then lower engine into bed, swap the strap for one that is longer, re-lift and lower to ground level onto a pallet. Or I could roll the hoist down a ramp - I have a nice one I use for lawn equipment.

 

[Rick Stephens]

Go zealer go!.

Simple enough. And if the hull and running gear is in good shape, well worth it. Having money is way over rated.

Rick

 

[zealer]

Thanks. Will take pictures and update once I start. Ideally I'll commence this weekend.

 

[500dollar744ti]

You can always deflate your trailer tires to get a few more inches as well.

 

[zealer]

That's another good point I hadn't thought of. I was out tonight on the driveway further inspecting the project I am about to embark on. The critical process of this entire operation is getting the motor out and back in. In this case, access to it is quite poor. The motor is so far recessed under the swim deck (1 piece moulded fibreglass) that the flame arrestor on the carb is even under the mold. My plan is to remove carb and manifolds while engine is in boat, and that ought to get me enough clearance to take it out (ever so gingerly). I forgot to snap a pic of the exact configuration, but it is similar to the following: (mine is farther recessed)

 

[zealer]

Here is an actual picture of my setup.

 

[achris]

OMG!! Batwings!!! You need to get those off the new engine or they'll kill that one too....

 

[NHGuy]

I bet you end up undressing that motor, removing the front mounts one at a time and rigging something to slide it forward far enough to pick up.
What a cluster!
Since installing it back in will be such a pain, I'd recommend running the replacement motor outside the boat before putting it back in. You can check for oil pressure, noises, smoke etc that way.
I did a cam run in that way in my yard on a jig I made out of 2 x8's.

 

[zealer]

OMG!! Batwings!!! You need to get those off the new engine or they'll kill that one too....

Hah, I had to look up what you were talking about. At first I thought you were talking about a dead bat somewhere... I was unaware there is 2 types of exhaust manifolds. I wasn't planning on replacing the manifolds, but I didn't know about the problems this model can cause. I've removed them from the motor and will test them this weekend. I read that using acetone is a great way to check for cracks. They look to be in decent shape (even the exhaust gaskets looked relatively unused). I'm hoping I can at least finish the season with these bat wing version. I don't really want to spend the coin for the conversion kit right now. --- NHGuy, that is exactly my plan. Remove carb, exhaust manifolds and pray I have enough room! (I think I will). Running the motor outside is a good idea, but I'm not sure how I would go about doing that - hooking up the water and gas in particular.

 

[zealer]

Did some more work today. Almost ready to lift engine out. Need to disconnect seawater inlet and some wiring harnesses, otherwise I'm good to go. They sure are hard to see at the back of the engine,especially due to that fibreglass deck. My original plan of using the cherry picker from my truck is not going to work. The legs of it are too long (in front of boom) and therefore will not be able to get boom close enough. I will use a chain block instead. Next I need to compile a list of what gaskets I'll need for reassembly.