Rebuilding own engine

rcon

rcon

New Member
Jun 16, 2011
481
Adelaide
Boat Info
Preparation
'93 300 Sundancer
w/ Kohler genset
Raymarine E7D
Engines
4.3l Mercruisers w/Alpha 1
I recently had my port engine let go and so this week a new (yeah, not reman but that wasn't my idea - I'd have got for 2x reman 5.0l V8s) mercruiser is being dropped in. This of course gives me something to play with in the shed for the next 6 months until I need to replace the starboard one (which has started leaking oil in my bilge :smt021)

So, what setup do I need to rebuild a 4.3l V6 mercruiser?
Any special (as in unique for a marine motor, I can research the basics myself) tools?
Anyone got a pic of a bench/shed setup at home that worked for them?
Is this worth doing or will I spend as much on parts/machining as I would on a reman engine.

Pretty sure it "dropped a piston" whatever that means. I'm off to talk to the mechanic Saturday morning so will get some idea of what is in store then but if anyone has some background reading I'd love to get started.
 
Er, if there is a mod around, could you move this to the gasser forum?
 
I suggest start with a good engine rebuild book. There is nothing unique about the 4.3L. It is basically a small block Chevy that is missing two cylinders. I would disassemble everything and inspect the parts before investing any money. If you have piston problems the block may be trashed. Also if the engine is salt water cooled you may want to start with a new block anyway. My guess to rebuild will run you around $3K (here in the US) for machine work and parts.
 
saopm said:
I suggest start with a good engine rebuild book. There is nothing unique about the 4.3L. It is basically a small block Chevy that is missing two cylinders. I would disassemble everything and inspect the parts before investing any money. If you have piston problems the block may be trashed. Also if the engine is salt water cooled you may want to start with a new block anyway. My guess to rebuild will run you around $3K (here in the US) for machine work and parts.
Click to expand...

Great advice! An engine stand is handy & cheap to have. Salt water in a 1993 block means the block could be shot if it's fresh water cooled. I'd do a new/reman short block if the heads and intake are ok. If not, a long block is the way to go if you want to be an engine builder the easy way. Boring out a bad cylinder and changing pistons and bearings has to be done right the first time, Mike.
 
Salt water boat with raw water cooling. Can I scope or somehow asses if the .... heat exchange(?) part of the block has deteriorated beyond repair?

I'm a little sh!tty my old man elected to go new without consulting me in the end, but I've got exams (I work full time too so this week was not the week for me to rush around with boats and its the start of the season here!) this week and I asked him to take care of it for me *rolls eyes*. I doubt very much I'll ever have the coin to drop another, new, 4.3l V6 in the other side, so i'll have mismatched, and slightly underpowered, engines from now on. For the coin we're going to be up for, plus another 25-30%, we could have had two, reman, 5.7l V8s in there with some reuse of parts. New MerCruiser engines, even TKS ones, are not friggen cheap. But, old man wanted the security of new + warranty and its done now, so we need to make the best of it.

The idea of having the engine in the shed for rebuild is two fold,
1. Being new to boating, I want to work out how they're put together properly so I'm able to make better decisions in future/emergency repairs on the water.
2. The idea of having 3 engines, two in the boat, one being rebuilt as a spare is appealing. Sounds like it might be easier/cheaper to just buy a reman and swap the "tin wear" over?

Perhaps I'll buy a runabout and drop a home rebuilt 4.3 in there....? :)
 
The intake manifold and therostat housing will show the extent of the internal corrosion. Take them apart and look inside. My freshwater 1990 7.4L/454 shows some corrosion in those areas but not to the level of replacement. My 1988 5.7L/350 is also the same, Mike.
 
Buy a factory rebuilt motor and use yours as a core. You will be money ahead.
 
There is nothing more satisfying or educational than rebuilding your own engine. My best friend lost a piston in his 1987 4.3L. It would appear at this point it was due to detonation. We have pulled both engines and I am going to teach him how to rebuild over the winter.

The post about the engine stand is spot on and a good investment. The rebuild book is a must as there are a lot of parts that have tight tolerances. Many parts will need to be measured to determine the amount of wear. Many of these tolerances are in the .001" (.025 MM) range so you will be doing a lot of measuring.

The discussion of short blocks, rebuilt heads and many other issues is something you will need to sort out on your own. I would start by buying the book and read it. That will help you decide if you are up to the task.

Cheers, Gary
 
I have rebuilt engines for a very long time, there is some great advice here. If you are not technically inclined you may want to let someone else, machine shop do it. You have to also consider you have counter-rotating engines. One turns port, the turns stbd. Differant parts.
 
I would get a factory reman long block and swap over all the parts. Money in the bank. Too much can go wrong and you would be back in the same boat so to speak.
 
I rebuilt my 4.3 that was seized. Got the parts from parts dinosaur. Com. Piston rings and bearings are the same as used in 4.3 truck engine freeze out plugs and cam are different in a marine eng. the only thing you have to ck is the dept of the rings. Also use plenty of eng assemble lube. When reassemble happens.
 
Please excuse my ignorance here, but what is the meaning of "Long block" or "short block"?

I also see mention of "bobtail" here and there.
 
rcon,

I have rebuilt many motors and will say I admire your ambition, but you might be better off not doing this yourself. If you do, raw water blocks are usally not taken as "cores" for a reason. My suggestion is to take everything to a reputable machine shop for motors ans they can give you an estimate of the machine work and if its worth saving stuff like the crank, block, etc.

To answer you (abbreviated) - Long blocks are usally an engine block complete with heads. This means crank, pistons, oil pump, timing chain, cam, lifters, etc. Check each manufacturer - some include "tin" which is timing chain cover and oil pans. The rest of the parts are taken from the existing motor.
Short block - no heads or pushrods.

I included a link as an fyi only- i have purchased a lot of parts here but no motors. Look around to get an idea of prices.

http://www.perfprotech.com/lb-43l-rm-86-92-14149r5/product/69298
 
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I would also recommend not trying to rebuild the bottom end yourself.

If you choose to tear down the old motor for your own educational benefit, then so be it. I would leave the assembly of the bottom end to a reputable builder or machine shop.

You would be money ahead to buy a new short block and assemble the engine yourself. Your would probably learn just as much as doing the complete rebuild yourself as well.
 
Thanks guys, this is all fantastic information.

I think I may have oversold my ambition here, I certainly intend to enlist profession machine shops where required.

Also like the idea of stripping my block and "playing" whilst building up a professionally reman'd short block with any parts that are still workable.
 
As mentioned by a few others it would not be a good idea to rebuild a 12 years raw water cooled engine, especially if it's been run is salt water. It will fail due to corrosion before it wears out. Check out Jasper Engines. I've heard great things about their reman engines and I think they may not require a core. Good luck.
 
19 year old engines, and I'm starting to get that picture! :)

Had a look at the engine this morning, and I'm told the issue is detonation, does that sound right? One "cylinder" has a hole in it and you can see it starting on the next cylinder over.

Thoughts?
 
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I have a bad feeling about this rebuild, but you have to start some ware or you never learn anything.

you were running to lean can cause the detonation.
 
There's a hole in the piston,
Dear Liza, dear Liza
There's a hole in the piston,
Dear Liza, there's a hole.
Click to expand...
attachment.php
 
How many R's did you run that thing and for How Long?
 
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