Rebuild advice needed - Chevy / Mercruiser 4.3l

You can read about the saga that started all of this over here: http://forums.iboats.com/showthread.php?t=520824

Short story: Old original 1988 block cracked - got a replacement 1992 4.3l truck engine to rebuild into a boat engine.

Starting a new thread over here to discuss a specific matter. I'm at a cross roads and can't decide what to do. I'm hoping you guys have some good talking points so I cam make up my mind.

The truck engine I got was rebuilt once already - I knew this when I bought it. What I found, however, is that it was bored .060" oversize already. Everything looks to be in good shape once I stripped it down. I'm just nervous. I don't like that it was bored so much. I've read several posts that state you really shouldn't go past .030 with the 4.3l engine. This one is already twice that. Then again, it has been running fine at .060" for 100k miles. My concern is that it will be stressed a lot worse as a boat engine. I wouldn't hesitate putting this back in a car, but I realize there are a lot of additional stresses on a boat engine.

I did basic cylinder bore measurements, and everything appears to be in spec as far as taper and out of round. In fact, everything is coming back pretty perfect at 4.060". Then again, I just have basic bore tools, so a .002" difference could escape me.

So, here are my options:

#1: Run the shortblock AS-IS. Just throw the heads / boat intake & carb / accessories back on this block and run it. This is simple and cheap, but probably my least favorite option, because who knows the condition of the rings & bearings on this shortblock, and I could end up pulling it again to repair what I could have fixed right now.

#2: I'm being too nervous - take it to a machine shop, have them check it out, hone it, put in new rings & bearings, and be happy that I have a rebuilt motor. This is still pretty simple and a reasonable cost ($125 for rings/bearings/gasket set + machine shop cost).

#3: I have a line on another 4.3l motor within 15 miles of me for $200. Owner says it was in good running condition, and hasn't been rebuilt. It's also a newer 93/94 style motor with balance shaft (which I think would be a good thing). Strip this one down, rebuild it fully including bore it .020" if needed with new pistons, bearings, timing chain, oil pump, core plugs, etc. Probably looking at $300 for the rebuild kit plus machine shop cost.

I spent $200 on the truck engine, and I can probably pretty easily make that money back up by just selling off parts (was a full engine with accessories and Centerforce clutch on it).

Let's hear your thoughts guys.

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

Here is something to consider. Engines that have gone through a gazillion heat/cool cycles make great race engines because any distortion in the block was maximized a long while ago. So the engine was already stabilized when it was rebuilt. It has since gone through more heat/cool cycles. Since you have shown that bore and taper are well within tolerance, if that engine were mine I would install a set of ring and rod bearing and run it. Perhaps freshen the valve and a new set of springs but beyond that, you should have a good engine. Racers love to get rebuildable high mileage engines because of the heat/cool cycling that has gone on.

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

Ayuh,.... I'd probably go with option #1, 'n worry 'bout it after it blows up, IF it blows up....

While a .060 motor ain't my 1st choice, it'll get ya on the water quickly, 'n Cheaply...
At 100,000 miles, it's proven it's capable of the big overbore...
(this is my 2nding of Silvertip's "Seasoned block theory" )

Sell off all yer Extra parts, 'n buy that $200. motor that's nearby, 'n start playin' with It...

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

Thanks guys. I appreciate it. Anyone else feel free to chime in too.

Bond-o, I had thought about that option too, as I'm always on the lookout for good parts for cheap and/or boats that need work that I could flip quickly with a cheap engine replacement. Probably a ton of them every spring when they realize they didn't winterize properly. I could always slap my boat together and run it for a season with this engine, and have the backup engine being built up as I find $$$ and time to do so. I could do the Vortec upgrade as well then.

Thanks for the thoughts!

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

Hey guys... Thought I'd drop in and update the thread.

Bond-o, you're the winner.

I'm going with option #1 and #3. I bought a complete gasket set for my 92 truck engine, and I'm going to throw it back together as-is and run it for the 2012 season at least. That will give me time to get some of my interior work done over the winter that is needed. I *might* drop a set of heads off at the machine shop to freshen up just so I'm sure they are good. I've got 3 sets now, so what the heck, might as well have at least one set gone over properly.

Option #3 panned out with a nice twist. I found a 1997 true Vortec engine out of a Astro Van on craigslist, and went and picked it up tonight for $200. Had to travel 40 miles for it, but considering I haven't seen a pair of Vortec heads for less than $250, I think I got a bargin. This will be the rebuild candidate, and will either get swapped into the family boat in the fall of 2012, or find its way into a dirt cheap nice boat with a blown engine if I happen across one. I'll leave that open to whatever happens.

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

I'm curious, how did it your project work. Did you have any problems intalling the engine, plumming the heads. Did you do anything to increase HP, cam or 4BBL. I'm about to start similiar project. Thanks. Brian

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

Here is my engine build thread:

http://forums.iboats.com/showthread.php?t=520824

Everything worked out great. In fact, just got back from a week long vacation with the boat. Spent every day on the lake(s). Everything has been running fantastic - and really happy with the fuel economy too.

I didn't do anything to increase HP - I'm happy with it the way it is. Plenty of power for what we do. Plus, I was doing a pretty "budget" minded rebuild. I probably only ended up spending $500 on it after selling off some parts from the truck motor. Of course, add to that another $500 for exhaust manifolds, which needed to be replaced, but that was going to need to be done either way.

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

Struc said:

Here is my engine build thread:

http://forums.iboats.com/showthread.php?t=520824

Everything worked out great. In fact, just got back from a week long vacation with the boat. Spent every day on the lake(s). Everything has been running fantastic - and really happy with the fuel economy too.

I didn't do anything to increase HP - I'm happy with it the way it is. Plenty of power for what we do. Plus, I was doing a pretty "budget" minded rebuild. I probably only ended up spending $500 on it after selling off some parts from the truck motor. Of course, add to that another $500 for exhaust manifolds, which needed to be replaced, but that was going to need to be done either way.

Click to expand...

I have read so many of these please excuse me if I ask something you have already answered.
1) did you use the standard truck cam or a marine cam?
2) did you change freeze plugs to brass
3) 2 or 4BBL carb.

Thanks a ton Brian

Re: Rebuild advice needed - Chevy / Mercruiser 4.3l

1) Used the standard truck cam, lifters, pushrods, and heads (rebuilt). Never pulled apart the shortblock at all. Inspected the cam to make sure it wasn't worn through the lifter galley. Never even pulled a rod/main cap. Didn't want to deal with mic'ing everything out and getting new bearings. I heard the engine running before I took delivery, and was satisfied it was in good enough condition.

2) Engine had been rebuilt previously, and had brass core plugs in it already, or I would have had to change them.

3) 2bbl Merccarb - standard 175HP setup