4.3 mercruiser rebuild vs reman

robg87

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Joined
Sep 23, 2014
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4
Hi guys, I just bought a 93 celeberty with a 4.3 mercruiser. I bought it knowing it needed work, exhaust manifolds and the starter reinstalled. I reinstalled the starter and checked the compression (before spending money on the new manifolds) both sides had one about 150 and the others were between psi 30-60. I put air to each cylinder with rockers removed, not only did I find leaking valves but it caused a slapping sound, like something was loose in 2 of the cylinders. Nevertheless the motors out and on the stand and ripped down with no major signs of something wrong other than a few stuck rings. Has anyone rebuilt one? Or is just as cost effective to buy a reman longblock?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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47,296
Welcome aboard

the longblock is almost identical to a GM truck longblock except the cam, head gaskets and core plugs. The truck cam will be close enough if you want to go the low $ route. the core plugs on a marine motor are brass.

Will you be rebuilding it yourself? if so, find a competent engine builder near by for the machine work. if your rebuilding, I would search for a 1996 or newer heads to get the vortec combustion chambers. this will require a different intake. If you are buying, plenty of places such as michigan motorz and rappido marine sell motors

I myself like to spec the rebuild vs buying off the shelf. depending on time, I usually do the tear down and re-assembly myself, except for the heads - I just have my local shop redo them.
 

sharkin95

Petty Officer 2nd Class
Joined
Jun 2, 2007
Messages
106
Since it's out send the block out to a machine shop for rebuild with the heads when it comes back install a new oil pump replace all gaskets and re-assemble. Break in 10-20 hrs stay under 3000 rpms change oil replace with Mobil 1 or 20-40 wt oil ...........RUN IT LIKE YOU STOLE IT.
 

robg87

Recruit
Joined
Sep 23, 2014
Messages
4
Thanks guys! I planned originally just buying the long block from rappido and reassembling it my self but since everything looks ok I might just send it out, and put it back together myself. I was told 250 to clean, check, line bore and bore cylinders does that sound about right?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,296
sounds about right. you will need new core plugs, pistons, bearings, gaskets, oil pump, timing set, etc. your local machine shop can get you those components.
 

boatnut74

Lieutenant Commander
Joined
Aug 29, 2010
Messages
1,835
I got my 4.3 long block rebuilt for $950. It was bored .030, vortec heads redone, polished crank, new flat top pistons, bearings rings and assemble the short block. I know a reman long block is around 2200. If you are willing to wait a month or so at the machine shop you can save some money.
 

robg87

Recruit
Joined
Sep 23, 2014
Messages
4
Was that with all the new parts? Were did you order your parts from? How extensive was the work on the block and heads?
 
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