4.3 Lower End Knock Knock no joke

[saltlydawg]

I have a 1990 4.3 liter Alpha one Gen one, which developed a knock and has been diagnosed as being in the lower end. My question deals with the various options for getting the boat back to operational status.

I know as an aircraft Mechanic many times we will do a top end overhaul or a lower end overhaul. Is the case with marine engines as well? So here are the options I am exploring.

1. Remove the crank have it ground get the bearings and replace any corresponding rods, which may have been elongated when the bearing spun. Since I am there add a new oil pump.

2. Have the local machine shop do a rebuild, which the quoted $750 with .30 pistons my cam, marine gasket set and brass plugs.

3. Rapido Marine $1450 delivered.

4. Thought about a truck lower as a Donner, but I am apprehensive based on the fact those block have a 100,000+ on the parts and who know how well they were maintained.

As always your input is greatly appreciated.

 

[BAproject]

Re: 4.3 Lower End Knock Knock no joke

It's hard to say and I'm not a mechanic, but with an engine that age (Mine is same engine, 1 year newer and overheats, fearing blockage in the water jackets) if you're going to get that far into it, might not be the worst thing to replace the block.

Sounds like you know what you're doing and you can probably find a block, ready to go, in that price range...then use everything else from the old 4.3 (assuming they are in condition) and you basically have a new motor!

IMHO

 

[Silvertip]

Re: 4.3 Lower End Knock Knock no joke

I've seen cranks with the bottom end of connecting rod seized to it and it was repaired and returned to service to live a very long life. Cranks can be rewelded, reground to factory spec so just because it spun a bearing does not mean the crank must be pitched. that work also does not cost a fortune. But since the engine is out, mic the cylinders. If within spec, deglaze the cylinders and re-ring the engine. You can even get .002 over size rings through GM if things are on the high side of the tolerance. That by the way does not require a rebore. Freshen the heads and go boating. A machine shop can hot tank the block to clean it up inside and out. Yes -- if a rod is damaged it should be replaced. In your case I see no reason not to rebuild this motor since you have a known block.

 

[Bondo]

Re: 4.3 Lower End Knock Knock no joke

Ayuh,..... #3 is the Quickest, Easiest....

#1 will still require most of option #2 anyways, so call it pretty much the Same...
There's no doubt Metal that's passed through that motor,...
A tear-down, cleaning, boiling, cleaning is needed...

#4 is Ok for a quicky fix. if the intention is option #2 during the off season...
A pickup core motor sounds better than a core motor, with a known Knock...

 

[saltlydawg]

Re: 4.3 Lower End Knock Knock no joke

Ayuh,..... #3 is the Quickest, Easiest....

#1 will still require most of option #2 anyways, so call it pretty much the Same...
There's no doubt Metal that's passed through that motor,...
A tear-down, cleaning, boiling, cleaning is needed...

#4 is Ok for a quicky fix. if the intention is option #2 during the off season...
A pickup core motor sounds better than a core motor, with a known Knock...

Bondo, I forgot about all that stray metal traveling through the engine passages. Well it is out of the water and I have time on my side so it looks like rebuild or Rapido Marine.

Thanks everyone who chimed in.

 

[FreeBeeTony]

Re: 4.3 Lower End Knock Knock no joke

I vote for #3 also............just passed 190hrs on my 5.7L Vortec from Rapido.

 

[saltlydawg]

Re: 4.3 Lower End Knock Knock no joke

I vote for #3 also............just passed 190hrs on my 5.7L Vortec from Rapido.

Good to know, I have heard a lot of good things about Rapido and honestly it is twice the cost of the rebuild but I think a better option.