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Mercruiser 43 v6 Block

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wmbock

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Can I use an automotive block

Can I use an automotive block and crank to replace my marine block or are there major differences in the durability?Physically they look the same.
Thanks Bill
 
"This is always an interesting

"This is always an interesting question.
If you are talking just the block that should be no problem.

But you should check both blocks over side by side closely to make sure that all the holes etc you are going to need for accessories, motor mounts, etc are there on the automotive block.

As far as internals, a marine cam is different, and I suspect the pistons, rings and rods are different. Marine engines use stainless head gaskets, and brass frost plugs instead of steel, just as examples. The flywheel may also be different; perhaps someone else here knows this for sure.

For my money I would find a rebuilt engine with marine spec components, and avoid the aggravation. What's wrong with your current marine block?

Rod"
 
"It's been discussed here

"It's been discussed here recently w/a variety of opinions. A "marinized" auto/truck engine has had a number of parts upgraded to withstand the corrosive salt/lake water environment. A number of stainless steel parts are used for corrosion durability. The block casting plugs are brass and not aluminum or tin. The cam is ground differently to close the valves quickly. Engineering includes consideration of the fact that the engine is run above 3,000 RPMs most of its life while a car/truck engine is mfgd. to run below 3,000 RPMs. Good luck if you do use it."
 
"[b]"Physically they look

""Physically they look the same."

Ayuh,.....

Because they Are the Same....
The Basic Block,+ Crankshaft anyways....."
 
My problem is I bought this bo

My problem is I bought this boat and it turned out the block was cracked from not being winterized I took it to the machine shop and the tech said it was the same as an s10 he set me up with a block crank and pistons from an automotive application and I used my original cam.Now 5 years later I'm developing a deep knock like a main bearing I was concerned perhaps the compression ratio or stroke was different and that caused my problem after a few years of use? maybe it just bad luck Thanks for your help Bill
 
"If it ran fine for 5 years, t

"If it ran fine for 5 years, there were no major issues that were different enough to warrant. Why in "H" didn't you tell us all this in the first place?
Sounds like you have a bad main bearing, or con rod big end bearing.
You're going to need to tear it down to find out whats ailing it.
The longer you run it the worse it will be to fix, and you may drop a rod and trash the whole block.

Rod"
 
Thanks much I'm not runnin

Thanks much I'm not running it anymore until I tear it down I just wanted to make sure the car stuff was ok or I was just going to buy a marine short block and not waist any more money on that block.It's easy to find car specs but I could'nt find marine compression ratio. I was afraid maybe it was too much stress on the bottom end.I've been a Nissan Tech for thirty years but I dont Know much about marine.Do you know what top speed for that boat should be it is a 1989 rinker captiva 206 I put a 4brl carb on it last year but it still only hits about 35 mph does that seem right? Thanks Again Bill
 
"[b]"It's easy to find

""It's easy to find car specs but I could'nt find marine compression ratio. I was afraid maybe it was too much stress on the bottom end."

Ayuh,.....

Basically,.... Run of the mill production Boat motors are whatever Chevy was putting into pickup trucks of whatever vintage you're talking about......."
 
"I would guess you should be g

"I would guess you should be getting more like 45 mph, but that depends wholly on the weight of the boat.
What WOT RPM are you seeing? YOu should be able to hit 4600-4800 RPM with one person on board.
What prop do you have on it?
Your drive ratio is likely 1.84.

My guess is that by the time you mess around repairing the 4.3 (especially if it has a few hundred hours on it), you would be better off buying a rebuilt drop in marine engine. You could save some money by buying a long block and swapping over your accessories and manifolds, but if you get a drop in package you are starting with all new parts. That should get you several seasons of "troublefree" boating (whatever THAT is!)

Rod"
 
What prop are you using? I ha

What prop are you using? I have a 19' w/a 4.3L and a 2 BBL that weighs over 3200 lbs. I use a 3 blade 21 Pitch 15.25" SS prop and get 40+ MPH on calm water w/the OD trimmed to the limit. It has a great hole shot w/only 175 HP.

Just curious; what oil/weight and filter do you use if I may ask?
 
"One more note: I can only re

"One more note: I can only reach 4400+ RPM. When I switch to a 19" Pitch, my RPMs climb but I loose my hole shot and top end speed."
 
I Have a 19 pitch 4 blade prop

I Have a 19 pitch 4 blade prop my rpm top is 4000 and going by the speedo 35 mph I'm not sure how accurate that thing is though.I'm using 20w50 oil.
 
"I bet the 4 blade gives you a

"I bet the 4 blade gives you a quick hole shot but they are lousy on the high end for speed.

Try this attached prop finder from Rod. Just select your boat and insert the highlighted data.

<center><table border=1><tr><td>http://www.marineengine.com/discus/icons/mime_msexcel.gif""" align=left alt=""application/vnd.ms-excel"">prop finder
[url=""][b]Copy of Boat_Speed_Finder-79780.xls[/b][/url] (22.5 k)</td></tr></table></center>"
 
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