I swapped 4.3l truck motor... now questions

[Knsierraa]

After swapping a truck motor 4.3l on my 1987 rinker 18 openbow I ran the motor up to 4200 rpm for about 20-30 seconds after about 2 hrs of break in run time then it dropped about 200 rpm I now have a knock in the lower end.
My question then...is 4200 rpm to much to expect and exceed the limits of this motor being from a truck of the same vintage. Is there a limit of RPM and did I exceed it?(Opinion of my mechanic) I'm leaning towards oil pump/pressure. After all the reading I have done I see no related topics covering this issue which again leads me again to oil delivery. If it matters the prop is stainless at a 21 pitch. The original motor used to pull 4500 rpm.

 

[dubs283]

Re: I swapped 4.3l truck motor... now questions

the oiling issue could be what happened, i have heard that some oil pumps don't keep up as well as others at higher rpm's

there are over 40 different versions of the 4.3L as well so it is important to make sure the cam is the same

was this a rebuild or just pull and install?

 

[Knsierraa]

Re: I swapped 4.3l truck motor... now questions

it was a pull and swap with changing all the externasl but i think with the truck oil pump

 

[dubs283]

Re: I swapped 4.3l truck motor... now questions

well, i guess you did not know the condition of the internal components of the truck long block, so its a WAG as to what went wrong

some folks here will say truck 4.3L long blocks are exactly the same as marine long blocks and others say they are not

myself, i just know that mercruiser orders long blocks from GM, the main difference being the camshaft and wrist pins in the long blocks (what i am told by marine engine rebuilders)

as far as GM making the long blocks any different, your gonna have to ask GM

 

[rs2k]

Re: I swapped 4.3l truck motor... now questions

You really should have a high capacity oil pump. I don't think any 4.3 should have trouble with 4200 or 4500 RPM as max.

 

[thorbuilt1]

Re: I swapped 4.3l truck motor... now questions

its a whole different cam for marine on the 4.3 all you need is different cam and brass freeze plugs you may need a different gasket set if your going in salt water but i think you'd be ok if your rinse it good

 

[thorbuilt1]

Re: I swapped 4.3l truck motor... now questions

just as long as you keep your manifold <intake> everything will bolt right over...i went from a 95 4.3 to a 97 4.3 and they changed the oil pan design the newer model 4.3's are much lighter

 

[Knsierraa]

Re: I swapped 4.3l truck motor... now questions

so nothing about rpm limitations then...sounded a little like a cover to me on the bearing daamage on the crank

 

[rs2k]

Re: I swapped 4.3l truck motor... now questions

When you tear apart the motor you can tell if it was an oil problem, clearance problem, or RPM limitation when you inspect the spun bearing. Each problem causes different types of scaring. I'm pretty sure it's not an RPM limitation problem. The out drive would have gone out before the engine would have.

What type of oil did you use? 10w-30 can foam up and cause bearing damage in high RPM high load situation.

 

[Knsierraa]

Re: I swapped 4.3l truck motor... now questions

the answer to the oil was full syn that was rated to 15,000 like I said it a had about two hrs of run time a low to mid rpm. the damage was on the inner two bearings...the explanation was that at high rpm the demand could not supply to the inners? because of demand /supply

 

[ryendube]

Re: I swapped 4.3l truck motor... now questions

redline is 5200 on that motor and aswell the factory marine motor uses the same oil pump as does the truck motor

heres a link to all the info on that motor

http://www.bucksengines.com/Data/24.pdf