4.3 knock after fuel pump replacement

[Mithories3980]

Hey folks.
Finally got a 4.3 for this boat in good shape, finally got it mounted up and running like a champ. Get it on the lake (8 hours from home... ), fuel pump goes... sent probably a gallon of fuel into the oil.
I was running it at full throttle and heard a tick start, and at the same time started loosing RPMs. Shut it down and got a tow back. Went to a local marina and got her a new fuel pump, drained the nasty oil. Put a new filter on and new oil (15-40. Probably not the best but it was the best i could get really). Idled it very gently on to the trailer and got it where it would be easier to work on. We then flushed another 2 oil changes through (8 quarts) and put another new filter on. After all that the oil looked pretty good. I'm sure another changed would be the best but at this point I was comfortable running it to make sure everything sounded pretty.

Back in the water we go. She fired up and runs really well as normal, but around 1800 rpm I get a nice rich, loud knock... sounds like it's on the lower starboard side...it didn't knock like that when I shut it down on the water, and I was at 3000+ RPM. So did I install the fuel pump wrong? Would the engine run that well if I have? Or did the fuel and oil situation take out a bearing? I didnt want to run it any more at the time but i can fire it up to get more details. It also sounds like there's a tick in the background somewhere but I'd rather worry about that after I get this knock figured out...

it's a 1990 Mercruiser 4.3

 

[Mithories3980]

Also forgot to mention, even at idle I briefly noticed the oil pressure was very high. Much higher than it had been running even at almost full throttle.

 

[Rick Stephens]

I wouldn't have thought to do multiple oil changes. One would get 99.9% of the gas out and the rest would fairly rapidly evaporate. But on to the real issue, what is happening inside. 50/50 gas oil isn't a great lubricant.... but if you caught it fairly quickly, it should be enough for a little while. Unfortunately the little while was at full load and RPMs. I'm not going to blow daisies your way. If you have new ticks and knocks you may very well have rod bearing damage.

 

[Mithories3980]

Small update.
We have lots of heavy rain coming tonight and I left the cover in my brothers truck, so I had to back her in the shed away from water. Figured I'd fire it up briefly before I did.

Someone asked me if I had the drive all the way down, thinking it was just the u joints rattling. Just to cover all my bases I made sure it was down.

At idle, oil pressure is 60, and I can hear a gentle rattle I suppose, at the front. Run up to about 1500 and I think what I'm hearing is the same rattle, just getting much worse into almost a knock. Thats where I shut it down .

So, crank bearing? Or still maybe rod bearing? I guess either way is a rebuild I'm just curious

 

[Rick Stephens]

Takes a LOT of damage to bearings before that shows on oil pressure. I feel bad for you. I have no clue what is first failure point on a 4.3 - Like any SBC, the rod bearings seem to be weaker than mains.. However, there will be damage to all the bearings if there is damage from low lubricity.

 

[Mithories3980]

That's nice to hear, lol. Thats ok though - like I said, no matter what, this means a rebuild so they'll all get replaced anyway.

The real question here now is, if I can find a reasonable clean environment, is this something I could do my self? Or is it worth just paying someone to do it? In both scenarios, worst case, what could it cost me?

 

[Rick Stephens]

I rebuilt my 4.3L in a shop on the farm here. Dirty dusty environment that I just cover everything when not working on it. Not sure costs until you look at it, most likely a crank grind minimum, which is not a lot of $$. Need to inspect bores and see if they need anything, probably not, but without looking, that's a guess. I'd figure $500 if it's just a grind, bearings and gasket set. Maybe less, depending on the cost of machine shops in your area.

You'll need at minimum a decent torque wrench.

 

[Mithories3980]

Well after a little thinking and research... I don't care for the idea of doing a total rebuild. The fine measurements and specs such that id have to do concern me a little with my lack of experience and tools...
So I'm thinking about getting a long block. I've done a little phone calling - local marina gets them right from quicksilver - $3500. Arnold Motor supply - $2500.

Do you know anything about the Arnold Motor supply brand? Are they decent? Any other places you know of that I should look in to?

Keep in mind that this boat really doesn't get that much use (unfortunately). Ill probably be lucky to take it out twice a month in the summer. So, a motor that doesnt last very long for someone who uses it every weekend, all weekend, will probably last me quite a while. Hopefully some day that can change but I've got a lot of years to work on that

 

[Mithories3980]

Update
Engines from Arnold Motor and NAPA are ATK.

 

[Scott Danforth]

Pull the motor, get it on a stand and pull the pan

At least, new oil pump, new crank (often cheaper than reconditioning yours) and new bearings.

A new short block is $2900. A reman is a bit less