Ran 305 low on oil and now making knocking noise under load

[mxguy132]

So I ran my 305 crate motor that had 17 hours on it very low on oil.:mad-new:
There is a non-threaded hole in the bottom of the plastic timing chain cover (Most likely for a sensor for GM truck). My boat does not require this sensor hole.
The crate motor came with a flimsy plastic shipping plug that when I asked an auto mechanic what I should do, he said use that plug and gasket silicone to hold it in with. I was a little unsure but being a Carpender asking a professional mechanic his opinion, I wasn't going to argue.
Well.... 17 hours into a perfectly running motor the plug let go at cruising speed (2500 RPM) for a very short period of time before I noticed there being a problem and shut motor down .
I opened the engine cover to see the plug and most of the oil in my hold. I towed the boat to the nearest Shoreline and drove to the closest automotive store and bought a frost plug that fit the size of the sensor hole with oil.
I thought I might've done little to no damage as I caught the problem right away but when I put the frost plug in and filled it back up with oil, I took it out and now makes noise under load (getting up on plane)
I did a compression test and everything checks out on the top end. plugs look good and got a even compression at about 180 on all 8.
I'm thinking it's main bearing and crankshaft that let go. Anyone else have any other opinions on what the common is on running to 305 low on oil before I start buying parts and pulling motor out???
To top it all off, the previous boat owner must have disconnected the audio alarm for the oil/overheating as I might've shut the motor off a few seconds earlier if the audio alarm went on.:mad-new::mad-new:​

PS

This is a freshwater boat

 

[biggjimm]

Sounds like main or rod bearings. Probably the mains since its knocking under load. Probably get by with a crank polish & new bearings but might need turned if the journal got roughed up at all. Machine shop will mic it & tell you when you get her pulled out. Hate to hear that on a new 17 hour engine. It's ashame your mechanic advised you to leave that silly plug in there. If you still have your old timing cover I'd change it if it's the same other than thath crank sensor hole or whatever it is. Good luck with it! Jim.

 

[flipbro]

Got an oil pressure gage? What's it reading ? If you've damaged bearings chances are good you will have low oil pressure.

 

[alldodge]

If you have a solid knock, its a con rod bearing. Your not going to be able to fix it with other lubes or adjustments. A real bummer

As filpbro mentioned, what's your oil pressure?

 

[mxguy132]

My oil pressure is good. reading normal at 175

 

[mxguy132]

Sounds like main or rod bearings. Probably the mains since its knocking under load. Probably get by with a crank polish & new bearings but might need turned if the journal got roughed up at all. Machine shop will mic it & tell you when you get her pulled out. Hate to hear that on a new 17 hour engine. It's ashame your mechanic advised you to leave that silly plug in there. If you still have your old timing cover I'd change it if it's the same other than thath crank sensor hole or whatever it is. Good luck with it! Jim.

Ya, there was a core fee with the new create moter and gave them the cover with the old block

 

[biggjimm]

Ya, there was a core fee with the new create moter and gave them the cover with the old block

Maybe you can source one at a salvage yard or even an aftermarket one at an auto parts store to get rid of that hole so you don't have to worry about this happening again once you get it fixed.

 

[ericcarr2000]

Oil pressure at 175.... I'm assuming you mean compression right?

My oil pressure is good. reading normal at 175

 

[81 Checkmate]

My oil pressure is good. reading normal at 175

Thats quite the oil pressure- Are you sure thats not the temp gauge reading?

 

[flipbro]

I believe he may be talking kpa rather then psi.. But 175 kpa is still kinda low unless that's just at idle.

 

[c1steve]

If you lost most of the oil, and the knocking is somewhat low pitch, I would expect the connecting rod bearings have been damaged and probably the crankshaft as well. Plan on disassembling the engine and having a machine shop check the crank for wear. Anything other than a mirror finish on rod or main journals indicate that the crank will have to be ground or polished.

Ideally it is best to have the alarm hooked up before anything but a very short test run.

 

[mxguy132]

I believe he may be talking kpa rather then psi.. But 175 kpa is still kinda low unless that's just at idle.

I'm back working on the boat today and that last oil pressure comment was a typo. Was extremely tired that day and sunstroke. I just bought a new compression tester as my old one wasn't reading proper. Compression PSI was between 175 and 180 and oil pressure cold was at 50 PS

 

[smokeonthewater]

Sad to say but the engine needs to come out and be torn down for repairs... Don't run it even 1 more second as the cost of repairs may be going up fast.

 

[mxguy132]

I took the motor out yesterday and found out it was the number one rod bearing let go. So at this point I'm into crankshaft, rod/main bearing, connecting rod.

I haven't flipped the motor around to inspect the intake/valve area but the lobes on cam looked good and hopefully all the shrapnel stayed in the bottom of block


PS This forum crashed and freezes every 30 sec:mad-new:​

 

[Bondo]

found out it was the number one rod bearing let go. So at this point I'm into crankshaft, rod/main bearing, connecting rod.

Ayuh,..... Long Block it with a 350 crate motor,.....

 

[mxguy132]

Sad to say I priced out what it would cost to buy the parts and Machine time compared to buying a new crate motor and the crate motor wins.
Anybody want a really heavy paperweight?!

 

[flipbro]

Really? Crank machined 150 bucks new rod and mains 100 bucks new oil pan gasket and rear main 70 bucks some green plastigage 2 bucks a socket set and torque wrench and you're good to go. No need to rebuild the hole thing. Unless you found other damage.. Even if it needs a new rod pressed on its still cheaper.

 

[mxguy132]

Sad to say I priced out what it would cost to buy the parts and Machine time compared to buying a new crate motor and the crate motor wins.
Anybody want a really heavy paperweight?!

 

[alldodge]

Since you only have 17 hours on it maybe a short block.

Will admit, I would be tempted to just send it to the machine shop

 

[mxguy132]

Sad to say I priced out what it would cost to buy the parts and Machine time compared to buying a new crate motor and the crate motor wins.
Anybody want a really heavy paperweight?!