300 6 Main/Rod bearings, etc.
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Fleet Mechanic
Joined: Jun 2015
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From: Central Michigan
300 6 Main/Rod bearings, etc.
Hi guys, I have a 1985 300 6 in my 1956 F100. The oil pan drain plug hole is stripped out- I now have a oversize plug in it that has a smaller pipe plug in the fitting- it leaks. I have seen the repop oil pans on Amazon, etc. I am planning on replacing the pan this winter. So, I MAW ( might as well) check the main and rod bearings and maybe replace them along with oil pump while pan is off. This engine runs great and no knocks or ticks. I have no idea what the oil pressure is. It is wired up thru the factory oil pressure sender to the oil light in the original dash. Oil light comes on when key on/engine off, and goes out almost immediately when engine is cranked/ starts. Sometimes when choke is on high idle it starts and sounds like a bunch of loose marbles rolling around in there- as I remember hearing on 300 6's back in the day. Noise stops as soon as oil light goes out. This engine has about 135,000 miles on it, came out of a 85 F150. I bought whole truck from original owner-(rusty). Where do you recommend to get bearings, etc. I am not going to order until I see what condition they are in. Thanks for any advice you can give? Thanks Greg.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
It sounds like on start up and the marbles is the oil filter draining back into the oil pan.
Some filters have anti-drain back valves that dont work too good as I had the same thing happening to me till I went with a Motorcraft FL-1A filter and cut that out almost all the way and mine sits for a week or more at a time.
As for the oil PSI you can add a tee out of the block and have your dash light and add a mechanical gauge under the dash so you can see just what the motor has when old and up to temp and running down the road.
A rule is 10 PSI for every 1000 RPM so 10 PSI at idle and say 30 PSI at 3000 RPM. You can have higher than that but lower is not good.
I would add the gauge so you know what you are getting yourself into if it does or does not have oil PSI and go from there.
Dave ----
Some filters have anti-drain back valves that dont work too good as I had the same thing happening to me till I went with a Motorcraft FL-1A filter and cut that out almost all the way and mine sits for a week or more at a time.
As for the oil PSI you can add a tee out of the block and have your dash light and add a mechanical gauge under the dash so you can see just what the motor has when old and up to temp and running down the road.
A rule is 10 PSI for every 1000 RPM so 10 PSI at idle and say 30 PSI at 3000 RPM. You can have higher than that but lower is not good.
I would add the gauge so you know what you are getting yourself into if it does or does not have oil PSI and go from there.
Dave ----
Tuned
Joined: Jul 2021
Posts: 486
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Like Dave above says, it can take a few seconds for the lifters to quiet if the oil filter drain valve is not keeping the filter full. I also use an FL1a, and that has been the best so far.
As far as the pan goes, with the crappy quality we see today in repop parts, I can't recommend that. Most of that stuff is made from much thinner material. If the OEM pan was 16 or 18 ga, the repop will most likely be 22 or 24 ga.
If you don't have the equipment or skillset to do it yourself, I would suggest taking the pan to a fab/welding/hot rod shop. There is a plate spot welded to the inside of the pan that has the threaded piece that the drain plug screws into. Cut that out, spot weld in a chunk of plate that you have drilled and tapped to the drain plug size you wanna use. You may also need to build up the flat sealing surface on the outside and grind that flat if it is boogered up.
But, if your existing pan has other significant damage.....then never mind what I suggested!
And if it comes down to it, best of luck with the Amazon pan. Experience tells me it'll leak from somewhere else.
As far as the pan goes, with the crappy quality we see today in repop parts, I can't recommend that. Most of that stuff is made from much thinner material. If the OEM pan was 16 or 18 ga, the repop will most likely be 22 or 24 ga.
If you don't have the equipment or skillset to do it yourself, I would suggest taking the pan to a fab/welding/hot rod shop. There is a plate spot welded to the inside of the pan that has the threaded piece that the drain plug screws into. Cut that out, spot weld in a chunk of plate that you have drilled and tapped to the drain plug size you wanna use. You may also need to build up the flat sealing surface on the outside and grind that flat if it is boogered up.
But, if your existing pan has other significant damage.....then never mind what I suggested!
And if it comes down to it, best of luck with the Amazon pan. Experience tells me it'll leak from somewhere else.
Last edited by MikeyLawless; Dec 6, 2025 at 02:13 PM.
Cargo Master
Joined: Mar 2008
Posts: 2,573
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From: Washington
I found a deal on eBay for my rod bearings. I just did rod bearings, and that's what I would recommend.
I don't believe you can remove the rear crank shaft bearing cover, with the engine in the truck.
Also be sure and use the newer style one piece oil pan gasket. There are posts on here with info. You will have to grind the pan flat.
If you do buy a newer pan , it will be flat.
I also had the head off to change the head gasket. I also replaced the rings due to extreme blow by issue.
You really should put a oil pressure gauge on it , to see what you have. I doubt that you need an oil pump. Just new rod bearings will give you an increase in oil pressure.
Jim
I don't believe you can remove the rear crank shaft bearing cover, with the engine in the truck.
Also be sure and use the newer style one piece oil pan gasket. There are posts on here with info. You will have to grind the pan flat.
If you do buy a newer pan , it will be flat.
I also had the head off to change the head gasket. I also replaced the rings due to extreme blow by issue.
You really should put a oil pressure gauge on it , to see what you have. I doubt that you need an oil pump. Just new rod bearings will give you an increase in oil pressure.
Jim
Last edited by JimsRebel; Dec 24, 2025 at 05:55 PM.
Cargo Master
Joined: Mar 2008
Posts: 2,573
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From: Washington
300 oil pan gasket information, one piece gasket.
https://www.ford-trucks.com/forums/1...l#post21638670
https://www.ford-trucks.com/forums/1...l#post21638670
FTE Legend
Joined: Nov 2015
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From: Angier, NC
It has to be 20 years or so since I bought bearings for a non-Ford and I went local parts store, not a AZ or O'Rielys when you had real parts stores
I would try a NAPA this way it there is a problem you head right back to them, try that when you buy on line.
Gaskets were also bought from that local parts store.
Dave ----
I would try a NAPA this way it there is a problem you head right back to them, try that when you buy on line.
Gaskets were also bought from that local parts store.
Dave ----
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FTE Legend
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From: Angier, NC
When you say "fine" how do you know this? Was the oil PSI good at all motor temperatures and if yes then the bearing are good too in my book.
The only way I know if a oil pump is good or not is to take it apart and measure clearances.
Dave ----
The only way I know if a oil pump is good or not is to take it apart and measure clearances.
Dave ----
Cross-Country
Joined: Oct 2019
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From: Crystal Coast, NC
Cargo Master
Joined: Feb 2004
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From: Central Texas
OML an oil pump is the most lubricated mechanical device on the whole mess! If there are no signs of advanced wear anywhere, I would not think twice about using the same pump. I'm questioning the need to even look at the bearings, because changing the mains is really not something for the meek with it in the truck. However, busting a main and rod open to look is not going to hurt a thing. Then you'll know. I'd wager they are fine.
For bearing inserts I always used Clevite, but have been out of the engine building circles for years so there may be better.
For bearing inserts I always used Clevite, but have been out of the engine building circles for years so there may be better.
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