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Oil plug

5

550Doug

Member
Location
Southern Ontario
The engine oil plug on my Case 446 garden tractor (Onan engine) has been leaking, so I've drained the oil and replaced with new oil but the plug will not tighten. I thought it was a gasket problem but it seems to be a thread problem, The plug has a 1/2 x 20 thread. I've now drained the new oil and found a thin circular piece of metal that looks to be part of a thread from the engine as the thread on the plug is good.
I have purchased a single oversized oil plug to install but it seems to have a fine thread on it. I don't want to install it and wreck more threads. What is the scoop on using oversized oil plugs? A Double oversized oil plug also came with the set I purchased, but it seems to be too big.
TIA
 
I used an oversized plug on a motorcycle years ago. It worked
just fine. Whether I just got lucky or not I was pleased with the
result.
 
Your original 1/2'' - 20 pkug IS ''fine
thread'' so if your new plug is ''fine
thread'' as well it should match/work
UNLESS it's metric.
 
I had to get a over sized plug for my diesel pick up, with a diesel engine, the dealer said it is 3 thousand over, that was 20 years ago, it worked out fine
 
I think my two Onans, P218 and P220 both have a short piece of pipe screwed into the back of the block, then an elbow and six
inches of pipe and a 3/8 cap.
These are both 2 cylinders in Wheel Horses.
 
I can't answer your particular question, but the gas station that I worked in when I was young had an assortment of oversized oil plugs. It was very rare to need one, and I was a nervous wreck every time that I had to use one to fix a stripped plug/oil pan. I don't remember a single time when the oversized plug failed to fix the problem.
 
Over tightening is the problem. I had one of those oil change places tighten the plug on the truck Cat engine with aluminum pan got it in and tight with no leaks. Used other plug after that and this was 20 plus years ago. I never had a problem with the other plug striping nor the other truck. I do the oil changes and with the plug snug just let the ratchet handle be the limit of tight. Still using the same plugs on this truck and it is 22 plus years old with over a 1,150,000 miles on.
 
A few years ago I bought an entire kit of
the oversized repair plugs with taps etc
to repair my ford pick up drain plug.
Probably 60 pieces for about 2x what the
autostore wanted for 1 plug. It has been
very handy, used it several times since.
 
(quoted from post at 17:58:29 11/21/22) A few years ago I bought an entire kit of
the oversized repair plugs with taps etc
to repair my ford pick up drain plug.
Probably 60 pieces for about 2x what the
autostore wanted for 1 plug. It has been
very handy, used it several times since.
Click to expand...

google

ABN Metric Oil Pan Drain Plug Thread Repair Rethreading 114-Piece Tool Set Rethreader Tap Kit Motorcycle Car Threading

The kit does work good. Most of the time I look for a longer plug as the treads may extend into the hole. If I have my doubts get a plug in it and suck the oil out from then on.
 
Nothing to lose by trying the oversize plug.

Just be sure to use the first oversize, it is not capable of taking a lot of metal out, it is not a tap!

Be sure it goes in straight as you only get one shot at it. A crooked plug will stress the threads and leak.

And above all, grease the plug to catch the chips. Run it in, take it out and clean it. Wipe and brush out the hole to remove any stray chips left behind.

Sometimes they work, sometimes they don't. Depends on the damage, if there is an inner weld nut, and it split, nothing short of removing the pan will fix it.
 
If the thread is 1/2 x20, you can get a helicoil kit for that size and it will put steel threads in the aluminum oil pan for more durability.
 
Back in the days when I taught High School Auto classes I kept a supply of Dorman self tapping, oversized drain plugs on hand. Always had good luck with them. I Googled them and they are still available. Good luck with whatever you choose.
 
I've had good luck with expanding rubber oil plugs. Slide them in, turn a small bolt - it contracts the rubber part, expanding to fit tight.
 
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