The other day, I knocked out the oil galley expansion plug from my 5.3 block with a long rod from the back as I have done several times before (albeit not on this particular block). But while the plugs have always come out clean before, this one looks like it must have gone out crooked. It built up a NASTY sharp edge, which I tried to file down. But the gash is just WAYYY too deep to clean up.





The plug itself looks like it was extra sharp, and may have been prone to catch unless extreme care was taken - care I guess I didn’t take because it has never been a problem before.




But the damage is done. What would be the best way to fix this? Have a machine shop TIG weld and recut the hole? Have the hole tapped for a screw plug like this one?



Or just stick a stock plug or something meant for the stock hole such as this


and hope and pray the thing build oil pressure when started and that I don’t lose oil pressure somewhere, say, 50 miles out of Eureka, Nevada?

 

Or, you could smear the inside bore of the hole with something like JB Weld and then tap in the new plug while it is still wet.

 

I tapped mine for a threaded plug. The OEM plug is basically a Welch plug, made to be inserted one way only. If the engine is on a stand, you could push it towards the back of the block with a long steel rod, or maybe a wooden dowel. I'd use steel. Anyway, it's supposed to lock when pushing forward, or oil pressure would be able to push it. It should slide easily towards the rear of the block. I've never done this, so maybe someone who has will chime in......

 

Something else I noticed about this LH6 block. Take a look at the hole from the front.




Notice that the surface is highly indented between about the four and ten o’clock positions. This corresponds EXACTLY to where the plug caught and gouged the bore. This indentation also exists on other blocks I have, but is more even and less pronounced. Take a look at my 6.0 block.




And my 6.2 block.




On the 6.0 block, the indentation almost completely encricles the hole and is a whole lot less deep. And the 6.2 has very little indentation on the bottom. My guess is that this indentation was an effort on the part of GM to stake the plug in there so that it couldn’t pop out. Because the staking was SO heavy and to one side on the LH6, that side of the plug dug in and gouged the bore when removed. The more even and less heavy staking on the LS2 and almost nonexistent staking on the LS3 meant the plug could pop out without incident.

This might be something to look out for before hammering this plug out on your block. MAYBE it wouldn’t have cocked if more even pressure could have been provided, or force could have been applied to the staked side. But I am not sure how much could have been done to prevent this on that particular block. In fact, I would say that, if you have thin indentation, LEAVE THE PLUG ALONE. You can still clean the galley quite well with a long brush if you remove the plug at the front passenger side. By removing this plug, you can clean the blind end of the long galley quite well. And by not gouging that bore, you will save yourself LOTS of headaches and worry (and potentially lots of money to fix it).

 

You can’t push it back. Take a look inside the hole.




As you can see, it bottoms out maybe a quarter of an inch down in order to keep it from blocking off the oil galley coming from the pump (left in this picture).

In any case, if you pop this plug out, I would NEVER replace it with a new one. If the hole isn’t damaged, a plug (such as this one from Sac City Corvette) is a far better option.

 

I would call a machine shop and see if they have a reamer that would take it up to the next plug size or thread it,, the press in plugs were for ease of assembly on the line. nothing sacred about them. Either way to do it 100% right,, I would want to be able to flush the galley after any cutting went on including the damage from driving the plug out.. YMMV

 

DEFINITELY thread it. I will NEVER, EVER, EVER use a Welch plug in an LS motor again. Something like this looks like a GREAT solution.

 

If what I'm seeing is a straight pipe thread, they make a special cutting tool that has a slight tapered angle on it at the end of the special tool. Anyway, that provides the surface the O-ring seats, and seals on. Without that angled area cut into the block, the O-ring has nowhere to go. There has to be an angle, sort of like a small chamfer, or a counterbored area, for the O-ring to seal on. But it will work great once done. I'm sure Grainger, McMaster-Carr, or a place like Mid States Bolt, could explain it much better than I am, lol......

NOTE!!!!!!! I used an old fashioned, tapered pipe plug, which I don't recommend!! If you tap the thread too deep, the plug can possibly go in far enough to restrict the feed galley from the oil pump. I had to grind/face the threaded end of the plug shorter than normal, to avoid this. It's been over 10 years, and when you can't remember what you ate last night for supper, 10 years can be challenging, to say the least!!! If I had it to do over, I'd use the straight pipe, as shown in the pics above. The reason I didn't is that I couldn't borrow the special tool from work at that time, and I was in a hurry. Should've waited!!