Oil Galley Plugs, Conventional Wisdom Options

[adolimpio]

I've read a few threads about the plugs, but there were some competing opinions, so I would like to ask for the latest thoughts.

1. What sealant should be used? One thing was clear - NO TEFLON. The most compelling suggestion was JB Weld. Is that a reasonable solution?

2. What kind of plug? Many opinions say NO to brass or aluminum because their head could be easily stripped. Steel was suggested. How about stainless? Any issue with the different expansion rates between the case and the plugs?

One thing is clear - they should be replaced. Of the 11 plugs, 2 almost fell out. They were definitely potential sources of future leaks!

Thanks for your thoughts!

[Mark Henry]

In this case it doesn't really matter which material you use, I only use steel plugs because one day I may have to take them out. Like with most engine builders it's hard to change the mindset when you have a solution that has worked for years, not to mention the couple hundred steel pipe plugs I have in stock. The dissimilar metals/leakage theory is just a no go with my thinking, metals don't expand in just one direction, they expand in all directions. If anything the pipe plug gets tighter as heat increases. I've never had a steel plug leak and I've done this mod on many of my own and customers engines. BTW the steel plug will never rust on the business side.

The pipe plugs I use have the micro-encapsulated thread sealant already on them, same as the 996 factory bolts. Took me awhile to trust this treatment, but they have never leaked. Tech tip if you get these plugs, is use a spare/bare plug to test fit the depth of the plug, then once happy install the ME plugs.

Always use a new or sharp 3/8" NPT tap, you drill to 9/16" and try to oval out the top hole, but best way is to carefully use a taper ream for proper size. I've cut the tip off of my reamer so it doesn't go in too deep. Lube the tap, there are special cutting lubes if you have them, but WD40 works good enough. Always check your test pipe plug depth as you cut with your tap. Don't worry about threads into a galley, but there's a blind plug in the front and one in the back, so don't drill in too far. The most outward hole (3-4 flywheel side) the plug must sit flush or just a hair proud or it will hit the flywheel. I leave the rest of the plugs a bit proud. There's holes with galley right behind them, the 1/2 flywheel hole (IIRC) is a hole really close to a cam galley, leave the plug almost half proud or some builders back cut the plug. Never over torque the pipe plug, but I know I put more torque on a steel plug than you ever could on an aluminum or brass plug. One thing I've never measured is the torque, the plug just stops in the taper, I give one more try and you're done.
Do install all the plugs before you start engine assembly, if there's any issue with depth you want to know before assembly.

[Superhawk996]

The dissimilar metals/leakage theory is just a no go with my thinking, metals don't expand in just one direction, they expand in all directions. If anything the pipe plug gets tighter as heat increases.

Nope. Quick materials science lesson:

You are correct that material expands in all directions.

However, in the case of a hole, there is no material at the center to expand inward or outward. The material that composes the circumference of the hole expands in all directions and increases the diameter of the hole. Something that wouldn't previously fit though the hole with a size difference of 0.001"-0.003" now can. All due to the growth in the diameter of the hole as it is heated and expands the material that composes the hole in all directions. The larger the hole, the more it will expand when heated.



Here is a quick video of the principle.


https://www.youtube.com/watch?v=3pnj4ytORQw


If there is a material of the same thermal expansion that fills the hole (i.e. an aluminum galley plug), it all expands at the same rate. There is no relative growth differential between the two parts. This is how the OEM aluminum press fit oil plugs generally stay in place for 40+ years. Without a thermal expansion difference between parts the press fit stays the same, hot or cold. No relative movement between the two parts.

If there is a plug material of a lesser thermal expansion (i.e. steel plug in our case) at the center, it doesn't expand as fast as the aluminum that composes the hole is expanding and the steel plug gets looser.

This effect is also how/why the steel pilot shaft of Type 4 oil pump shaft is able to be pushed outward though the aluminum oil pump housing. The aluminum housing shaft hole grows faster than the steel shaft and the interference fit between them becomes less. The steel shaft is looser in the aluminum housing. Oil pressure then slips behind the steel shaft in the pump body shaft pocket, and now we have a small hydrualic ram effect that is actually working to push the looser steel shaft though the housing. As we all know, with enough time and especially with an overheated engine, the shaft can actually be pushed out into contact with the cam gear. (IMG:style_emoticons/default/sad.gif)

As you've noticed in application, the difference between our two positions (steel plugs vs. aluminum plugs) is minimal but it is indeed there. The steel plug is getting looser in the oil galley hole. In the case of the steel NPT plug, the threads will prevent the plug from being pushed out by the oil galley hydraulic pressure. Most likely any potential for oil weepage is being addressed by the thread sealant you use with the steel plugs.

Again to be completely clear, I'm not trying to imply you don't do quality work. Just that difference between our positions is minimal in practice.

You are spot on that as an engine builder, you have a lot higher risk of engines coming back. Especially if they are race engines. I completely understand why you do what you do, and wouldn't question the quality of one of your motors. Heck, I'd love the luxury of being able to pay you to build mine. (IMG:style_emoticons/default/biggrin.gif)