BigBadWolf

I'm rebuilding my 12A, and can't find any information on this. Spent the last 3+ hours through at least 50 threads.

My housing surfaces are fine since I can't catch a nail, but I've got pitting where the water seals are that's got me concerned. Here's a picture of the worst spot:

[attachment=45416itting.jpg]

Any suggestions on what to use to insure a good seal, or am I worrying about nothing. My thoughts were either a good gray RTV such as Yamabond, or JB Weld. I figured I'd run a razor over to get a nice flat surface.

This is my rookie rebuild, so I want to get it right.

Lynn E. Hanover

This is typical of older irons.



Just lay a very small bead of 100%GE silicone tub ans tile calk into the bottom of the groove. It will ectrude around the "O" ring as you torqure up the stack and seal off the water. Once assembled, spinr the engine backwards a few revolutions and remove any excess silicone from the exhaust port.



Lynn E. Hanover

BigBadWolf

Thanks Lynn. I figured I'd have to go a little more high tech than that, considering the heat. Seen a lot of your posts on here, so I know you speak from a wealth of knowledge.

Lynn E. Hanover

Well, just standing around for this long will get you somewhere......I have shoes older than you guys.



The water "O" ring has a great name, (the black one around the outside of each housing) because it keeps "Water" inside the engine.



The multi colored "Compression "O" ring is assigned a misnomer. (a bad name) Because it does not seal in compression.

Even though you seldom see one fail, they are not under much of a load. The compression sealing is done by the several thousands of pounds per square inch of pressure generated by the case bolts crushing the rotor housing between the irons.



If you were to expose the "Compression "O" ring to the combustion process, it would exit the engine as fast as the exhaust.

It just some reclaimed rubber products. The cardboard it is taped to cost more than the "O" ring. Since there is no such thing as perfect machining, there is some compression gas leakage into the ring groove, and that forces the ring tight against the outer wall of the groove. That is it, nothing more. On cooldown the "O" ring prevents coolant from entering the combustion area.



Mazda used to send along a strip of metal with a bit of a "V" bend long ways on it. It was just less wide than the groove is deep. This was called a seal protector. However, it was installed along the outside of the "O" ring. So what was it protecting the seal against?



There are rules that must be followed when installing "O" rings into grooves. There is a whole field of engineering involved in

the installation and use of "O" rings. Each type of "O" ring has a subset of rules based on use and materials. And after that rules about the excess volume allowed after a ring is installed. And then another book on the shapes of "O" ring grooves.



Some "O" rings must flex a bit in order to seal. Some "O" rings must be square or rectangular, while others must be round.



An example of an "O" ring that must flex, would be the square one in your brake caliper. When pressurized the "O" ring is forced to the outside of the groove. The bit of space between the piston and the caliper allows the outer part of the "O" ring to extend outward a bit further than the outer groove wall. So, when pressure is removed, the deformed ring returns to it's normal square shape and as it does so, retracts the piston just a bit. Cool, so what retracts the outer pad on my single piston slider (piece of crap) brake system?



Almost nothing. Notice the outer pads wear out faster? In some cases, the outer pads are a harder compound than the inners. Every once in a while you get a groaning sound while backing up and turning, or running slowly over a bump. That is the caliper moving in the bracket. Damn hard to move isn't it? So you rely on system flex and runout in the rotor to remove pressure from the outer pad. You trust rotor flex, and runout to knock the pad back. This works on low pressure systems like Moms car or van. In racing where pressures a often and high, then pistons on both sides of the rotor are used. The round "O" rings in these systems do the same thing as the square "O" rings but get stiff quickly from flexing and should be changed on a time basis.



There you are, more than you wanted to know about "O" rings.



Lynn E. Hanover



Picture is housing mods for a "J" bridgeport.

BigBadWolf

Thanks for the 411, I work on a lot of automated espresso/coffee equipment. The variety of orings involved in both material and shape is certainly an aspect most people wouldn't begin to understand.

Can you give me the low-down on why you recommend the tub seal as apposed to something designed more for heat/solvents. Do you use same for the legs and oil pan. Never heard of anyone using that for anything on a car beyond a window leak or firewall grommet. Personally I prefer Goop Marine for window leaks, etc. Its like liquid duct tape IMO.

If you've got shoes older than me, could you please throw them out!?!

Many thanks,

Ed Levine

Lynn E. Hanover

Yes on the legs. It hurts like hell to finish up an engine, and see nothing squished out from the legs, because you forgot to goop them up.



In that and similar applications, the amount of silicone that remains after the stack is torqued up, is microscopic. There is no load on the stuff. It can't get any hotter than the aluminum. It is cheap and of good quality, and available anywhere. You can glue an oil pan on with it. It comes in many colors to go with your outfit. Its easy on the hands, and you can caulk a tub or shower with it. You can glue things together with it.



When I ran Weaver brothers pumps I used it between sections, as the pumps had no "O" rings. I use it between the engine and the header flanges, instead of a stainless gasket. If there is no gasket, it can't blow out. Also the intake has no gasket.



Years back when we used Hewland gearboxes, the gear cover was off and on many times each weekend, and you can only afford so much Hylomar. So we used Tub and Tile caulk. Never a problem.



Some of the airplane guys use the exhaust flange idea. Actually if you don't have a lot of back pressure, there is a low pressure (below one bar) at that junction anyway. Bernoulli.



I would not suggest that the GE silicone is better than some other brand, or some other material like Hylomar. I like Hylomar, but for 10 cents worth of sealant they want $14.00, and the stuff is not that much better than anything else. And it is getting hard to find as the brand is sold every other month.

The two Permatex sealants work well when used in the proper applications. And that is the key piece of data. Used in a proper application.



Lynn E. Hanover

BigBadWolf

Facinating! I'd of never thought it could be used in such applications. Now I know how you gained so much knowledge about orings. When I get my baby back together I'd love to bring over a six-pack and listen to you for an afternoon!

Lynn E. Hanover

No more beer please.



I go through Orlando from time to time. Took the wife to and back from a cruise ship. Back and forth from the 24 hours of Daytona.



My friend had AJ Almandinger in the number 6 Riley in the lead when the Roush engine lost its ignition reluctor. 7 new spec Ford powered cars fell out with the same problem. AJ was in another (Dodge) car today and finished 3rd in the 500 on his first try.



The kid has talent, no doubt about that.



Here is the Ford in the Riley chassis. Mike has 2 of these.

Complex enough for you?



Lynn E. Hanover

BigBadWolf

That's sweeeeet! Go figure, I've been an AJ fan since his rookie season in F1.

Thanks again

Ed Levine

BigBadWolf

Gosh Darn! I realized as I thought about it later, I meant CART. He got out at the right time. I hope to G_d that Indy goes back to it's roots and runs different manufacturers again now that they merged back.