Epoxy compatability with ceramic coating process?

[Roy]

Hi all, looking for some recommendations. I have a seat of heads I picked up used where the previous owner had ported out. That in itself is not a problem as the heads are performing well. The problem is that he broke into the pushtube holes in several spots and used filler to patch back up (normal I know)... BUT When running vacuum on the motor it is causing SEVERE wet flow issues (I suspect). Once vacuum is put to the motor it detonates, I did not let it run long enough to find out O2 readings, but after removing the vacuum it returns to normal. Upon pulling the heads off I can see several oily areas where the oil is being pulled through the epoxy during high vacuum idle conditions. While off I am wanting to get the combustion chambers ceramic coated as well as the intake and exhaust runners. I imagine all port work should be redone before sending out for coating.. So my conundrum is this, what epoxy works well on cast iron heads and can reliable hold up to the 3hr @450F cure time for the coatings? My first thought is JB weld muffler putty, but I am afraid of it coming loose and going into the chamber. First post by the way, just wanting to say you guys are all awesome!

[mag2555]

Cotronics in NY makes a ciramic epoxy (902) if I recall right that can be machined and is good to 2500 f.

I would redo all of your push rod hole patch job's with this material.

[Roy]

Thank you sir. I know there are quite a lot of various epoxies everyone used but I could not for the life of me find a discussion on how well they survived the coating process.

[modok]

I don't know what you are doing with the epoxy.
to sleeve pushrod holes i would be more inclined to use something like brass tubes and loctite 510
Epoxy is good for building up and filling in areas,
but most kinds of epoxy are not very good to use as an adhesive/sealant for tight fits. For that anaerobic cure loctite is superior.

[mag2555]

The above comment has its points in that I guess at 450 f you could just use red high temp gasket maker to seal up the tubes,
permatex red is good to 650F.

[Roy]

I did debate on sleeving the push tube holes but was thinking there might be an easier way. I by no means consider myself an expert at this, I have found that those that are experts generally know the easiest solutions from experience. I never thought of using loctite as basically a gasket maker but that is one heck of an idea.

Edit> The only issue with loctite is that it softens up at a much lower temperature than they advertise, which I do not know if it becomes permanently soft or reverts back to its cured high strength state when it cools. I don't know what temperature it begins to soften at, but I use red and blue loctite religiously on all external (and some internal) engine bolts (Ever see a flywheel come loose after 100k miles? Clutch? Bellhousing? I've seen just about everything come loose... ) To remove a red loctited bolt without breaking it when it is only a 3/8 or smaller thread, a few seconds of heating the head with the MAP torch is usually all it takes. After removing the bolt is only hot enough to burn you with prolonged contact, not momentary... I would suspect in the 250-350 range.

[modok]

I researched this a while back,
Both loctite and epoxy do become weaker when hot.
And, they can be degraded by exposure to chemicals.
JB weld "claims" it can take 500 degrees F, and that's true.... but for how long....and in an atmosphere of what? probably an argon atmosphere
And how strong is it when it's that hot? Is really the missing info there.
At 300F and exposed to gasoline it's just a matter of time before it gets all screwy.


The strength of the bond changes with heat, time, and exposure to different chemicals.
Loctite 510 (and red threadlocker and sleeve retainer also) actually become stronger with time, and they are stronger if cured rapidly. They do cure rapidly when applied to fresh brass or iron surfaces. Being applied in a thin film to metal IMPROVEs the cure, while with most epoxy that would make it work worse.
Panelbond epoxy for instance, has small glass beads in it so that sets "the gap" even when you clamp it, because if you squeezed it all out it wouldn't work right.

And there is also heat aging, as far as, how much the strength degrades over repeated heat cycles, and exposure to gasoline and alcohol, also rather good for those loctite products in the long term. The factors cancel out somewhat because it get stronger with age, but weaker with heat cycles, still holds up decent.
After a year of service It might be 70% as strong as it was the first day after you applied it.

IMO, significantly better than epoxy in that particular environment,
Which is why loctite is used to seal injector tubes and oil plugs, and affix shotgun barrels, glue gears to shafts, ect, and epoxy isn't.
And of course there are WAAY too many kinds of loctite.

510 would be my choice for this app, or sleeve retainer if you achieve a very tight fit.
518 which is slightly flexible and better for aluminum, but not quite as sturdy
515 which has high resistance to water and coolant, but worse resistance to fuels....( maybe for core plugs).