Your comments are interesting.
Two summers ago a good friend needed to have an exhaust leak repair on his 2012 Ram 1500. I suggested that he might want to have the exhaust manifolds machined to get flatness, and there is a auto shop near here with a good reputation. He took them there and I was later surprised to learn the machinist tried to talk him out of having it done! The reason is the machinist said "they all warp" and "would warp again." He explained that cast iron, unless wickedly out of spec., will conform to it's matting surface in an high heat applications.
The shop did eventually agree to shaving 0.015 off which didn't bring them into pure flatness. Another reason given was that taking too much material of the matting surface could cause cracks around the outward flange mounting stud area. His ultimate solution was to install a quality tube header.
He did re-install the machined exhaust manifolds using the revise Chrysler parts and so far it's holding (truck now has over 240,000 miles on it). Time will tell.
Regards,
Dusty
2019 Ram 1500 Billet Silver Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 3 June 2018. Now at 85807 miles
How long as he had them on after being milled?
I believe in the warping happens as material is heat cycled but there is a limit to where it stops. That is dictated by time m, temperate and usage. Gaskets that compress will and rebound will fix leaks and probably stop bolt breakages but they don’t stop the warping which is a natural process. Only way to stop the warp is season the material or do everything u can to prevent the only real issue which is the tick and that can be probably solved with remflex gaskets and larger dia bolts. Now to fix the warping you run them for years and I would say 50k is a safe mileage if you haven’t broken a bolt yet. Pull them and milk them flat and say you took off .060”. If they continue to warp from that point you can go another .060 and with the remflex gaskets and stock bolts I didn’t get a bolt snap. I would rather pull and mill with a .060 total warp vs having a .120” warp and broken bolts/leak. Add the stress of the rear manifold being pulled on by the hanging exhaust while hot I’m sure that doesn’t help.
Some interesting reading which more scientifically describes what I’m kinda saying.
“The root cause of the problem is that when poured, castings shrink and when they shrink they are full of compressive stresses. Those stresses just wait to be sprung free by any way possible, one day, one week, one month....100 years.
Old school was to let castings age for 3 seasons to let the stresses anneal naturally before machining and in truth done that way they never warp later.
But in the world where time is money, castings like manifolds were hustled through and cleared the line in less that a shift. Even today they are machined in what is referred to as 'green'.
If manufactures of todays manifolds baked the casting for 4-6 hours at 375-400 Fahrenheit before machining, there would have been no internal stress 'springs' to cause the problems of warped manifolds later.”
youtu.be
