RENIX or no RENIX?

Can you people enlighten me in regards to RENIX? It seems that the RENIX years tend to make it to a much higher mileage before dying... Can those in the know tell me why that is?

Thanks in advance...

Simple...It was Pre-Mopar.

RENIX years are 1990 and back, with a highlight of 1987-1990 w/4.0L (242cid.)

The RENIX blocks are designed to an AMC specification, using a relatively high nickel alloy (which is tougher than the hinges of Hell) and after ChryCo revised the castings in 1991, they lightened them in concern of NVH (Noise, Vibration, and Harshness.) The casting lost something like 50-60 pounds in 1991, and something like another 30 for 1996 or so.

So, with the lightning, you have reduced durability due to less material. It's also been done where the RENIX blocks can be bored out +.125" (one-eighth inch, to a total bore of 4.000",) while the typical "maximum" overbore is typically held as being .060". Granted, a block should be ultrasonically checked to make sure there will be a minimum cylinder wall of .100" all around, but it should only be an issue in the case of "core shift."

So, with the better material, and more of it, is it any wonder that the RENIX blocks last longer than the ChryCo? I don't know why they considered NVH in a truck (if you want a quiet, smooth ride - buy a Cadillac!) but they did, and they decreased the longevity of the block slightly as a result.

That doesn't mean that the later 242 blocks will wear out quicker - you just might not get a half-million miles before a rebuild. With the AMC blocks - let's just say that I've got an 88 with just over 250Kmiles on it, and I consider it to be "just broken in." My 87 with 220Kmiles and a failed oil pump had a top cylinder ridge (the part where the rings don't go - since they're below the piston head somewhat) of .0010" TOTAL - meaning a ridge sticking out .0005" from the surface of the cylinder all around. I'd like to see a "Big 3" do something like that - I've taken down SBChevvy engines with that much mileage, and had to have them bored +.010" just to get rid of the ridge!

5-90

I'm confused... how does a tougher block make the engine last longer? Most engines fail because of the rings, valves, etc... is there a difference in those components as well in the RENIX models? Seems that a tougher block would last longer through rebuilds...but not necessarily initially. Am I way off here?

A tougher block makes the bore last longer. "Tougher" doesn't always mean "harder" - the factory is putting iron rings against an iron block, and I'd be surprised if the rings weren't the same high-nickel alloy as the block.

Since the block casting is tougher, it takes longer for the bore to wear away to the point where the engine loses compression - either due to the increase in bore size or due to the loss of ring tension (due to the increased bore or due to the rings wearing.)

If it were a steel block and iron rings, then ring wear would be a very real issue - because the steel is much harder than the iron.

If the rings have a "barrel" face, they'll last longer, and applying a vapour-deposited molybdenum coating also helps (both reduce friction.) However, I'd take a high-nickel cast iron alloy for an engine over not, and I'd take thicker cylinder walls (to help support the cylinder bore face) than thinner ones - the extra weight in the casting is worth it. Of course, I prefer to build for reliability than speed anyhow - so weight isn't as much of an issue to me.

5-90

So basically you figure the RENIX motors used better rings as well? Is that what you're saying?

so that would explain why the newer blocks are cracking out