terryd said:
Very well put!!! There is a need for the HP pump due to the law of "objects in motion tend to stay in motion" as applied to the piston/connecting rod in high RPM engines (over 7000 RPM in my "opinion" again). It helps to keep the bearing from striking the crank journal at these higher RPM's and causing bottom end failure.
Cleaning up the drainback system on an engine is a very good idea. I spent a day with a die grinder cleaning casting flash out of my camaro motor and opening up the front and rear drainback ports in the cam galley. I also plugged the holes in the galley that drain back over the crank to help eliminate the oil from striking the crank, and added a windage tray to "scrape" the excess oil off the crank at the higher RPM's it shifts at.
Slo-Sho, I'll admit it, I've never built or serviced a 4.0L Jeep motor internally, this is due to the fact that the engineers designed them well enough that I've never had to get into mine. (I'm assuming it has an oil pump, never been in the oil pan). You can scream till you're blue in the face, if you're trying to get me mad it won't happen. I'm sure you know people, who know people, who've talked to people. You've also not proven that the HV pump offers any added benifit, seeing as how stock pumps can last 300,000 in these motors without having problems, I dont see the need to waste money on something that's apparently (according to the "how many miles does yours have" threads I've read) not needed....
Thank you - that's why I'm writing books now.
I forgot to mention one thing tho - the production AMC six usually doesn't see the far side of 4500rpm at the crankshaft, unless it was owned by Barney Navarro (who raced a modded AMC199 at Indy...) So, the starvation issue would be reduced - but it's still something to watch out for. It's also made up for somewhat by the fact that we have a six-quart sump, instead of the regular four or five (and I'll not even wander into the differences between a "wet-sump" system and a "dry-sump" system - that's a whole new can of worms. Murphy's Law sez "The only way to re-can a can of worms, once opened, is to use a larger can.")
Oh - and FYI, the AMC six (199/232/242/258) has an oil pump that is driven by a tang on the bottom of the distributor shaft. No ancillary oil pump drive shaft. Consider yourself edified.:dunce:
One principal element of the longevity of the AMC six has to do with the alloy used to cast them - it's a high-nickel cast iron, similar to the alloy used in the second-generation Chrysler Hemi engines. The increased nickel content results in a tough alloy that's not too hard - but it's tougher than the hinges of Hell, let me tell you. I lost the oil pump (OEM) in my 1987 ~220Kmiles. When I opened up the engine to see about servicing it, there was a ridge of .0005" (one side - .001" total) at the top of the cylinder, vice the more usual .007-.010" I've seen at that mileage on most other engines.
Sadly, Chrysler decided to reduce the nickel content of the alloy starting in 1991, along with lightening the casting (for NVH reasons. I don't understand that - if you want a quiet ride, get a Caddy or a Lincoln!)
What I said about cleaning up the cast surface to improve drainback still applies - since pretty much all production engine blocks are sand-cast (it's cheaper,) the surface sucks. I'd like to see investment cast engine blocks and cylinder heads, but it's not going to happen - sand can be cleaned and reused, while the "lost wax" investment casting process results in just that - lost wax. Can't reuse the casting blanks... Too complex to die cast engine blocks at the moment as well - at least, in a single piece.
But, that's a pivotal issue that you probably didn't consider (since your experience is with high-RPM racing engines) - the AMC six is horribly subject to potentially destructive crankshaft harmonics (can snap the crank and/or cam) in the 6Krpm band - but most of these engines don't see the far side of 4500, they redline at 5000, ChryCo did a crank limiter at ~5300 or so (I don't recall exactly - may be 5500,) and they make best power and best cruise down around 2300-2800rpm anyhow. I'll touch redline in my rig about twice a year - just to check. However, I know my rig
lives down around 2000-3000 rpm. This is due to the design of the engine - not the way I drive. You just don't
need to run the thing any faster (unlike a SB racing engine - that spins around 6000-8000rpm. Or a balanced and tuned Wankel, which can turn 16-18krpm all day long.)
The AMC six also has relatively large oil drainback passages - as Slo-Sho mentioned. This doesn't mean I want to take chances, but the design and operation of the AMC six is rather forgiving. However, if it works, I don't see any need to fix it - and, like you, I've got just enough bad experiences that I don't want to play with it. Granted, quite a few people have put in HV oil pumps without incident - it works for the reasons stated above. (Advantage to having worked on damn near everything - from a three-horse one-cylinder Briggs on up...) AMC engineers did a good job, so I just don't feel the need to mess with what works.
Unless, of course, I want to make it work
better!
eace: 
