Used 3.7L Motors

[dljacko]

I am wondering if it is usual when buying a used motor from a 4x4 dismantler, for them to remove the water pump. I recently had to replace mine because it did the normal thing and spun the big end shells and seized (no, it is regularly serviced, this is a common problem).
When the motor arrived from Newcastle it had the water pump missing, when I rang and questioned them I was told that it was common practice, so you have to put a new pump on.

[Nobster]

I've been on here a few years now, when you say a common problem "how common" first I've heard.. Water pump for a 3.7 $100 and your better off putting a newbie in anyway..

[dljacko]

These motors apparently have a weak drive system for the oil pump, so I am told, and if it chews the sprocket out you lose oil pressure and on mine the oil warning light is the smallest and in the bottom of the cluster so it is hard to see over the steering wheel. Mine shit itself and by the time I pulled over off the highway it had already made a terrible noise and stopped. When they dismantled the motor they found the big-end shells spun around on three cylinders. The oil pump had chewed the gear off and stopped turning. I was given a price to rebuild the motor so I rang around wreckers all over Australia and a few of them told me that it was common problem as the positioning tag is not very strong and if it grabs even slightly there is the likelihood that it will spin around the crank.

[dljacko]

Further to my last post, it appeared that when the motor was stripped down after removal the cam shaft on the passenger side had snapped and there was irreparable damage to the head itself. The mechanic did a bit of a backflip over the big end bullshit that he told me about earlier and said that the noise was normal for big end problem. So it appears that it had a flaw in the casting since new and only recently decided to snap. I now have put in a complete motor from a mainland supplier which was far cheaper than getting a new head and a repair job. The head had the bearing post chewed to pieces where the loose bit had run amok. Any how it turned out that you should always wait for the final verdict before listening to experts. (He still assures me that they have problems with the big end bearings?)

[senatorjohn]

Positioning tags on bearings are not designed to hold the bearing in place. The assembled bearing shells should be a little bit bigger in diameter than the hole in which they fit. In other words, the shells suffer some "crush" when the cap bolts are torqued up. The resulting clamping force between the shells and the rod / cap prevent the shells from turning. The amount of crush is specified in workshop manuals and should be measured as the engine is assembled. If oil supply fails, the bearings can pickup on the shaft and turn with it, even if the crush was within specifications.
John

[Hanna]

Yep - sounds like an arse-covering exercise there by the mechanic. I've never heard of spun big-end bearings on this engine and only one that I can recall on the 4.7L V8 in the Grand Cherokee (same engine with 2 extra cylinders) and this was due to overheating.

As John says, a spun bearing is going to be the result of an oil supply issue (or overheating issue) and not from a bearing/locator design flaw.

I hate when mechanics make shit up!!

[dljacko]

Just a quick reply about my seizure problem with the 3.7 engine. when stripped down the last two cam bearings had seized and that is what caused the cam to snap. I had a good look at the oil galleries and must say that in the cam bearings they are minute! I spoke to a member of "JeepKJ country" forum and it seems that there was a serious problem with seizures in these motors in 2002 and 2003 in the states, mainly crank bearings. They operate under more varying climatic conditions there so I guess the oil probably doesn't get to where its supposed to as often. I looked this up after confronting my mechanic and quoting your responses to my original query, and he told me that "Jeep Australia" had a lot of these motors seize earlier on whilst he was working at a distributorship.