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I found this on the internet about the 351M/400.. This guy says otherwise..
All I know, is mine was fine once the bearings were replaced!
All 351M/400's have crankshaft oiling problems because Ford enlarged the main journals from 2.75" on the 351C to 3.0" on the 351M/400 but did not decrease the size of the oil galleries leading up into the top of the engine to properly balance the oil pressure -- This myth is one that most everyone, even people who like the "M" engines, hold as being fact. Some people believe that because the "M" engines have a larger journal diameter than the Cleveland engines that Ford "forgot" to restrict the oiling galleries to make up for it. Well, if this is so then why isn't the 351W rumored to have the same problems due to fact that it has the same journal diameter as the "M" engines?, Also, installing a 400 crank shaft in a 351W has become a popular "stroker kit" for this engine, yet no one is complaining about 400 CID Windsor engines throwing crank shafts! And what about all of the "M" engines out there with 200 or even 300K miles on them without a rebuild? Despite all this, some people still insist that there are abnormal oiling problems with this engine. There is even an "oiling restrictor kit" available from Moroso to supposedly "fix" this "problem". This kit is designed for high-volume oil pumps in racing applications only. From my experience the only time an "M" block may experience oiling problems on the crankshaft is if someone installed a full-competition high-volume oil pump in an engine driven on the street. I used a standard volume Melling oil pump on my engine and it has fantastic oil pressure! The only thing I can think of that may have "fueled the fire" on the "M" oiling problem rumor is the fact that this engine was installed mostly in full-size 4x4 trucks and even saw duty in many 1-ton F-350s. Many of these trucks were used to tow enormous amounts of weight back in the days before overdrive transmissions. The "M" engines were also some of the first small block engines that were now being asked to do the job previously reserved only for super heavy-duty big block engines. It is quite possible that some "M" motors may have worn out sooner than some of the older HD big block truck engines. However, I believe that the "M" engines are the only small blocks made by anyone that can even attempt to take this kind of abuse. I think the "M" engines simply got a bad rap because they were being used in applications where no small block engine should have been in the first place. In short, if you need to tow a 10,000+ pound trailer on a daily basis, then get a diesel or a HD rated gas engine. But if you use the "M" small blocks they way they were intended to be used (i.e. in a half-ton Bronco) and you don't exceed your Bronco's rated towing capacity, then you should get many, many miles of trouble-free service out of it.
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