Changing rod bearings

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Jun 18, 2020 | 07:39 PM

Nitro1168

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Tuned

Joined: Dec 2015

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Changing rod bearings

I just bought a 79 150 with a 400 in it. Bought it off a dealer that just sells older western trucks, needs a lot of work but the body’s pretty nice. Not sure if the oil pressure gauge works (shows nothing) there is no knocking. He deals with a lot of 70s trucks and recommends me to change rod bearings. He said he does it all the time And is good for another 100k miles. I have never heard the but I have to change oil pan gasket anyway, what do you guys think have you heard that too.

Jun 18, 2020 | 08:12 PM

440 sixpack

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You won't get another 100,000 but it will buy you an undetermined amount of miles depending on the overall condition.

this isn't uncommon in any engine but it was standard practice with 335 series engines and has been since the early 80's. we rolled in new rods and mains and installed a high volume oil pump at 50-60 thousand miles and most often it would get us to 100,000 before it needed a major.

I've done this on all our pickups and it's not a big job in a 4x4. in a 2wd I can't say.

Jun 18, 2020 | 08:55 PM

72rtchallenger

Fleet Mechanic

Joined: Jul 2017

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From: KY

If not knocking ,,,Hook up a real oil pressure gauge before doing anything , find out the real oil pressure ,,and dealers are liars by trade in general , maybe not all but most never tell everything and many know nothing about an engine , especially one from 1979

Jun 18, 2020 | 09:01 PM

slashfan7964

Fleet Mechanic

Joined: Sep 2013

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From: Indian Falls, New York

As mentioned, get yourself a real oil gauge and hook the sending unit up at the back of the block. These 351M and 400 engines are notorious for incredibly low oil pressure at idle (sometimes as low as 5psi warm) under stock circumstances, so don't let that spook you if it runs nice. General rule of thumb is 10 psi per 1000 rpm.

Personally, if it were me and I was going to go through the hassle of putting bearings in it, I'd go through and rebuild the whole motor, especially as you don't know what you are getting as far as condition goes, and being that old I certainly don't think it will come with any kind of dealer warranty. Not only that, but to do the oil pan gasket the motor has to get jacked up anyways, regardless of whether or not it's a 2 or 4 wheel drive truck.

I would leave it alone and drive it. Scoop up another 400 to rebuild on the side, they are a dime a dozen (make sure it's a 400 and not a 351 or you are going to have some fun with part matching) and you can get them in running condition for as low as $200. That way, you can drive the truck and have a new engine on the way.

Jun 18, 2020 | 09:02 PM

85e150

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Joined: Apr 2004

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And check the stroke when you pull that pan. 351m motors turn into 400s just like 360s grow to 390s under the magic grow lights on the dealer lot.