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401 making metal and no oil pressure

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ALWNDUP View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ALWNDUP Quote  Post ReplyReply Direct Link To This Post Topic: 401 making metal and no oil pressure
    Posted: Nov/29/2021 at 4:00pm
I'm in the process of tearing down the 401 in my Matador. It's supposed to have less than 250 miles on a fresh build (I bought it with the car).

So far, I've found metal mud in the pan and a few small pieces on the pickup. I've only taken the #8 rod cap so far and it looks pretty good. What I did find is a timing chain that is super sloppy and damage to the inside of the timing cover. I think that's my initial problem but I haven't found the culprit for the lack of oil pressure yet. I believe metal has clogged the pressure port (mechanical gauge).

I've talked to a friend who has built hundreds of engines (no AMC though) and he believes the timing chain issue comes down to machining of the crankshaft and/or the camshaft journals. I know the crank was turned .010 on the rods but not sure about the mains.

I've seen a few mentions that the timing set needs to be custom ordered due to the journal machining but do you guys know what or where to order a set like that from?
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Nov/29/2021 at 4:12pm
Journal machining does not change the CC distance between crankshaft and camshaft.
AMC's are known for having aftermarket camshaft fit issues and most have to have the bearings "massaged" in some manor to have the camshaft rotate freely.
Guessing someone just put in the camshaft and it was too tight - wiped the camshaft bearings.
The are other oiling modifications that should be checked with an AMC build and those are well documented with a search on the Forum.
No custom timing set required!



Edited by Trader - Nov/29/2021 at 4:14pm
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PHAT69AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Nov/29/2021 at 4:27pm
ALWNDUP - Opinion seems to be pretty much all modern AMC Timing Chain sets all have sprockets from
the same global source / supplier and pretty much all of them should be assumed made incorrectly.
There's a good chance the problem may have been from the Distributor Drive Gear Oiling circuit,
but there are other possibilities.  It's not really an inherent AMC problem, so much as it is
a global sourced, lost documents, lost specifications, 1987 Chrysler buyout, dumpstered records,
always relatively small market demand, small volume, low profit, to old & too few, situation.

There's a mountain of information here on this forum.
There is a lengthy thread here with a title containing Mandatory Oil System Modifications
which is only a title and by no means should be taken literally.
As with anything there are varying opinions, best to read it all, draw own conclusions.

For now the first thing to suspect is the Distributor Drive gear Oiling Circuit
as seen in this self-made diagram drawing.
The Hole in the camshaft front journal forward face & the notch in the sprocket usually fail to properly line up.
Modern replacement camshaft mounted distributor drive gears have also been found to have the small oil squirt holes
drilled in the incorrect axial location (towards the rearward side rather than the front) where they will receive no oil
to be squirted out of the holes, as the 4 holes mush be towards the front and be above
the small cavity that remains in front of the cam snout once the heavy washer and bolt
are in place and tightened, as visible in this drawing.

The AMC oil pump imho actually is "too good", all the oil ends up in the heads & valley, special
attention to various oil discharge locations & sizes & details & particularly adequate timely
drainback of oil to the oil pan are the areas which pay the biggest dividends imho...
But there will be other opinions, I'm sure...  Peace


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SCRAGTOP View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SCRAGTOP Quote  Post ReplyReply Direct Link To This Post Posted: Nov/29/2021 at 4:56pm
Your "buddy" is sort of on the right path.  Its actually align boring that changes the dimension between Cam to Crank distance.  Oversize bearings .010 or even .040 have no effect as someone already stated.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Posted: Nov/29/2021 at 8:31pm
Hopefully you haven't been a victim of the " 0.001" bearing clearance for 1" of journal " rule. I got mired in that years ago. Car would have good oil pressure when cold but after it got warm pressure dropped off bad.

The main and rod bearing clearances on an AMC are pretty tight. Mine were twice what the AMC tech service manual said they should be. That let a lot of oil past the mains and caused a lack of oil to the cam bearings and burnt them up.

-Steve-

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Nov/29/2021 at 8:37pm
When align boring, the CC crankshaft to camshaft is normally kept within 0.002". You can take material off the main caps, but very little is bored off the block. With the camshaft you machine and get oversize bearing shells (hard to find those now) or machine and press a sleeve to stock bore.
If the block CC is that bad, you get a new block.
Never seen a custom AMC timing set to make up for a messed up align boring job. Cannot find one for sale either, but it may exist!
If a main has had a spun bearing, the block is normally welded so there is material to correct. Only done on expensive blocks 390/401's.
If someone has align bored this block so the CC is wrong, a new block is the best option.

If this was an inexperienced builder, they may have put the camshaft bearings in incorrectly also, so they had no oil feed.


Edited by Trader - Nov/29/2021 at 8:40pm
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