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401 Crank oil passages "wrong"?

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jpnjim View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Topic: 401 Crank oil passages "wrong"?
    Posted: Aug/23/2015 at 8:22pm
I had seen something similar to this statement here a few times:

"all sizes of AMC cranks have their Main to Rod oil passages drilled a little bit differently from one another,
 all work OK, except for the 401 crank, which has two of it's passages inexplicably drilled backwards/wrong."

I went through a bunch of cranks today,
what I found was interesting,
but I don't know if it means that the way a 401 is drilled is bad,
or atleast not any worse than a 290.


I checked oil passage location, and direction in an (unknown year) ArmaSteel (cast) 290,
 2x 1970 360's, a 1972 360, a 1968 390 & a 1973 401 crank.

Here's what I found with the 290 & 360/390's:


All 360s & 390 cranks were drilled exactly the same as each other.

The 290 crank is drilled exactly the opposite of the 360/390 cranks.

The connecting rod journal holes of all the cranks seem to be in identical locations,
 it's the main journal oil hole locations that vary.
The 290 location was always on the opposite side of the main journal compared to the 360/390's location

Simple explanation:

View the engine/crank from the front
rod journal is at TDC,
oil hole on all is located at your top right hand side of the rod journal.

 The 360/390 oil holes then travel from right to left, through the center of the crank
to exit on the bottom LEFT side of the crank journal.

The 290's oil holes stay on the right side of the journal straight down, in line with the crank throw,
 and end up on the lower RIGHT side of the main journal.

The 290 holes are also heavily chamfered compared to the 360/390, due to the steeper angle of the hole (relative to the circular journal).

So this generated some questions for me:

 are the 360/390 cranks drilled like that for strength?
 (going through the center of the crank has to be the strongest place to drill a hole)

If the 360/390 way is stronger,
 why drill the 290 another way (especially since the longer slot of the 290 would take more work/effort in manufacturing to clean up)
Was this a running change, after the 290 method was found to be bad?


OK, with those unanswered questions looming,
 I dug out the 401 crank.

Connecting rod oil holes 1,3,4,5,6&8 are drilled exactly the same the 360/390's I checked.
Hole exits top right on the rod, bottom left on the main.

But the rod oil holes for rod #2 and #7 are "almost" the same as the 290.

(I say "almost" because those two oil passages do travel a bit closer to the center of the crank than the 290 passages do, and pop out on the main the slightest bit over from where they do on the 290... maybe for a tiny bit more strength?
 but they still pop out on the right side of the main journal as the 290 does).

So if the 401 is considered drilled backwards for those two passages,
then the 290 is "drilled backwards" for all it's passages (and at a slightly steeper angle backwards).

Sorry this isn't a picture thread (yet),
 and I am still trying to wrap my mind around what the oil is doing at each point in the rotation relative to rotation, oil inertia and tons of other stuff that hurts my brain.

 But if anyone followed this far into this post,
and has a better grip on what this means than I do,
 I would appreciate the explanation. LOL



Cliff notes:
AMC history says 401's have a couple of the oil passages drilled funky/wrong
 
290 crank oil passages drilled straight down, from right of rod journal to right of main journal

360/390 oil passages angle drilled across the center of the crank from right of rod to left of main

401 oil passages #2 and #7 drilled straight down right to right like a 290
401 oil passages #1,3,4,5,6&8 angle drilled across the center of the crank from right of rod to left of main like a 360/390

If it's bad for the 401 to have 2 passages drilled like this.
 wouldn't it be TERRIBLE for the 290 to have ALL it's passages drilled that way?

Has anyone heard of 290 (and I'd presume 343) failures due to crank oiling issues?

Thoughts?
Thanks!
71 Javelin AMX P-code Go pac 360/4spd/3.91's
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2015 at 8:43pm
Oiling system failures in AMC products were
legion back in the day. But the stockers
rarely if ever failed due to the drilling of the
crank oil holes. The AMC oil system was a nearly
exact copy of the worst oiling system of the day
that being the Buick V8 and V6.

AMC added a little plastic button on the bottom of the oil pickup
that failed often and umbrella valve oil seals that
shattered after the heat got to them blocking the
oil returns in the heads. IMO the oil system was marginal
even when working properly.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2015 at 8:56pm
OK,
 I found the other thread that goes into depth on this:

http://theamcforum.com/forum/390-cranks_topic67162.html?

and the info I found with my own cranks today that conflicts with this is:
 my (73) 401 crank has journals 1,3,4,5,6&8 drilled identically to the 360/390,
 it was journals #2&7 that were different, mimicking the 290 journals, only with slightly less angle & less chamfering.



In that thread I did ask and get a good answer there from Hurst390:

Originally posted by Hurst390 Hurst390 wrote:

Originally posted by jpnjim jpnjim wrote:

Great thread!

I've been meaning to start a 401 crank oiling discussion (and HOPE it would be this informative)

So the main part of the 401 crank problem is ONE journal's oil passage is drilled backwards so the oil flow has to fight inertia as it oils the journal (correct?) 



A 401 amc crank oils #6 rod ADTC. The oil has to go straight down out of the block,enter the #4 main journal and make a hard right angle back up to oil #6 rod journal AT THE WRONG TIME. It also has this scenario at #1 rod. But #1 main only has to oil the #1 rod bearing...not 2 rods like the other 4 mains. So #4 main becomes an issue. Endurance will kill it. even with a dry sump eventually.
A 390 crank is drilled so that each rod gets its oil coming up on tdc when it needs oil.
A 400 chevy crank oils correctly


But after rereading it I just went and double checked my 73 401 to the 68 390,
  1,3,4,5,6 and 8 (including journal #6) are drilled identically
it's 2&7 that mimic the 290/343.

I am certainly not trying to call anyone out thats been doing this stuff (and doing it very well!) for 20-30-40+ years,
 just trying to get the facts straight & wrap my head around it.

I have a 77' 401 crank tucked away.
 My next step will be to dig that out and see if that is drilled the same as the 73 401 crank.

Thanks
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was Green/green now T/A red w/blk leather

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2015 at 9:08pm
Originally posted by Boris Badanov Boris Badanov wrote:

Oiling system failures in AMC products were
legion back in the day. But the stockers
rarely if ever failed due to the drilling of the
crank oil holes. The AMC oil system was a nearly
exact copy of the worst oiling system of the day
that being the Buick V8 and V6.

AMC added a little plastic button on the bottom of the oil pickup
that failed often and umbrella valve oil seals that
shattered after the heat got to them blocking the
oil returns in the heads. IMO the oil system was marginal
even when working properly.



Thanks Boris,
 yeah I think the engineers spent a little too much time thinking of that company on the other side of the lake,
 Buick was the wrong design to copy for sure,
 but it's the cranks that has me thinking.

Up till now I thought the 390 crank had an advantage of better oil passages,
 and that still may be true,
 but wouldn't the 290/343 cranks be the worst of all since all their rod journals has the "right side to right side oiling" like the 'bad' #2 and #7 401 journals have?


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was Green/green now T/A red w/blk leather

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2015 at 9:43pm
This is interesting. I'm going to look over some of my cranks and see if I can wrap my head around this. Looking at some pics from previous builds the main #3 bearing has the oiling groove in both the top and bottom but mains 1, 2, 4 & 5 only the upper main bearing has the oiling groove. If all cranks were drilled dead center from main to it's respective rod it would seem the odd number rods fed by all mains other than #3 would oil ATDC and the even number rods fed by all mains other than #3 would oil BTDC. Rods (4 & 5?) fed by main #3 would oil 360 degrees.

I guess offsetting the passage tries to get those non #3 main fed odd numbered rods closer to BTDC oiling?

I'm probably missing something.

-Steve-



Edited by Rebel Machine - Aug/23/2015 at 9:50pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2015 at 9:56pm
I haven't gotten to the point of sitting down to figure what it all means for crank position and the oil feed hole in the block.
I've also read a lot of different things concerning which engines got full groove, half groove & no groove main bearings.
I wasn't thinking different mains got different bearings in the same engine.

But to clarify,
 the hole location on the #2 main that feeds the #2 rod is different 401 vs 360/390
the hole location on the #4 main that feeds the #7 rod is different 401 vs 360/390

^these two oil passages more closely mimic the 290/343 oil passages (which are all opposite from the 360/390)

all other passages on my 401 crank were the same as all the 360's and the 1 390 I checked.

Clear as mud? Tongue
 
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was Green/green now T/A red w/blk leather

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401jim Quote  Post ReplyReply Direct Link To This Post Posted: Aug/24/2015 at 7:13am
Oh boy am I dizzy now! I think I will stick to the fully grooved mains and hope for the best. WOW!!!!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amc67rogue Quote  Post ReplyReply Direct Link To This Post Posted: Aug/24/2015 at 9:20am
From the factory 71 401s had half groove mains , 73 up were full groove. All the others 290 -390 were half groove. In the early to mid 70s all the after market replacement main sets had the full grove center main.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SC397 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/24/2015 at 11:28am
Originally posted by 401jim 401jim wrote:

Oh boy am I dizzy now! I think I will stick to the fully grooved mains and hope for the best. WOW!!!!!!
Time to bring up the internal oil line debate again?......LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Class Guy Quote  Post ReplyReply Direct Link To This Post Posted: Aug/25/2015 at 7:24am
So a destroked 390 crank for a "high performance" 290-343 would be better than the stock crank? (besides being forged)
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