|
|
|
Your donations help keep this valuable resource free and growing. Thank you.
|
401 crankshaft main clearances |
Post Reply 
|
| Author | |
Rocketman 
AMC Fan 
Joined: Aug/20/2011 Location: uniontown pa Status: Offline Points: 19 |
 Post Options
 Thanks(0)
 Quote Reply
 Topic: 401 crankshaft main clearancesPosted: Aug/20/2017 at 1:15pm |
|
Hello, I am assembling my 401 and the mains are ragged edge of too tight, I am going to call the machine shop tomorrow but I figured I'd ask here too. All 4 front mains range .0012- .0013, 5 is at .0015.
5 is definitely tighter than the recommended .002 to .004, the others are just scary to someone used to dirt track small blocks. Is that over tightness on 5 going to cause damage on a street engine? It might see a dragstrip once or twice just to see what I can do. Also what weight oil do you recommend? Instinct had me buy 10w40, but with clearances so close it has me thinking thinner. But the rods are all .0025- .0029, opposite of my other problem. Or am I just overthinking it all? I want to put the engine in once, just want to double check. Thanks |
|
 |
|
|
401MATCOUPE
AMC Addicted 
Joined: May/20/2010 Location: Salisbury, MD Status: Offline Points: 5367 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/20/2017 at 4:11pm |
|
This is a limited response, only based on my experience.....1-4 mains are fine....#5 see what some others say. 10W30 oil is my recommendation.....
|
|
|
Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar) 68X,GoPac,390,4sp,52A 69X,GoPac,390,4sp,64A 70X,GoPac,390,4sp,87A,8 70X,GoPac,390,4sp,BBO,8 70 Jav SST,390,AT,BSO 74MatX,401,AT,Prototype 74MatX,401,AT |
|
|
|
|
Rebel Machine
AMC Addicted
Joined: Jul/03/2007 Location: Western Il Status: Offline Points: 5121 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/20/2017 at 6:45pm |
|
Spec is 0.001"- 0.002" on #1-#4. 0.002"- 0.003" on #5. #5 has 0.001" more clearance due to flywheel/flexplate movement. Rods clearances are the same as mains #1- #4.
For what it's worth, mine are set 0.0017" on mains #1-#4 (and rods) and 0.0025" on #5. I shift at 6100 RPM. Running 10W30 Mobil 1 synthetic. I have roller lifters so low ZDDP isn't an issue as it would be with a flat tappet. -Steve- Edited by Rebel Machine - Aug/20/2017 at 6:49pm |
|
|
|
|
FSJunkie
AMC Addicted
Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/20/2017 at 9:42pm |
|
1977 specs were a little more specific. They say .0010-.0030 (.0017-.0020 preferred). That was with aluminum bearings, not the sintered copper-lead ones used before about 1974. Bearing type has a little consideration in clearances. The harder you run the engine, the more clearance it will need on just about everything. For normal daily driver and highway use your main clearances would be fine I'd say. Racing could use a little more space. The rods are too loose for my liking.
|
|
|
1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
|
|
|
|
jcisworthy
AMC Addicted
Joined: Jul/23/2009 Location: North Carolina Status: Offline Points: 2805 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/21/2017 at 4:17am |
|
The general rule of thumb is .001" per inch of journal diameter then add a half thou for performance applications. With good parts you can get away with tighter clearances than that..
I usually run .0025 on the rods and .0025-.003 on the mains for a performance application so your mains are tighter than I would run them. It will probably be ok but I would not run them that tight. The engines I build are performance applications though making 500 plus HP where yours may be closer to stock. I use 5W30 Chevron Supreme oil in my engines.
|
|
|
Specializing in dyno services, engine building, and cylinder head porting
rbjracing.com Phone Number 518-915-3203 |
|
|
|
|
Rebel Machine
AMC Addicted
Joined: Jul/03/2007 Location: Western Il Status: Offline Points: 5121 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/21/2017 at 6:54am |
My experience is that rule of thumb works for engines that oil the mains first like a Cheverolet but not AMC. I had a 401 built several times trying to figure out why it had low oil pressure and was eating cam bearings. It was due to excessive main bearing clearances. They measured twice what the TSM specs listed. Mine is a street/strip engine making about 460 HP. -Steve- |
|
|
|
|
Rocketman
AMC Fan
Joined: Aug/20/2011 Location: uniontown pa Status: Offline Points: 19 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/21/2017 at 11:05am |
|
Well the mains are king aluminum ones rods are clevites, the machine shop spec'd them out. I stopped after putting the crank in so thr rods weren't double checked. Itd sure be nice if they offered odd bearings for these. Its not a race motor but I didn't want a slouch either, 10 to 1 fairly lumpy cam. 5 is still my personal biggest concern.
|
|
|
|
|
jcisworthy
AMC Addicted
Joined: Jul/23/2009 Location: North Carolina Status: Offline Points: 2805 |
Post Options
Thanks(0)
Quote Reply
Posted: Aug/22/2017 at 2:33am |
|
I do not have those issues. The amount of oil pressure is based on the spring pressure in the oil pump. Make the bypass valve spring adjustable and you can get whatever pressure you want.
|
|
|
Specializing in dyno services, engine building, and cylinder head porting
rbjracing.com Phone Number 518-915-3203 |
|
|
|
|
Post Reply
|
|
Tweet
|
| Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |
Click for TheAMCForum Rules
Topic Options
jcisworthy wrote: