TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC 6 Cylinder Engine Repair and Modifications
  New Posts New Posts RSS Feed - Piston to bore clearance tsm typo?
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Piston to bore clearance tsm typo?

 Post Reply Post Reply Page  <12
Author
Message
RobinPDX View Drop Down
AMC Apprentice
AMC Apprentice
Avatar

Joined: Dec/07/2020
Location: Oregon
Status: Offline
Points: 184
Post Options Post Options   Thanks (0) Thanks(0)   Quote RobinPDX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/27/2021 at 10:52pm
Aluminum whether Cast or forged does NOT expand and equal the coefficient factors Cast iron does!
Aluminum is 21-24, (greater amount)
Iron in general is 9.5 - 11.

Might want to ask the piston MFG “their spec gap” recommendation. And ask a few machine shops a general question being coy and ask them about this as if they were to build it for you do they go by the book #’s you Think is right or Piston MFG.

you will get your answer there!!!

I have never seen these tight clearances in my decades or even or hear of these like this. 

Thermal Expansion
(10-6 in/(in oF))




Edited by RobinPDX - Jan/27/2021 at 11:00pm
Rob Wiley
Back to Top
WesternRed View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Aug/03/2010
Location: Australia
Status: Offline
Points: 5787
Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jan/28/2021 at 6:45am
71 TSM has 0.0005-0.0013" for all 6 cylinder engines.
304 is 0.001-0.0018"
360 is 0.0012-0.002"
401 is 0.001-0.018"
I've finally given up drinking for good...........now I only drink for evil.
Back to Top
farna View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar
Moderator Lost Dealership Project

Joined: Jul/08/2007
Location: South Carolina
Status: Offline
Points: 19608
Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Feb/17/2021 at 6:18am
Just for kicks I checked my 65 TSM. The earlier books sometimes have more details. 65 was the first full production year for the 199 and 232.

Piston to Bore Clearance
Top Land - .027"-.031"
Skirt Top - .0009"-.0025"
Skirt Bottom - .0009-.0015"

Skirt Bottom measurements are very close to the 1971 measurements. I'd say the tight clearances are correct.

Also looked up the 4.0L specs. Looks like they are measuring at the skirt bottom, the tightest spot. 

Piston-to-bore clearance.
1998 and earlier.
Desired. 0.0013 to 0.0015 inch.
Allowable. 0.0008 to 0.0015 inch.

The "modern" AMC six clearances are tight! I had one that a machinist bored to Chevy V-8 specs with 0.006" clearance and it caused early excessive wear. Had to rebuild at 70K miles, and that was probably 10K over when I really should have. Anything around and over 0.002 can cause slight piston rocking in the 4.0L, which is indicated by a "tick" that sounds like a valve tick, but is lower in the block. Won't hurt to run it that way, but the sound can be disheartening.

Chrysler increased the clearance to reduce rejected blocks shortly after taking over AMC. After a rash of warranty returns they told dealers it was "normal" and wouldn't warrant the engines. A few people who knew what was going on got great deals on traded in Cherokees in the 89-90 model range! The engines will run 200K or so with the tick -- which usually developed after 60K or so miles.  I knew one person who did that and had over 200K on it last time I talked with them... must have been over 10 years ago now.


Edited by farna - Feb/17/2021 at 6:26am
Frank Swygert
Back to Top
FSJunkie View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/09/2011
Location: Flagstaff, AZ
Status: Offline
Points: 4741
Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Feb/18/2021 at 2:46am
AMC engines have really tight fitting pistons in general, but the sixes especially. You can feel it when you drop the pistons down into their bores. 

You can feel it while they are breaking in too. Most of mine ran hot and didn't like high speeds for their first few thousand miles until they loosened up a bit. After that they ran much cooler and started loving high speeds. AMC wasn't kidding in their owner's manuals when they specified a break-in procedure that slowly worked the vehicle up to higher and higher speeds. 

Chevy engines are sloppy. They just are. 
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
Back to Top
First_Gear View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/18/2010
Location: Mukilteo WA
Status: Offline
Points: 644
Post Options Post Options   Thanks (0) Thanks(0)   Quote First_Gear Quote  Post ReplyReply Direct Link To This Post Posted: Mar/12/2021 at 5:22pm
I finally got round to inspecting these pistons. They all had cracked skirts and I threw em out. I ordered new forged pistons. I was surprised to find a maximum piston to bore clearance of .0035. it seemed excessive but the machine shop told me that because they are forged pistons they machine them slightly under size and they expand. I can't find the manufacturer s spec sheet since they are new old stock from ebay. All the forged pistons measured about 3.748 My cylinders were about 0.0015 over the nominal 3.7500 bore diameter at the worst one so I think I will run it and if it piston slaps itself to death I'll pull it out and have them overbore it but hopefully that won't happen. I do think the cylinder to piston clearance is not a typo.
Back to Top
tomj View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/27/2010
Location: earth
Status: Offline
Points: 7522
Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Mar/12/2021 at 10:37pm
Don't forget most pistons are cam ground, so they're oval to compensate for expansion at operating temperature (one of the important functions of a thermostat). THe steel inserts and the fat metal wrist pin support etc cause expansion to be non-linear. 

I don't really know but I would guess that the tight clearance is 90 degrees from the wrist pin? I'm too lazy to google it, lol.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

Back to Top
farna View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar
Moderator Lost Dealership Project

Joined: Jul/08/2007
Location: South Carolina
Status: Offline
Points: 19608
Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Mar/15/2021 at 6:12am
All forged pistons expand more than cast, so the bores are always larger for forged pistons. It will likely make a little noise (piston slap) until it comes up to full operating temp, so for 5-15 minutes depending on outside temps. After that the pistons should have expanded to full size and sound should be as a normal engine.

Brother had a steet/strip car with forged pistons. When first started it almost sounded like a diesel! It was intentionally bored "loose" though, looser than actually required. Supposedly spun up a bit quicker that way, but had to be rebuilt every 20K miles or so though... wore rings out quicker, and the bore wore more also.
Frank Swygert
Back to Top
JGRANTAMX View Drop Down
AMC Addicted
AMC Addicted


Joined: Jun/02/2017
Location: Maine
Status: Online
Points: 1663
Post Options Post Options   Thanks (0) Thanks(0)   Quote JGRANTAMX Quote  Post ReplyReply Direct Link To This Post Posted: Mar/15/2021 at 6:24am
 I have read back in the sixties Chevy used forged pistons in some performance engines 327, 396 new they were known to be noisy when cold so they changed from having the wrist pin centered to a slight offset that took care of the noise depending on application street or race only that offset might still be used today?

J
Back to Top
wittsend View Drop Down
AMC Nut
AMC Nut


Joined: Apr/15/2020
Location: California
Status: Offline
Points: 413
Post Options Post Options   Thanks (0) Thanks(0)   Quote wittsend Quote  Post ReplyReply Direct Link To This Post Posted: Mar/15/2021 at 10:35am
Originally posted by JGRANTAMX JGRANTAMX wrote:

 I have read back in the sixties Chevy used forged pistons in some performance engines ... .
J

I have a 1985, L-98, Corvette 350 in my '64 Studebaker. It has forged pistons from the factory. Reference: http://https://www.corvetteforum.com/forums/c4-tech-performance/895558-forged-pistons.html  The 1988 T-Bird Turbo Coupe engine in my Pinto wagon also has factory forged pistons.

 Yes, both cars need to be warmed up. Even with the slightest acceleration they can be heard when cold. But then they remind me of one of my favorite movie lines. Airport (1970) "Mr. Petroni didn't you hear him? He said to shut down and get out. - I can't hear a thing..., there's too much noise." (everyone in the theater audience cheers!Smile
'63 American Hardtop
Back to Top
 Post Reply Post Reply Page  <12
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.156 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or