4.0 piston size? - JeepForum.com
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Wrangler Forums > YJ Wrangler Technical Forum > 4.0 piston size?

FS: Wranger BRIGHT License Plate LED! Just $3! Great valueBlack Friday and Cyber Monday Sales at JeepHut.comThe Jeep Forum Discount is ON!

Unread 04-24-2009, 03:18 PM   #1
Registered User
1991 YJ Wrangler 
Join Date: Apr 2009
Location: NC
Posts: 14
4.0 piston size?

I have a 1991 4.0 with pistons marked 50. Anyone know what size this is? Thanks Dave

Lockley is offline   Reply With Quote Quick reply to this message
Unread 04-24-2009, 04:23 PM   #2
Registered User
1989 YJ Wrangler 
Join Date: Apr 2009
Location: Phoenix, AZ
Posts: 24
Re: 4.0 Piston size

Typically pistons marked with a numerical like 010 or 10 are indicating they are an oversize piston,

010 for .010"
20 for .020"

.050" oversize seems larger than normal, but i am not a machinist so I can't say whether the 4.0 bores can accept that large a piston for sure.

Not a ton of info here, but HTH.

Last edited by BDKR; 04-24-2009 at 04:24 PM.. Reason: crappy spelling
BDKR is offline   Reply With Quote Quick reply to this message
Unread 04-24-2009, 05:02 PM   #3
from here it gets rough
Opihi59's Avatar
1993 YJ Wrangler 
Join Date: Dec 2007
Location: Beyond Honolulu
Posts: 4,847
98.4 mm or 3.87 inches is what I found online. Are you able to mic it and see how this corresponds to what is listed as stock specification?

....I'm not smart, but I can lift heavy things.......

Fill out your PROFILE, and don't forget to look in the FAQ for writeups

I'm stuck on da Rock http://kamfamily.wordpress.com/2009/...waiian-limpet/

Originally Posted by Brian4.2 View Post
We will be going Metric every inch of the way.
Originally Posted by 40dog View Post
yes I'm a some guy and have always put gasket sealer on my surfaces before mating
Originally Posted by Virjeep View Post
You should go to Pirate. I hear they are real smart over there. You'd fit right in.
Opihi59 is offline   Reply With Quote Quick reply to this message

Quick Reply

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools

Suggested Threads

Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.