Create an account Home  ·  ·  Forums  ·  ·  Articles  ·  ·  Downloads  ·  ·  Photo Gallery  
Login
Nickname

Password

Don't have an account yet? You can create one here.

Navigation
· Home
· Article Archive
· Article Submit
· Downloads
· FAQ
· Forums
· Members List
· Photo Gallery
· Private Messages
· Web Links
· Your Account

Search Articles



Forums

Wiper motor...which is the correct one?
Lead additive, one more question.
M31C mount with or without replica weapon
Backfire and Hesitation
Wanted: Steering column and shaft for M38-1952, or late CJ2A
2024 CT. MILITARY VEHICLE SHOW AND FLEA MARKET- JUNE 15,2024
Brake Line
How to link full size photos in posts
Clutch release bearing support cast tab for return spring
T90 case replacement required?

Willys M Jeeps Forums


willysmjeeps.com :: View topic - Cracked piston?
 Forum FAQForum FAQ   SearchSearch   UsergroupsUsergroups   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Cracked piston?
Goto page 1, 2  Next
 
Post new topic   Reply to topic    willysmjeeps.com Forum Index -> Technical Knowledge Base
View previous topic :: View next topic  
Author Message
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Wed May 25, 2016 5:08 pm    Post subject: Cracked piston? Reply with quote

Am i looking at a cracked #4 piston? If so, do all 4 need to be bored out and a larger piston installed or just the one? All four pistons have .030 stamped on them. Does this mean the bores have already been opened up .030"?




_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
4x4M38
Member


Joined: May 30, 2014
Posts: 3440
Location: Texas Hill Country

PostPosted: Wed May 25, 2016 6:15 pm    Post subject: Reply with quote

Brad,
It doesn't look good, but magnafluxing or pulling it is the only
real check. The other concern should be that chunk out of the edge.

Yes, .030 stamped means it has been already been overbored
to 30 over. Only looking at the bore will determine whether
you need to bore more. Possibly all you need is a new piston
and a home job.

The real question here is what caused the piston to crack if
it is. You have to solve that first, otherwise there may be another
cracked piston and maybe more damage. It may be worth
the trouble to check the rods, as well as the valve train.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php
Back to top
View user's profile Send private message Send e-mail
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Wed May 25, 2016 7:41 pm    Post subject: Reply with quote

Thanks Brian. I will being my bore gauge home from work on the weekend. My dial caliper reads bores 2 and 3 at 3.155" so hopefully its just a piston swap.
I dont know much about engines so i will google the reasons and see what comes up. Maybe i will find a paragraph about it in one of my manuals as Well.
Brad
_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
jason
Member


Joined: Oct 10, 2010
Posts: 22

PostPosted: Wed May 25, 2016 8:07 pm    Post subject: Reply with quote

what octane gasoline were you using? A cracked piston could be the result of detonation or it could be a cheap piston.
_________________
Jason M38A1
Back to top
View user's profile Send private message
wesk
Site Administrator
Site Administrator


Joined: Apr 04, 2005
Posts: 16225
Location: Wisconsin

PostPosted: Wed May 25, 2016 11:05 pm    Post subject: Reply with quote

Save yourself a lot of time and worry. Pull the piston, bead blast the piston clean. Then inspect it. A crack you should be concerned with will be visible to the eye and confirmable with a simple dye penetrant check. Often very thin layers of carbon and lead form on the top of a piston and flake off a bit. What you see right now could be that simple.

I wouldn't get to excited about that small notch. Many builders will do that to a piston to mark the spot that goes towards the front of the engine. I stamp a small arrow in the head of each piston and a number so I can keep them properly organized and re-install them in their original/correct positions.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
Back to top
View user's profile Send private message Send e-mail Visit poster's website
4x4M38
Member


Joined: May 30, 2014
Posts: 3440
Location: Texas Hill Country

PostPosted: Thu May 26, 2016 6:05 am    Post subject: Reply with quote

Hi Wes,
I remember marking the pistons that way from old Hot Rod
days now that you mention it.

Makes sense.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php
Back to top
View user's profile Send private message Send e-mail
jam51m38cdn
Member


Joined: Feb 06, 2008
Posts: 69
Location: Findlay, Ohio

PostPosted: Thu May 26, 2016 7:02 am    Post subject: Reply with quote

your pics indicate to me that your engine is a fairly new rebuild.030 oversized is a pretty small amount,due to my machine shop told me he can go .080 over before he has to sleeve the block.The notch in the piston is from the manufacturer of the piston.Many of your questions can be answered by a good machine shop.Mine has been doing willys engines for 3 generations. I would put an indicator on the crankshaft and check end play and make sure your within tolerance.A lot of machine shops like to reface the face of the front main journal which actually rides against the rear of the front main journal and determines the crankshaft end play. If the machine shop takes to much off excessive end will be the result,and then your pistons WILL NOT be in the center of the bore. There is is no way short of spray welding that face and turning the crankshaft to the correct dimensions to achieve the correct endplay. Usually you will see wear and scaring inside the bores front to back in the block if this has occured. Jim
Back to top
View user's profile Send private message
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Thu May 26, 2016 6:12 pm    Post subject: Reply with quote

Thanks so much for all the replies. I bought this engine used but heard it run and sounded like it was running good. He had pics of the recent rebuild but not sure if that is when block was honed. I do not know what fuel he was using and if riming was optimal.
So i opened up my manual and figured out how to pull the piston. Stopped at a hot rod shop here in town and asked if they would take a look. I am practically a virgin when it comes to engine blocks. Anyways, he tells me those are surface scratches, likely from the time they were installed. He grabbed scotch brite pad and rubbed them out. He had to put elbow grease into it but i dont see the marks anymore. I left as soon as i could, feeling a bit awkward.
I now come home and decide, since the piston is out, i would measure the dia. of piston.
I get a .016" difference from size parallel to camshaft and perpendicular to camshaft. 3.134 to 3.150 time to go pull out the book.
Thanks again for all the help.
Brad
_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
charlesfitton
Member


Joined: Jun 07, 2010
Posts: 69
Location: Maryhill On

PostPosted: Thu May 26, 2016 6:16 pm    Post subject: Reply with quote

Piston are oval when they are cold....
_________________
M38 CDN 52-30105
M38 CDN 52-30883

and other green crap...
Back to top
View user's profile Send private message
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Thu May 26, 2016 6:16 pm    Post subject: Reply with quote

I can see now in pic #2 of post 1 that i see the "crack" lone extend onto the block. I was using a razor blade in a handle to scrape carbon earlier.
_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Thu May 26, 2016 6:17 pm    Post subject: Reply with quote

Thanks Charles.
_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Tue May 31, 2016 3:51 am    Post subject: Reply with quote

Just to follow up, i pulled all 4 pistons and broight them into work and a quality control inspector on the night shift did a LPI (liquid penetrant inspection) on all 4 pistons and found no signs of cracks. I feel much better now that he was able to confirm that it was in fact just a scratch on the top of piston.
I guess i can put them back in and continue the build.
Thanks for all the help.





_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Sun Jun 05, 2016 8:43 am    Post subject: Reply with quote

It looks like when the block was bored 0.030" oversize and new pistons were installed, the original rings were reused. I get a gap of 0.075" which i believe should only be 0.008-0.013" Please correct me if im wrong before i order 0.030" oversize rings


_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
wesk
Site Administrator
Site Administrator


Joined: Apr 04, 2005
Posts: 16225
Location: Wisconsin

PostPosted: Sun Jun 05, 2016 9:21 am    Post subject: Reply with quote

Bores are finished carefully by final honing to match each cylinder specific piston which is then stamped with the cylinder number it belongs to. This often results in small bore variations to ensure proper piston fit. Ring gaps are filed to fit one piston in one bore. A wee bit of mix and match on re-assembly can easily lead to the error in gap you see. As can excessive wear to a 0.030 OS bore. Are you inserting the ring using a piston the full length of the piston into the bore before you measure gap?

Before you order anything you should confirm ACCURATELY each piston diameter, each bore diameter and then match largest diameter piston to larger bore and so on and then match rings to bores based on gaps. When you have ascertained positively that you cannot custom match all four bores with correct fitting pistons and rings then a decision must be made. All this said be sure you are using TM 9-1804A and check all ring clearances, not just gap.

Is a new overbore needed or not? Are new pistons needed or not. Are new rings needed or not.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
Back to top
View user's profile Send private message Send e-mail Visit poster's website
southpw
Member


Joined: Jun 15, 2014
Posts: 268
Location: Cambridge, Ontario, Canada

PostPosted: Sun Jun 05, 2016 9:52 am    Post subject: Reply with quote

Thanks Wes. I took ring off of piston #3 and inserted ring 2.5" down from top of block into cylinder #3 and made sure ring was at same depth all the way around.
This is how i got this gap size.
Are you saying i should check gap when i push ring in like photo below? If so, I still get that oversize gap. Surprizing the gap is so large compared to the spec of max 0.013"

I have also measured bore diam with an inside micrometer and is right on the .03 oversize size. Measured in multiple directions. I need to bring home a bore gauge to check full depth of bore as my hands cant fit very deep to check diam all the way down the cylinder


_________________
1952 M38 project
Brad
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    willysmjeeps.com Forum Index -> Technical Knowledge Base All times are GMT - 6 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

Powered by phpBB © 2001 phpBB Group
Forums ©

 



PHP-Nuke Copyright © 2005 by Francisco Burzi. This is free software, and you may redistribute it under the GPL. PHP-Nuke comes with absolutely no warranty, for details, see the license.