pinholes in top of piston - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 03-12-2011, 09:44 PM
Registered User
 
Last photo:
Join Date: May 2010
Location: Des Moines,Iowa
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
pinholes in top of piston

I took the heads off my 388 because they have bad valve guides. I noticed on piston #3 there are 5 very small pinholes in the KB Hyperutectics. Do I need to replace these or just run them as is? They are not deep at all. Im hoping to be able to run them until next year when I can replace with forged....Or should I just do it now?
Attached Thumbnails
Click image for larger version

Name:	PIston.JPG
Views:	137
Size:	114.1 KB
ID:	53531  

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 03-12-2011, 10:02 PM
Registered User
 
Join Date: Mar 2011
Location: Vancouver
Posts: 4
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
When you say "pinhole" I'm assuming they aren't right through and are just small indentations. In that case I don't see why you couldn't run them till next year. If they actually go right through I think the blowby could be excessive for the engine. Wonder what caused it?
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 03-12-2011, 10:08 PM
Registered User
 
Last photo:
Join Date: May 2010
Location: Des Moines,Iowa
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Yes they are just small indentations. I did a leakdown test on all cylinders before taking heads off and this particular cylinder had the best leakdown percentage of them all at 5%..

I'm guessing detonation did this as this was one cylinder showing a little lean
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 03-12-2011, 10:19 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,460
Wiki Edits: 0

Thanks: 2
Thanked 322 Times in 319 Posts
They could be detonation peck marks but the raised edge looks more like something got in there between the head and piston.

Closely inspect the piston ring lands and piston pin bores and connecting rod bearings (shiny and or loose fit in cap) for even minute stress or distortion.
Shiny piston ring end gaps edges indict ring butting from detonation.
This tends to scuff the cylinder walls and distort/crack the ring lands.
Needs more top ring end gap.

Oil in the combustion chamber will create detonation. So will excessive timing, compression ratio and or low octane fuel.

Smooth the raised edge if you are going to reuse.

You can get those pistons in singles. A new set are cheap.

You need better cylinder heads not forged pistons.

Last edited by F-BIRD'88; 03-12-2011 at 10:33 PM.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 03-12-2011, 10:35 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,460
Wiki Edits: 0

Thanks: 2
Thanked 322 Times in 319 Posts
Oil in the cylinders give false leak down readings.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 03-13-2011, 05:48 AM
Registered User
 
Last photo:
Join Date: May 2010
Location: Des Moines,Iowa
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by F-BIRD'88
They could be detonation peck marks but the raised edge looks more like something got in there between the head and piston.

Closely inspect the piston ring lands and piston pin bores and connecting rod bearings (shiny and or loose fit in cap) for even minute stress or distortion.
Shiny piston ring end gaps edges indict ring butting from detonation.
This tends to scuff the cylinder walls and distort/crack the ring lands.
Needs more top ring end gap.

Oil in the combustion chamber will create detonation. So will excessive timing, compression ratio and or low octane fuel.

Smooth the raised edge if you are going to reuse.

You can get those pistons in singles. A new set are cheap.

You need better cylinder heads not forged pistons.
Thanks. Plans for next spring are to put AFR 195's on it and was hoping to not pull the engine for anything. Guess I'll just run these pistons for now and pull it next spring to get rid of these KB's and put the new heads on.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

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.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to fix pinholes in welds? Bluesbrother Body - Exterior 6 05-18-2009 07:46 AM
Using lead to fill pinholes xpsyclonex2002 Body - Exterior 9 03-17-2008 07:57 AM
Pinholes in single stage over FG Grogetter Body - Exterior 4 09-04-2006 06:23 PM
Pinholes in clear in 2nd-3 coat Bee4Me Body - Exterior 7 04-30-2006 11:11 AM
Finding pinholes, imperfections. kenseth17 Body - Exterior 1 11-18-2005 04:58 AM


All times are GMT -6. The time now is 10:29 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.