PT Cruiser Forum  
       

Go Back   PT Cruiser Forum > General Forums > Tech & Performance Forum

PT Cruiser Forum

Cylinder Head Torquing Problem

 
Reply
 
LinkBack Thread Tools Display Modes
  #1 (permalink)  
Old 01 Aug 2011, 01:04 pm
Young Cruiser
 
Join Date: Jul 2011
Posts: 70
Default Cylinder Head Torquing Problem

This past weekend I installed the cylinder head on my '02 PT Cruiser (2.4L DOHC) using new head bolts. I followed the OEM specs for torque (25, 50, 50 , 90deg) and pattern. When I was done, I thought it would be a good idea to check the head bolts, so I set my torque wrench to 80FT-LBS and started checking. Well, bolts 1 through 6 clicked over the wrench, but 7 didn't. After 7 didn't click over I checked 8-10 and they clicked over. At this point I started thinking that I somehow missed the 90deg step for bolt 7. I was 100% positive that I didn't miss the 50Ft-Lb step since I check them all 3 times. Without much more thought I turned bolt 7 90deg. I then checked it with the torque wrench and it still wasn't clicking over at 80Ft-Lbs like the others. What should I do?

1. Assume I missed the 90deg step and not worry about it.
2. Assume I over-torqued number 7 and replace it.

If I replace it, it seems like I should loosen the rest of them. If I loosen the rest of them, should I replace them as well? What about the head gasket?

I am usually very detail oriented when it comes to engine work. I feel awful that I may have missed the 90deg step. Hopefully this doesn't end up being a huge problem. It could have been worse. The bolt could have snapped.
Reply With Quote
  #2 (permalink)  
Old 01 Aug 2011, 02:03 pm
Regular Cruiser
 
Join Date: Jun 2011
Posts: 199
Default Re: Cylinder Head Torquing Problem

There are a number of considerations here, but generally speaking you can't go back and check torque with a torque wrench after the fact, especially not on tty bolts - as you torque a fastener down the relative load on the surrounding fasteners is lessened. Going back over a second pass would yield different values than the first pass. They know this when the assign the values, which is why they are specific and why there is a progression. Additionally, you don't know what that last 90 degrees is - it could be an additional 1 lb ft or an additional 10 lb ft. It's a calculated value that the engineers knew, but you don't.

Here's the deal:

1. These are torque to yield bolts. The final 90 degrees puts some amount of stretch on them. Reusing them may be ok or may be no good, depending on what that stretch is, and you don't know it.
2. In theory, putting incorrect torque in an incorrect order could warp the head or damage the gasket/sealing. Again, that's what there is a prescribed order and a prescribed progression.

The right way to fix this is:

1. Remove the head bolts in the prescribed order (start in a corner, go CCW IIRC)
2. Take the head to a machine shop to have it checked for flatness
3. Put a new head gasket down
4. Install the checked head with new bolts

Leaving out steps is "at your own risk." Were it me, I'd eat the $60 in materials and $50 of machine shop time to ensure it works and I don't have to take it apart again, but what you do is more or less up to you.

IMHO, you can't be too careful or too cautious when doing head bolts. It's a pretty sensitive aspect of the engine.
Reply With Quote
  #3 (permalink)  
Old 01 Aug 2011, 03:25 pm
UptownSport's Avatar
Veteran Cruiser
 
Join Date: Jan 2011
Location: 55403
Posts: 3,832
Default Re: Cylinder Head Torquing Problem

No one replaces Neon headbolts any more. After Chrysler went to 11mm headbolts in '85-'86, they don't deform.
Chrysler tells you how to check them, laying a razor blade on threads.

What you're saying is you don't think he bolt's getting sufficiently tight?

I use paint sticks on critical fasteners, no second guessing.

These heads / blocks are very good pieces, unless engine's heated next to turning red, they stay pretty straight.
Reply With Quote
  #4 (permalink)  
Old 01 Aug 2011, 04:27 pm
Young Cruiser
 
Join Date: Jul 2011
Posts: 70
Default Re: Cylinder Head Torquing Problem

thesameguy,

I understand that you can't really "check" the torque in this application. I guess I was afraid that I missed one of the bolts and felt the final torque must have well above 80ft-lbs based mostly on the amount of force I had to put into the breaker bar to get to 90deg. Since 9 of the 10 didn't budge at 80ft-lbs I think it was a pretty good guess.

The angle torque step will indeed put a significant amount of preload into the bolt. All "torque angle" specifications (including torque to yield applications) are designed to get to a specific bolt preload with as little error as possible. Standard torquing is generally considered to have an error in excess of 25%. To minimize the total effect of this error, the standard torque step of a torque angle specification must be well below the final desired preload (well below yield for torque to yield applications).

Since the bolt I may have missed is one of the outer ones, I am not concerned at all about head warpage.

Thanks for the "safe" answer. I was hoping to find someone who did something similar, loosened and then re-torque the bolts and has been driving the vehicle for 50,000 miles.
Reply With Quote
  #5 (permalink)  
Old 01 Aug 2011, 04:33 pm
Young Cruiser
 
Join Date: Jul 2011
Posts: 70
Default Re: Cylinder Head Torquing Problem

I guess I will be removing the bolts, checking them as UptownSport suggests and retorquing using a little more vigilance than the first time, perhaps even a checklist to make sure I don't miss any bolts. Perhaps I will discard the replacement bolts and re-use the factory ones.

Any comments on the head gasket? As long as I don't remove/move the head it seems like I should be able to re-use the gasket.
Reply With Quote
  #6 (permalink)  
Old 01 Aug 2011, 06:29 pm
Regular Cruiser
 
Join Date: Jun 2011
Posts: 199
Default Re: Cylinder Head Torquing Problem

Re-using TTY bolts is an at-your-own-risk-but-probably-okay thing to do. Reusing an MLS head gasket is a big no no.
Reply With Quote
  #7 (permalink)  
Old 01 Aug 2011, 11:47 pm
UptownSport's Avatar
Veteran Cruiser
 
Join Date: Jan 2011
Location: 55403
Posts: 3,832
Default Re: Cylinder Head Torquing Problem

That's been done.

For 'sky is falling' crowd, here's from Mopar FSM:
Reply With Quote
  #8 (permalink)  
Old 02 Aug 2011, 12:35 pm
Regular Cruiser
 
Join Date: Jun 2011
Posts: 199
Default Re: Cylinder Head Torquing Problem

I dunno about sky is falling, but my opinion is that new bolts are $20, and the time spent doing a head gasket and the other materials involved are worth a LOT more than $20. When I did the head on my PT last month the bolts that came out looked brand new, but I put them in the recycling bin because $20 buys a lot of peace of mind. I positively cannot stand doing the same job twice, especially when a $20 part was the cause. Just my $0.02, YMMV. I've seen people at the junkyard buying used head gaskets, so whatever.
Reply With Quote
  #9 (permalink)  
Old 02 Aug 2011, 01:16 pm
Young Cruiser
 
Join Date: Jul 2011
Posts: 70
Default Re: Cylinder Head Torquing Problem

While doing some web surfing on the topic of torquing head bolts, I found a document written by Elring (http://www.ekag1.de/pdf/1_zks_praxis/ZKS_Praxis_en.pdf), a manufacturer of cylinder head bolts. The most interesting part of the document was their description of how they test TTY head bolts: torque to manufacturer specs then turn another 2 full rotations. The result must be no significant decrease in bolt force.

What does this document tell me about my situation? At worse, I put on an extra 1/4 turn which is 8 times less than the bolt was likely designed to handle. Additionally, the extra 1/4 turn did not change the bolt force much and therefore the distribution of clamping force across the head did not change much.

The best case is still that I missed the 90deg step for that bolt. In the process of "checking" the torque I put on the required 90deg (give or take a little). Since this was an outer bolt, the slight out of sequence pattern does not concern me at all in terms of head warpage.

Conclusion: I am going to leave it alone and continue re-assembling. I will post updates when I fire it up and after a few thousand miles.
Reply With Quote
  #10 (permalink)  
Old 02 Aug 2011, 02:32 pm
Regular Cruiser
 
Join Date: Jun 2011
Posts: 199
Default Re: Cylinder Head Torquing Problem

I don't disagree with your conclusion, I'm just speaking from a by the book safety first time is money position...

FWIW, Elring makes an extremely high quality product - superior to the vast majority of competing products in their space. I have run a LOT of boost through engines built with their gaskets and bolts and never once had a failure. If they're available, they're always my choice.
Reply With Quote
Reply


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

Posting Rules
You may not post new threads
You may not 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
Cylinder head interchange Floundering Tech & Performance Forum 5 28 Nov 2011 10:15 pm
2.4 Cylinder Head '03-'10 UptownSport Classifieds: For Sale/Trade 1 29 Mar 2011 10:04 pm
F/S OEM Cylinder head w/ valves sincitymax Classifieds: For Sale/Trade 0 10 Nov 2010 03:58 pm
Cylinder Head Question for a 2003 GT customer20 General Turbo Discussions 15 23 Dec 2007 10:47 am
Cylinder Head Blow Up Colorado_Aztec Tech & Performance Forum 7 28 Dec 2005 10:45 pm


All times are GMT -5. The time now is 12:01 pm.




Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
LinkBacks Enabled by vBSEO 3.6.0 PL2 © 2011, Crawlability, Inc.
vB.Sponsors