Cummins 4BT & Diesel Conversions Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
645 Posts
Discussion Starter #1
Here we go again. I read the sticky on this subject and my shop manual and just talked to the shop foreman at the local Cummins distributor. My shop manual, printed June 06, says to take the 4 long bolts that go thru the rocker pedestals to final 89 ft-lbs plus 90 deg and the 10 medium and 4 short to 66 plus 90. The shop foreman said that is the correct procedure and the one they use. As a side note, due to corrosion pitting, I replaced the four short bolts that are on the exhaust side. The new bolts (Cummins OEM) are threaded the entire length vs the original ones only partially threaded., This conflicts with what Cummins told Paul to take all 18 bolts to 89 plus 90 so what to do?
 

·
Registered
Joined
·
808 Posts
Steve;
Back when we were discussing the torque, I went to Cummins and they photo copied the head torque page from a January 1985 Shop Manual. I thought I posted that information.
This is what is on the Photocopy page;
Step 1 40 NM (29 ft Pounds)
Step 2 85 nm (62 foot pounds)
Step 3 126 NM (92 foot pounds)
The tightening sequence is the same as in my shop manual. I can scan and post the picture of the 1985 Cummins Shop Manual Page if anyone wants to cut and save it. Just ask.

The bottom line in that thread as I remember, It was confusing !!
When , at what point did you stop torqueing to the above specs and change to the new ones of Torque + Angle specs. And are the head bolts on the old engines the Torque To Angle Bolts or Not. I never saw a solid answer come out of that thread. I too have to find out soon as I have a head to go back on the parts engine I am building.

Paul
 

·
Registered
Joined
·
808 Posts
Page 3

I have a concern if we tighten the old bolts that follow the torque specs forund on these pages to the current specs, we may end up twisting off head bolts ????

Paul

 

·
Registered
Joined
·
3,391 Posts
Thanks for the postings, Paul. In general I'm confused, maybe I should stop there haha. But general confusion as to the accuracy of the method described of adding 90*. What the heck kind of torque spec is that for accuracy? Why not just give the final torque value, with a TORQUE WRENCH instead of the 90* silliness?!? Seems to me it's just about impossible to know the final torque spec without knowing the final torque spec?

To me this former tech info is a prime example of the 'Cummins Attitude' I've seen in much of their tech stuff. Several things are caged up in some proprietory 'Need to Know' hoop-dee-do, and "You, simple minded non-engineering degreed sots, DON'T NEED TO KNOW!" BS, man, buncha BS.

Rant over, thanks again, Paul!
 

·
Registered
Joined
·
808 Posts
I understand about TTY ( Torque to Yield) Bolts = Torque to Angle. Below is a explanation
from the Federal Mogul-Fel Pro Gasket Site on he Web. I have this saved on my computer, but I tried to go to the site and get a link so you could read the entire presentation. They have created a new web site, and I cant find it on the new site. To much info is presented to be browsed at 24.4K ha ha.

So here is the important part. This is a cut and paste.

"How to Prevent Head Gasket Failures Caused by Low Clamping Force

4. Many engines today use "torque-to-yield" (TTY) head bolts. These are specially designed bolts that stretch slightly when installed. This provides more even head loading and allows the bolts to hold torque better for improved head gasket sealing.

When the bolts are installed, they're first tightened to a specific torque -- then tightened an additional amount that's measured in degrees of rotation. This final twist stretches the bolts to their yield point and creates the elastic clamping force that provides more even loading across the head and gasket. Because TTY head bolts stretch slightly (only a few thousandths of an inch), some auto makers say they should not be reused when the cylinder head is removed. Reusing TTY bolts will cause them to stretch further, which increases the risk of breakage.

A stretched bolt also will not hold the same torque load as before, which may cause a loss of clamping force resulting in head gasket leakage. Ford says TTY head bolts on the 1.6L Escort engine should not be reused. Though not required, it may be wise to replace TTY head bolts on other engines if the vehicle manufacturer doesn't say to do so. Replacement TTY head bolts are available from Fel-Pro, and are recommended for Chrysler 2.2L and 2.5L, Ford 1.6l and 1.9L, and GM 1.8L, 2.0L and 2.5L fours, 3.0L V6 and 381 V8 diesel engines."

Paul
 

·
Registered
Joined
·
4,089 Posts
That's odd because the head bolts from Cummins are not pre stretched,and they are reusable .

I was just at the parts dept ,he said that was odd as well.So he ask the service manager and he said that is the wrong info and they have only set them by the 02 manual .So they only replace them only if they are not up tp spec.

So at this point I will only use the old spec and use the old bolts.

Crewcab59
 

·
Super Moderator
Joined
·
8,815 Posts
Basically when a bolt yields the clamping force vs wrench torque relationship flattens out.
So if you can yield a bolt, you can reasonably accurately determine the clamping force it's got.

There's an interesting post I've put up in the 4BD1 section about head torque. It mentions TTY installation for the first time, then torque specs for any time they've been reused.

But giving used bolts the TTY approach can cause them to neck down (stretch thin in one place) too much which makes them both more flexible in tension and weaker.
 

·
Registered
Joined
·
3,391 Posts
Well that does clarify things, Paul and all, thanks! I see now that at the point of maximum torque application anything further might result in an inaccurate torque wrench reading as the bolt stretches. No, it doesn't sound right to me, but I can at least envision what they're talking about.

I wonder how much new bolts would set a guy back? Can't be cheap, from Cummins...
 

·
Registered
Joined
·
645 Posts
Discussion Starter #11
Checking in after being out of town. I fixed my problem by replacing all the head bolts, as I looked closer at some of the other ones they had corrosion pitting too. the total for the 18 bolts came to about $75 plus tax. The bolt heads have the markings shown in my manual "'T + 90" and the marks to determine when a 90 deg arc has been met. I'm going to use the method in my book ie. final torque of 89 plus 90 deg for the four long bolts in the pedestals and 66 plus 90 deg for the other 14. I think they torque the four long bolts to a higher final torque because they will stretch more due to their length and as a result need a higher initial torque before the 90 deg arc to give the same clamping force as the other 14 shorter ones. Does that make sense?
 

·
Registered
Joined
·
45 Posts
I believe the resson for going 90 degress at the final step is because at about 120 lb to 125lbs the bolts begin to stretch and the tourque value stays the same. Ive seen it with my on eyes. Soom friends and I have been playing with that and they continue to stretch and never broke one yet. We have come to the conclution on high performance stuff that the final tourque can be 180 degrees and that will hold much more boost.
 

·
Registered
Joined
·
915 Posts
Anyone have definative specs for a 6BT 12 valve?
 
1 - 14 of 14 Posts
Top