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Rocker-bolt torque for GM 3100 (2003 Buick Century)


Sigea
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Misfire on cylinder 6; I pull engine apart, I find the intake rocker on cylinder 6 moves freely, because of the following. Not sure what happened here.

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Decided to change the LIM gasket since I was in it, so I need to remove the push-rods, which requires loosening the rest of the rocker-arms. These seemed exceedingly tight to the point I was afraid that something might break...they seemed way tighter than the suggested 124 lb-in (below).

I get replacement rocker-arm, I dig up torque specs.

- 2003 Buick Century

- valve rocker arm bolt

- post-9074-143689138678_thumb.jpg

 

Consulting technical service bulletin "TSB 02-06-01-034" (just google'd it):

File In Section: 06 - Engine/propulsion System

Bulletin No.: 02-06-01-034

Date: October, 2002

SERVICE MANUAL UPDATE

Subject:

Revised Rocker Arm Bolt Fastener Tightening Specification

Models:

(blah, blah, blah)

This bulletin is being issued to revise the rocker arm bolt fastener tightening specification found in several procedures in the Engine Mechanical - 3.1L sub-section and the Engine Mechanical - 3.4L sub-section of the Service Manual. Please replace the current information in the Service Manual with the following information.

The following information has been updated within SI. If you are using a paper version of this Service Manual, please make a reference to this bulletin on the affected page.

The correct torque for the rocker arm bolt is 14 N.m (124 lb in) plus 30 degrees. This specification can be found in Fastener Tightening Specifications, Valve Rocker Arm and Push Rod Replacement and Lower Intake Manifold Replacement (for 1996 Chevrolet Beretta/Corsica, 1996-1997 Buick Skylark, Pontiac Grand Am, Oldsmobile Achieva and 1997 Chevrolet Malibu ONLY).

 

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[TD]Torque wrench used; you can see it's lb-in/Nm

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[TD]The exact setting I used.

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In this engine, the exhaust push-rods are 6" and the intake push-rods are 5.x" (they're shorter). For cylinder #1, the push-rod closest to the drive belt is an exhaust (6") push-rod. I made sure they were in their correct positions, and finger tightened them. I then turn the engine over until cylinder 1 is TDC on compression stroke, so valves are fully closed. They're not adjustable, so I torque them both to the suggested 124 lb-in (or 14 Nm) using a brand-new, never-been-used torque wrench (came with calibration certification & all) until it "clicked". Tightening the first (exhaust) rocker seemed fine, I moved to the second (intake) and it started spinning...the bolt stripped the threads:

post-9074-143689138692_thumb.jpg

 

For the final kick-in-the-nuts, I rotate the engine and pop goes the exhaust rocker, right out of the cylinder head, taking the aluminum threads with it.

So now I'm needing to do a thread repair job on the first two rocker-bolt holes, out of two attempts at torqueing them to the correct (as far as I can tell) specs.

I'm deathly afraid of doing this again. What the hell am I doing wrong here?!

Edited by Sigea
Schurkey correctly pointed out that the rocker was moving freely, but the valve was not.
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You may not hav done anything could have been a po mebbe go ahead and helicoil? :)

Misfire on cylinder 6; I pull engine apart, I find intake valve on cylinder 6 moves freely, because of

 

Decided to change the LIM gasket since I was in it, so I need to remove the push-rods, which requires loosening the rest of the rocker-arms. These seemed exceedingly tight to the point I was afraid that something might break...they seemed way tighter than the suggested 124 lb-in (below).

I get replacement rocker-arm, I dig up torque specs.

- 2003 Buick Century

- valve rocker arm bolt

-

Consulting technical service bulletin "TSB 02-06-01-034" (just google'd it):

File In Section: 06 - Engine/propulsion System

Bulletin No.: 02-06-01-034

Date: October, 2002

SERVICE MANUAL UPDATE

Subject:

Revised Rocker Arm Bolt Fastener Tightening Specification

Models:

(blah, blah, blah)

This bulletin is being issued to revise the rocker arm bolt fastener tightening specification found in several procedures in the Engine Mechanical - 3.1L sub-section and the Engine Mechanical - 3.4L sub-section of the Service Manual. Please replace the current information in the Service Manual with the following information.

The following information has been updated within SI. If you are using a paper version of this Service Manual, please make a reference to this bulletin on the affected page.

The correct torque for the rocker arm bolt is 14 N.m (124 lb in) plus 30 degrees. This specification can be found in Fastener Tightening Specifications, Valve Rocker Arm and Push Rod Replacement and Lower Intake Manifold Replacement (for 1996 Chevrolet Beretta/Corsica, 1996-1997 Buick Skylark, Pontiac Grand Am, Oldsmobile Achieva and 1997 Chevrolet Malibu ONLY).

Here are my rocker arms:

Here is the torque wrench I used to tighten them

And here's the exact setting I used:

In this engine, the exhaust push-rods are 6" and the intake push-rods are 5.x" (they're shorter). For cylinder #1, the push-rod closest to the drive belt is an exhaust (6") push-rod. I made sure they were in their correct positions, and finger tightened them. I then turn the engine over until cylinder 1 is TDC on compression stroke, so valves are fully closed. They're not adjustable, so I torque them both to the suggested 124 lb-in (or 14 Nm) using a brand-new, never-been-used torque wrench (came with calibration certification & all) until it "clicked". Tightening the first (exhaust) rocker seemed fine, I moved to the second (intake) and it started spinning...the bolt stripped the threads:

 

For the final kick-in-the-nuts, I rotate the engine and pop goes the exhaust rocker, right out of the cylinder head, taking the aluminum threads with it.

So now I'm needing to do a thread repair job on the first two rocker-bolt holes, out of two attempts at torquing them to the correct (as far as I can tell) specs. I'm deathly afraid of doing this again. What the hell am I doing wrong here?

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Did you do the 2nd torque pass of a "30 degree" turn after you got them to 124 in-lbs or only go to 124 in-lbs as your first post suggested? 124 in-lbs isn't a lot of torque(basically about 10 ft-lbs) if you only had them done up to that point. I would try to verify that your torque wrench is not grossly inaccurate before using it again.

 

What brand torque wrench is that out of curiosity?

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As another poster noted, you might not have done anything wrong. I just went through helicoiling the exhaust rocker thread on #6 on my parent's '03 3400 Grand Am GT...that engine had NEVER been apart. The threads came out of the head while the engine was RUNNING as she was waiting for a red light to turn green.

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I actually torqued the exhaust rocker only *to* the click (the second/intake rocker pulled the threads before it clicked). As a sanity check, I never felt like I exerted all that much torque on either rocker...in comparison, when I initially loosened them, I had to exert what seemed like much, much more force. Playing devil's advocate, the torque wrench is probably 3-4 inches longer, which might account for some of the perceived difference in force. 3/8" torque wrench vs. 1/2" ratchet.

 

Anyway, I ordered the torque wrench new from NAPA a "Carlyle" for $220 or so...here's the calibration certification it came with:

post-9074-143689138759_thumb.jpg

From this, you can see that it's actually losing a few in-lbs near 150, so if the calibration is still reasonably close, when setting it to 124 in-lbs, it should actually be just a shade less than that. I didn't have the presence of mind to check what it was set to when I first opened up...I hear they're supposed to be stored under no load to prevent spring memory.

Edited by Sigea
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I pull engine apart, I find intake valve on cylinder 6 moves freely, because of the following.

1. How can a broken rocker arm make the intake valve move freely?

 

I get replacement rocker-arm

2. ONE rocker arm, or a set? You got replacement pushrods, too--at least the one that's obviously damaged when it poked through the rocker arm...right?

 

3. Where is that torque wrench made? NAPA just switched to Carlyle tools from their previous supplier a few months ago. I'm thinking it's all Asian, now. For not much more money than you paid, you could have bought a Made-In-USA Snap-On with a torque range of 40--200 inch-pounds.

http://buy1.snapon.com/catalog/item.asp?P65=&tool=hand&item_ID=640949&group_ID=675226&store=snapon-store&dir=catalog

 

or a few dollars less from MAC

http://www.mactools.com/ShopOnline/Product/tabid/120/productid/329422/variantid/320181/Default.aspx

 

4. Before using a torque wrench, always click it a few times on a larger, tighter bolt. A lug nut works great for smaller torque settings. Set the torque to whatever you're going to need, then pop the torque wrench on the lug nut a couple of times--THEN torque whatever it is that you need tightened. Gets the mechanism "warmed-up" and ready for use.

 

 

 

Beyond all that, were the pushrods properly seated in the lifters and in the pushrod sockets of the rocker arms? Were the rocker pedestals properly aligned to the cylinder head?

Edited by Schurkey
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1. How can a broken rocker arm make the intake valve move freely?

I apologize for that; I meant that the rocker was articulating freely, though, still attached to the cylinder head.

 

2. ONE rocker arm, or a set? You got replacement pushrods, too--at least the one that's obviously damaged when it poked through the rocker arm...right?

Correct; I've purchased replacments for the damaged rocker arm and the pushrod associated with it. I have not purchased any further replacement parts other than what was clearly part of the/an issue. I wasn't sure if I should get a replacment lifter as well, but I've read on a different forum that if you're replacing the lifters, you're well-advised to replace the cam shaft as well. I don't have the wherewithal to tackle a repair on that scale.

 

3. Where is that torque wrench made? NAPA just switched to Carlyle tools from their previous supplier a few months ago. I'm thinking it's all Asian, now. For not much more money than you paid, you could have bought a Made-In-USA Snap-On with a torque range of 40--200 inch-pounds.

http://buy1.snapon.com/catalog/item.asp?P65=&tool=hand&item_ID=640949&group_ID=675226&store=snapon-store&dir=catalog

or a few dollars less from MAC

http://www.mactools.com/ShopOnline/Product/tabid/120/productid/329422/variantid/320181/Default.aspx

I really have very little knowledge of tool brand-names...I don't know what is good and what isn't...would you strongly suggest I return this one for the Snap-On or MAC brand? Considering that I've stripped two out of two bolt-holes, I'm 100% on fucking myself thus far.

 

Before using a torque wrench, always click it a few times on a larger, tighter bolt. A lug nut works great for smaller torque settings. Set the torque to whatever you're going to need, then pop the torque wrench on the lug nut a couple of times--THEN torque whatever it is that you need tightened. Gets the mechanism "warmed-up" and ready for use.

Thank you for this suggestion; this is where my inexperience really shows...this isn't something reading directions can tell me, but it might've saved me having to buy the heli-coil kit I just bought today.

 

Beyond all that, were the pushrods properly seated in the lifters and in the pushrod sockets of the rocker arms? Were the rocker pedestals properly aligned to the cylinder head?

I was pretty certain the pushrods were properly seated in the lifters...each bank of cylinders has a guide-like thing that attaches to the cylinder head, exposing the tops of the lifters only through dime-sized holes, which the push-rods go through. Now, with first (exhaust) rocker I secured, this might have caused the problem as when I rotated the engine, it might have caused the pushrod to force the rocker out. However, recall that when I was attempting to secure the second (intake) rocker, the threads broke free before it even got to 124 in-lbs (again, according to this torque wrench, which may be suspect), so push-rod can't have even played a part in it. As far as being properly aligned to the cylinder head...I believe they were...in the pictures above, you can see they have an alignment ridge running along the bottom of the rocker assembly where it connects to the cylinder head. This would remove any side-to-side alignment...couple this with the fact that the original rocker arm bolt hole can be assumed to be properly aligned in addition to my finger tightening them first, I'm certain the pedestals were properly aligned to the cylinder heads.

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I really need to get this thing back together; my ride to work & back. I'm considering only torqueing 62 in-lbs (half the suggested 124 in-lbs). I really don't know much about cars or their operation in general (at least, not in my humble opinion)...what would the fallout of doing something like this be? Clearly it has the potential to cause misfires if an intake rocker arm again comes loose, highly inconvenient, but not debilitating or permanent. What else might go wrong?

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I really need to get this thing back together; my ride to work & back. I'm considering only torqueing 62 in-lbs (half the suggested 124 in-lbs). I really don't know much about cars or their operation in general (at least, not in my humble opinion)...what would the fallout of doing something like this be? Clearly it has the potential to cause misfires if an intake rocker arm again comes loose, highly inconvenient, but not debilitating or permanent. What else might go wrong?

If the bolt loosens, the force applied by the pushrod and valve spring will "wobble" the bolt in the threads of the head, possibly damaging both.

 

The aluminum threads of the head are suspect. More important is the torque wrench. I have a lot of trouble understanding how the threads can shear when torqued to a mere ten foot-lbs or less. 124 inch pounds divided by 12 (12 inches in a foot) is just more than 10 ft/lbs. What size is the rocker pivot bolt? I'm guessing that it's the metric equivalent to 3/8-16, or close to that. Given the length of threads pulled out of the aluminum (about one-and-a half bolt diameters on one, but only about one bolt diameter on the other) thread engagement may be an issue.

 

Snap-On is the foremost name in tools. They own many other brand-names as well, including Williams, who custom-labeled the Lowes Kobalt line until a couple of years ago when Lowes Kobalt line was cheapened by contracting to Asia. Among the Snap-On brands is a company that specializes in torque wrenches, selling under their own name, but also custom-boxing for other companies. Anything Snap-On is expensive...but there are companies (including Snap-On) selling Asian product at Made-In-America prices.

http://www.cditorque.com/about.html

 

MAC tools is a competitor to Snap-On. MAC is owned by Stanley, who also owns Proto. My primary two torque wrenches were purchased from MAC about fifteen years ago; and have given me absolutely zero issues.

 

Matco is another competitor in the professional-tool category. Matco is a Danaher-owned company along with Armstrong, and many other brands including Fluke instruments/meters. Danaher was a prime supplier of Craftsman tools for decades, and they supplied NAPA tools for years. Matco is the "quality leader" of the Danaher brands. Much of the Danaher product line is Asian, now. Matco used to stand for "Mac Allied Tool COmpany", but Mac and Matco got divorced decades ago. Later the claim was "Mechanics American Tool Company, but I'm not sure that's accurate any more since lots of their stuff comes from Asia. I always thought of Matco as overpriced Craftsman stuff.

 

If your torque wrench is Asian, I'd throw it back in the box and hand it to the NAPA counterperson. You can do much better whether the thing is in calibration or not.

 

At minimum, you need to verify the accuracy/repeatability of your torque wrench.

In my garage, very low torques are accomplished with an ancient "deflecting-beam" torque wrench. The 124 inch/lbs needed would be a mere four inch-lbs beyond the markings on the label, but I'd use that torque wrench anyway, and just going a touch off-scale. Deflecting-beam torque wrenches are inconvenient to use, they require the utmost in care when pulling on the handle, but they're very accurate, very inexpensive, very repeatable IF THE OPERATOR SHOWS APPROPRIATE CARE when torquing. They're hateful to use at higher torque levels, but low torques are easy.

 

This is the closest thing I can find to what I use on the Amazon web site. Mine is 0 to 120 inch-pounds, 1/4" drive. This one is larger, 0 to 600 inch/lbs, 3/8 drive. $45. Says "Made In U. S. A." in small letters on the tool. (I'd buy a used American-made unit before a new Chinese unit.)

 

Deflecting-beam torque wrenches NEVER need to be calibrated by a specialist. Tweak the indicator rod left-or-right so that when at rest, it aligns with the zero mark. Done. The wrench can be used on right- or left-hand threads. There is no ratchet, and that sucks.

http://www.amazon.com/Park-Tool-TW-2-Torque-Wrench/dp/B000NVAHMW/ref=sr_1_6?ie=UTF8&qid=1378514843&sr=8-6&keywords=torque+wrench+inch+pounds+1%2F4

 

71%2B-kt1TXiS._SL1500_.jpg

Edited by Schurkey
corrected tool company ownership errors
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Well, heli-coil #1 is in and holding, fully turned the engine. Only problem afterwards was a severely puckered asshole. As you suggested, I did fool around with a lug nut on the wheel first this time, to make sure both myself and the wrench were "ready" ...as laughable as that is. What blows my mind yet is how much force I had to apply to loosen the bolts initially...way more than what this wrench is telling me is 124 in-lbs.

 

*fingers crossed for the rest of this*

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Well, heli-coil #1 is in and holding, fully turned the engine. Only problem afterwards was a severely puckered asshole. As you suggested, I did fool around with a lug nut on the wheel first this time, to make sure both myself and the wrench were "ready" ...as laughable as that is. What blows my mind yet is how much force I had to apply to loosen the bolts initially...way more than what this wrench is telling me is 124 in-lbs.

 

*fingers crossed for the rest of this*

Keep in mind that the torque procedure is 124 inch-pounds PLUS an additional thirty degrees. That thirty degrees is going to make a big difference in the final torque--although you'll not be measuring that torque.

 

The bolts were put in by GM without lube. Some of the breakaway torque you experienced when loosening them is the bolt having seized to the aluminum with the many years of heat/cold cycles. When I removed the head bolts of my 3.4 DOHC, it took close to 160 foot/lbs to crack them loose, and in the process I broke a Snap-On socket. The torque spec is something like 29 foot pounds plus 90 degrees, which I then measured as --approximately-- 70 foot/lbs to install the head bolts. Breakaway torque is not an indicator of assembly torque, especially when the bolt is installed "dry".

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Based on the experince with my parent's 3400, it should do just fine. Properly installed helicoil generally speaking is stronger than the original threads.

Those heli-coils are pretty nifty. I replaced the two with stripped threads and secured those and the remaining rockers to the suggested 124 in-lbs + 30 deg. Here's praying everything holds together.
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Well it's all back together; took it for a spin. I got rid of the misfire in cylinder 6...hurray! However, after a quick test drive, I had it scanned and now it's P300 & P302, which are apparently "random misfire" and misfire on cylinder 2, respectively. I want to hope it's something simple, but it's making a very pronounced clicking/ticking/knocking though, which probably means a serious failure to properly reassemble it. Other problem is that while disassembling it, I cracked the EGR pipe. It's basically a hair-line crack near the exhaust side, where the pipe is ribbed. Would this have anything to do with the random misfire?

 

In any case, I think it'd be useful to clear all the codes to see what comes back.

 

I replaced all the spark plug wires with new Bosch wires, was pretty careful to assign them to their respective cylinders based on their relative lengths.

Maybe I'll get lucky and the wire is simply not well-connected

 

The car had been disassmbled for almost 2 weeks while I was fooling with it, but it *seems* like the acceleration is back (such as it is/was), so I'm wondering if the misfires were temporary. Also doesn't seem to be idling rough anymore. Seein's how it's been two weeks though since I last drove it, I'm not sure I'm willing to trust my memory on any of this.

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it's making a very pronounced clicking/ticking/knocking though, which probably means a serious failure to properly reassemble it.

Ideas on WHERE the noise is coming from? Was it noisy before you took it apart?

 

Other problem is that while disassembling it, I cracked the EGR pipe. It's basically a hair-line crack near the exhaust side, where the pipe is ribbed. Would this have anything to do with the random misfire?

I wouldn't think so, but you'll still want to fix it.

 

 

In any case, I think it'd be useful to clear all the codes to see what comes back.

Agreed.

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  • 3 weeks later...

I had some time this weekend to fool around with it some more. I'm pretty sure the newly-created misfire on cylinder 2 was from a loose spark plug wire. Like a perfect idiot, I pulled off the valve cover before checking the wire. In my defense, it sure sounded like a mechanical noise though. The wire wasn't fully attached to the spark plug post, so perhaps some kind of arcing?

 

Anyway, after putting it back together & holding the horn & the window switches to clear the codes (one of the two, or simply having the battery disconnected for an hour seemed to work), the "service engine soon" is no longer lit. However, neighbor's moving and they've got me blocked in, so I can't do anything more than idle it in the garage at the moment.

 

I did manage to create a leak at the metal coolant pipe that I had to take off to remove the front valve cover, so that was cool. Hopefully that's a simple o-ring fix.

 

Anyway, I'd like make a general thank you to everyone for your input in this thread; gave me some pointers & assurance where my lack of experience was failing me.

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  • 7 years later...

#1, you don't know what you are doing, #2 their is nothing wrong with the torque wrench, the reason why you are pulling the threads on the head is because when you try to tighten the rocker arm bolt down, the cam lobe is at the highest position , in turn is pushing the push rod up and when you are torquing the bolt, you are pushing the valve spring with it, there is pressure on the spring and that what making the thread pulling, you have to rotate the engine to relieve the pressure on the spring before you can tighten the bolt, the push rod should be at the lowest position, when you are removing the bolt, notice the spring is coming up and there is no pressure on the bolt

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