Help! - Rocker Arm Stud Question

[ckrobins]

I'm new to the forum - if I've posted in the wrong place, I'm sorry.

My son and I are rebuilding the engine in his 1995 Grand Am SE.
This is a generation II 3.1L V6 (VIN "M")

I purchased new pushrods and new rocker arms for the engine last week, because an earlier mishap damaged some of the old ones.

The rocker arms on this engine are the ball and nut type, and they are not the roller type. The rocker arm studs are narrower where they are threaded than on the unthreaded part. (I estimate the threads are 8mm dia. and the unthreaded stud is 10 mm - but I'm just eyeballing)

The new rocker arms came with a nut that's too big to fit the old stud, so we attemped to use the new rocker arm and ball and the original nut. The manual we are using said we should torque the nut to 18 ft-lbs. Well, the nut bottomed out on the threads. Alex was using a "click" type torque wrench to tighten it and before the wrench clicked, we had a broken stud. The nut and threaded portion of the stud broke off.

Most of the parts houses in town couldn't find a number for a replacement stud. I stopped at the Chevrolet dealer's parts department and they checked for me. They said the type of stud I have is a discontinued part

One parts house did find a stud and we ordered a complete set. The new studs have no "shoulder" on them. That is, the threads are the same diameter as the lower unthreaded portion of the stud. The new studs are threaded farther down than the old ones, and the nuts on the new rocker arms fit these threads. So, it looks like I can't just tighten a nut to the stop and torque it properly - I need to know how to properly adjust the rocker arms. My manual doesn't give this information - it must assume that I have the original non-adjustable type of rocker arm.

Will the new studs/rocker arms work with my engine? If so, how do I adjust the rocker arm nuts correctly?

Thanks in advance for your help.

(I know that I can probably rummage in the salvage yard of the machine shop and possibly find another of the old type studs. I suspect that some of the old ones are fatigued, though, and I'd rather replace them with new if I can)

[1988GTU]

I would suggest going to the local "u-pull it" and using one of those.

I looked for the spec for you and came up with nothing helpful.

[SappySE107]

I have some gen 2 studs which will work on your gen 3. The 94-95 3100s didn't have the roller rockers but they are still 1.6. If you get rockers for a gen 2, they will be 1.52:1. I am not sure why you are having problems with your replacement parts if they were designed for your engine.

How much are replacement rocker arms?

[bszopi]

Rocker arm should be 10nm+30º or 89in-lbs+30º.

http://60degreev6.com/showthread.php?t=24938

As far as the engine, if its a 95 GA, then its a Gen3 engine, although I'm pretty sure its still a VIN M. Do you have a picture?

Here is a picture of what I think you have as far as the studs go...



And here is what your rocker arms should look like...



As far as adjusting the rockers, there is none. Torque them to spec and go.

[ckrobins]

I have some gen 2 studs which will work on your gen 3. The 94-95 3100s didn't have the roller rockers but they are still 1.6. If you get rockers for a gen 2, they will be 1.52:1. I am not sure why you are having problems with your replacement parts if they were designed for your engine.

How much are replacement rocker arms?

The ones that I picked up were Sealed Power (pn R-881) which at least two parts houses agreed were the right ones for the engine. They were $4.95 each.

I'm afraid I don't know what 1.6 and 1.52:1 refer to.

[ckrobins]

The pictures show exactly the old stud and old rocker arms that I have. Right on. The new parts I have don't match these, and the dealer claims I can't get the old ones any longer from them. Am I just asking for the wrong things or are these really that hard to get?

89 inch-pounds is more like 7 ft-pounds, isn't it? That might explain how we broke the old one.... :sheepish:

[bszopi]

Should be GM Part Number 12521876. If the local dealer "can't get them", you can order them via www.gmpartsdirect.com and for almost half the cost. Unfortunately, if you only order 1, then the S&H will bring it back up to the list price...

GM List - $14.70
GMPD Price - $8.72

Comes up as:
Category : Engine Valve Rocker Arm
Description : Arm Kit
Pack Qty : 1

Its a special order item, so it'll take a couple weeks to get. I'd just goto the delaership and give them that PN and see what they come up with. If you are lucky, that'll come with the stud as well.

Oh, and the 1.6 and 1.52 Ben listed was referring to the rocker ratio.

[1988GTU]

89 inch-pounds is more like 7 ft-pounds, isn't it? That might explain how we broke the old one.... :sheepish:

SO the nut is 7ft lbs? I thought it was 4X? ft/lbs

[bszopi]

I was looking at my All-Data account, and it actually lists 24Nm (18ft-lbs). That seems a far cry from 10 Nm+30º. And I just checked my 94 GM Service Manual, and it also lists 24Nm. So I guess diregard my previous spec, and I'll have to update the specs page.

The stud is 64Nm (47ft-lbs) for when you go to torque that down.

[torq455]

The pictures show exactly the old stud and old rocker arms that I have. Right on. The new parts I have don't match these, and the dealer claims I can't get the old ones any longer from them. Am I just asking for the wrong things or are these really that hard to get?

89 inch-pounds is more like 7 ft-pounds, isn't it? That might explain how we broke the old one.... :sheepish:

Yeah, more like 7.4 ft/lbs. I torqued my rocker studs to 25 ft/lbs. I didn't have that degree tool, so I estimated. I estimated 35 ft/lbs origionally and broke the threads in the head--pulled them clean out. Had to heli-coil. Been over 2 years and still ok. lucky me! Not sure as to why you broke a stud.

[1988GTU]

So 17.7ft/lbs for ?

[bszopi]

Yes, the nut is 18ft-lbs and the stud into the head is 47ft-lbs.

[ckrobins]

Thanks for confirming the torque spec, Brad. I have the Grand Am's GM shop manual and both of those numbers - 18 ft-lbs for the nut, 47 ft-lbs for the stud - agree.

As for why the stud may have broken - the earlier mishap I mentioned was six bent intake valves, six bent or broken pushrods. I knew the pushrods for the intakes were supposed to be the short ones and I still managed to screw up. I showed the broken stud to one mechanic at a motor supply shop and he said he thought the stud had been cracked before we tried to torque the nut on it. I figure if there was enough force involved to bend a valve and break a pushrod, there was probably some stress put on the studs too. Oh yeah, and one of the pushrods was jammed through a rocker arm. The rocker arm and pushrod came out as a unit....

[ckrobins]

FYI - the nut in 1988GTU's last post looks like the new ones they're trying to sell me. The old nuts have a shoulder cap on the bottom

[bszopi]

Ahh, that would definately explain the broken stud. I would definately make sure to check the rest of the studs before I got everything buttoned up. Wouldn't want something to happen a few miles down the road.

Edit...

REALLY?!?! If you have a digital camera, I'd love to see what they gave you as a replacement!!