Broken rocker arm in 68 396 Grande Parisienne

68 Grande · Guru

Broken rocker arm in 68 396 Grande Parisienne

Pontiacanada · A Poncho Legend!

Looks like that rocker was fracturing for some time ... it appears the whole fracture is not a fresh break.

4SPEED427 · A Poncho Legend!

Very common problem on 396/427. I would just replace the pushrod and rocker to begin with. I've had a couple of them do that and was 100% successful with replacing just those 2 pieces. I wouldn't be concerned about the cam just yet.

Taylor55 · Poncho Master!

Get another rocker arm ball and nut assembly either new or used.Count the number of threads on the other rocker arms and tighten the replacement one that many threads.Change the oil and oil filter before starting. Have someone crank the engine over and visually watch the rocker arm move and if the travel is appx the same as the others you should be ok. Loose rocker arm nuts do happen on both small and big blocks. You can properly set all the lifters after the repair is complete. Follow the maintance manual .

Al

JC2+2 · Poncho Master!

Back in the eighties I had a 396 which would break them in pairs. They would either break or the pushrod punch right through. It had a higher lift cam which definitely put more stress. After the third pair broke I changed them all and no more issues.

68 Grande · Guru

Well, the feedback is helpful and informative. Hopefully it will be a simple fix as this appears to be quite common. What about the lifter, should the lifter be replaced as well while I am at it?

Thx for your responses!

Jake

4SPEED427 · A Poncho Legend!

You should be able to look in with a flashlight just to make sure the lifter is fine, and make sure the snap ring is intact. If that all looks good, I would just do a pushrod and rocker.

68 Grande · Guru

OK, Thx for all the responses! I will post how the repair goes once I locate the parts!

Jake

4SPEED427 · A Poncho Legend!

To match the pushrod, they will need to know intake or exhaust and 5/16" or 3/8" diameter. Forgot to mention that.

MC · Canadian Poncho Superstar!

Sorry to hear about your bad luck. Might be a good idea to carefully inspect the other rockers to make sure you don't have fractures starting in others as well.

If it were me, I'd probably replace all of them, but that's just me. I'm kinda paranoid about known issues that are hard to detect until failure occurs.

4SPEED427 · A Poncho Legend!

Replacing all the rockers is not a horrible idea.

68 Grande · Guru

Yes, most likely replacing the whole lot of them is not a bad idea. Any suggestions on type of make to use? Any preference or any types to avoid?

4SPEED427 · A Poncho Legend!

I've used GM, TRW and Sealed Power, all have been fine. GM rockers are discontinued now though.

4SPEED427 · A Poncho Legend!

As far as adjusting it, I've always been taught on a used cam/lifter, tighten the rocker nut just to the point it starts to move the lifter plunger, than another 1/2 turn.

As the disclaimer says, "your experience may vary" i.e. others here may have their own specific recipe that works for them!

Mike Ward MB · Addicted!

Years ago a friend showed me the best way I've seen to set them. At TDC you set half of them, with the timing mark aligned at #6 you set the other half. Tighten until the pushrod can't be spun by hand, and when all are set give them a half turn.

I've got a list of which ones to do when but beats me what I've done with it. Wouldn't take much to figure it out but if I come across it I'll add it to the thread.

Tin Injun · Addicted!

Mike Ward MB wrote:
Years ago a friend showed me the best way I've seen to set them. At TDC you set half of them, with the timing mark aligned at #6 you set the other half. Tighten until the pushrod can't be spun by hand, and when all are set give them a half turn.
I've got a list of which ones to do when but beats me what I've done with it. Wouldn't take much to figure it out but if I come across it I'll add it to the thread.

The procedure is as follows, Mike.

A- mark the distributor with chalk at the position s of the #1 and #6 plug wire terminals. Remove the cap.

B- Turn the engine until the rotor lines up with the #1 terminal mark.

C- adjust the following valves, counting from the front of the engine:

inlet valves of cylinders 1-2-4

exhaust valves of cylinders 1-3-5

back off the rocker nut till lash can be felt at the pushrod, then tighten nut until all lash disappears. Now turn down adjuster nut one full turn. repeat for all . [ if your lifters are older and carboned up, you may have to play with that last full turn]

D- Turn engine until rotor lines up with #6 chalk mark.

repeat the previous procedure for the following valves , again counting from the front:

Inlet valves of cylinders 3-5-6

exhaust valves of cylinders 2-4-6

This sequence works - utilized it when I changed heads on my 327. Also works with mech. lifters. You just set appropriate lash with feeler gauges. Big blocks are numbered the same as small and all use 1-8-4-3-6-5-7-2 firing order.

Correct me if I am wrong. Hope this helps.

Fred

4SPEED427 · A Poncho Legend!

I'm not seeing 7 and 8 in your list Fred.

Or am I just too tired from this heat today?

Tin Injun · Addicted!

Carl, you got a point there - I will investigate my documents.

Fred

Tin Injun · Addicted!

Carl Stevenson wrote:
I'm not seeing 7 and 8 in your list Fred.

Or am I just too tired from this heat today?

Well, Carl, now that I have instructed everyone on how to set the valves on a SIX CYLINDER , I will try to explain an EIGHT CYLINDER.

Set the timing mark on the timing mark on the torsional damper on th " O " mark on the timing indicator. If the #1 valves are moving, the engine is in #6 firing position and the crank must be rotated 360 degrees. If #1 valves are not moving, then the piston is at top dead center, which is correct.

With the engine in this position, the following valves can be adjusted: [counting from the front of the engine, cylinders 1-3-5-7 are on the left- hand cylinder bank while cylinders 2-4-6-8 are on the right- hand cylinder bank.]

Inlet valves of cylinders 1-2-5-7

Exhaust valves of cylinders 1-3-4-8

Next rotate the crank through 360 degrees so the mark on the damper is once more aligned with the "O" mark. # 6 piston is now at TDC and the following valves can be adjusted:

Inlet valves of cylinders 3-4-6-8

Exhaust valves of cylinders 2-5-6-7

As with the 6 cyl. back off the adjuster nuts untill you feel play on the push rods. Retighten until no slack felt and then turn one more complete turn.

Like before, if your lifters are old or carboned up you may have to play with them a bit, but this should do the trick.

Sorry about the missing 7 and 8 cylinders. I should have known to go to the grease covered instructions the first time. Anyhow, mistake corrected [I hope}

Fred

Mike Ward MB · Addicted!

Thanks for clarifying the procedure Fred. I wasn't sure about the ½ or full turn for final tighten after adjustment. I didn't guess on the valves for each position, shouldn't have taken a shot at final lash.

Mike

4SPEED427 · A Poncho Legend!

I'm a bit leary of the full turn advice. I've had guys tell me that opens up the possibility of burning a valve.

But this is one of those things where you ask 10 guys and get 10 unique answers!

GLHS60 · Poncho Master!

Tin Injun wrote:

Correct me if I am wrong. Hope this helps.

Fred

Next time we have coffee Fred I'll show you the right method!!

Thanks

Randy

68 Grande · Guru

Tin Injun wrote:

Like before, if your lifters are old or carboned up you may have to play with them a bit, but this should do the trick.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Well, the car will 50 years old in November 2017 so I am going to go with yes, they are old and most likely carboned up! LOL

But joking aside, thx for all the responses! This gives me good instructions on adjusting this old, old valve train!

Jake

Tin Injun · Addicted!

GLHS60 wrote:
Tin Injun wrote:
Correct me if I am wrong. Hope this helps.
Fred
Next time we have coffee Fred I'll show you the right method!!
Thanks
Randy

Randy, my muse, I'm sure you will.

Fred

Tin Injun · Addicted!

Carl Stevenson wrote:
I'm a bit leary of the full turn advice. I've had guys tell me that opens up the possibility of burning a valve.

But this is one of those things where you ask 10 guys and get 10 unique answers!

Carl, many years ago, when I did my training on these same old cars, the theory was one full turn after removing lash would center the pushrod seat in the bore of the lifter. Any more might cause a valve to not seat properly due to thermal expansion and cause burning. Therefore, always have the engine to operating temp when adjusting your valves. If they are too tight, misfiring should be obvious and further adjustment can be done.

Some of the racers back then used to set hydraulic lifters to zero lash then back off just enough to hear faint clicking similar to solids in order to avoid lifter pump- up at high RPMs.

In any case, I got this information from a service manual.

Fred