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Post Info TOPIC: Broken rocker arm in 68 396 Grande Parisienne


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Broken rocker arm in 68 396 Grande Parisienne


My 68 Grande Parisienne is the June feature car and now I have a valve train issue that happened Sunday on the Winnipeg perimeter by pass.  How ironic is that? 

On late Sunday morning, I was heading out to Stonewall (45 minute drive) to watch my daughter play ball and I get about 16 km from home and at 70 mph the engine starts to hesitate and then starts popping and backfiring.  At first I thought a fuel issue was occurring then there was some clattering and backfiring and eventually I limped the BBC home (16 km), which was quite stressful.  Later on in the afternoon I popped the valve cover off the passenger side head as that was where the clattering was coming from and saw the broken rocker arm.  I picked the rocker arm right off the ball and it fell into two pieces in my hand so removal was quite easy!  I pulled the push rod out and it appears to be clean and clear and appears to be straight.  No bending in the rod at all.  The ball and nut are still on the head stud so here is an update on the June feature Grande Parisienne!!    

I made it to the game, although a bit late but now I have this issue.  I have to wonder what the cam lobe looks like for this exhaust valve.  I didn't want to cheer this engine up quite yet but I have to wonder if the failure might be the result of a rounded lobe, failed lifter??  Hmmmm...........  Any suggestions from the CP members???

 

Jake

 

IMG_inspection.jpgIMG_rocker bank.jpgIMG_broekn rocker.jpgIMG_pushrod & rocker.jpgIMG_rocker.jpg



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Earl36


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



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'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.



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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.

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1966 Strato Chief 2 door sedan 283 "survivor"


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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

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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.

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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

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Earl36


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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.

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

Jake

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Earl36


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

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MC


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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.



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Replacing all the rockers is not a horrible idea.

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1966 Strato Chief 2 door sedan 283 "survivor"


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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?

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Earl36


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

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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!

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1966 Strato Chief 2 door sedan 283 "survivor"


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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.



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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

 

 



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

Or am I just too tired from this heat today?

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

Fred



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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

 

 



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Thanks for clarifying the procedure Fred. I wasn't sure about the ˝ 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



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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!

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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



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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

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Earl36


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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



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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



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