Push rod mushroomed - Pontiac GTO Forum
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post #1 of 11 (permalink) Old 04-22-2019, 01:37 PM Thread Starter
 
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Push rod mushroomed

I have a pretty new rebuilt 68 400, maybe 400 miles on clock. The other day as I pulled in the drive I noticed a tapping noise like in the valvetrain. Took off the valve cover on passenger side and the very first push rod is mushroomed on the tip. Curiously, the rocker stud has a small hole in it about a 1/4 inch from the casting at the bottom of it. There is no corresponding hole in the casting though. I sort of assumed that the stud may have pulled out and that possibly it was pinned in a prior life. Than I took off the next push rod and rocker assembly and measured both of the stud lengths and found them to be identical or very close to, at around 1.72 inch exposed. Now I'm not sure if the stud has been pushed out or and wanted some advice on what to do next. I have no indication why the pushrod mushroomed, but would you get a new single rocker set and pushrod and replace that to see if it torques down correctly and runs, or is there another process that I could use to help identify the root cause? Any helpful idea will be greatly appreciated.
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post #2 of 11 (permalink) Old 04-22-2019, 06:28 PM
 
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I have a pretty new rebuilt 68 400, maybe 400 miles on clock. The other day as I pulled in the drive I noticed a tapping noise like in the valvetrain. Took off the valve cover on passenger side and the very first push rod is mushroomed on the tip. Curiously, the rocker stud has a small hole in it about a 1/4 inch from the casting at the bottom of it. There is no corresponding hole in the casting though. I sort of assumed that the stud may have pulled out and that possibly it was pinned in a prior life. Than I took off the next push rod and rocker assembly and measured both of the stud lengths and found them to be identical or very close to, at around 1.72 inch exposed. Now I'm not sure if the stud has been pushed out or and wanted some advice on what to do next. I have no indication why the pushrod mushroomed, but would you get a new single rocker set and pushrod and replace that to see if it torques down correctly and runs, or is there another process that I could use to help identify the root cause? Any helpful idea will be greatly appreciated.

First, what lift cam? Stock?

Second, what is that mark I am seeing on the rocker arm near where the rocker arm strikes the valve stem?

Third, not sure what the hole in the rocker stud is. Doubt it is from pinning it as pinning it would go through the rocker arm stud pedestal lower down.

Fourth, is that pushrod shown in the photo still in the engine the one you are using now? Or is a damaged one? The end does not look correct at all. Should look like a ball on top.

Fifth, what is the mark that I am seeing in the top of the valve stem in the pic?

Sixth, I measured a press-in stud on one of my 1972 455 heads. From the pushrod plate that goes over the stud (and is seen in your photo as well) to the very top of the stud, it measures 1.67". Breaking this down further, I measure .894" from the plate to the edge of the 7/16" stud right where the machining is done where the taper starts. Then I measured .642" off that same edge up to where the 3/8" threads end, not including the non threaded shank at the end.


I would check all rocker arm geometry. If heads have been milled or even deck surfaced, it could change the length of the pushrod and a stock length may be too long.

You may have the incorrect ends on the pushrods.

If a high lift cam, you need to check for coil bind and clearance between the spring retainer and the rocker arm at full lift.

Check to see if the pushrod is binding/hitting on the head where it comes though below the pushrod plate. This could deflect the pushrod and not allow it to seat correctly into the rocker arm pushrod cup.

No or little oil going through the pushrod. Wrong lifters, or too long of a pushrod bottoming out the valve lifter, or even a collapsed lifter.

Piston-to-valve issues I would think would have bent the pushrod as well. If it is straight, then this is probably not an issue.

It looks like you have the Competition Cams 1.5 long slot rockers? If you have a high lift cam, you need long slot rockers so the rocker arm does not bind on the rocker arm stud at high lift.

Just a few things to check, but I would not be driving it until I found the cause of the destruction. I would pull every pushrod and look at them all. Then check rocker arm geometry.

If you had a local machine shop rebuild your engine, bring him on it as he may have some things to check or may be tearing it down to find the problem.
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post #3 of 11 (permalink) Old 04-23-2019, 10:17 AM Thread Starter
 
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Thanks for taking the time to reply.
First, cam is a comp cam 51-223-4, nothing too special lift .477/.480, Duration 268/380. stock spring etc
Second, I see the mark and the next stud down has an identical set of indents. No sign of it hitting anything tho and they are very smooth to the feel.
Third, I agree it is too high and there is no hole in casting. On further inspection, other studs in that bank also have holes.
Fourth, That is the pushrod from the intake side and it does not have the ball type ends that I have seen on others, but I do see that style for sale for that motor on the net. The overall length, close as I can tell (my micrometer not long enough) is 9.136"
Fifth, That is a trick of the picture, it looks just like the neighboring stem.
Sixth, I did similar measuring and while my measurements are not identical to yours, they are very close and are the same from stud to stud. (intake and exhaust). I measure 1.71" bottom to top, and .859" first measurement, and .604" on the other. Had a hard time measuring thse, but locked my micrometer to match up to the next stud and they are very very close.

I did check the remaining length of pushrod on a glass surface and it is straight. One thing I wonder about is the amount of valve stem that protrudes from the keepers. You cant see in the pic, but the Exhaust side seems deeper in the keeper than the intake side by just a little bit. just eyeballing the other sets of valves they look consistent with the intake side. Not sure what if anything this may mean, but it would seem to affect geometry on that valve.

Also, how do you identify a collapsed lifter? It has been moving that pushrod, that much is clear, just curious.

I may be in a little over my head, but I really want to take this car on a roadtrip with my son this summer and Appreciate your input.
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post #4 of 11 (permalink) Old 04-23-2019, 07:34 PM
 
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You don't have the 1968 GTO #16 heads or high performance heads - these will have screw-in studs. I still do not know what the small hole is in the studs. Maybe the engine builder can tell you and you could pass that along to us.

I also do not see the factory Pontiac "oil splash shields" installed over the valve springs, but may not be needed if you had the Viton valve seals installed. Factory specs allowed for a slightly larger clearance on the valve guides than when using the aftermarket bronze valve guides many machine shops use, so the factory shields, along with the factory valve seals, helped to keep excess oil off the valve stem and minimize oil burning.

Did you read the "Recommended Components" at the bottom of the page? 51-223-4 - Xtreme Energy? Hydraulic Flat Tappet Camshafts

I am going to say that stock springs may not be adequate for that high of lift. You could have the valves bouncing off the seats when they close.

The Comp Cams XE grind has fast (steep) ramps on the cam lobes which can cause fast opening rates and fast closing rates - more than what factory springs may handle. I used the XE274 on my last 400 build, but it was a 1972 8.2 compression engine 7K3 heads with screw-in studs and 1.5 rockers. The Comp Cams 110 LSA works well with low compression engines. I do not like them for factory high compression engines - my opinion. I went with Comp's recommended springs and did not do any machining - I just stuck them on.

Pushrod length according to the 1968 Service Manual is 9.16". for the GTO, FB 400, GP, & 428. Others used the 8.72" which in the SM is called the "Standard" engine (I would say any low-performance/HP engine). Looking at the Comp Cams pushrod selection, their High Energy pushrods for Pontiac use the welded ball end while the Magnum pushrods use the one piece formed tip. http://www.compcams.com/catalog/comp...12_292-311.pdf

Valve stem stick-out above the spring retainer should not be a problem. It is the clearance between the retainer and the rocker arm, and the clearance between the inside base of the retainer and the cast valve guide. You don't want the retainer to slam the guide.

You also want to check for coil bind on the valve springs and ensure you have the needed clearances between the coils at full lift.

The factory 1968 GTO heads use exhaust valve (5.08") and intake valve (5.09"") - slightly different in length, but nothing you should see. The "Regular Fuel 400," which I am going to say was the 265 HP 2 bbl engine used 4.98" length exhaust valves and 4.99" length intakes. Shorter over all than the HP engines, but still nearly the same length as compared to each other. Also, the valve could be "sunk" depending on the way the valve job was done, how many times it was done, and if you used the old valves or went with new ones. The tops of the valve stems should be perfectly flat, no groove or depression.

A collapsed lifter will usually cause the rocker arm clicking sound you get when the rockers are out of adjustment when the car is running and tightening the rocker arm nut will not cause the sound to go away. It is not common from my experiences as I have never had one collapse on me. So, not saying you have this, and probably do not, but it could be something to consider if you do not find anything obvious.

At this point, as a minimum, I would first check my valve train geometry using what you have installed. Check for any kind of clearance issues or binding. I would email Comp Cams as to whether or not you can use stock factory spring pressures with their cam.

Take a look at this post, read the first post with photos and a few after. This may apply - https://www.gtoforum.com/f170/centra...review-106018/

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post #5 of 11 (permalink) Old 04-25-2019, 08:53 AM Thread Starter
 
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Those links you sent made me go look at more pushrods, I'm not sure but the ends look pretty ragged and jagged up close and I feel like they may all be failing. Should the hole in pushrod be clean and machined looking? I was gonna put one rod in to test, but now I don't think so. I will take your advice, contact Comp cams to discuss
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post #6 of 11 (permalink) Old 04-25-2019, 05:15 PM
 
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Originally Posted by rlitcher View Post
Those links you sent made me go look at more pushrods, I'm not sure but the ends look pretty ragged and jagged up close and I feel like they may all be failing. Should the hole in pushrod be clean and machined looking? I was gonna put one rod in to test, but now I don't think so. I will take your advice, contact Comp cams to discuss
Yes, they should be smooth. Looks like you may have caught them before you experienced complete failure of the pushrods and/or engine.
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post #7 of 11 (permalink) Old 04-25-2019, 05:27 PM
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Jim's advice is right on. Those pushrods are on their way out, and soon.
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post #8 of 11 (permalink) Old 04-27-2019, 06:11 PM Thread Starter
 
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Thanks guys have a new set of pushrods and rocker kits on order
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post #9 of 11 (permalink) Old 04-29-2019, 08:51 PM
 
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It seems with only 400 miles and pushrod failure, maybe the length is not right. I bought new stock ones for a rebuild (9.12) only to find the geometry with my flat tappet voodoo cam and roller tip (1.5) rockers needed 9.00 length. Unfortunately no one sells a cheap pushrod that length and I had to pay for better than I needed. To the tune of $172.
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post #10 of 11 (permalink) Old 04-29-2019, 09:32 PM Thread Starter
 
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One follow up question. When reassembling the pushrods and rockers, should I use an assembly lube on the ends and the contact points? Any other special prep or cleaning of the new parts?
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