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Old 02-17-2010, 02:11 AM
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Stuck Lifter Plungers on '76 Pontiac 350

We recently built a '76 Pontiac 350 for my son's '79 Trans Am.
I selected a Summit Hydraulic Cam and Lifters. The cam has nearly exact spec's as the Edelbrock Performer Cam designed for idle-5000RPM with smooth idle. We did the usual valve adjustment as on other Pontiac V8's (1/2 turn past 0-lash) We use Penzoil 10W40 with a bottle of STP to compensate for the lost Zinc additives in the oil.

The engine ran fine the first 800 miles, but it would occasionally have lifter tick for a few seconds after startup which immediately went away as oil pressure came up. We double-checked the lash and found no problems so I passed it off as a characteristic of the Summit lifters.

We had just stopped by a sub shop for lunch and started the car only to hear a loud pop, then a very rough miss in the engine... we also had a large stream of oil pouring out the oil pan! After towing it home, we discovered a pushrod stuck through the oil pan. Pulling the valve covers, we discovered the 1/2 of the #7 intake pushrod laying in the lifter valley. It had come off and fell through the cam area and was snapped in half by the crank!
Thankfully, no other damage. We ordered a new pushrod, removed and welded and reinstalled the oilpan. Adjusted the the valve and sealed it back up and we were good to go... for another 80 miles.

Again after startup the engine made a pop, then began running rough... at least no hole in the oil pan. This time, we found the #3 Exhaust pushrod had popped off and had again got flung into the oilpan. One piece was laying in the lifter valley and the other half was laying in the oil pan. Again, no other engine damage. We did find the adjustment nut on that rocker arm had slightly backed off but only a bit. Again we ordered and installed a new pushrod, re-adjusted, but this time there was considerable torque required to turn the adjusting nut the 1/2 turn past 0-lash. On closer inspection, what I discovered was that the lifter plunger was not going down at all, but rather the valve was being pushed open! The lifter would not compress at all!

I checked the others and found 6 others with plungers stuck completely in the fully extended position. We had changed oil at 500 miles and again at 800 when we fixed the oil pan, so the engine was very clean. I pulled the affected lifters and all of them looked fine with no visible contamination, dirt, sludge or unusual wear pattern on the face. After reassembly, they now compressed like normal!!!

We pulled all the lifters and installed a set of Comp Cams hydraulic lifters and have since driven 200 miles with no issues and no ticking during engine starts.

My question is if anyone else has had issues with Summit lifters or should I be wary that some other problem is lurking?

Our Pontiac 350 is a mild performance build with 6X-4 heads, a 0-decked block, and a set of headers with a good dual exhaust and 60PSI Melling oil pump. When the heads were rebuilt, we upgraded to Comp Cams 7/16 Rocker studs and Roller tip 1.5:1 Rocker arms. We also double checked that the pushrods had adequate clearance and that the valvetrain geometry was good.

Thanks!

Kevin

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Last edited by Bigolotava; 02-17-2010 at 07:49 AM. Reason: Mis-spelling
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Old 02-17-2010, 08:22 AM
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When I first started reading your post, I thought for sure that you were using the Chevy technique on a Pontiac rocker set-up that uses bottle neck studs that have to be tightened all the way to 20 ft/lbs.

I see, though, that you've replaced the studs. This leads me to believe there is either a problem w/the adjustment procedure you used, OR the nut is backing off.

If you're convinced the nuts aren't backing off (what I suspect is the prob.), then I'd suggest you use more preload than 1/2 turn. While this should be fine, obviously, there's enough lash coming back into the train to allow it to kick the p-rods.

What type rocker nuts are you using? Those studs should NOT use lock nuts. They're made for polylok-type nuts. And the PL nuts have to be jammed w/a bit of force- and should be ARP.

I also see that you've changed lifters and seem to have gotten away w/using new lifters on a (slightly) used cam- this doesn't always have a happy ending, but I digress.

Check the lifters you removed.

If they sent you Chevy lifters, that may very well have been your problem. The lifters physically fit (height and diameter), but the differences in the oil band location can cause problems.

A Pontiac lifter will have the oil band beginning ~1.125" (~1.170 for Rhodes lifters) up from the foot. Chevy's will be ~0.875".

EDIT- That's a real trick, getting TWO p-rods into the pan! Never had (or heard of) it happening. I DID have a Pontiac p-rod get shot past my head w/enough force to shoot it well over 150 feet! Would certainly have killed me, had it hit me in the head...

Last edited by cobalt327; 02-17-2010 at 09:32 AM.
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Old 02-17-2010, 08:52 AM
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A good machine shop should have told you about valve adjustment when they installed the studs and recommended the poly locks for use with your new studs.
Like Cobalt said, the locking nut's are backing off. I messed up one time after a rebuild on a 455 and was thinking Chevy while working on a Pontiac and din't make it 12 mi. when the ticking started and it started running like crap.
After realizing what I had done while sitting on the side of the road waiting for a buddy to come tow me back home, the first thing I did was torque the rockers down and problem solved. I couldn't believe how fast the nut's backed off. The locking nut's WILL back off if not torqued down.
Get the poly locks and adjust them to 0 lash and your problem will go away.
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Old 02-17-2010, 10:56 PM
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Guys,

Thanks for the feedback!
I didn't want to add too much more detail to the original post as it was getting pretty darn long, so here's the rest:

Originally, the heads were rebuilt, but the shop left the original 3/8" bottle-neck studs in there. When we replaced the factory rocker arms, we used the supplied cinch nuts that came with them. (not posi locks)
When the first pushrod came out, we did indeed find the nut had backed-off, but the lifters were still OK with no stuck plungers.

We then went and bought 3/8" posilocks and installed the new pushrod, re-adjusted lash on all the valves and buttoned it up.

80 miles later when the other pushrod came out, we found its posilock tight, but the top of the stud it was locked to had cracked-off! (a valuable lesson to replace 34 year old rocker studs!)

So, we bought brand-new Comp Cams 7/16" studs and a new set of 7/16" polylocks and another new pushrod. When we put all this in and tried to adjust the valves, that's when we noticed the plungers stuck in the "up" position. Again, disassembly revealed no contaminants, sludge or dirt, but after putting them back together they seemed to again function fine.

Not wanting to chance it, we went ahead and got new Comp Cam lifters. We did use Comp Cams Cam lube and following assembly and startup ran the engine at 2500rpm for 20 minutes to break the new lifters into the almost-new cam. I know... not ideal, but this is already getting expensive, time-consuming and pushing my limit of wanting to be under the hood of this car! (We also always use a bottle of STP oil treatment at every oil change to add back the zinc and other anti-wear agents)

Following the 20 minute break-in, we re-adjusted the lash and so far, everything is good! Also, the difference in strength and thickness from the original 3/8" to 7/16" studs is amazing!

200+ miles and not a tick or click! I'm writing this from a hotel room tonight as I'm out of town this week on business. Will check the measurement on the old lifters Saturday to see if they are perhaps Chevy lifters and advise.

Thanks again guys - your feedback and help is so appreciated!

Kevin
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Old 02-17-2010, 11:36 PM
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Quote:
Originally Posted by Bigolotava
we noticed the plungers stuck in the "up" position. Again, disassembly revealed no contaminants, sludge or dirt, but after putting them back together they seemed to again function fine.
This could have just been due to the lifters being "pumped up" i.e. full of oil. Oil won't compress, so it will take time for the plunger to compress- this can take a while to happen.

I'm not sure which STP has any zinc in it, but generally speaking, new rings do not seal/lap in well to the cylinders if the thick, sticky STP is used on a new bore/rings.

One commonly used supplement is ZDDPlus.
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Old 02-22-2010, 07:22 PM
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OK... we checked the band on the Summit lifters and they do indeed start at darn near 1.125" from the lifter's base... so I'm still puzzled why they didn't compress and were rock hard. Again, when I tried to turn the posi locks past 0-lash, the valve was pushing open, rather than the lifter bleeding-down. I've adjusted lash on both Chevy and Pontiac V-8's over the years and never had this happen before.

Anyhow, we now have 450 miles on the new Comp Cam lifters, 7/16" studs and poly-locks and all is well, and still no ticking when the engine fires-up as it used to with the Summit lifters.

Lastly, I just use the regular old STP oil treatment. I agree not as much Zinc as the other additives out there, but seems to do the job. We don't have any issues with oil burning/consumption, so I have no reason to believe the rings haven't sealed properly.

Thanks again everyone for your comments and suggestions!

Kevin
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Old 07-18-2010, 10:59 PM
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5,000 mile update!

Guys,

Well, we've now put 5,000 miles on our Pontiac 350 with the new lifters and she's running great with no issues!

I'm going to chalk up the pump-up problem to the Summit lifters.

Thanks again for all your advice and help!
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Old 07-18-2010, 11:02 PM
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Good news, gotta' luv updates! Have fun.
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Old 07-01-2011, 10:56 PM
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Update #2... nearly one year later and 13,000 additional miles, plus multiple passes at this year's Pontiac Heaven Drag's and still going strong with the Comp Cam's lifters/studs/polylock combo!
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