Broken Rocker Set Screw/Poly Lock! - Team Camaro Tech
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post #1 of 4 (permalink) Old Mar 12th, 03, 09:08 AM Thread Starter
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My car started ticking recently so I changed the header gaskets thinking I had a leak. After changing the gaskets (oh joy!) the ticking was still there. I pulled the valve cover to find that one of my poly locks had broken in half. Luckily the largest part-containing the set screw-was caught in one of the drain back holes on top of the head.

The remaining piece was still holding the rocker arm in place, but it was loosening up. These poly locks came new with my Edelbrock roller rockers.

Has anyone else had a problem like this? I am worried now that this might happen with some of the other ones while I am away from home.. Should I just change them all out, or was this maybe just one bad P/L? I have had them on the car for over 3 years now and then this happens. I have checked for valve spring bind and I have plenty of clearance.

1969 383CI, T-56, 12 bolt-3.31 posi, 13" C5 Rotors, PBR Calipers, rear disc system..
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post #2 of 4 (permalink) Old Mar 13th, 03, 01:44 AM
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A broken poly lock. You checked coil binding and it was okay. Did you check retainer-to-guide clearance inside the spring? Rule of thumb, I believe is 0.060 inch of clearance between the two items.

Could also be an over hardened, read overheated at time of heat-treated, p/l at its manufacture, and not come up again. Could the tightening of the setscrew caused too much pressure exerted onto the small area remaining of the p/l's body? Maybe, but, I would think the threads would have stripped out from either the setscrew or p/l before splitting the p/l.

I'd probably buy a new set of p/l's and install, throw the rest away. One might use a microscope and inspect the same area of the side of the p/l for cracks just to see if the others were going to break.

Too much lift on the cam? Even though you have no coil bind, the lift action of the lobe multiplied by the rocker arm ratio may have swung the r/a past its designed arc at the fulcrum bearing causing the pushrod to continue to push up on the arm past its arc end.

Check to make sure the pushrod(s) is/are straight by rolling on a sheet of glass or mirror. If its bent, something has stopped the opening motion of the r/a.

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post #3 of 4 (permalink) Old Mar 13th, 03, 06:09 AM
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I have had my stud ends ground flat when using these so the center had an even place to sit, not a hole or offset part of a stud. I just did not like the way they snugged up. Is this the problem? I don't know, but I fugure idf the set scew is sitting on a part that is not strait or has an even seat that can't be good. This could be in my opinion the long term effect of this. Something to check out.

When I did mine I pushed rags all around my heads and taped with duct-tape around the rocker studs. I then ran a die just past the top of the stud. Them made a die ginder set up. I took a die grinder with a little clamp attachment I made from a hose clamp all thread and a one inch long nut I bought at the hardware store. I attached the die grinder to a stud next to the one I was going to gind and grond the top flat. I then ran the die back off the stud and moved to the next one.

It took me a few hours, and a few beers to do but I have never had a problelm with them. I was running the summit cheapie roller rockers and locks.



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post #4 of 4 (permalink) Old Mar 13th, 03, 11:32 PM
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if you aren't binding or smacking a retainer into a valve guide, it could be from over tightening. as you may know, poly locks seem to stay better if you tighten the outer part slightly after setting the center set screw. i have seen a buddy of mine split a poly lock while tightening them, just from getting slightly ham fisted with it. maybe the last time you set them it was a bit too much, and it finally let go. it could also just be a weak lock. it's tough to say, really. but IMO, replace all of them, with good ones from say, arp. just make sure they are compatable with your rockers. good luck with it!


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