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Old 09-05-2012, 11:02 AM
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Broken Poly Locks

I purchased a couple of Sprint cars this past weekend. I was checking them over and pulled the valve covers on one of them just to check things out. I removed the stud girdles and when I did, one poly lock on each side was broken. They both seemed to break right at the end of the rocker stud. Has anyone else had this problem with the long poly locks and stud girdles?
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Old 09-10-2012, 02:01 AM
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poly locks

the stud girdles are suppose to stop this from happening. stud girdles are not easy to install. my suggestion is to replace all broken parts and have the stud girdles re-installed properly.
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Old 09-10-2012, 07:04 AM
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The locks were over-tightened.

tom
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Old 09-10-2012, 08:20 AM
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Quote:
Originally Posted by S10 Racer View Post
I purchased a couple of Sprint cars this past weekend. I was checking them over and pulled the valve covers on one of them just to check things out. I removed the stud girdles and when I did, one poly lock on each side was broken. They both seemed to break right at the end of the rocker stud. Has anyone else had this problem with the long poly locks and stud girdles?
I agree overtightening the set screw is likely the cause. Use top-shelf locks like ARP. A poor quality lock is likely to fail before a good one, all else being equal.

Be sure the alignment of the stud girdle is good. Breaking locks isn't necessarily caused by this, but it's just a good idea to verify the studs/locks aren't being stressed by being forced out of alignment by the girdle. A bit more on the subject is HERE. It is kind of rudimentary (and may be old news to you), but it may help someone doing a search for info on polylocks.

Good luck.
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Old 09-10-2012, 11:20 AM
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What size stud?
If the stud is flexing and the girdle is not, the polylocks would have a bending load on it.
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Old 09-11-2012, 04:29 PM
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Quote:
Originally Posted by lmsport View Post
What size stud?
If the stud is flexing and the girdle is not, the polylocks would have a bending load on it.
X2 and highly likey. Check where the stud screws into the head for cracks forming in the stud boss.

Bogie
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Old 09-12-2012, 06:42 AM
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The engine(s) is/are SBC built for competition (Ideas to build high RPM SBC). The stud should be 7/16"- not much sense in installing a stud girdle on 3/8" studs.
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Old 09-12-2012, 07:47 AM
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Dart 64110002 - Dart Stud Girdles - Overview - SummitRacing.com

Dart Heads Rocker Arm Stud Girdle, Aluminum, 3/8 in.-24 Thread, Chevy, Small Block, 23 Degree Heads
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Old 09-14-2012, 06:29 PM
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The issue isn't that it is available. The issue to me is to girdle a 3/8" stud is lame unless there's a rules restriction mandating it. Most rules like that are to "save the racer money". But in this case, outlawing a 7/16" stud- while allowing a girdle- makes little sense.
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Old 09-15-2012, 01:06 PM
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+1 on stud moment(flex, misalignment). Man i dont have much to contribute except that my best friend used to run 360 sprints and I used to help him wrench on them. It was probably the most fun I've had racing. I miss it for sure. Expensive, but awesome. Nothing like it.
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Old 09-15-2012, 05:34 PM
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Quote:
Originally Posted by S10 Racer View Post
I purchased a couple of Sprint cars this past weekend. I was checking them over and pulled the valve covers on one of them just to check things out. I removed the stud girdles and when I did, one poly lock on each side was broken. They both seemed to break right at the end of the rocker stud. Has anyone else had this problem with the long poly locks and stud girdles?
Hopefully it's just a case of the locks being overtightened (being broken even w/the end of the stud would indicate that, IMO), but until you take a good hard look this is only a guess. And if there's more underlying damage, using them as-is could get expensive quickly.

If the heads (who makes them, BTW?) have 3/8" studs and there are no rules against 7/16" studs, I will suggest the engine might have been built from parts and pieces not generally used in competitive sprint car engines- where they need to be very durable under some hard pounding.

I will also suggest that unless these engines are well known to you personally you should strongly consider pulling them apart for inspection and freshening up if needed. Sprint engines are often worked hard and put up wet, so you need to see if any valve(s) hit pistons, are the valve springs weak/broken, and to see the general condition of the shortblock.
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