Bent pushrods again!! why?? - Team Camaro Tech
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post #1 of 8 (permalink) Old Dec 6th, 01, 06:50 AM Thread Starter
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We have a std. 350 with performer rpm spec hyd. cam - a summit brand knock off;
and so we bought Edelbrock Sure seat valve springs which the say fit rpm spec. cam

Installed on early style vortec 305 (yes 305) heads - early because my friends checked numbers as vortecs and they had to elongate some holes on the std. chevy style intake to bolt up - but it doesn't have the complete change intake bolt pattern that current vortecs are known for -

anyway the springs slot right in spring pocket - they removed the original spring covers or caps that cover the spring and fall around down the sides with a hole in the top (best description) and just used the top cover that sits directly on the spring and keepers etc.

after a few runs - we had missing - we found a few of the new summit hyd. lifters stuck - fully compressed - so they had some converted hyd. to solid lifters which we installed - later found three bent pushrods -
we switched out those - adjusted lash a little bit more - a few pushrods bent again!

only when we left the lash really loose did we get to complete a run or two but the car ran very ordinary!

the guys want to get hardened pushrods - so far we have used two sets of stock used ones - and adjust everything right

I am afraid something else may be wrong and something bigger and worse may break instead!

we wound the spring right down by tightening the lash ( i think thats they said they did) as much as possible and hand turned the engine - it did not have an interference with the guide at such an extreme position so we don't think its bind ?

any suggestions - my last one was to check lifter bores for trueness or interference - what do you think ??

could the sure seat springs be so strong as to bend pushrods??

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post #2 of 8 (permalink) Old Dec 6th, 01, 07:44 AM
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A few things to check, after purchasing/installing two new push rods, two solid lifters, and remove the spark plugs:

1. Turn engine by hand to bring valve at full lift, one valve at a time,
2. Make sure coil bind does not happen, this means the coils in the spring do not touch each other,
3. Make sure there is plenty of room between the bottom of the valve retainer and the head's valve guide,
4. Check the strength of each spring on a spring tester, could be weak due to miles and overheating.

Some of the problems could also be weak valve springs, too high of rpm's, piston and valves kissing each other.

Others here may have some good suggestions....

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post #3 of 8 (permalink) Old Dec 6th, 01, 05:22 PM
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Check to ensure the rocker arm slots are not contacting the studs due to the increased lift of the new cam.
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post #4 of 8 (permalink) Old Dec 6th, 01, 06:03 PM
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My 1st thoughts are retainer to guide clearance issues or insufficient slot length in the rockers. Vortec heads are known to only have enough clearance for around .475-.480 lift between the retainers and guides...unless they have been machined. Also, stock rockers will usually bind around .490-.500 lift...even less if the valvetrain geometry is way off. Either of these kinda follows what you was seeing...with very loose lash the engine runs ok. The rpm cam has .488/.510 lift...definately enough to get you in trouble. Take a look at the rocker studs for signs of the rockers hitting the studs...you may see indentions on the intake and/or exhaust side of the stud. If so, comp cams makes a guided 1.52 roller tip rocker that will work great. If everything looks good there, then you will need to dis-assemble a few valvesprings and check the retainer to guide clearance. If you are having binding problems, then its very likely the cam is trashed...enough bindage to bend pushrods can easily knock a lobe or 2 off the cam.

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post #5 of 8 (permalink) Old Dec 6th, 01, 06:36 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by caribbean camaro:

after a few runs - we had missing - we found a few of the new summit hyd. lifters stuck - fully compressed - so they had some converted hyd. to solid lifters which we installed - later found three bent pushrods -
we switched out those - adjusted lash a little bit more - a few pushrods bent again!


<HR></BLOCKQUOTE>

are you saying you put a few solid lifters on a hydraulic cam? and those same ones bent the pushrods?

the heads you are using aren't vortecs- they are just regular 87-93 305 heads.
you might have retainer to seal clearance issues, or maybe the valves are hanging up in the guides from too little clearance? just a thought.
how are you adjusting them? i hope you don't just tighten them down until you can't tighten anymore.that would lead to issues, but it would run like total crap, due to all valves hanging open at all times.

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post #6 of 8 (permalink) Old Dec 7th, 01, 06:48 AM Thread Starter
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I think lash adjustment was done on baseline specs for solid cams - the guys are pretty good at tuning chevys from scratch - they have been messing with all types for about ten years now - as far as I know they only overtightened the lash when they were hand turning the engine to see if the guide touched the retainer or the spring would bind

but what is the best way to measure retainer to guide clearance without complicated tools?? i.e. feeler gauge!

what is the chevy manual safest spec for clearance for retainer to guide and for coil bind using the said Edelbrock sure seat springs!
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post #7 of 8 (permalink) Old Dec 7th, 01, 08:01 AM
 
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make sure you put the shorter bolts for the intake manifold in the center.

years ago, my brother and I went through a couple of bent pushrods, until we realized the intake bolt was too long -- literally torqued it into the pushrod and held it in place.

no wonder the car backfired and the headers glowed!
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post #8 of 8 (permalink) Old Dec 7th, 01, 10:31 AM
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Use a large paper clip for checking clearance

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