I've got a pushrod problem. My #5 intake pushrod has bent for the second time. the motor is about a month and a half old and here is my setup:
355 9.75:1 compression fully balanced and blueprinted comp 270 camshaft hydrolic flat tappet wp torquer s/r heads with 2.02/1.60 stainless valves the springs are supposed to be good up to .560" lift but I am only running a .470" cam. it also has flowtech headers, edelbrock performer intake, and a 625 cfm Demon jr. And 1.5 ratio roller tip stamped long slot rockers
The first time this happened it broke the rocker stud on the exhaust side, this time it didn't. I am a little frustrated since I know my pushrods are the correct length because of the shadow on the tops of the valves are in the immediate center about a 16th inch long. That should tell me my rockers are set correctly too right? I called around town and one guy said it could be my rockers walking off? another my pushrod length was incorrect? another my rockers are out of adjustment? another that my rockers are backing off thier adjustment after I set them? Does this sound screwy yet? I tried getting a hold of comp cams today but no one picked up the phone. I also called jegs and they blamed it on every product exept what was on the invoice, World did the same too. I think I might call dart or crane next to get an unbias opion. graemlins/sad.gif
thanks, and sorry for the long post.
Zac

I'd pull the head and take a close look at the guide clearance and valve stem diameter on the #5 intake. Possible mis-clearanced guide or out of spec valve stem. You're only dealing with very small clearances on the guides, Any tolerance variation and the guide'll pinch the valve. Then something's got to give. Just an idea, but it does happen.
Be sure a valve seal hasn't come loose and lodged between the retainer and the top of the guide. If the retainer contacts ANYTHING, the pushrod will bend or stud will break.
Also check that the top of the guide is the same height as the rest. If it was incorrectly installed, the retainer may be hitting it.

Randy

If you want to check for correct pushrod length, here's how to do it:
---With a valve cover off, turn the engine until the valve lift is .235". This means you will need a dial indicator on the retainer.
---When you are at .235"(1/2 of the net lift--.470"/2), see where the rocker arm sets on the valve stem. If the pushrod is the correct length, the rocker arm contact point will be right in the center of the valve stem.
---If it is not right in the center of the valve stem, you need to do it over with a adjustable pushrod, and change the length until the contact point is right in the center of the valve stem.
This is the correct pushrod length for your cam.

Everyone, this works for any type of cam. You just have to use 1/2 NET valve lift. For a gross lift of .626" and a net lift of .600", you would use .300".
I would not sweat a few thousands off on net lift, and if the correct pushrod length is within .025" of a readily-available length, I'd use that....

UDHarold

Do your heads have pushrod guideplates? If they do, have the original pushrod guide holes in the head drilled to .500 or so? The pushrods can't be guided in two places, only one. If someone adds guideplates to the heads without hogging out the original holes the engine will bend pushrods.

Also, on some of the heads from this and associated vendors there was a quality control problem where the pushrod holes drilled in the heads were slightly off-center, enough to cause problems with bent pushrods. The rockers will run off the sides of the valves and the pushrods will bend.

Summing up: if it has guideplates the holes in the heads must be drilled out so as not to bind the pushrod. if it doesn't have guideplates it may need them.

Tom

Thank you for the replys. I hve no guide plates and I had my machine shop calculate the pushrod length because I don't have access to a dial indicator. I'll ask my shop teacher if he has one in his personal stash and see if he'll help me use it. could all of this have messed up my valve? would I be burning oil if the seal is in bad shape? are the guide plates you are talking about the ones that bolt on under the rocker studs? Thanks again guys
Zac

do a compression check, number 5 will be lower on compression if the valve is bent. I bet the valve is ok though. When you find the problem let us know what it was, I'm curious. Did the failures happen at high rpm?

I agree with the guy saying check the guide to retainer clearance. Don't forget to verify rocker arm interferance too. You could have rocker to stud contact.

this has happened at medium rpm both times. first I was about to start slowing down to get off the freeway going about 75 mph at 2600rpm where the tick started. last time I started it up to leave letting it warm up to about 150* and the tick started about a mile later at 1400rpm in third gear (TH350).
There are no marks or visible fractures in the studs or signs that they could be making contact in the slot area. the stud broke above where the rocker and fulcrum washer meet, in the middle of the fulcrum. the retainer clearance is about the only thing left unless someone else thinks of something.
Zac

Zak,
A camshaft lobe that is starting to wear a bunch will cause the pushrod to jump out of place and bend. I think that would be the next thing I would be looking at.

that's not good. will there be alot of metal shavings? I have not seen anything and I'm on my 3rd oil and filter change.I first started this motor on Jan. 2. and has been running fine exept it has spit 2 pushrods and a stud. my first oil change was at 500 miles and the oil looked clear with a little assemby lube in it. the next time I changed it after I changed my jets to 68s instead of 70s because it was waaaay rich and the oil was getting dark too quickly, I just changed it again this last wednesday in shop class to use the filter cutter and it looked good and clear. I really don't want to replace that camshaft. graemlins/sad.gif
Zac