So part of my 305 rebuild were ProForm 66927C 1.6 roller rockers arms and slightly bigger pushrods (+.100'' - 7.900) for the cam I got, and now I've gone thru 3 shattered rocker arms, (2 on #8 cyl. and 1 on#3) 2 of which broke when setting valve lash the day after i first started the motor with the new parts(about an solid hour of run time)...and today after waiting a week for a alternator to ship(hasn't been started in a week) I had the motor idling for about 10 minutes and hear a loud DING on the right valve cover and sure enough another broken rocker...could it be just cheap rockers? or maybe the factory springs are to stiff and the rockers can handle the stress?


PLEASE HELP!!!!!!!!

 

Your previous post has been answered with a possible cause of your problem.

 

dude,stock springs aint gonna break ANY rocker arms. including the stockers. what you have is probably made in china. comp cams have rockers with about the same design. but with vastly superior composition. and they are cheap too.id ship the rockers you have on it now, back to wherever they came from ,bits and all. and go buy some good stuff. however. have you checked the valve train geometry?do you have any binding? 305 heads in their stock form need work, if you want more than ,say .425 lift.if you went bigger than this, remove the rocker arms and look at the rocker stud bosses for signature marks(contact patterns). post up the cam specs .lets see what you built

 

Appreciate the reply, it's a jegs 200105 flat Tappet roughly .460 .480 lift, I checked the rockers and pushrods for any kind of premature wear but nothing, lifters are sound there valley too, actually I just took the rockers entirely out and one on the other side broke too!small chip off the seat where the ball sits

 

http://www.jegs.com/i/JEGS+Performan...00105/10002/-1 theres the cam specs

 

How did you determine the required length ?

 

i didnt get to in depth with it,just figured I could get more out of the cam's lift with longer rods after seeing what some people have done with there head work

 

Proform rockers are cheap for a reason.... And they've been known to break in anything remotely above stock applications.

 

Stock springs arent going to handle that cam first off

Need to see if your retainers are hitting the guide boss bet they are probably whats breaking things. Somethings binding up and snapping those.

Get a pushrod length checker tool +spring and do it right.

measure twice, cut once.

 

I've personally seen them come apart on a mild LT1 (I'd read the warnings, but hadn't seen anything... and then that happened). I think he's still doing something wrong, but those rockers are junk in general.

 

I take it you failed physics and geometry?
If the cam has 1/2" of lift that is all that it has ;you could use a push rod 3 ft long and still not get any more lift ......

At a guess I suggest you check the actual pushrod length required ;
possibly the reason your rockers are breaking

 

appreciate the lesson there prof, im 17 so don't be so quick to judge
and yes I believe VALVE Lift would be affected by simulating a bigger lobe on the cam(cam lift) pushing the rod down more then say stock spec which is obviously smaller

 

wrong.

I think the problem is you're throwing in random pushrods because you don't know any better.

Measure for the correct length, get some good rockers and you'll probably be ok.

Think of it like this. go outside with bare feet and jump as high as you can. Lets say you just 8 inches.

Then you put on 4" platform shoes and jump again. the bottom of your shoes will only go up 8 inches, just like the bottom of your feet did.

Same applies to the pushrod/lift thing.

 

That's a good point I didn't think about that
I believe stock is 7.200? I got 7.900's

 

holy **** thats a monumental increase in length

 

side by side they only measured near a 1/4 of an inch didn't seem like they were too big

 

1/4 inch is a ton when your measuring for hundredths of an inch.

 

regardless could it be the reason 4 rockers have shattered to pieces?

 

absolutely!

 

Probably a combination of things
Those are way way too long

Summit sells the tool...its cheap

Then check for interference and buy the correct springs/pushrods. Bet stock or .100 over are fine but you need to measure and get it just right to avoid more problems

Did something similar once I was 19 I think
.480 lift cam on stock 462 heads. rotor exploded every time I hit 5000, car never made power above 4k couldnt figure it out lol. Lucky I never broke anything.
It had problems....the owner that was working on it.
You learn.

 

Hell yes! Your valve train geometry is WAY off and the 1.6 with that cam are probably hitting your guide boss. Valvetrain geometry is EXTREMELY important. You can get by slightly on a street engine over a race engine, but either way it's better to be right.

 

its been awhile since I've seen a troll thread on here.....but this has me wondering lol

 

Like I said ; physics and geometry.

Cam lifts the pushrod ,pushrod moves the rocker ,rocker hits something and stops , cam keeps pushing up.
Something has to give; in your case the cheap rockers.
I suspect if you had quality rockers you would be bending the pushrods instead

 

Love how guys who know nothing come here asking for help , then get defensive when told they are wrong.

Old saying
" a little bit of knowledge is dangerous "

 

Get a pushrod length checker and a GOOD set of rockers and springs or things will just get worse

 

Problem is probably not the push rod length. 7.9" on a flat-tappet cam, while who knows whether it's "right" or not, is close enough that it shouldn't be creating disasters.

More likely the problem is one of 2 things:

Coil bind. .488" "nominal" lift with 1.6 rockers will end up around .520"; FAR ABOVE what stock springs can handle.

Or, the bottom of the retainers smashing into the top of the guide bosses.

This whole thing sounds like it needs to be torn down and rebuilt properly, with correct parts and some MEASUREMENT, from the head gasket up.

I'd suggest getting a REAL cam instead of the cheeeeeeeeeeeeepest thing the law will allow to be associated with the word "cam".

The rockers are GARBAGE, regardless of anything else. Throw what's left of them in the trash since they've all been stressed beyond their tolerance by whatever is hitting whatever it's hitting. Same deal as the cam-shaped object you now have. Get something decent instead of the cheeeeeeeeeeepest thing that they can legally print "rocker arms" on the side of the box. Preferably steel; either Comp or Crower. (NOT "CAT" or any of the rest of the Chinese knockoff crap)

 

When you get springs get new retainers and locks with them
Chances are they are so beat up the locks are ready to pull through the retainers by now and its drop valve in a cyl time. Again they dont cost much.

Always time to do it twice, rarely can afford to. lol
Dont worry this is all part of learning how things work.

Fwiw I had a set of those blue Proforms needle bearings turn to dust in 300 mi on a valvetrain where everthing was right that was back in the late 90s when they came out if I remember right. Spending money twice.....didnt know any better

 

sofakingdom covered it fairly well, the valve train clearances or geometry are not correct, if your interested,in correcting the issue... heres some links with related info

http://forum.grumpysperformance.com/...php?f=52&t=181

http://forum.grumpysperformance.com/...hp?f=52&t=1376

http://forum.grumpysperformance.com/...hp?f=52&t=9613

http://forum.grumpysperformance.com/...hp?f=52&t=6198

 

Hit the nail right on the head with this post!

 

Coil bind is a great way to flatten a cam. Guess what idiot learned the hard way with that.