Breaking Rocker studs and bending push rods

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Breaking Rocker studs and bending push rods

Post  cbsuperduty on October 11th 2012, 6:11 pm

OK guys. Have a set of DOVE's that were max ported a few years ago by the Mad Porter. Been running a few years in our pulling truck. I know that they need checked out. We run Lunati Blue full roller rockers from Lem and Jomar stud girdles. Last winter we had our bottom end checked out and our engine guy didn't do anything with the heads. When we fired for the first time it ran fine. After about 10-20 minutes of run time it started missing, popping, all sorts of weird stuff. We found a bent push rod, broken rocker stud, and mangled rocker. We took it back to the engine guy on our way to the first pull and he checked things out. Piston was fine and valve appeared to be fine and straight. Ran 1/2 the season fine and on one pass I noticed that it stumbled a little at the end of my pull. We got home and pulled a valve cover. Same thing as before but different cylinder. We patched her up and finished our points run that gained us our first points championship! Now this winter I would like to find the cause before we send them to get freshened. The engine builder wasn't sure what happened first the push rod, rocker, rocker stud, or keepers.

Anyone have any theories or advise on were/what to look at first?
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Re: Breaking Rocker studs and bending push rods

Post  c.evans on October 11th 2012, 9:21 pm

Where to look first; broken valve springs, inners as well as outers.

Charlie

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Re: Breaking Rocker studs and bending push rods

Post  dfree383 on October 12th 2012, 1:02 am

I'm with Charlie, I'd look at replacing the valve springs.

What pushrods and parts are you running? What cam and rpm are you turning?
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Re: Breaking Rocker studs and bending push rods

Post  ianxy351 on October 12th 2012, 5:16 am

I agree. Some more details would be good. Cam type, lift, duration @ 50, etc plus spring pressures open and closed. Plus a run down of the valve train specs.

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Re: Breaking Rocker studs and bending push rods

Post  quick 52 on October 12th 2012, 7:03 am

studs need to be replaced. have notice if a valve adj. is done than the poly lock is tighten alittle more after the allen is set there seems to more stud failure

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Re: Breaking Rocker studs and bending push rods

Post  LivermoreDave on October 12th 2012, 7:53 am

cbsuperduty wrote: Last winter we had our bottom end checked out and our engine guy didn't do anything with the heads. When we fired for the first time it ran fine. After about 10-20 minutes of run time it started missing, popping, all sorts of weird stuff. We found a bent push rod, broken rocker stud, and mangled rocker. We took it back to the engine guy on our way to the first pull and he checked things out. Piston was fine and valve appeared to be fine

Considering the above highlighted items, some have experienced damage and related items (as to the damage) have no noticeable damage, with the items broke or damaged there must be an interference of parts. Is the rocker arm, rocker stud and/or rocker stud support interfering with each other? Could the rocker arm geometry be at fault, allowing the pushrod to get out of the rocker arm and creating a "stack" of components? Also as has been mentioned, rocker studs will bend over time and discount the rocker arm's geometry. I exercise attention to the rocker studs at each service of the engine and during routine maintenance.

Just a few questions that come to mind,
Dave.

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Re: Breaking Rocker studs and bending push rods

Post  cbsuperduty on October 12th 2012, 9:43 am

Like I said we plan to pull the entire top end and get it gone through and serviced. When we have checked the valve springs none have been broken. Don't really want to share the cam specs on here (at least right now) as I know some competitors read this board. We agree that the studs need replaced and we do think that some are stretched. Push tubes are Comps I believe. Just wanted to make sure that there wasn't some kind of oh duh check that first type of thing.

Thanks,

Chris
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Re: Breaking Rocker studs and bending push rods

Post  dfree383 on October 12th 2012, 10:44 am

Theirs not a whole lot of help your going to get with out letting people know what you have and how your operating it. If sHaring your valve train specifications is a big secret I'd suggest going back to the person who furnished and speced everything and ask them why it's failing.

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Re: Breaking Rocker studs and bending push rods

Post  k.pascoe on October 12th 2012, 11:34 am

Make sure you use ARP rocker studs. Broke a few Manley studs in my day. The quality between the two makes is easily seen.

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Re: Breaking Rocker studs and bending push rods

Post  bbf-falcon on October 12th 2012, 11:53 am

How thick are the pushrods? On a pulling truck engine that has high rpms and heavy spring pressure you should have the best pushrod that can be used for that application. They will flex alot under load and destroy a drive train. Valve train maint. is critical on your truck imo.

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Re: Breaking Rocker studs and bending push rods

Post  c.evans on October 12th 2012, 11:55 am

You may not be breaking the valve springs, but you're probably killing them. Seeing as how you are a truck puller, I am suspecting that you are floating the valves and that's the real problem. Do you have titanium retainers, I hope so. Do you have titanium valves? I suspect not. Anyway, when you operate a engine at high rpm for an extended period of time, with stainless steel valves, you need to check your valve spring pressure frequently and change valve springs often.

Signs that you are floating the valves are; a wagon wheel spoke pattern on the tip of the valve,,,all the black oxide being worn off of the locks, and the seat cups,,,burrs around the keeper groove,,,,are your roller lifters wearing out fast,,,and the list goes on.

Hope this helps,
Charlie

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Re: Breaking Rocker studs and bending push rods

Post  ianxy351 on October 12th 2012, 6:46 pm

Another possibility could be to check that your pushrods are not contacting the rocker next to the pushrod cup. If your cam has enough lift you may find that the pushrod and rocker are touching eachother at max lift. This will shock load the valve train and lead to failures. We run a 545 in a drag car here with 700 thou lift, Crane solid roller lifters, 3/8" Trend pushrods and Crane roller rockers. We had to relieve the back of the roller rockers to get clearance. The contact was only very light when rolling the engine over by hand - just became obvious with some bearing blue on the back of the rocker - but at high revs it would have been a massive problem.

As discussed above, the other thing to look at is your spring pressures to make sure you havent lost some pressure.

Any of these things not being up to scratch will induce shock loads in your valve train at high revs and in your case the weak link sounds like the studs. We have seen roller lifters loose needle rollers, bend pushrods or break springs before - each can be a weak point. So really you need to closely look at each element of the remaining valve train to identify other signs of possible failure. My bet is that you will find something other than the studs with signs of wear or fatigue.

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Re: Breaking Rocker studs and bending push rods

Post  cbsuperduty on October 13th 2012, 9:11 am

Thanks all. I will let you know what it was when we find it. The Cam is above .700 and below .750 both intake and exhaust. Push rods I believe are comps but I would have to double check the brand 3/8" .080 wall. Rockers are Blue Lunati from Lem. Jomar Stud Girdle. SS valves (where in there when we bought) but may go to Titanium next round. I believe TI retainers but will have to double check that.

Thanks again. We will check everything out in the next month or so when we get stuff apart.

Chris
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Re: Breaking Rocker studs and bending push rods

Post  Paul Kane on October 13th 2012, 9:45 pm

Make sure the rocker bodies are not contacting the underside of the stud girdle (interference fit); make sure the valve train geometry is optimized and not overwhelming the sub-components of the valve train assembly; make sure none of the valve train components are binding against each other; check the valve springs for proper spring rate and proper loads.

Paul
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