Crane Rocker Arm Stud Failure
 

Has anyone experienced break off of a Crane (or other) rocker arm stud at the interface plane between the rocker arm stud lock nut and the Crane roller rocker arm on a BBC (7/16-20 thread) where the rest of the valve train for that location is completely functional and in good working order? This was with hydraulic lifters, moderate load springs and lift (0.6") and 3000 rpm. There was ~200 hours total on the stud mostly cruise rpm but some WOT running up to 5800 rpm.

How much of the stud is being threaded into the nut?

1/2". It is a polylock nut.

Floating the valves can break a rocker arm stud. 5800 rpm is fairly high, what do you have for lifters, springs etc.

Incorrectly adjusted valves can break a stud also!

I was breaking studs on the exhaust side years ago. (Manley and ARP) After I tore my heads down and reconditioned them, I found out that I had inner broken valve springs. Merc 425's, flat hydraulic lifters and mild cam 5200 RPMs.

Is that for solid lifters only or hydraulic lifters as well?

If hydraulic lifter can causee stud failure as well is it when the lifter is too loose or too tight that causes the stud to break?

Comp Cam CCA-929 springs and the stock 496HO roller lifters.

I run at 5500 - 5800 occasionally but mostly cruise at 2500 - 3000 rpm which was the speed I was running when the stud let go. Does the floating of the valves have to be occuring when the stud breaks or can the stud be damaged and break later at a lower rpm?

Thanks. I will check for that.

wrong lenth pushrods will cause the problem as well....Rob

mrfixxall
 

the stock roller lifters are rated for .570 lift max!!! of the rockers wont get enough oil to them... also check the bottom of the rockers for binding at max lift,may need to massage them a little to keep from binding on the stud..

I have seen it more on Solid and when the rocker is too loose but if the initial adjustment is way off on a hydraulic I would imagine you could also break stress the stud!

Seems reasonable that you can crack the stud and have it fail at lower rpm.

Looks like there are some good ideas to pursue. Found anything yet? Broken spring is easy. Checking pushrods is easy. I would think that you would hear tapping if a rocker arm was loose, right? Also I would think that too tight a lash on the rocker arm would hold the valve open and you would've noticed a lot of problems before the stud broke.

My 502's with Crane hydraulic lifters floated the valves on the dyno at 5600 rpm, just a thought. Morel lifters didn't float up to 6000 (stopped the pulls at 6000).

If you were putting all the springs into coil bind you wouldve broke a lot of stuff before 200 hours.

Don't know about the lift issue with 496 lifters, definitely something to look at there.

Let us know how it goes.

Thanks. Where is the 496HO lifter max lift rating information available at/from?

Your experience is that a valve train with too much clearance can experience rocker arm stud breakage...............as apposed to the valve train being too tight as being the cause for rocker arm stud breakage.

Thanks!

Should know more Thursday.

My dyno pulls were with the same springs, different lifters.

Also check to make sure that the pushrods are the correct length, a long shot but it is part of the process.

Don't know about the lift issue with 496 lifters, definitely something to look at there.Yes but then why no problems of insufficient oiling for all those hours? Good point

rage i had a lifter go bad ,,,it knocked the push rod off the rocker arm,,,the hydraulic lifter would not compress at all,,,was told it could of broke the stud,,,in my case it didnt

mrfixxall
 

Sorry i didnt realize you had a newer 496 ho,i was refering to the gen 6 style lifters, you may want to check with comp cams and they could tell you.. on aanother note, your lifter adjustment is also critical as well..most hyvrolic lifter now a days have a pre load adjustment which means they can be compressed before it opens the valve..most people have their own way of adjusting hydrolic lifters and some set them to their max limits which is not good for the valve trane..a lifter can be comppressed a max of .100 1 full turn, i like to set mine at 0.25-.050 1/4-1/2 turn, this will allow a little cushion just in case your lifter shoud malfunction and fully pump up it wont go the full .100 and the valves wont crash into the pistons..

That is very interesting. Exactly how does a hydraulic lifter malfunction so that it would pump up its adjustment length and thereby hold a valve open against the valve spring preload?

Thanks. I checked the rocker arm contact point on the valve stem tip using the current push rods and it was dead center when built.

Good point. How does one confirm the function of a hydraulic lifter to determine if one is now defective?

That is interesting. Do you know if the valves floated with the Crane hydraulic lifters at 5600 rpm because they were pumping up?

Don't know why but you can definitely see the airflow, tq and hp numbers drop off when the valves float.

mrfixxall
 

oil pressure!! if the retainer clip that holds all the internals in the lifter comes out then the lifter will keep expanding and could cause the valve to hit a piston at higher rpms..

Good to Know. So if the lifter snap ring is still in place this should not be a problem at present....correct?

thats what broke on my lifter,the retaining spring,,,each lifter should be able to be pushed down so far,,,so yea if the clip is there and it is able to push down a little,,,i would say its good,,

mrfixxall
 

here's a little clip on how a hydrolic lifter works, if the preload is set too far into the lifter theirs no cushion on the valve trane(acts like a solid lifter) thats why i set them 1/4 to 1/2 turn..the more you tighten the rocker at zero lash the less protection..

http://www.youtube.com/watch?v=lorANZ1Tptw

The exterior of my broken stud ( ie the way it was manufactured) looks significantly different from the ARP studs I just bought.

Happened to me once...aluminum heads at high rpm, I installed stud girdles

Well I just finished checking the last few items that could have contributed to the stud failure. The spring was fine as was the lifter functionality. All tha seems to be left is a stud fatigue failure. Thanks for all the input. New ARP studs now installed.

Just read this,I had the same problem last year.I would be just cruising and hear the pop in the valve cover.The top of the polylock was laying in the head.Long story short broke two.I replaced all the studs with ARP and a little longer.I was only using about 3/8 + of the threads with the poly.I figured I needed more thread into the poly.Problem solved,I broke some lifters also,bottoms shattered.Put all new lifters in also,different manufacture.

How profetic you should post your experience. I reassembled everything and even though it now runs there is a noticable lifter/valve train noise similar to a solid lifter set up that is not normal for my engine. All I can figure is that the hydraulic roller lifter now will not hold pressure. Maybe that was the original cause of the failure.

I plan to replace the lifters. Anyoen know if there are any issues with this brand for a 496HO engine?
http://www.jegs.com/i/Comp-Cams/249/900-16/10002/-1

mrfixxall
 

What is your maximum cam lift? remember as i posted .570 lift max on stock gm lifters..if it were me i would call rm builders and ask bob if he has a set of moral lifters for your engine..as far as im concerned moral is the best lifter money can buy and remember the valve trane is the hart of your engine and takes the most abuse..

Dont know if this was mentioned,did yu check coil bind on the valve springs?

I thought that you had remembered that the 0.570" max stock GM lifter lift limit did not apply to the newer 496 GM engine? I have had an inguiry into Bob on what is available for my engine from Morel.

Yes, no coil bind issue.

Thanks.