newly rebuilt 305TPI in 86TA. less than 5000 miles engine makes loud knockin noise, now a yr later we finnally get the time to rip it out. ends up the new roller tipped steel stamped rocker was broken... the rocker nut on the rocker stud had to have been tightening itself on the stud as the engine was running which eventually led to the nut tearing through the rocker. how does this happen? and we thought we had a broken bent rod cap. anyone seen/heard this before? i thought the stamped steel rockers would be stronger than the stud nuts?

will this happen again if we put new rockers on this head?
also does anyone kno the max lift of the 305 TPI stock heads?

 

Insufficient lubrication under the trunnion ball. I'd want to know where all that metal went.

 

Best bet is to get better rockers. The sheet metal used to make those look to be thinner then stock ones. For decent roller tipped rockers get the Comp Cams ones. Heavy duty investment castings. And grab a set of poly locks to go with them.

Or move up to the fuller rollers. The Comp steel ones are nice.

RBob.

 

no lube to rocker , plugged up pushrod and/or bad lifter .

 

yea we think it was a lifter... we checked the pushrod they are clear and clean. just lucky nothing bent or broken. the metal made it down to the oil pan and most got grabbed by the magnetic oil pan plug we put in the rest got caught by the metal screeen before goinin into the filter.

these rockers were like 90$ they are just as think as the stockers but a roller tip... .its not my car its my dad and hes kinda a cheapy... so i made him get new ones... went wit full roller extruded aluminum 1.6 summit rockers with poly locks... got them tday... they are pretty nice. i agree the compcams are nice too. also got new lifters... he wanted those rhoads lifters. and comp cams high energy new stock length pushroads

 

I wouldn't count on it. If you're lucky, most of the metal got stopped by gravity, the magnetic plug, and the oil filter. None of those catches everything though, and when you wear through a part you're putting a lot of metal in the oil.

 

The picture isn't very clear, but it looks like the lube slots in the trunnion are clean, and the surfaces still shiny. I'd guess it was just over stressed - either a cheap Chinese made part, or interference in the valve train. Stamped rockers aren't exactly known for strength - the trunnion is much harder and stronger than the rocker.

Stock heads are good for no more than .480" lift, sometimes less. I'd say you've got a lot of checking to do. 1.6:1 rockers only make a potentially already bad situation worse. What's the cam lift?

 

well we drained the oil and filtered it and found nothing. it was just s few big chunks. that was trapped at the pan plug and at the filter screen. from wat we can see without dissasembling the short block there hasnt been any damage. the lifters where a cam/lifter kit

http://store.summitracing.com/partde...0&autoview=sku

204/214 .420/.442 lift 112 lobe.

with 1/6rr were still in good shape. the heads were freshly rebuilt when the motor was. our guess is that the lifter failed didnt lubricate the trunnion and its just tightend and tightened and then ripped throught the rocker. i convinced him to get the base and heads ported by a buddy of ours that does engine building/machine work.since he has a alil better cam than stock. and to get a few more poines outa it.

were gona def retorq all the bolts of the bottom end... maybe i'll convince him to dissasemble it and check the bearings and crank. the car hasnt been drivin since the noise and that was only a few miles after it happend that it was driven home. we didnt even start it to get in in the driveway.

 

If you found broken chunks then it's probably as five7kid says, just a weak part that broke under load, not a part that wore.

 

1.6 would put you at .471" lift on the exhaust. You may not have had that much travel available on that valve (differences between valves on the same head are not uncommon) - remember, I said .480" or less.

I really doubt that. If you can get a clearer picture of the trunnion, or at least verify whether it shows wear - you don't starve a component of lubrication without signs of wear. This looks like simple failure (overstress) of the rocker itself, not accelerated wear. Whether it was due to a weak part or interference is the only question remaining in my mind.

 

the roller tip lifters that failed were stock ratio... 1.5. these are 1.6rr hopeing to give him alil more lift with the ported heads for sum extra HP and maybe add alil duration to that cam. i told him the heads would take max .480 so with .471 it should still be in a good range. esp since the others were 1.5 and only one failed it must of been just a failure except the trunnion carved its way through the rocker where its seated.

the trunnion doesnt look that worn... its alil shinny but the rocker base where the trunnion is seated looks really worn... like it cut into the rocker and just broke through.