[psbaker75]

Ok, here's the info sb 350 with 062 vortec heads, press in studs, stock self-aligning rockers, summit valve spring kit pn 174001 (to allow more lift w/o head mods), comp thumpr cam pn 12-600-4. Had trouble w/ the timing due to a bad vac canister and stuck mechanical advance on the GM hei dizzy, so I squared that all up and started noticing a whining noise. Pulled out the stethoscope and started listening, when I heard a noise that sounded like rocker chatter, so I pulled the valve cover on the left bank only to find that #8 cyl was shut down. Exhaust rocker was laying on the head and the intake pushrod on the same cyl was broken in 3 pieces. I'm bringing it to the machine shop in the morning to have the stud replaced, but I want to prevent something similar from happening in the future. I have a new set of comp high energy pushrod coming, but does anyone have any insight into what the probable cause was in the first place? I really don't want to put a band aid on a broken leg.

[DoubleVision]

Did you have the valve guides clearanced for the use of a higher lift cam?
Did you check for interferance when you assembled the valve train and go over the valve train geometry?

[oldschool hero]

Sounds like you need to replace all the studs with screw in type.Stronger push rods are only going to shift the problem to the studs and or rocker arms.

[F-BIRD'88]

You replaced the valve springs but did not address the issue of retainer to valve guide boss clearance at full valve lift.
Get the valve guide boss/seal combo cutter and arbor and fix it.
(shorten the guide boss, reduce diameter for aftermarket type seals)
Stock GM rockers may bind with more than .480" lift.
Lengthen the rocker arm slot or get long slot type.
You crashed the valve train. It takes a lot of force to break a rocker arm stud and bend a push rod. I bet you have at least 1 bent valve too now.

If you didn't want to do the vortec head valvetrain mods for high lift you should have stuck to a .450" lift rule cam.
EG: a Isky #201278 or #201288 will give the same rough racey idle of a thumpr cam without the high valve lift. Both have .450" lift.
Need better than stock vortec springs for max performance.
More torque and power than thumprs easier install, same radical rough racey idle. Lots of duration and overlap (106LSA) , Need a high stall converter for best results. Needs the distributor advance curve modified for best results.Degree them in to verify valve tming, best when slightly advanced (3 to 6deg advanced from straight up) 100 to 103 degree intake C/L.

This is the easy goof proof way of putting the "thumpy idle" in a vortec motor.

[cobalt327]

Originally Posted by psbaker75

does anyone have any insight into what the probable cause was in the first place?

The installed height being too short, or insufficient retainer to guide boss clearance at full lift are two things that could be the cause.

What leads you to believe those springs will allow more lift before the retainer to guide boss clearance is an issue? I don't recall seeing anything on that- not saying there isn't anything on it, just that I haven't seen it. A link would be appreciated.

Otherwise, cutting down the boss would be the best move at this point- along w/CAREFULLY inspecting the remaining valves/retainers/seals/etc. to be sure nothing else was damaged and just hasn't broken yet.

Here's a list of some areas of the valve train that need to be verified. This is a general guide, and is not all-inclusive. There is no substitute for physically measuring everything.

• Springs for installed height

• Coil bind

• Retainer to seal/valve guide boss at full lift

• Retainer to rocker

• Trunnion to stud boss

• Piston-to-valve clearance (both before and after TDC on overlap)

• Push rod to guide slot in head (if used)

• Can use EITHER self aligning rockers OR pushrod guide slots in head OR guide plates, not two or more of these at the same time

• ”Rails” of self aligning rockers (if used) to retainer

• Rocker to valve tip (by adjusting guide plates if used)

• Rocker slot to stud (if using stamped/cast rockers w/pivot balls)

• Proper geometry (push rod length)

• Rocker/polyloc to valve cover or baffle

• Camshaft endplay

• Distributor shaft and gear endplay

• Distributor gear material compatible with cam material

• Hydraulic lifter preload or solid lifter lash setting

• Timing set phasing

• Cam gear to crank gear alignment

• Cam gear end play if roller cam

• If using the SBC OEM roller lifters and retainers (aka dogbones), lobe lift must be kept below 0.354” so the lifters don’t lose contact w/the retainers

• Cam lobe to connecting rod on strokers

[psbaker75]

Thanks for all the great feedback. First, the increased lift clearance info for the springs came from summit tech support, they recommended the springs stating "they will increase lift range to .480 with no head mods." I took it at face value (my mistake) after all of my research suggested I should machine the valve guides. I just ordered the valve guide cutter and arbor (comp cams pn 4726 and 4732) and also picked up the spring seat cutter pn 4718 so I'm going to cut down the valve guides, but I want to double check my info. Does .25" sound correct? Anyone have any input on how far down I should take them? Also, I'm only running single springs now, so should I hold off on cutting in the spring seat inside diameter or just go ahead and do it now since I have the heads off? Any negative impact from doing it now with the singles on it? It seems like every pic I could find of people who have modded their guides also modded the seats. Also, even though I'm only running stock 1.5 stamped rockers, should I open up the pushrod holes to allow for 1.6 later down the road or just wait and see if I ever decide to go that route before making that change?

[F-BIRD'88]

You do not need to ask anyone how much to shorten the guide boss height.
on your vortec heads.
All you need to do is cut one guide boss for the new seals diameter and mock it up with a seal, valve, retainer and locks and measure between the new seal and the retainer. You need a minimum of the gross valve lift+.060" extra. make sure the seal is all the way down on the guide top.

now take it back apart and cut the guide boss shorter, with the seal dimater cutter to get the required additional clearance and re-mock it back up and double check. Now do the other 15 the same height as the first. A straight edge across the guide tops will show you the way. Not that hard to do. Do the other head the same way. Do one first, get it right check and then do all the rest the same.

When I do my 305HO heads for high lift and aftermarket seals, but stock diameter spring seats I routinely shorten the guide top by .200" for .550" lift stock GM retainers and locks and valves and aftermarket seals.

When we did my vortec heads we cut the spring seats for the 1.44" medium dual springs like the Comp 987's even thou I am running stock diameter isky racing springs right now. They run fine on the now larger spring seats.
I don;t remember exactly how much we shortended the guide boss top height but it was a good bit.

If you are going to do the larger spring seats, do the pressed in studs to screw in studs and guide plates conversion too.

When you install the new screwin studs put some RTV sealer on all the exhaust rocker stud threads. They hit water in the vortec heads. Don't forget to re-torque them after the heads are installed and after checking the push rod and guide plate slot. Sometimes minor adjustment of the pushrod guide plate position is nessessary. You will only have to do this once.

If you want to enlarge the push rod pass thru hole in the cylinder heads for 1.6 rockers make the hole longer towards the rocker stud, not wider. elongate the hole with a 5/16" rat tail file in a drill by about .030-.040". Thats all you need to do.

Use moderate cutting speed and something ( oil, auto trans fluid, cutting fluid, WD 40, Beer to lube and cool while cutting. Don't rush.
It can all be done on the bench with a decent electric drill.
High drill speed will overheat and dull the cutters.

[psbaker75]

Ok, good info on the cutdown procedure, thanks. I checked the retainer to seal clearance when I got the head back and it came in at .438 on the valve that had the broken stud... well below my cam exhaust lift of .465. Once bitten, twice shy. I'm glad the cutter and arbor will be here tomorrow, so I will cut and re-check until I get it right. With my work schedule being what it is this week, I should have her up and running by Friday afternoon. I'll post some project pics as I'm going along so that maybe my experience with this can help someone else down the line.

[cobalt327]

Originally Posted by psbaker75

I checked the retainer to seal clearance when I got the head back and it came in at .438 on the valve that had the broken stud... well below my cam exhaust lift of .465. Once bitten, twice shy. I'm glad the cutter and arbor will be here tomorrow, so I will cut and re-check until I get it right.

Good job

Now, be sure to check that none of the other pressed in studs have started to "pull" from the head. The time to catch them is NOW, before reassembling the heads and having problems down the road. Then roll the cleaned pushrods on a piece of glass, etc. to check them for straightness.

If it's in your budget, it would be a good investment to go w/screw in studs.

[psbaker75]

I'm replacing all of the pushrod just to be safe, and I will definitely check the other studs. I really wish I could just replace them all right now, but me and the wife got a little one on the way in May so money is real tight right now. I'm planning on some bottom end work in the next several months, so when I do that, I will definitely budget for the screw ins.