NORT

I have an 84 Z28 with a 350 in it.A month ago I put a 268H Comp Cam in the motor, and have had nothing but trouble since then.Amoung other things the guy at the machine shop gave me LT1 head gaskets for my L31 vortec heads.Well they dont work I poured about 3 gallons of water in the oil pan,Oh Boy.Now that I have that figured out with new gaskets,oil, and antifreeze,I finally got it put together today.It ran beautiful for about 5 minutes on the cam break in and then gave a big bang and bent all but 6 of my pushrods.I thought I hadn't run the rockers down far enough so I put another set of pushrods in the motor.It ran for about 30 seconds and big bang again this time it only bent 2 pushrods.Looking it over it appears to me that the holes in heads where the pushrods go through are too small and the pushrods are binding in the holes,you can see real heavy wear marks on the pushrod and it fractured right there.As I said before they are L31 vortec heads.Does anyone out there have any idea or maybe running the same cam with the same heads and have you had any problem?This little cam swap has turned into a very expensive deal and i need it to end(HELP!!!).Would appreciate any advice anyone may have.Thanks.
NORT P.S. the cam is a 268 extreme Comp cam and has a 477/480 lift.

[This message has been edited by NORT (edited May 30, 2001).]

ColinOpseth

holy smokes, and I thought I was the only guy that ever had that trouble

I went through the exact same problems you did.. I put an '89 shortblock with rebuilt '86 heads into my '86 IROC... the '89 has a roller cam so i used the roller lifters and shorter pushrods with the self-aligning rocker arms..

I was fortunate to stop the engine when I first started it to check and see why the motor ran so bad.. turns out I had the same problem as you..

I went down to the hardware store and bought a Black & Decker dremel with one of those flexshafts (the ones that have a cable in them) and i hogged out the pushrod holes a bunch with a tungsten bit.. the best bit to use is a barrel-shaped on because it's straightness will help you cut a more square hole..

I hogged out all of the pushrod holes wide enough that I could fit a 2 paperclips down the side of the pushrod (one on either side, essentially).. I used a big magnet that was kinda wedged under the pushrod hole to catch most of the shavings... BE CAREFUL CUZ THE BIT COMES OUT EASY!!!!!!! It did on my 3 times, I was able to get the bit out each time but then I started tightening it every few seconds, lol..

once that was done I cleaned up the last of the shavings with one of those telescoping magnets you can get for like 2 bucks from a parts store..

i fired the motor and it ran alright... I changed the oil right away once I felt the motor had run long enough to wash all the shavings into the pan..

hope this helps,
Colin
Webmaster: www.IROC-Z.org

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Webmaster: www.IROC-Z.org

AlkyIROC

A 268 xtreme cam shouldn't give you any problems. It's only .477 lift with 1.5 rockers.

The pushrod holes in the heads will be a tight fit but shouldn't be the cause of the problem but as stated above, you could enlarge the hole. The lifter will push it up and the valve spring will push it back down. Check to see if any of the valve springs are broken. Any cam swap should include new valve springs. Old springs get weak after a couple of years.

Other than actually looking at the engine, that's all I can think of right now.

Set the valve lash on all the rockers, take all the plugs out and rotate the engine by hand. If there's any sort of interferance or binding, you'll notice it.

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Follow my racing progress on Stephen's racing page
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[This message has been edited by Stephen 87 IROC (edited May 30, 2001).]

[This message has been edited by Stephen 87 IROC (edited May 30, 2001).]

sleeper

I have to agree with Steve. Your problem is not just the hole size. Make sure the pushrod length is right and then set your lash.

At this point your cam needs inspection (sorry). It's very possible that you have worn down the lobes on the cam. I've done that before with too much lift on the cam.

camaro1j

iTrader: (1)

Roller rockers normaly need shorter push rods than flat tappet.

ede

i suspect the push rod length is wrong, but you don't really have enough cam to require longer push rods. i'd make sure the rockers were correct and the valve springs in good shape.

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ICON Motorsports

1st & 3rd
MM Black Diamond 538 F&AM

RB83L69

What has happened to others using those heads, is that the retainers hit the top of the valve guides.

Take a valve spring off from a location where a pushrod has bent, and look at the top of the valve guide and see if there's any sign of interference.

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"So many Mustangs, so little time..."
ICON Motorsports

Mark W. Winning

Aren't you supposed to use only self aligning rockers with Vortec heads? If not, you have to drill out the guide holes and then install guide plates. If you are using normal style rockers, that may be your problem.

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1992 Pontiac Firebird 350/Six Speed
1987 Toyota Pickup 383/500+ HP

RB83L69

As far as self-aligning rockers, and the push rod holes, here's the deal.

Something has to hold the rockers more or less centered on the valve stems. There are 3 common methods used on stud-mount rocker systems. They can be either held in place by having the hole through the head hold the pushrod straight, which will also hold the rocker in place; or by enlarging the hole through the head and using a guide plate, which does the same thing; or by having an enlarged hole and using "self-aligning" rocker arms, where there's a little lip on the tip of the rocker on either side of the point where it contacts the valve stem.

Only one of these systems can be in effect at any one time. If there are more than one, they will almost certainly try to guide the rocker arm to different places, and something will bind somewhere.

It will rarely cause pushrods to bend though. Usually what will happen is the push rod will be forced out of its seat in the rocker arm, and that point will wipe itself out. You'll either have push rods with wasted tips, or rockers with wasted push rod seats, or both; but not bent push rods.

DON'T enlarge the push rod hole in the head unless you are sure you have self-aligning rockers. If the hole fits the push rods tightly (.010" clearance or so) then the heads are designed for old style rockers, and you should put that kind on there. If you don't have SA rockers, and you enlarge that hole anyway, then there will be nothing holding the rocker centered on the valve stem, and you will experience destruction at that spot.

Bent push rods is almost always caused by some part hitting some other part. Either the valves are hitting the pistons (unlikely in your case) or the springs are reaching coil bind (also unlikely) or the retainers are hitting the top of the valve guides. I'd bet that's your problem.

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"So many Mustangs, so little time..."
ICON Motorsports

Dan87IROC-Z

The problem is that you need to have the valve guides shortened with that new cam. I had to have mine shortended when I installed my LT4 HOT Cam, you could check to see if you need to have similar work done, that's where I would put my money.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End with 2.77:1 Gears.

Current Mods: LT4 HOT Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

Soon to Come: 7.625" 10 Bolt with 3.42s and Accel TPI Intake Base

NORT

Thank you for your intrest in my problem. First yes I do have self-alining rockers and I also had the valve guides cut down before I installed the cam. It sure appears as if the pushrods are binding in the guide holes there are real shiny marks where the pushrods go through and I found stress fractures in those spots. Now that you have this info what do you think. NORT

mrgto

My guess, your geometry is WAY off. Did you change the springs on the heads when you installed the cam? Did you bend any valves?

NORT

Thanks for your intrest in my problem.I do have self-alining rocker arms and I had the valve stems cut down before I installed the Cam.The holes in the heads for the pushrods are very small and it appears visualy that they(the pushrods) are binding in the holes. The pushrods are extremly shiny and worn in that spot and I found stress fractures there as well.The pushrods that bent first where brand new with the Cam installation as well as springs,seals,retainers,locks,the whole thing and I had a valve job done do to another problem that I had.Does this info.tell you anymore than before if so I can sure use some help!!Thanks. NORT

94-6spd

I have those heads and that cam. I even have 1.6's on there. I use guide plates to keep them in line. I don't have that problem with mine. Are you sure that your valve lash isn't too tight?

Damon

RB is right. If you have the oval-shaped pushrod holes that allow very little side-to-side movement of the pusrod then you DON'T want to use self-aligning rocker arms becuase the alignemtn methods can fight against eachother and the pushrod is the part that usually gives.

One or the other. Not both.

mrgto

Well, I just read a older Hot Rod and they used the Vortec heads and they said you have to use the stock grooved tip rocker arms. And that a cam with .500 lift would cause interference problems. Just a FYI. The article is in the Jan. 2001 Hot Rod.

FastBroker

Still sounds like an alignment OR an interference problem somewhere to me. Or your psitons are hitting your valves again or the guy didn't maching the guides enough for you.

[This message has been edited by FastBroker (edited June 02, 2001).]

bender431980

so i keep bending the intake pushrods on my 5.7l l31. It has summit 8802 cam,prw 1.6 steel roller tip rockers, behive springs, 7 degree retainers, valve job full port and polish. stock rods and pistons, factory roller. i set the valve lash with 1/2 turn the first go round. bent all the intake pushrods. did a 1/4 turn the next time and ran good but when got into the rpms it bent a few of the intakes but not as bad. do i need shorter p-rods? oh and i drilled out the p-rod holes in the stock vortec heads. what am i missing here??/

Tuned Performance

iTrader: (92)

Are the springs going into a bind ?

sofakingdom

iTrader: (1)

What's the clearance from the bottom of the retainer to the top of the guide at full lift?

Dyno Don

iTrader: (7)

What timing chain set did you use and how did you install it?
Single notch crank gear or 3 key way notches?