Hey Y'all,

I've been out of communication a while because of starting up a new venture. Anyway, last fall I rebuilt my '65 vert 327 L79. I installed:

Comp Cams Cam and lifter kit COC 12-242-2

Comp Cams roller tip rockers

ARP Head Bolts

New Timing chain & sprockets

Complete FelPro gasket set

I have matched “461” heads fully reconditioned with stainless 2.02/1.60 valves, hardened seats, new springs, retainers, locks, seals etc, etc.

I drove it around all fall and the day after thanksgiving I was cruising at a modest 65 mph and got this horrible miss. Pulled it over, had it towed back home and found no compression in #7. I pulled the intake & valve covers to find a bent up pushrod and very a slightly damaged intake valve. It didn't smack the piston luckily.

Could not find the cause. Lifter looked good, plenty of oil pressure, WTF!?! I replaced the #7 intake valve, spring, keeper and push rod and put it back together. I get great oil pressure. Drove it around a couple of times and then set out to take a 50 mile trip. I got about 20 miles from home and - you guessed it - happened again!

This time it was the #4 exhaust push rod all bent up.

Everything I bought from Comp Cams was a matched set (except the roller tip rockers, very slightly used, I got from a friend)

I am so bumed that I can't even face pulling it appart again Any ideas what the F--- is going on here?

Thanks in advance!

Bob

 

Offhand, I would say you have a problem with your valve stems sticking in the valve guides, but that is just a guess.

Or, your cam gear timing is off.

Were your heads milled?

Did you do a clay piston/valve clearance test?

Doug

 

Were the lifters adjusted correctly, if they were adjusted lose, that could have been the problem. It happened to me I know with an improper adjustment you can bend a puah rod

 

Just a thought but could it be that you have the incorrect ratio rocker arms? 1:5 when they should be 1:6? You said that you got them from a buddy. Maybe they are incorrect for your cam application.

Steve

 

I would definitely look at valve train geometry. There is obviously something wrong causing this to happen. I would check the simple stuff first, like coil bind, push rod length and rocker slot length. Look over the rocker arm stud for any evidence that the rocker is binding on it.

I had an issue years ago with a 302 that was snapping certain rocker studs off. I was using a Crane cam with slightly higher than stock lift but with stock rocker arms. When checking out the geometry of the valve train I discovered that the slots in the rockers varied by as much as 20 degrees from the longest to the shortest. Needless to say the short ones were the problem. I used a Dremel to elongate and match all the slots and never had a problem with it again.

Good luck... GUSTO

 

I hope there is no problem with the rockers as he got em from me. Bob it's interesting that you keep bending pushrods. I have a pushrod length checker if you need to check geometry on the valve train. Dave

 

Do you have screw in studs or push in?

 

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

Dave,

Do you remember what the ratio for the rocker arms were? What were you running the rocker arms on with respect to cam grind? It was just a thought on my part, wasn't trying to blame anyone.

Steve

 

I had the same problem once with #4 and #5 exhaust pushrods. Turned out the intake manifold bolts were a tad too long and interfered with pushrods. Something to check!!

 

Steve,

No offense taken If I remember correctly they are std 1.5 Comp Cam Magnum Forged Roller tip rockers. I ran them for less than a year with no problems. The set up was not much different than what Bob is running now as respects to the cam grind. I wonder if it could be an issue with the guide plates? Dave

 

OK, jents. I am working on the car now. The first valve definitely had seized in the guide. I think we will find that the second did also. We are looking at a situation where something is causing the valve to seize. The bent pushrod is a consequence of that. Thoughts?

 

Who ever did your head work, maybe not so good?????

 

Did it with the heads that Bob had on it. Completely re-worked the heads after the first occurence. Did it again on a different cylinder. The man builds engines that have won races at Daytona.

 

Wayne, I forget does Bob have guide plates and screw in studs installed? If so could it be that the pushrod holes were not properly clearanced? Or could it be a dissimilar metals issue with mixing and matching parts? By this I mean could it be that once the SS valves heat up they expand more than the bronze umbrella seals expand and this is causing the pushrods to stick? Now you say a local builder built it was it Ashworth?

 

Hi Dave,

I had trouble with the guide plates right from the get-go so I took them back off. On the 461 heads, the guide hole "D" does not allow enough room to use the guide plates.

Real head scratcher.

B

 

OK, I know what your problem is.

When you removed the guide plates you screwed up the geometry.

Get some hardened washers the same thickness as the guide plates and put them under your studs.

Yes, I have run into this problem before.

 

ttt

 

Makes no difference, as long as the pushrods are the same length as they were before; the pivot point of the rocker arm will still be at the same height from the head on the threaded portion of the stud, regardless of what's at the bottom of the stud.

 

Bad gas will do this. Did the same thing on my boat eng.

 

Have you ever heard of valve train flex?

When you lower the stud, the nut is not on as much, the rockers move around too much with every movement. At lower RPM it has time to recover, at high RPM it does not have time to recover and something has to give (the weakest point).

Bob, what do you have to lose?