When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Replacement Cam and you don't know what. you need to know the valve lift. You can get pretty close with a good little steel ruler. Stand up next to a valve and have somebody bump the starter. obviously subtract up from the down measurement go around and check a bunch of them. Intake and exhaust separate. 20 buck digital caliper would be better. What 427? Head casting numbers? Orig o-ring valve seals or umbrellas or positive seals under springs? You also want to get a cheap lever style spring compressor and feel the valve that bent the rod for binding. Is valve bent? Compression test. https://www.ebay.com/itm/OEMTOOLS-25...cAAOSw7thb-KAa
The heads are original cast iron. 3931063
L36 427 3963512
Excuse my ignorance but how did you determine the push rod is 2 piece. Is the ball removable?
I'm at work so I can't examine the rods.
If you look at the pushrod you can see the parting line. Basically they take a piece of hollow tube and pres in the ends. Those are cheap pushrods. Pony up the $$$ and get a set of god one piece rods. Find out what bent it in the first place. As said above coil bind or some other clearance issue. I would pull all the pushrods and check them all. Also the tip of that rocker arm has some scoring. Pull al the rockers and check them.
Valve stems are much stronger than the light weight push rods. So it is good that they can flex and bend. Flexing and bending also decreases the valve lift and effective cam duration. That is why some of the other poster said to go to stronger push rods. You can do a leak down test and a bent valve or leaking valve can be heard from the hissing of escaping air. Who ever installed the bigger cam cheaped out and used some marginal parts. Bent push rods are a sign of over revving the existing springs. Hydraulic flat tapped lifters use lighter pound compression springs compared to the other 3 types of cams and they are the red line rpm limiting factor. Because they go into valve float at a lower rpm.
What every performance motor needs is a quality sequential digital rev limiter multi spark box. Another item is a shift light that you can set to what ever RPM.
I agree. I believe some contact was made between the two. Sometimes just setting the valvelash too tight puts things in jeopardy. Sometimes valvelash has been set so tight that the lifter is bottomed out = no clearance for the piston.
A sloppy timing chain retards the cam timing. Retarded cam timing puts the distance between the exhaust valve and piston a little bit closer to each other.
Not saying that's what happen, but always a possibility.
They're 1.7 ratio , thats what is stamped on the rocker.
I don't know a lot about BBC rocker ratios but I believe stock is 1.6. Your 1.7 might be too much, forcing some really bad valvetrain geometry or placing the valve head too close to a piston.
These folks got you covered, all I can offer is "Welcome to the BB/C3 money pit", you are officially on board. I say that with a smile, I love my Vert but the BB takes a bit more money and patience. I'm sure you'll get it sorted.
The stock pushrod is the weak link when slightly over-rev'ing the engine. Just because the pushrod is bent does not mean there are other serious problems. If the pushrod is not badly bent, it can be straightened across V-Blocks with a dial indicator and a rubber mallet (this method is FAA-approved for straightening aircraft engine pushrods, believe it or not..). Or you can replace it. If this is a near-stock engine with a 5500 rpm redline, and there are no other engine problems or symptoms, I'd straighten it, run the engine, and have fun.
Don't over-think it...
Don't make the problem worse than it is...
Lars
I got one for you Lars, guess how much over-rev you get on a Tri-power when the throttle return spring can't overcome the outboard diaphragms. I found out the hard way, nothing damaged but it really got my attention. (I had just gotten the secondaries functional after buying the car in a non-running state, I learned a good lesson there)
Last edited by suprspooky; Mar 8, 2019 at 06:21 PM.
I'm not completely up to speed on big blocks, never owned one but I've seen the same pushrod damage in a small block caused by intake manifold bolts getting mixed up. The end 4 bolts are shorter than the other, inboard bolts. If you install a longer, inboard bolt in one of the end holes the bolt will interfere with the pushrod. Check the simple stuff first-might be a tempest in a teapot! Good luck.
Ok...so you have the Comp rockers that I mentioned......that is why the pushrod bent because those particular rockers are pretty tough with a thick cross section.....GM rocker would have probably broke right off......
So......you have a crash going on....you need to determine if it is the retainer to boss or spring coil bind.......I personally pop one off the I and the E (use air holder or the rope trick) and start inspecting....you can put a light tension spring on both I and E and use an indicator to check distance to bind and distance to retainer crash. Record these number and compare with the cam lift. Don't know your cam? Take the same indicator and go off the tip of the pushrod while rolling the engine over.....it will move like .300, record the movement and multiply by 1.7.......subtract that number I and E from both the retainer and spring bind number.....you need at least .060
If you do not have clearance.....you will have to find a retainer/spring/locator setup that works......
But buy new one piece pushrods......99% of them are made by Trend no matter what brand name is on the box.
Jebby
What is the rope trick?... I have used air pressure to hold the valves in place on a 347 ford a while back
Have piston down. Feed about a foot or two of clothesline into plug hole. Rotate crank to jam rope between piston and valves. Using a wrench, not the starter.
Yes. And valves so you might as well get guides and seats. I am putting 11/32 guide inserts and new valves. Then figure how much valve travel you have and measure how much valve lift that cam makes. If that guy is. 6 lift, it is overwhelming all of the stock 40 year old valvetrain.
Need to inspect all RA studs and RA slots to see if they hit.
Need to determine if there's any coil bind.
Measure several lobes lift both intake & exhaust
I'd have checked the above w/ valve train assembled but you can do it disassembled.
or straighten a couple PRs (I & E) enough to reassemble One cylinder. Roll motor through and check gaps between coils / coil bind when valves fully open
count your blessings ... seriously ... you caught this before it got much worse!
I'm still of the opinion that this is straight coil bind because somebody cheaped out and didn't replace the springs with the new cam. If you look at Comp Cams website for example, even with one of their fairly mild cams whether it's a roller or flat tappet hydraulic, you must replace the stock 427 valve springs in stock heads or risk coil bind. I think that's what's in the pics, not pistons hitting valves. It isn't a valve timing issue. When you're changing the springs (throw in some valve seals at the same time) and using compressed air to hold the valves up on that cylinder you will know right away if you have a bent valve. You will hear it and it won't hold pressure. Your main problem is figuring out what cam you really have and what or whose springs to use.
First thing I think I'm doing is measuring the lift of the cam since I have all the rockers off.
I plan on using a good intake & exhaust PR , and setting up a dial indicator.
How is this done? Get the cam lobe at its max lift and multiply by 1.7?
Thanks
Mike
