panic

Yep but I've checked the valve train a hundred times, all semms nice, clean and tight.

Cavu2u

Pushrods and cam followers too?

7t2vette

I have to agree with it sounding like a cam lobe has gone flat. Remove the valve covers, disable the ignition, and watch all the rocker arms move as the engine is turning over. A flat cam lobe will be very obvious as the rocker will not move as much as the others. Been there, done that.

Hofs01

panic

It sounds likely, if I understood properly then a flat cam lobe would make the valve to be at the wrong position when the combustión happens and instead of going through the exhaust it would get back to the intake?

Hofs01

A flat Exhaust lobe could cause the valve to not open at all. Then once the intake valve comes open, that compression and burnt fuel in the cylinder ends up in the intake causing the "pop" and then messing with your air fuel ratio for the other cylinders.

panic

I'll check that this afternoon...thanks a lot!

Cavu2u

Is there enough room up front to remove & replace a cam with the engine in the car (350 or 454)?

mysixtynine

Sounds like a wiped exhaust lobe to me as well...

stick a straight pin into all 8 distributor boots at the cap (deep enough to hit the wire core) and then take a multi meter lead and clip one end to the carburetor stud. then start the engine and touch the meter lead to each pin (hold the meter lead with an insulated tool) one at a time and rev the engine for each pin to see if its gone. You need to short the wires to ground NOT leave them open. If one pin makes it stop you have your bad cylinder location.

Also:
I also wonder if it could be "cross fire" in the distributor cap or between wires or a malfunctioning IGN module (not sure of what ignition u have)? Just a thought.

Do you have one of those correct a caps on their... i can just barely see your cap in the videos?

Amorget

I replaced the cam in my 81 w/ a 350 with the engine in the car. Removed the hood, radiator and radiator support and it had plenty of room.

63mako

Need to figure out why that one rocker was worn. My bet is that it was an exhaust rocker on the cylinder causing the intake backfire and it was worn due to a bad lobe. Do you have a flat tappet cam or roller cam? If you have a flat tappet time to go roller. If it is a solid roller it likely had a lifter wheel failure and took the cam lobe out.

Cavu2u

roscobbc

Can't open vid to listen - I had an unexplained noise on my BB - sounded like it was coming from lifter area - stripped top end and re-set everything several times - lifters, cam, pushrods, rockers & springs all OK - engine still performed well! The problem with ally headed engines I think is that noise tranferrence makes it difficult to pin down the source of these sort of noises. My problem - no. 1 big end shell had spun and broken up. No-one who listened to the noise had the slightest clue it was a big end - the noise appeared to come from far 'higher' in the engine - fooling many 'experts'

panic

I found out the problem.

A (roller) cam lobe worn out...

I've already asked one to the engine builder (American Speed of Ill), but I guess I should get some other hardware to top up the new assembling and have , for example I've found out that the pusher of the rocker shaft has a very small excursion hence I guess it's worn out too...

Postal123

Glad you found your problem. I guess it could have been worse...? Good luck getting back up and running!

doorgunner

Thanks for the timely update......I'm glad you don't have to gut the engine!

panic

I still have a doubt, should I gut the engine looking for small particles of steel spread around from the worn out lobe?

I've changed the oil and checked if any trace of small bits of steel was by the oil cap, there was none, and the change was done about a week after I started to have the issue...

Cavu2u

Panic,

There is such a thing as an Oil Filter Cutter, with which an oil filter can be opened up and the filter element removed, spread out, and inspected for metal particles. In your case, a good idea.
http://www.jegs.com/i/JEGS/555/80532...FRSIfgodbb8A0Q

Also, there are companies out there that do chemical analysis of oil samples. They show if any excessive amounts of specific metals are present, which also helps to determine which component and how much wear was going on in the engine.

Maybe you did already, but what really needs to be done is determine the height of that cam lobe the worn cam lifter was riding on. A precision Dial Gauge that measures the height, and along with a Degree Wheel, the duration of a cam lobe, will make the decision to replace or not to replace your cam. Or, if you can just visually see the lobe not raising the lifter/pushrod up as much as the others (), just go ahead and replace the cam and be done with it.

Good luck.
Steve

forman

ok this will sound far fetched but it sounds to me (sounds) like you broke the spring or arm on your carb <<< the sound does no seem too deep in the motor ,,, its sounds right on top <<<< i would inspect the bottom part of the carb,, check the flaps it sounds like its flapping in the wind with the flow of the motor ,,, Im also 4000 miles away from you but I thought I would give it a whirl ,,, have you looked down the carb

63mako

How does the lifter wheel look? I would swap out the lifters, cam, pushrods, rockers, springs. A 570 HP 406 that sees High RPM and racing use with 10,000 miles on it is due. Cost of over 1.4 HP per CI. and driving it like you want. Hope your oil filter bypass was blocked. If not your bearings are likely trashed.