valve lash or stuck valve

[wyckedtanker]

Well I finally got my 340 6 pack idling nicely and feeling good at that point.  But it has developed a nice valve train ticking on the left bank as well as, as soon as I drop her in gear or attempt to accelerate I get a backfire through the left pipe (like it's firing when the exhaust valve is open.  there are so many options to trace down I know.  it's a 1970 block with 70 heads on it.  I figure it wouldn't hurt to change the wires cap and rotor, possibly the coil.  I was hoping someone here might have some insight or experience with something like this before I tear through everything and end up doing a complete rebuild.  I also found that it was easier to get it to idle after moving the fuel filter from between the tank and pump to between the pump and carbs.  Isn't inheriting someone else's troubles fun. 

[cudabob496]

ticking, and backfire, I'd pull the valve cover and inspect

backfire can be a timing issue also

[Strawdawg]

sounds like a broken valve spring, but it could be a wiped lobe

[7212Mopar]

check firing order? 2 and 4 get wrong a lot.

[wyckedtanker]

Firing order is right, I checked and rechecked it a few times.  I pulled the rocker cover inspected the valve springs, didn't see anything, so I removed the rocker arms/shaft to get a better look at the valve springs, again didn't see/feel any cracks or damaged springs.  with the rockers removed I was able to get 3 of the valve springs to shift/wiggle ever so slightly maybe 1/32-1/64th of an inch whereas the others didn't budge could this be part of the problem or am I just finding a problem where there is none

[Oldschool]

While you have it apart, pull the pushrods and make sure they are all straight....   

[roadman5312]

sounds like a broken valve spring, but it could be a wiped lobe

                                                              Camshaft lobe possibly, spin motor plugs out, watch rocker arm movement, if you have a worn lobe you will see it at the rocker, usually an exhaust valve.

[wyckedtanker]

I spun the motor over yesterday and looking around the hood (just me at the house) everything seemed to move alright.  I will have my wife crank it for me tomorrow after work.  I am starting to think the motor swallowed something.  I really don't want to pull the motor apart yet I was hoping to enjoy the car some before rebuilding.

[cudabob496]

I spun the motor over yesterday and looking around the hood (just me at the house) everything seemed to move alright.  I will have my wife crank it for me tomorrow after work.  I am starting to think the motor swallowed something.  I really don't want to pull the motor apart yet I was hoping to enjoy the car some before rebuilding.

have you done any work on it in the previous few months, that might have contributed to this situation?

[Beekeeper]

I helped a friend rebuild his 318 last year and we noticed once the stock rocker arm assemblies were installed, several of the pushrods had a tiny bit of slop in them. We checked each one with the valve fully closed (cam lobe 180 degrees from its high lift point) and found nearly a third of them had about 10 thousandths clearance between the top of the valve tip and the rocker arm. The others were just barely long enough to eliminate slop but not long enough to depress the plunger in the hydraulic lifter. In the end, we ordered pushrods 1/16 inch longer (62 thousandths) and ran those. Not a hint of ticking and it's runs fantastic. It's always been my understanding that hydraulic lifters work best when the push rod is just long enough to depress the plunger about 50 thousandths or so. I always shoot for this and have had great results with no problems.

It could be something that simple with the backfire being unrelated like a lean condition.

I'd take a couple hours to remove the valve covers, spin the motor and check the clearance between each valve tip and the rocker tip. At the very least, grab the rocker and try and wiggle them.

The guy who set up your heads might have made a mistake. I've had that before on motors.

[cudabob496]

you can get a noise from the side of the pushrods hitting against the head. been there!

[wyckedtanker]

It could be something that simple with the backfire being unrelated like a lean condition.

I'd take a couple hours to remove the valve covers, spin the motor and check the clearance between each valve tip and the rocker tip. At the very least, grab the rocker and try and wiggle them.

I do know I was able to get a couple of the rockers to wiggle (slide back and forth on the shaft) when the valve was closed.  It just started about a week ago. 

The only engine work I have done to it since buying the car a month ago is trying to tune the carbs etc the pushrods looked fairly centered in their holes but I will get in there today and check things out with some of the tips from here.  so possibly worn out pushrods etc nice to know.

[Beekeeper]

On my friends car, we never bothered to examine why. We just identified the problem and that was an easy fix.

I believe that cam regrinds have a smaller base circle than a stock cam would so theoretically, the pushrods would need to be a tiny bit longer when the lifter is riding on the base circle. I'm told the reason they do this is because higher lift cams would have a bigger bump and not fit through the holes when you install it so they make the base circle smaller in relation to the bump so it fits and you get the lift you want. If you have adjustable rockers, no big deal.

The guy who builds your heads can also do it wrong so that some valve tips are lower than others.

I figured this is not that hard to check out and costs nothing. If it's the case, the best fix is a set of adjustable rockers. Then you snug them down till the slop is gone and add an extra half turn before locking them down.

[wyckedtanker]

Well I got the wife to crank the motor over while I inspected both banks of rocker arms and all the rockers slide fore and aft with the valve closed and cylinder 3 exhaust and cylinder 2 intake rockers I can rotate back and watch the pushrod depress with it so I am thinking collapsed lifters or worn can at this ppint

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[wyckedtanker]

Sorry my phone is not the best worn cam at this point

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