Collapsed lifter, bent pushrod
08-18-2014, 07:01 PM
#21
Registered
Yep me too.
Unless you are running some incredible unheard of cylinder pressures that is creating air so dense it can not be measured on earth there is no way that a intake pushrod will bend trying to open a valve in a non evacuated cylinder.
Think about this Once the cylinder has built up 150 lbs of pressure after it has taken a gulp of air from the intake stroke and compressed it why doesn't the exhaust valve pushrod bend trying to open the exhaust valve against that 150 lbs of pressure? They are all one and the same pushrods.
After the second stroke of the exhaust valve not opening the intake would be able to take in very little more air so at best the pressure may build anothee 10 or 20 lbs .
Every other stroke as the pressure would build from the exhaust valve not opening the pressure would relieve itself through the intake valve and pop out the carb causing a backfire.
Just for some history my dad had one of the old soft cam problematic sbc in a brand new 1978 305 Chevrolet that ground the exhaust lobes off 2 cylinders of the cam.
He ran it a couple thousand miles back from a trip with it backfiring thru the carb the whole way and no bent exhaust pushrods,
Unless you are running some incredible unheard of cylinder pressures that is creating air so dense it can not be measured on earth there is no way that a intake pushrod will bend trying to open a valve in a non evacuated cylinder.
Think about this Once the cylinder has built up 150 lbs of pressure after it has taken a gulp of air from the intake stroke and compressed it why doesn't the exhaust valve pushrod bend trying to open the exhaust valve against that 150 lbs of pressure? They are all one and the same pushrods.
After the second stroke of the exhaust valve not opening the intake would be able to take in very little more air so at best the pressure may build anothee 10 or 20 lbs .
Every other stroke as the pressure would build from the exhaust valve not opening the pressure would relieve itself through the intake valve and pop out the carb causing a backfire.
Just for some history my dad had one of the old soft cam problematic sbc in a brand new 1978 305 Chevrolet that ground the exhaust lobes off 2 cylinders of the cam.
He ran it a couple thousand miles back from a trip with it backfiring thru the carb the whole way and no bent exhaust pushrods,
Last edited by tommymonza; 08-18-2014 at 07:06 PM.
08-18-2014, 08:36 PM
#22
Registered
Join Date: Jan 2007
Location: Murrayville Georgia
Posts: 1,818
Likes: 0
Received 893 Likes
on
320 Posts
back when I was working on a Trans Am series Corvette we qualified in Detroit with and broke an exhaust rocker. motor still turned 7k during qualifying and never bent the intake pushrod. even with 200 psi in the cylinder the intake would only need to move a few thousands and the pressure would push out the intake and all the load on the pushrod would go away. unless you have some cheap pushrods the only time I have seen them bend is when a moving object meets an unmovable object. just my 2 cents.
08-19-2014, 05:50 AM
#24
Registered
after cyl fires, piston goes down and exh valve opens. i betcha that on a 8;1 4cyl with 1/4 inch pushrods the exh valve is being pushed open into more than 200 psi. engine builder will tell you ANYTHING...except "yup, it is my fault and we will cover it." pull heads. check valves.
08-19-2014, 06:45 PM
#25
Registered
Join Date: Jan 2007
Location: Murrayville Georgia
Posts: 1,818
Likes: 0
Received 893 Likes
on
320 Posts
after cyl fires, piston goes down and exh valve opens. i betcha that on a 8;1 4cyl with 1/4 inch pushrods the exh valve is being pushed open into more than 200 psi. engine builder will tell you ANYTHING...except "yup, it is my fault and we will cover it." pull heads. check valves.
