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-   -   Collapsed lifter, bent pushrod (https://www.offshoreonly.com/forums/general-q/316904-collapsed-lifter-bent-pushrod.html)

tommymonza 08-18-2014 07:01 PM

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,

compedgemarine 08-18-2014 08:36 PM

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.

formula18 08-18-2014 08:49 PM

Motor will reassembled this weekend...will keep you all informed...lots of good information here

dereknkathy 08-19-2014 05:50 AM


Originally Posted by formula18 (Post 4173753)
Just as suspected. Engine shop says one caused the other. Collapsed lifter not allowing gases to escape
..caused pushrod failure on intake....said it's prettu common

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.

compedgemarine 08-19-2014 06:45 PM


Originally Posted by dereknkathy (Post 4174003)
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.

back when we were running Class One in APBA and blew up a lot of motors our engine builder said the same thing with everything we broke. "never seen that break before!" they were still happy to sell us another engine each time.


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