Found a bent intake push rod

ardeprint

ardeprint

Member
Nov 1, 2010
688
Miami, Florida
Boat Info
2003 Formular 40PC and a 185 SRX 2002
Engines
T Yanmar 440's with V-Drives / 4.3 Mercruiser with Alpha I
Went out for a boat ride this weekend and while running at 3100 RPM a load tap started. Backed off and shut down. Limped in with one engine.

Today I pull the rocker covers and find an exhaust rocker bolt almost off. At first got a little happing thinking this was my problem. Before I could set in a grin I decided to check if any other rockers where loose. Well, the intake rocker on the same cylinder just slides off the valve and rocker. I pull the rod and it looks like an S.

Any thoughts? Do you think the loose exhaust rocker could have caused in the intake to bend? Perhaps unrelated? I must mention the heads have less than 5 hours. Just replaced with "remanufactured" Mercruiser heads. So could the mechanic just be a incompetent?
 
Last edited:
Damn Robert, sorry to hear this, I'd be on the phone w/the mechanic!!!
 
Called him several times today. All of a sudden he is M.I.A.!
 
It sounds like the mechanic used the wrong procedure for setting the valves on your engine. Depending upon which 4.3's, the valves are either adjustible, tighten to 20ft-lb torque, or tighten to the shoulder bolt meets the head. If your guy left them loose, the push rod can escape and get bent. You really need to get this figured out before trying to run the engine again. If it happened on one cylinder, it may well occur on others in the near future.
 
fwebster said:
It sounds like the mechanic used the wrong procedure for setting the valves on your engine. Depending upon which 4.3's, the valves are either adjustible, tighten to 20ft-lb torque, or tighten to the shoulder bolt meets the head. If your guy left them loose, the push rod can escape and get bent. You really need to get this figured out before trying to run the engine again. If it happened on one cylinder, it may well occur on others in the near future.
Click to expand...

Hi Frank,

The rod came off one of my 5.7's. Serial number 0M310001
 
Last edited:
Frank is right, I would start from scratch myself and do the valve torque sequence per the merc manual, if your going to tackle it yourself.
 
If this was me, and given the result, I'd really prefer the intake manifold be pulled and the lifters inspected - I believe they are joined with a keeper and spider cage on this engine - a renegade pushrod may have allowed them to rise too high and escape. A peek at the camshaft may be warranted as well.
 
Depending on the last time someone was in there I would also be worried that the valves hung and the piston whacked them.- I'd scope the cylinder or look in the manifold for signs of water/rust on the valves. I had a similar issue at one point but my early evidence was bent pushrods (yes sloppy rockers).
 
Correct me if am wrong, but this is my theory.

When the bolt on the exhaust rocker came loose it did not allow the exhaust valve to open. This left the hot gases in the cyliner. As the piston surpassed top dead center the intake valve tried to open, but the gas build up did not let the valve open bending the rod.

What am worried about is. If my theory is correct, where did that compression go to. Could the lack of valve action have coused other problems to my bottom end? Who knows how long that was like that????
 
Last edited:
I don't think so.

When the exhaust rocker malfunctioned, the exhaust valve stayed closed, as the intake opened, exhaust gasses were in the cylinder and when piston passes TDC, a vacuum is created in the cylinder which is how the next gas charge enters the cylinder,; however, in this case, where the cylinder if full of exhaust gas, the next fuel charge cannot fully enter and is left in the plenum/intake, and the cylinder doesn't fire.

Remember, the gasses in the cylinder are either a mixture of fuel and air or exhaust. Both are air and are compressible so your theory doesn't work because it takes something non-compressible like water in a cylinder to bend stuff.
 
fwebster said:
I don't think so.

When the exhaust rocker malfunctioned, the exhaust valve stayed closed, as the intake opened, exhaust gasses were in the cylinder and when piston passes TDC, a vacuum is created in the cylinder which is how the next gas charge enters the cylinder,; however, in this case, where the cylinder if full of exhaust gas, the next fuel charge cannot fully enter and is left in the plenum/intake, and the cylinder doesn't fire.

Remember, the gasses in the cylinder are either a mixture of fuel and air or exhaust. Both are air and are compressible so your theory doesn't work because it takes something non-compressible like water in a cylinder to bend stuff.
Click to expand...

Thanks for your reply!

You don't think the gases, as compressable as they are, could have created enough resistance on that intake valve?
Or... the rod looks like that after running with this resistace for a while until it bent a little and then came off and hit something else.
 
Ok just thought of another. Could fuel have built up and created the resistance?
 
susanandlance said:
I'd go w/Mitch on this one, if anyone knows something about this I'll bet he does (ASE Mech)
Click to expand...

I agree with you Lance, but I hope that's not the case. I am not sure if he feels its unlikely I bent the connecting or I am in for it.

Mitch if you can elaborate it would help me.
 
My guess is a sticking valve. Pretty easy to check, try to push down on the valve where the push rod bent. If it has a smooth motion it's fine but if you feel it hang up that's your problem. The repair is a valve job.
 
You must log in or register to reply here.

Forum statistics

Threads
113,253
Messages
1,429,377
Members
61,133
Latest member
Willbeckett
Back
Top