470 bent pushrod

[natemoore]

Tomorrow I'm going under the knife to get hip resurfacing (the Birmingham Hip) on my left hip. One of the things I wanted to do before being laid up for a few weeks was get my boat motor running after a summer/fall-long complete rebuild.

Well......a few minutes after startup--after verifying good oil pressure--I heard a brief, metallic clankity-clank.

When I took off the valve cover, I saw to my disappointment that the #1 intake (?) valve (the second one back) was bent and out from under the rocker arm.

I think the clank I heard was the camshaft slapping the bottom of the lifter or the push rod bouncing off the valve cover. I hope that the oil pressure kept the lifter up off the camshaft because I do not want to have to pull all that crap off again, although I think I can remove the lifter cover without removing the intake manifold.

I scrupulously followed the instructions in the manual concerning adjusting valve clearances, torquing the rocker arm bolts, etc. In fact, I probably quadruple-checked all my procedures, clearances, and torques, so I'm clueless as to what caused the pushrod to bend like a banana.

I rolled all the push rods on a piece of glass to check their straightness. All my clearances were all on the low end of the .110"-.210" range. I did have to buy a couple of Ford pushrods that were shorter than the shortest ones offered by Mercruiser to achieve the correct clearances....but of course I threw away the scrap of paper that had all that information, so I don't know if the bent pushrod was a Ford, a Mercruiser, or an original one.

Also, I primed the engine with a drill with the valve cover removed to confirm that oil was coming out of the top of each pushrod.

Any ideas?

On the bright side: no oil leaks and my trim indicator works!

 

[dakine]

Re: 470 bent pushrod

Here is how I have bent pushrods...

Over rev
Weak valve spring
Wrong valve spring stack height leading to coil binding
Mis adjusted valve clearance
Carbon build up in valve guide
Wrong valve stem to guide clearance causing bind when hot (more common on exhaust valves)
Wrong pushrod length

 

[natemoore]

Re: 470 bent pushrod

Here is how I have bent pushrods...

Over rev
Weak valve spring
Wrong valve spring stack height leading to coil binding
Mis adjusted valve clearance
Carbon build up in valve guide
Wrong valve stem to guide clearance causing bind when hot (more common on exhaust valves)
Wrong pushrod length

I can eliminate several of these: over rev, wrong valve clearance, carbon build up, wrong pushrod length.

The cylinder head was rebuilt by a reputable shop who came recommended by several marines and individuals, so I'm assuming he would have checked all that other stuff you mentioned. He did have to replace a couple of valves and valve seats, as well as the guides. Since, I had to buy a couple of shorter Ford pushrods to get the correct valve clearance, I wonder if he screwed something up.

After I get well enough to climb back into my boat, I'll remove all the pushrods and see if it is just that one cylinder, or more of them. I read at wikianswers that preignition due to bad timing setting could cause it. That could certainly be a possibility.

 

[EddiePetty]

Re: 470 bent pushrod

Here is how I have bent pushrods...

Over rev
Weak valve spring
Wrong valve spring stack height leading to coil binding
Mis adjusted valve clearance
Carbon build up in valve guide
Wrong valve stem to guide clearance causing bind when hot (more common on exhaust valves)
Wrong pushrod length

....add at least one more to the list:
Push rod NOT seated in the center of the lifter at assembly

FWIW...Ed in 'ol Virginny

P.S. Wishing you a speedy recovery and the Best of the Seasons!

 

[JustJason]

Re: 470 bent pushrod

and people wonder why 470 threads go south quickly.

 

[natemoore]

Re: 470 bent pushrod

and people wonder why 470 threads go south quickly.

Yeah, the "speedy recovery" comment really irked me!

Any opinion on whether or not 6 month old fuel will cause varnish/sticky valves, ergo, bent pushrods? Read that on a hot rod forum.

 

[dakine]

Re: 470 bent pushrod

Nah!
Maybe after a thousand hours.

The fact that you had to use extra short pushrods is suspicious.
If a new valve was in that hole I'd guess the tech didn't check the valve length after he sunk the seat a bit doing the valve job.
If he didnt do that, he might not have checked the stem to guide clearance.
Maybe he knurled the guides and didn't ream them out to dimension.

I've never seen preignition slam a valve hard enough to bend a pushrod.
Here is what preignition and resulting detonation can do...

http://i257.photobucket.com/albums/hh225/daCommodore/Motorcycle/BMWPistonlq.jpg

EDIT: Make your pictures smaller if you want to post them in the thread

That is from an antique BMW engine where the spark advancer failed and gave it about 60 degrees BTDC timing advance.

 

[JustJason]

Re: 470 bent pushrod

That looks like just straight pre-ignition to me. If it was detonation you'd see it more on the edges of the piston, especially on the exhaust side.

On a side note, and back to the original question. Your a bit screwed on this one Nate. You need some 8inch verneers and need to measure what you have. You also need some feeler gauges and the special tool from Merc if you want to get the valves adjusted correctly. The procedure is all in the manual.

 

[natemoore]

Re: 470 bent pushrod

Nah!
Maybe after a thousand hours.

The fact that you had to use extra short pushrods is suspicious.
If a new valve was in that hole I'd guess the tech didn't check the valve length after he sunk the seat a bit doing the valve job.
If he didnt do that, he might not have checked the stem to guide clearance.
Maybe he knurled the guides and didn't ream them out to dimension.

I've never seen preignition slam a valve hard enough to bend a pushrod.
Here is what preignition and resulting detonation can do...

That is from an antique BMW engine where the spark advancer failed and gave it about 60 degrees BTDC timing advance.

Sheesus H! Wow!

Pulling the cylinder head is certainly not what I want to do, but I'm sure that the machine shop will take complete ownership of the bad work, redo the cylinder head at no cost, and reimburse me for the gaskets I'll have to buy, and buy me a meal at The Bonefish Grill for my trouble.

What can I do prior to pulling off the head? Will it hurt to replace the push rod and see if it happens again?

Free download: easy thumbnails

 

[dakine]

Re: 470 bent pushrod

Start by taking off the rocker and whack the top of the valve stem with a rubber hammer. If the valve opens a bit then sticks you know you have a tight guide. Actually, you don't even have to take off the rocker if you are in a hurry...just be sure the motor is close to bdc on that hole.

Things get complicated in a hurry after this in my experience.

I would then put in a leakdown testing connector and pressurize the cylinder so I could get the keeper off the spring and examine the valve stem for evidence of scoring or sticking. Sometimes you can see enough scoring or coloration looking through the spring where the valve emerges from the guide to diagnose this.

If you put it together with the pushrod off center all you would have would have is a lot of clearance when it located properly. This would cause a bunch of clicking but not likely a bent pushrod.



Re pic:
Pre ignition is the cap...detonation is the dynamite.
I shoulda paid attention when I saw those little balls of aluminum on the plug.
Lesson learned....tuition $1200.

 

[stonyloam]

Re: 470 bent pushrod

Start by taking off the rocker and whack the top of the valve stem with a rubber hammer.

Occam's razor is the principle that "entities must not be multiplied beyond necessity" and the conclusion thereof, that the simplest explanation or strategy tends to be the best one. Stuck valve would seem to be the simplest explination.