Had this happen today in my plane while flying. Sounded like a jackhammer was in the engine, then it stopped. My mechanic and I are trying to figure out exactly how the rocker bearing went through the valve cover.

Any ideas what would make this happen?

How did your underwear fare the experience?

It was worse on the ground.

When the pounding in the engine stopped, I looked down at my guages thinking what the heck just happened. No huge difference in oil pressure, I wouldn't have guessed this at all. If I wasn't already going to the airport, I would have kept flying to my destination had it been farther than it was. The scary thing is that hole is just a milimeter or so small enough to hold the bearing in.

Can you think of what would cause that side-load on the bearing to force it through like that?

I've seen them worn on the inside, but never a hole.
Don't the new 0-200's have set screws in the boss to keep this from happening?
Dave

907Pilot wrote:Had this happen today in my plane while flying. Sounded like a jackhammer was in the engine, then it stopped. My mechanic and I are trying to figure out exactly how the rocker bearing went through the valve cover.

Any ideas what would make this happen?

Was that from the bushing or the pin that goes through the bushing and rocker?

It's from the bearing that holds the rockers in place.

Call Mike Skup or email him the picture. He'll tell you precisely how it happens.

If you don't have his contact info you can get it off the supercub.org site.

d.grimm wrote: I've seen them worn on the inside, but never a hole.
Don't the new 0-200's have set screws in the boss to keep this from happening?

The valve cover itself is what keeps the rocker arm shaft in place on the older engines. At least in the C145 in my old 170. Don't know what would cause enough side load for it to wear through the valve cover like that. I seem to recall hearing something about a set screw on the new 200's and some sort of AD/service bulletin addressing a problem with them, but not the details. ??

Check to make sure the top of the valve stem is perfectly flat, if it has a bevel to it that will make the rocker arm torque to the side a tiny bit each time it strokes and that MAY make the bearing "walk" sideways. Uneven wear on the bearing surface of the rocker arm itself can cause the same thing.

Really glad that you stopped and checked out and did not continue in flight.

Shorton -

Good thinking. I have been so caught up in thinking it was something on the bottom side of the pushrod that that didn't occur to me. I will check that on Tuesday before we tear it down.

Can't say enough how good of a learning experience this was, despite the cost.

shorton wrote:Check to make sure the top of the valve stem is perfectly flat, if it has a bevel to it that will make the rocker arm torque to the side a tiny bit each time it strokes and that MAY make the bearing "walk" sideways. Uneven wear on the bearing surface of the rocker arm itself can cause the same thing..........

Seems to me that the rocker arm surface is ground at a slight angle to rotate the valve, at least on my old C145. What engine did this happen on?
On the C145, there are no bearings, there is a bushing press fit into each of the two rocker arm shaft bosses. The shaft is free to slide L&R in the bushings, kept in place by the valve cover. if the bushings move in the bosses, I believ the fix is to rebore (line bore) the bosses & fit oversized bushings. There's also an AD on minimum wall thickness for these bosses, which often do not meet spec after being rebored.

Unfortunately for me, I am pretty smart guy but I am not sure I follow what you are saying. This engine is a o-300a. The portion that forced it's way through the valve cover is a shaft about four inches wide that holds the rockers in place. On the bottom side (as looking at it) are the push rods and on the top side are the valves. I am calling it a bearing, but perhaps the correct name is something else?

On cleaning and re-looking at the valve cover today, it was far less obvious at the time but way more obvious now that it was a matter of seconds before it came through the other side as well. It is all cracked apart and the hole is almost through.

907Pilot wrote:It's from the bearing that holds the rockers in place.

That's a rocker arm shaft, NOT a bushing. As for why, "shit happens" is the best I can come up with. I never heard of that happening before-- wear marks on the inside of the valve cover, but not a wear-through. If the rocker arm shaft, bushings, & rocker arms are all a good fit with each other, just replace the valve cover & move on.

The other thing that strikes me as odd on that is that particular valve cover has had a recurring issue of the screws vibrating off of it.

Hopefully I have an answer by Tuesday.

I suspect that you will find either the shaft worn loose in the bosses' or loose rocker arms. However I've seen worn out rockers before, but never saw one through the cover. Weird!

oldtech wrote:......never saw one through the cover. Weird!

I agree,, weird for sure...There is ALOT of side thrust on that shaft and looking at the pic it looks like there is rotation too by the way it wore through the cover... My guess is the cyl was repaired and during the align bore process they got the shaft bushings in there crooked... IMHO

It's common on Continental 0-200/300(same cylinder) to find the shaft wearing the cover.It is pretty normal to see some rubbing but it can be caused by worn rocker bushings,worn or broken rocker stand,badly worn guides.
This has happened on even the new 0-200s with very low time.The late cyls did come with an allen set screw retaining the rocker shaft BUT they began falling out.Continental tells you to replace the shaft with the old style with no retaining screw.I polish the ends of the shafts to make sure they are smooth where they contact the cover.

Bill

Thought you guys might appreciate a follow up, just for educational purposes.

It appears that the unscheduled departure of the side of my valve cover was due to vibration in the engine caused by the top and bottom bolt being pulled off. It looks like they weren't torqued properly and either had play in them or were too tight. Hard to tell now:



And this little guy was stuck in the baffling:



After picking my jaw up off the ground, my mechanic (who started without me, but thankfully saved me from a heart attack) told me he went through and checked every cylinder bolt on the engine and every single one was not tight enough to spec except two. He even found one that was finger tight.

It's funny to me. I am really curious to see how the engine runs after this. I have always thought my prop was out of balance because the engine always seemed to me to have a vibration in it. I had 2 different mechanics look at it previous to this, and 3 flight instructors fly with me to see if they felt the vibration. All of them said they didn't. Makes me wonder!

This afternoon we are going to check the remainder of accessable bolts on the engine.

So......... Who bolted this engine together? And how long ago?

Gump

I will just say that a lot of people know him and is purported to have a great reputation from what I understand.

Matt