Pushrod Problem - R60/5

[20774]

From another forum...I thought I'd offer this for viewing to see what people thought of this problem. The bike is a '73 model. I believe the bike is new to him. The owner has been having problems getting the left side to run. He tried various things including swapping plugs, coil wires, etc. Then he pulled the valve cover. The intake is the one with the problem.

I have an idea what's going on...I'd be curious as to what you guys think.

 

[mneblett]

The obvious bits:

the mushroomed intake pushrod tip, likely from being hammered from excessive clearance;

this must have been going on for a long time, since the adjuster screw has been screwed in as far as possible, and the gap is still huge

The other end of the pushrod is likely still relatively normal, as the aluminum shaft appears to be extending from the pushrod tube roughly the right amount (comparing the intake with the exhaust, and recognizing that the exhaust valve is being actuated, the place where the pushrod diameter changes is at roughly the right place).

The first thing I would want to inspect is the cam left intake lobe and the lifter -- if the pushrod has been hammered enough to mushroom the tip, I'd wonder how the surfaces of these components have survived.

 

[20774]

Mark -

A couple of things that I noticed... It appears if the round ball-end of the pushrod tube is stuck inside the adjuster. I see an uneven surface just past the hex adjuster head.

The other thing is note that the jam nut for the adjuster has been rotated to the other side of the rocker arm. I think this was done to allow for more travel on the rocker arm. And I think more travel was needed because the intake valve is sinking into the head.

It might be that what broke the end of the pushrod tube off is that with the extreme rotation of the rocker arm to compensate for the sinking valve, the rocker arm was no longer merely pushing on the tube, but pushing and trying to bend it since the motion of the rocker arm had more sideways direction than along the shaft of the tube.

I don't have a lot of details, but I think the guy is trying to get the bike started...it's relative new to him. So, the hammering of the pushrod tube could have happened in as little as a few minutes. So, I'm thinking the cam is OK. But I think the head has to come off. If you're going that far, it's easy to just take the cylinder off and look at the cam and it's surfaces.

 

[mneblett]

Interesting thoughts, but with valve recession, the valve stem would be rising toward the rocker arm, closing the gap.

On the intake side (right side in the pic), the pushrd end appears to be smooth, not fractured (even if smoothed by rubbing if the tip welded itself to the adjuster screw, I'd expect to at least see some ridges or irregular surfaces). That, coupled with the extent of lateral mushrooming and what appears to be the oil bore still in the center of the tip, suggest to me that the tip has failed by deforming.

What has me stumped is how this problem initiated -- was it something as simple as absence to maintenance? Doesn't make sense to me yet.

 

[20774]

So as the valve sinks into the head, the valve stem moves farther out. In order to get the proper clearance, the rocker arm has to be rotated by the adjuster. When the adjuster runs out of room, the jam nut is switched to the outside, allowing more remove for rocker arm rotation in order to attain clearance.

That's the progression that I envision.

And I'm not aware that the pushrod proper has an oil bore. I didn't think that oil migrates through the middle of the pushrod. There's a small dimple in the round end of the pushrod, but AFAIK, it doesn't actually penetrate the ball end.

 

[mneblett]

So as the valve sinks into the head, the valve stem moves farther out. In order to get the proper clearance, the rocker arm has to be rotated by the adjuster. When the adjuster runs out of room, the jam nut is switched to the outside, allowing more remove for rocker arm rotation in order to attain clearance.

That's the progression that I envision.

And I'm not aware that the pushrod proper has an oil bore. I didn't think that oil migrates through the middle of the pushrod. There's a small dimple in the round end of the pushrod, but AFAIK, it doesn't actually penetrate the ball end.

Ah! Makes good sense -- and as I think about it, I think you're right about the push rod -- I was thinking of a different engine.

 

[ebeeby]

He must be new to airheads as it is unbelievable that he tried all those other things while the left side must have been making a horrible racket.

With that much damage, he needs to pull the entire left side as suggested and start his inspection with the valve seats, cam lobe and lifter.

 

[20774]

He must be new to airheads as it is unbelievable that he tried all those other things while the left side must have been making a horrible racket.

No argument from me. I would never have started the engine without pulling the valve covers. If I was that much of a noob, I would have enlisted the help of some expertise.

So far everyone is saying the same thing...the head and/or topend must come off for a looksee and to assess any other deeper damage.

 

[mymindsok]

Geeze...!

I've never seen anything like that before and I'm wondering whether the new owner caused that damage or if perhaps thats the reason why the PO sold the bike!

Either way, at least that side of the engine is going to have to be completely stripped down for inspection. Seeing that much damage in the top end, makes me curious about the condition of the cam and lifter.

How about this scenario: PO sets the valves completely wrong and with with no clearance and then rides th bike. Then, as the bike heats up, parts begin to pound themselves into shrapnel. Somehow, that looks like more damage than you'd get with a recessed valve.

If I'm completely off base, it's because I'm still awaiting my first cuppa Joe.

 

[bmwwrench]

The lock nut for the exhaust valve adjuster is under the rocker because the valve is protruding farther into the combustion chamber than it should (or is not protruding far enough on the tip end). This could because the exhaust seat has been replaced with one that is too thick, or that the seat is creeping out of the head, or that the valve is bent and is no longer closing. The adjuster on the intake side is also wound way out.

It may only appear this way in the picture, but it looks like the lower clamp on the intake rocker shaft is installed upside-down. If this is so, the valve adjuster could be putting a severe thrust into the pushrod end, thus tearing it off.

Are these standard pushrods? My memory of /5 pushrods is that they are one-piece, while these appear to have separate tips. Check whether the tube is steel or aluminum-the stock ones are steel.

I look forward to seeing what's going on in there.

 

[AnnapolisAirhead]

I've seen this before. It happens when a Briggs & Stratton mechanic does a valve job with his Dremel from last Christmas, replaces the pushrod tubes with chopsticks from the local Chinese restaurant he wooed the customer into allowing him to do the work, then proceeded to set the valves with the popsickle stick (dessert).

Otherwise, its pretty astonishing. I'd hope he has stopped trying to start the poor thing and is removing the head.

 

[20774]

I've passed on the information that everyone has offered. I've told him he should disassemble the left side and investigate what is going on. He lives near Daytona, FL, and asked about other BMW mechanics other than Daytona Beach BMW. From some posts here a year ago, I referred him to Tom High at Rennsport BMW in Deland.

I'll report what he finds.