1971 BMW Airhead rocker arm issues

[bigvic54]

I have a 1971 BMW Airhead R/75. While reassembling I found the Rocker Arm won't rotate when torqued properly, (26 ft/lbs). It rotates freely when not torqued.

The support blocks, shafts, bushings and arms look fine. The endplay is set, (oil moving in the gap).

Can anyone think of anything else?

Thank you in advance.


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[20774]

So you're reassembling. I take it then that the bike was working OK before, but now upon reassembly you're finding the binding. Is there an intake-exhaust mixing in the same head issue? I assume you've kept the rocker parts separated, left side on left and right side on right.

Anton has a small amount of info on the early /5 rockers here:

http://largiader.com/tech/rockers/

The /5 rockers required extra alignment steps as the rocker ends have quite a bit of movement to them. Snowbum discusses this at the end of this page:

https://bmwmotorcycletech.info/headassy.htm

In Oak's pushrod seal manual, he references criteria for adjusting the rocker arms so that they form what is probably a perfect square.

 

[pglaves]

In a nutshell the /5 rocker support blocks do not have the machining that automatically aligns them. So the blocks can be positioned in quite a variety of positions, allowing them to bind if not centered. It appears that is your case. Loosen the nuts and reposition the support blocks to be as centered as possible in the stud holes.

There was at one time an aligning tool to help position the support blocks. I never had one but hope somebody more acquainted with this issue can weigh in here.

 

[bigvic54]

So you're reassembling. I take it then that the bike was working OK before, but now upon reassembly you're finding the binding. Is there an intake-exhaust mixing in the same head issue? I assume you've kept the rocker parts separated, left side on left and right side on right.

Anton has a small amount of info on the early /5 rockers here:

http://largiader.com/tech/rockers/

The /5 rockers required extra alignment steps as the rocker ends have quite a bit of movement to them. Snowbum discusses this at the end of this page:

https://bmwmotorcycletech.info/headassy.htm

In Oak's pushrod seal manual, he references criteria for adjusting the rocker arms so that they form what is probably a perfect square.

Thank you

 

[20774]

This is the tool that Paul was referring to. I got this from my Haynes manual. The four rocker blocks should fit in the four corners of the tool. The key dimensions are the 114.5mm at the bottom. This is the outside-to-outside dimension for the rocker blocks. The other dimension that goes with this is the inside-to-inside dimension between rocker blocks...it should be 71.5mm. If you find that your outside-to-outside measurement is say 115mm, then the inside-to-inside dimension should be 0.5mm shorter or 71.0mm. Similar logic if your measurement is 114mm.

 

[ebeeby]

First, I use 25ft/pounds as it is sufficient.
Second, how does the pushrod look as centered in its hole? This also indicates correct alignment.
Third, you should be able to rotate the bushings after the studs are torqued.
The special tool is really unnecessary.

 

[20774]

The special tool is really unnecessary.

I likely agree, but since the four rockers can be located most anywhere, seems like paying some attention to basic alignment and dimensions might be a starting point.

 

[bigvic54]

First, I use 25ft/pounds as it is sufficient.
Second, how does the pushrod look as centered in its hole? This also indicates correct alignment.
Third, you should be able to rotate the bushings after the studs are torqued.
The special tool is really unnecessary.

The bushings were the issue. When I removed them and reinstalled everything the arm turned. I'll have to get new, thinner bushings.

 

[drost]

Maybe the picture is misleading, but I do not see the spacer under the blocks. The blocks on my /5 are not split either. Anton Largiader shows the difference between the rockers on airhead engines at www.largiader.com. Could it be someone assembled the engine wrong in the past?