/5 Style Rocker Arms on a 1/74 production R75/6?

Hello all,

Just recently dove into the airhead world by picking up a 74 R75/6 in complete but non running condition.

Did the usual new to me bike routine (fluids, filter, cables, tires, carbs, etc. etc.) and she is up and running, but still not quite right yet.

Basically, I have a lot of valve noise coming from the left head. I have adjusted the lash to 0.008/0.006 a couple of times, re-torqued heads, even pulled the pushrods and lifters out and gave them a good look along with the cam. Everything looks fine, yet the valve lash seems to want to wander about 0.002-0.004, especially on the exhaust side, seems to open up a little.

The bike has a ton of miles (120k) and pouring through the PO records, the relevant points are:

Heads redone at about 60k (valves, guides, everything, mentioned something about unleaded gas being the issue)
Timing chain/gear/tensioner/spring also replaced at about 60k
No mention of ever replacing the bushings in the rocker arms.

So, I'm thinking I have to replace the rockers (bushings not available best I ca tell, and the rockers have a little bit of "rock" in the wrong direction) and probably also put a timing chain on the short list.

Did a lot of searching and read the usual reference sites and still have a couple of questions, hoping someone can help.

For the rockers, it looks like my only option is the needle bearing style and that is probably the way to go anyway.

Do I just need to buy the new rockers (the $64 ones), and just transfer over my adjuster nut, ditch the old style thrust bushing and sleeve bushing, and I'm done? Do I keep the "spring washer" on the bottom block? Reason I ask is these replacements seem to span the entire area block to block per the pix on the max bmw site.

The bike has a mix of 14 and 15mm nuts, so I read that some minor beveling of the end of the rocker arms may be required, I think.

Also, with the timing chain, I think the tensioner is also a source of noise and the timing marks are not all that steady with a timing light, so I know I ought to attack that too. Is it necessary to also replace the sprocket with each chain replacement? 60k seems a little short for a timing chain, but then again I'm used to 100K plus on autos so who knows.

Thanks in advance for the advice.

Chris

Have you tried adjusting out the up and down play in the rocker arms, as this is a major source of noise?

Yes, I squeezed the blocks, both by hand and then re-did using a clamp and a couple of sockets and light pressure, backing the adjusters off to make sure it all still moves freely. Pushing hard on the adjusters to check clearance to the point I have sore thumbs... I can get the right side sounding like a sewing machine, but the left just refuses, sounds more like a ball peen hammer in there after it warms up.

There is visible wear marks on the brass bushings, so I think that is the issue with not being able to find the sweet spot between tight and loose on the arms.

As Charles says you need to remove the vertical movement in the rockers.

For most things about BMW Airhead rockers refer to Anton's pages;

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

If you have the /5 style rockers I think it would be a good idea to find some later style used rockers.

Chamfer the edges of the rockers to clear the 15mm nuts. The 14mm nuts are not available, if you should find them they may cost 7 or 8 dollars each.

Tell us if the rockers you have have plain bearings or needle bearings.

The pertinent information would be whether the valve job included lead free valve seats. May be called simply seats. It is the seat material and the replacement of the valve seat that is most often omitted. It would be a good thing to have lead free valve seats but on the smaller bikes it's not always a problem. I think a 750 is sort of a medium size.

They are the old style with the brass "bearing", i.e. /5 style on Anton's site, however they have the split blocks (/6 style per Anton's site).

I get them tight to the point of almost binding, no slop up or down, but still get some twist/slop when snugging down the adjuster; considering the mileage and visible wear on the brass bearings, I think I am best served to upgrade as you just also suggested.

I guess my question really is how to best approach the upgrade. I'm looking at the upgrade rockers for up to 9/75 http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51887&rnd=08102012 first valve train fiche,
which have roller bearings. I assume I ditch the old rocker and brass bearing, and put these in reusing the rest of the existing parts.

Just want to confirm with someone who has done this. I'd rather buy a new part then an ebay part with unknown pedigree.

I don't think you have /5 rockers. The /5s have the shorter rocker that uses a spacer. Some of the /6s had bushings.

Sometimes wear is in the shaft and a bit of the play can be taken out buy rotating them. If there are oil hole locating dots make sure they are properly placed.

I'll post a picture of what I have. It does match the 5,6,7 ... assembly on the fiche for before 9/75 production so I don't think this is a non-stock configuration however.

I have the shorter rockers and the t-shaped spacer that sites on top, spring washer (flat actually) on the bottom and the brass bushing inside the rocker, but then the split blocks.

I did already try rotating the shafts 180 degrees as well as flipping the bushings end over end. Didn't do much, still some side to side slop.

Thanks for the input, maybe I can keep flopping and rotating until I find a "tight" configuration.

I always called those /5 rocker arms. The early /6's have them. I think they are junk. I rarely run into them and they are not completely toasted. The bushing wear. They spin in the rocker and wear out the rocker out AND they wear out the shaft. The whole setup eats itself on a regular basis. I have converted quite a few but it has been a while. If I remember right, you need rockers, shafts and blocks. Maybe that is just because it all has always been worn out? I don't remember. Good luck!

OK. If you have the T shaped spacers you have /5 rockers. I did have /6 rockers with bushings once. So I was thinking you had /6 w/ bushings.

Get some '76 to '84 rockers. But that would be out of the question if you have to have new.

I was contemplating upgrading to /7 setup, but one thing I noticed on the parts fiche is the pushrods have different p/n and pricing. This is looking to get expensive in a hurry... Agree, new would cost prohibitive.

I'm still intrigued by these $64 roller bearing rockers listed on the max site... I guess I'll give them a call.

I am not following disston. I thought early /6 rockers were /5 rockers? Is there a difference?

The only difference in the pushrods is that yours are steel and the later ones are aluminum.

The late /6 setup IS the /7 setup. Beware getting /6 parts. A lot of even long time parts guys do not know how to look up the right /6 valve train parts. 3 years of /6's and 3 different rocker arm setups!

Just nabbed a nice used set off of eBay complete with pushrods and nuts, look exactly like the 76-84 photos on Anton's site. Wish me luck!

I certainly haven't seen as much as SS but I had a 1974 R90/6 that had the one piece rockers with bushings instead of needle bearings. As many times as I've mentioned this I may be the only rider to ever have a bike with this set up. The fact that this was on an R90 engine seems to make it especially weird too.

These parts last a long long time. The bearings sometimes go bad from having too much vertical movement and they may go bad from too many miles but that seems to be lotsa miles like over 60 or 70K maybe more. I put in some used rockers last year and have now bought the new bearings for when I get around to it. But so far the used set is hanging in there. MotoBins does sell the bearings cheaper than anywhere in this country so look at them also.

I don't want to sound argumentative but I guess that I am a used parts kind of guy. I've had good luck with it. Not all good but mostly good. Another part of the rocker that goes bad is the tip that contacts the valve. They get pitted. Make sure you look at the tips if you are checking these things out.

You don't need the Aluminum push rods. Might be nice but I personally don't notice a difference.

The photos of the tips on the set I picked up looked good and the price was less than one new rocker, so getting the pushrods was a bonus. Obviously won't know till I have them in hand....

This bike has over 120k on it and best I can tell 3 of the 4 rockers are original. That is a testament to how long the parts can last.

I'm optimistic that this will quiet down the ball peen hammer sound and finally allow me to get the bike into a good state of tune.

I was just thinking in another thread: I wouldn't run aluminum pushrods in the smaller tubes. They flex too much for the small tubes IMO. I use to think that they couldn't flex that much but I recently loooked into the situation a little closer and they DO flex quite a bit.

Interesting point to consider. One would think that the valve clearance specs would be different to account for flex; less actual lift realized at the valve during operation. I admit I had not looked to see if there are any differences there, or in the cam or if the larger tubes could be on account of some other issue, like resonance or maybe just a supplier change. I guess I got the option to try it both ways, see if there are any wear marks mid rod. Thanks for the comment, need to take that into consideration.

When you install the /7 rockers it is best to make sleeves that will slip over the posts in the head. This will stabilise the rockers, and the /7 rocker clamps will allow you to use 15mm (hex size) nuts, a far better nut than the 14mm An old pushrod tube fits nicely; just cut one or two up and have their ends turned to fit properly.

Only the R90S got needle bearing rockers in 1974. Everything else got bushings.

That's yet another thing I liked about R69S engines. They had needle bearing rocker arms!

Don't look in the middle of the push rods. Look ot the out side half where the push rod tube starts in the cylinders and where it ends in the heads. Closest to the head gasket on both sides. That's where the aluminum push rods always rub and that's with the bigger tubes.

Ah, I think I get it now. The aluminum ones are probably slightly larger diameter and as the rockers move outward relative to the fixed lifter end, the pushrod moves "lower" in the shaft. Would make sense that the larger tube would be needed as the steel ones can rub already if the rod is not positioned correctly.

I think I'll use the steel ones and avoid any issues.

My '93 R-100GS makes a constant racket from somewhere inside the rocker covers. It sounds like there's a tiny gnome sitting in each side, tapping on the head with a tiny hammer, in synch with the engine RPM.

I replaced the needle bearings on one intake rocker because they came apart (discovered during routine valve adjustment), and on the other side's intake rocker, just as a preventive measure. I haven't gotten to doing the exhaust rockers yet, but that will come soon.

I also adjusted (with shims) all four rockers to get the end play down to absolute minimum. As supershaft once said, the shims don't come in small enough increments to completely eliminate all end play, so I get them as close as possible without acutally binding. (Of course, this may not apply to your setup, where you simply squeeze the blocks together with a clamp as you tighten the nuts.) I believe it's better to have them a little too loose than too tight.

The gaps are set at exactly .004" intake and .008" exhaust, checked with the engine cold. Everything in there looks to be in good shape.

But they are still noisy. Even noisier before the engine warms up, but always tap-tap-tapping.

I've decided that's just how some engines sound, and there's probably nothing I can do about it--or I would go crazy trying too hard to do something about it. So I just ride the thing and try to ignore it. It runs smoothly, and that's really the important thing.