1974 R75/6 Engine noise

[130253]

After riding all day Sunday and it being late, I chose to cruise back home on the Interstate in order to get home before dark. After riding at 75-80 mph for about 45 min, I got off at the exit I needed. At that stop I noticed that the engine was rattling, chattering and making noises like my old truck does when its a few quart low on oil.:uhoh The bike was running and idiling fine, but hot, no smoke, oil fairly fresh. Got home and checked fluids, all OK. Let it cool off a few hours and started it up and ran just fine with the normal engine noise. Rode today out and about running errands and ran fine. My question: Is this normal after a hard ride?:dunno


Thanks,
Mark

[20774]

I would think that most would say that's not normal. You say it was idling fine but yet rattling and chattering...doesn't sound like a nice idle. Has it ever done this before? Any recent maintenance? Did the noises change with the clutch hand lever pulled in versus out? What type of engine oil and transmission oil are you running? I'm guessing you might have a light weight oil that's thinning down after it gets hot when run hard...

[130253]

Kurt

Maintain the bike all the time, the day before I had set the valves and points, timed etc. I use Castrol 20-50 in the engine and Castrol gear oil in trans and drive. At the time no difference with the clutch lever in or out. Never done this before, but never rode this bike that hard for so long before but have taken a lot of long trips on her carrying a lot of gear plus my fat ass.:laugh Let me restate, no smoke, smooth idle, ran fine, normal power, just hot and noisy at the time when I pulled off the exit and the rest of the way home , 1 mile. No problen since.

Mark

[20774]

Sounds like you're doing everything right... Seems like two options. Don't worry about it until other symptoms show up or go out and repeat the situation and try to make the bike do it again. I don't really like the second option...

[130253]

Me neither!!!!!!!!!!!!!!

[benway]

"the day before I had set the valves and points, timed etc"

I would recheck the valve settings etc

Most people think that when some new behavior occurs right after you've done something to the bike, that 99% of the time its related to what you just did.


hope that helps

[73986]

In adverse conditions....heat and racing etc...The airhead motor moves around quite a bit,and I have found that if the rocker arms..you know the ones you pinch together with a big "C" clamp as you tighten the heads down...are a tad on the loose side then it will make noise...especially when you open the throttle and give it gas but it does subside when it cools down again...Make sure the timing is correct to eliminate pinging also.....:bikes

[130253]

I rode all that day w/o a single problem. Rode today around town and took a cruise on the back country roads, no unusual noise. But I will check the valves clearence and timing again just to be sure. I never had pinging in the engine, like the timing was off, just chattering and rattling for that brief period of time. I don't know, I will keep an eye out and a ear open and hope that it was a 1 time event.

Mark

[Junkle]

Depending on what you call a "chuttering noise" . . . if it only does it when hot you might want to get an experienced ear to listen to it. It might be the rear main seal (at least that is the case on R90's unsure how well it translates). If you are a member of the Airheads club see who is in your area and buy them lunch and have them listen to your bike. Don't expect them to fix it but they will probably help with a diagnosis (or at least try).

good luck mystery noises are no fun,

j

[beemerPhil]

What's the mileage on your /6? Timing chains start to be heard anywhere from 75k and up-
The tensioner for this chain is oil-damped; if it gets bubbles in it, even a newer chain can get noisy. Castrol has a propensity for foaming, and might contribute to this problem.(You may also find that your engine consumes more Castrol than some other brands)
Apart from riding it with your ears open(recommended) or tearing it apart to find the gremlin(not), I might change the oil & filter(regardless of mileage, it's cheap!) and....
:brow

When you've got the old filter in your greasy mitts, carefully draw a sharp razor blade around each end,(of the filter, not your greasy mitts!) and then up & down each side of the seam on the side. Pull off the pleated paper, flatten it out under a good light, and take out your reading glasses. You want the paper laid down with the OUTSIDE UP.
See the little flakes?(LITTLE flakes- anything bigger than the head of a pin is reason for deeper exploration)

Brassy-colored bits are from valve guides or wrist-pin bushings- not usually a problem on these bikes, and considered normal wear & tear if there aren't too many.

Silvery-colored bits are more common-

Take out your handy magnet, and wave it a quarter-inch or so over the filter paper.
See the bits that move? They'll 'stand up' as the magnet passes- these are steel, probably from the oil pump rotor, timing chain/sprockets, camshaft/lifters etc. Some of this is just normal wear & tear; a lot, or anything bigger than a pinhead, is cause for concern. Check your rocker bearings- an engine with excessive rocker end-play can break the ends out of the bearing cage in the rocker arm, and the bits will migrate. Believe it or not, the bearing rollers CAN escape between the rocker arm and the pinch-block, moving down the pushrod tubes to raise cain down below.....but this is a clatter that won't go away, and doesn't sound like your bike.

The silvery bits that don't 'wave' at your magnet are aluminum, and are usually benign bits of the front main-bearing carrier from the timing chain slapping it once in a while. On a really bad motor, you'll see lots of them, in thin flat flakes, maybe together with some coppery-looking flakes....these are bits of main or big-end rod bearings, probably damaged by lubrication failure.
:violin
But- these make a pretty ominous knock under load; doesn't sound like what you're talking about. Besides, if you're careful about your oil, these parts will usually outlast everything else on the bike!(Exception: airheads are susceptible to oil pressure loss under hard braking- all the oil is pulled to the front of the pan, and the oil pick-up is starved. If you ever see an oil-pressure warning light when you hit the brakes, check the oil level right away, and check on oil-pan mods that address this problem- either a deeper oil pan and pick-up, or baffles that trap oil around the stock pick-up)

My knee-jerk response to any kind of unidentified weird motor noises is the oil & filter change w/ filter dissection. I suspect you got some bubbles in the timing chain tensioner, and no further attention is needed.

YMMV- tell us what you find-

[AirheadTed]

A recent error that I made was setting my valves with the engine cold rather than warm.

After freeway riding, I noticed increased valve clatter (though any fully warmed up engine would probably do it).

Setting the valves with the engine "baby bottle warm" eliminated the problem.

-Ted

[20774]

A recent error that I made was setting my valves with the engine cold rather than warm.

After freeway riding, I noticed increased valve clatter (though any fully warmed up engine would probably do it).

Setting the valves with the engine "baby bottle warm" eliminated the problem.

-Ted

Hmmm...I didn't think that was an "error". The manual says to do it cold... You should be hearing some valve clatter when warmed up. If you don't then there's a real possibility that the valve is not completely closing or at least only coming to rest on the seat for a fraction of the time that is necessary to help with heat transfer, not to mention proper valve timing to build compression and contain the explosion of the fuel. By setting the valves to a tighter than required spec, the valves will close early (getting less air-fuel) and open early (letting some of the power escape through the exhaust).

As they say, loud valves saves lives (of engines)...

[beemerPhil]

OK- a little review on /6-7 airhead valve adjustment.

Valves on the airhead engines are always set cold. The original spec for your engine was .006" intake, and .008" exhaust. This was later revised to .004 and .006, resp.- I remember this being due to introduction of a new pushrod alloy.....naturally, this would be quieter right away......
But- the bikes didn't like the new clearances, valve problems developed, and in a short while, a service bulletin advised to return to the original spec.

The valves should be set with the engine cold, after the rocker end-play has been checked/set and the heads re-torqued if needed. It's not important to be exactly at TDC, the cam's base circle is fairly large- as long as you can see "OT" somewhere in the timing window you're fine.

Remember that pushrod engines like a little valve slop- don't be tempted to go on the tight side. The valve that will bite you is the one you can't hear! Actually, the valves are pretty quiet anyway, if they're set right- most of the noise comes from excessive end play. On most of the earlier engines this is easily set by moving the pinch blocks while you're re-torquing the studs- after 1981 or so you need to use shims, the pinch blocks are captive by design.

[20774]

OK- a little review on /6-7 airhead valve adjustment.

Valves on the airhead engines are always set cold. The original spec for your engine was .006" intake, and .008" exhaust. This was later revised to .004 and .006, resp.- I remember this being due to introduction of a new pushrod alloy.....naturally, this would be quieter right away......
But- the bikes didn't like the new clearances, valve problems developed, and in a short while, a service bulletin advised to return to the original spec.


That's not the way I remember it... My rider's manual that came with my /7 indicates the "spec" was 0.004 and 0.006...I assume that the /6 would have been the same...I could be wrong there. The only bulletin I've seen on changes to the clearances came out in March 1984 which said to go to 0.004 and 0.008 after break-in. I've even heard people suggest 0.006 on the intake, but 0.004 would probably be OK as the seat is cooled by the inrushing air, to some degree. The 0.008 on exhaust is a little more critical. It's a balance act from good valve timing and having the valve rest on the seat for a fraction of a second longer to help with heat transfer. The 0.008 exhaust might not eliminate the need for valve/seat replacement, but it could delay the inevitable. A little noise couldn't hurt and it might do some good...

[beemerPhil]

By setting the valves to a tighter than required spec, the valves will close early (getting less air-fuel) and open early (letting some of the power escape through the exhaust).


The valves will not close early because of tight clearances. Unless, of course, you have one of the rare /7 Desmo BMW's, it just don't work that way at all......
:stick

The new pushrod alloy was introduced in '77 IIRC, so your bike would have shown the new specs in the manual. The exhaust spec was abandoned almost immediately, and the whole idea was dropped a while later.
:brow

The bike 'we' were discussing was a 75/6, which would show .006 and .008 in the manual.:nono

:nyah

[20774]

The valves will not close early because of tight clearances. Unless, of course, you have one of the rare /7 Desmo BMW's, it just don't work that way at all......
:stick

You're correct there...I didn't think that totally through.

The new pushrod alloy was introduced in '77 IIRC, so your bike would have shown the new specs in the manual. The exhaust spec was abandoned almost immediately, and the whole idea was dropped a while later.
:brow

The bike 'we' were discussing was a 75/6, which would show .006 and .008 in the manual.:nono

:nyah

I'm not sure who's bike we're talking about now and unless I missed it, I can't actually find a year/model listed...but I did give myself an out :D ... I do have a Clymer (not the most trusted book!), printed in 1975 which indicates the clearances were 0.006 and 0.008. So you might be on to something...

Regardless how we got there, the clearances should be set with the engine cold to the latest specifications...

[130253]

quote: What's the mileage on your /6? Timing chains start to be heard anywhere from 75k and up-
The tensioner for this chain is oil-damped; if it gets bubbles in it, even a newer chain can get noisy. Castrol has a propensity for foaming, and might contribute to this problem.(You may also find that your engine consumes more Castrol than some other brands)
Apart from riding it with your ears open(recommended) or tearing it apart to find the gremlin(not), I might change the oil & filter(regardless of mileage, it's cheap!) and....

Phil,

The bike has only 41K, and I did change the oil but threw away the filter before reading your post. Next time I will check the filter as you suggest for foreign material. Rode 300 mile this past Sunday throughout West Ky and West Tenn, engine did fine and no unusual noise. Had rechecked timing, points, rockers and valves. Resynced carbs. One valve needed adjusting as it was tapping a bit, other than that everything is set within in specs. Thanks for the info for what to look for in the filter.

Mark

[AirheadTed]

Hmmm...I didn't think that was an "error". The manual says to do it cold... You should be hearing some valve clatter when warmed up. If you don't then there's a real possibility that the valve is not completely closing or at least only coming to rest on the seat for a fraction of the time that is necessary to help with heat transfer, not to mention proper valve timing to build compression and contain the explosion of the fuel. By setting the valves to a tighter than required spec, the valves will close early (getting less air-fuel) and open early (letting some of the power escape through the exhaust).

As they say, loud valves saves lives (of engines)...

Kurt, Thanks!

I've just spent time combing through snowbum, Duane Ausherman, Clymers and the service manual, and I can't now remember where I heard that it should be done warm (odd, because that "baby bottle warm" phrase stuck with me. Anyone recall seeing that in relation to airhead maintenance?).

The only slightly contradictory thing that I found was Ausherman stating that it does not matter if the engine's warm or cold on /6 and later.

Always good constantly recheck what you believe to be true.

-Ted

[clone432]

I just did mine lastnight. Clymers says .004 &.008 on an engine that is no warmer than 95 degrees F. I have always learned that it is most accuratly adjusted on a cold engine since it eliminates other varibles that affect the clearances.

My two cents!

[beemerPhil]

Some engines/manufacturers DO spec valve adjustment at operating temperature- BMW just doesn't happen to be one of them. I'm glad because setting hot valves is tough on your fingers!
:dance

In any case; the performance gained (?) by setting your valves tight is, at best, immeasurable. The performance (and longevity) lost by setting your valves too tight, is measurable, certain, immediate, and expensive!

In the early/mid 80's, BMW was swamped with warranty valve jobs on low mileage airheads, because of a poor choice in valve seat material.
My 'Last Edition' R100RS was one of the many effected bikes. The warranty rep insisted that "There is no such thing as intake valve erosion" until I brought him a handful of destroyed intake valves- face to face- at service school. The floodgates opened, valve jobs were warranteed, and the close valve clearances were abandoned altogether. I was working at Lindner's BMW in New Canaan CT at the time, right down the street from BMWNA.

Unfortunately, while BMW stalled, many valve jobs had to be repeated- the most common diagnosis was faulty valves, since the valve was destroyed, but the seat appeared untouched. New valves, however, failed in the same way shortly after installation, and the culprit was eventually found to be a too-hard seat, with poor heat transfer.

BMW STILL took some time in choosing a suitable valve seat replacement- I had, by then, already discovered a Subaru(!) seat that was a drop-in fit, and worked perfectly with the stock BMW valves. (Courtesy of a cylinder head tech at a local machine shop, who solved the whole problem in, no kidding, under 5 minutes) These seats are still in my RS, over 100k miles later.......

If you can't hear your airhead's valves, you're getting ready to replace them!

[20774]

Phil -

Yup, that's what I've heard as well. I believe the pre '81 bikes will have the problem with valve seat erosion while the '81 to '84 bikes (and especially the 1000cc models) will have valve face pastic deformation...because of poor heat transfer into the seat, so the valve took all the beating. These are terms that I've read on Oak Okleshen's discussion of the problem...he's a metallurgist by training and trade. Another issue I believe was the fact that the amount of the seat that actually touched the valve face was also reduced. Not sure if I have the numbers right, but I thought the flat seat portion that touched was supposed to be like 2mm while in some cases, due to a poor valve grind/seat cut, it was like 1mm, thus reducing the area for heat transfer.

Some bikes it happened to quite quickly...other's it took a long time. It probably depended on how the bike was ridden. My Dad had a '81 R100RT, always maintained by BMW. No problems with the bike at all to the point he traded it in...it had about 65K miles on it. He tended to be easy on the bike...no canyon carving or high RPM riding...