Throttle body noise

[HALMC]

'96 R1100RT: previous owner explained, but I didn't pay enough attention.

According to his explanation, one of the throttle bodies on this bike makes a clunking noise (not to be confused with clutch clank) when the engine is at idle. Any increase in engine RPM seems to eliminate it, and I've never heard it while the bike is in motion. There are no other associated symptoms: the bike runs like new.

The sound is not entirely unlike hitting a bolt on a wooden block. By that I mean I don't detect any metal-to-metal should. Since I've ridden the bike about 4,000 miles since buying it, I agree with the seller that it's not such a big deal, but nonetheless, I don't particularly like it.

Comments? Suggestions?

 

[dbrick]

The throttle body shaft (on which the throttle plate is fixed) is worn, and vibrating in the throttle body housing. To diagnose: with the bodywork removed and the engine idling, press your thumb on the aluminum pully that carries the throttle cable; if the noise stops, the shaft is worn.

New TBs are expensive; used are available from the usual sources, but of course of uncertain states of wear. General information here: http://largiader.com/tech/tb/ A more specific discussion of doing the work is here: http://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/386137-throttle-body-rebuild.html

 

[PGlaves]

Bing now sells a kit that includes a new shaft.

In the early stages it is just an irritating noise. But after a while the wear increases to the point that you have an air leak. This leans out that side a little bit. If you have trouble getting good synchronization at idle and it drifts off when RPM is increased then check at the shaft for a leak and fix it.

 

[HALMC]

Mucho gracias. Intuition would take me to both answers, but it's mighty fine to have two knowledgable folk to chime in. Thanks . . . and dbrick, thanks for the links.

 

[guitardad]

Definitely check it sooner rather than later. I just placed an order with Bing for a rebuild kit for the left side, and a new TB for the right. I let the noise go on too long, and the bushings in the right TB are worn. It's about $85 for a rebuild kit including the shaft, vs. $234 for a new TB.

 

[ANDYVH]

I'm at 145,000 on my 94 RS, with the original TBs, and I have the "thuk, thuk, thuk" rattle sound at idle. So I know my TB need to be rebuilt. Another indicator of an air leak may be the position of the big brass air screws. I know on my bike one is turned in significantly more than the other, to get the balance close.

 

[flars]

tb noise

"...one of the throttle bodies on this bike makes a clunking noise...not entirely unlike hitting a bolt on a wooden block..."
Another possibility not mentioned yet, which does not involve any worn out parts or money changing hands:
With the bike at idle, open the throttle a TEEENNNNYYY bit (just 100 rpm maybe). Does the sound go away? If so, the throttle cable on that side is probably too tight, and is holding the TB slightly open, and the noise you are hearing is the throttle pulley bouncing against the throttle stop screw. Loosen the throttle cable on that side so there is 1-2mm slack, and do a throttle body sync.

 

[cycleman2]

"...one of the throttle bodies on this bike makes a clunking noise...not entirely unlike hitting a bolt on a wooden block..."
Another possibility not mentioned yet, which does not involve any worn out parts or money changing hands:
With the bike at idle, open the throttle a TEEENNNNYYY bit (just 100 rpm maybe). Does the sound go away? If so, the throttle cable on that side is probably too tight, and is holding the TB slightly open, and the noise you are hearing is the throttle pulley bouncing against the throttle stop screw. Loosen the throttle cable on that side so there is 1-2mm slack, and do a throttle body sync.

Throttle butterfly rattle, what everybody is hearing, is normally caused by no play in the cable as noted above. Wear also contributes to the sound. You can also get this same sound on the left side when doing a throttle body sync if you get that cable too tight. It has to have just a bit of slack, then it won't rattle. In fact that's the easiest way to adjust the slack in the left cable. Tighten it until you hear the rattle then loosen it off until the rattle disappears. Then do you sync with the right cable adjuster. This procedure sets the right amount of slack in the left cable and makes it much easier & quicker to sync the throttle bodies.

Improper amount of slack in the cables is no doubt part of the cause in the butterfly shaft wearing & having to be replaced.

 

[hacksaw496]

This is an old thread but it's new to me. I had a very noticeable clacking on the left side at mainly at idle or just above. While working other items today I pulled the TB's for cleaning and inspection.

The bushings and shafts seem pretty well anchored. I have just a small amount (~1 -2 mm) of play along the shaft axis on right side TB, and less on the left. But when I wiggle them in and out they make a noise similar to what I was hearing.

If the pulley and cable are in pitch axis, when I move the pulley in yaw, I get maybe 1 mm or less play at the edge of the pulley.

How much play or looseness would be considered too much, and require a rebuild?

I'm thinking maybe the noise I was hearing is cable related now. I believe that back when the bike was running I could stop the noise by pressing on the left side pulley or changing throttle postion.

Thanks,

Pat

1999 R1100RT
Left TB 45/111, Right TB 45/112

 

[dbrick]

Pat,

I think the answer depends on how the shaft/bushing wear has contributed to noise and airflow.

The posts above talk about noise - the impact sounds that appear when the shaft moves laterally within its bore. If the noise is bothersome, then the TB(s) should be rebuilt.

The other result of shaft/bushing wear is air leakage: even with the throttle plate fully against its seat at idle, gaps in the shaft/busing connection will allow additional air to pass into the intake tract. This uncontrolled air entry will impair the big brass screws' ability to control idle speed and balance. If the valves and throttle cables are correctly adjusted and the spark plugs in good shape, and you still can't get the big brass screws to set a correct and consistent idle, then the TB(s) should be rebuilt.

-David

 

[hacksaw496]

Good info. One thing I failed to mention was that on my last TB sync I got best results with the right side BBS totally closed. So I guess that points to a leak somewhere. The right side TB seems the sloppiest, but the left side makes the most noise...
(But then my right ear is worse than my left, so who knows... )

I have the Cata Dan kits, so I suppose I will just proceed with that...

Also, any recommendations on where to get aftermarket vacuum hose material for this bike?

Thanks,

Pat