Alternator belt squeal when blipping throttle while cold

[dmsantam]

Good morning all, my R1100RT 1995 model seems to have the alternator belt squealing just a little if I blip the throttle from idle, when it's cold. After a minute or so of running, it will not happen again. It does not squeal unless I blip the throttle abruptly. Does this indicate that the belt is not tensioned correctly? I did replace the belt about 1,000km ago with a brand new continental brand one, and tensioned it to 8Nm. 

 

cheers,

[fatbob]

That certainly sounds like loose belt symptoms to me.   

[dmsantam]

thanks for the reply. I may just have to open it up and tension it again. 

 

cheers

[Lowndes]

Remember, the alt is trying to recharge the batt after the slight drain from starting, but the alt won't "kick in" until it gets up to 2 or 2.5K RPM the first time after startup.  That is to help the engine warm up without extra load.  New belts might stretch or break-in a little, too.  Tighten it up a tiny bit, or just don't blip it.

[dirtrider]

14 hours ago, dmsantam said:

Good morning all, my R1100RT 1995 model seems to have the alternator belt squealing just a little if I blip the throttle from idle, when it's cold. After a minute or so of running, it will not happen again. It does not squeal unless I blip the throttle abruptly. Does this indicate that the belt is not tensioned correctly? I did replace the belt about 1,000km ago with a brand new continental brand one, and tensioned it to 8Nm. 

 

cheers,

Morning dmsantam

 

If the belt isn't wet then it does sound loose.  I usually re-tension (or check anyhow) at 1000 miles. 

 

You can do a quick check, if you can easily twist the belt past 1/4 turn (90°) at mid point then it is too loose. 

 

To me 8Nm initial on an older motorcycle with a new belt is too low (those usually have higher friction at the alternator movement points). I usually just go by belt twist, or depending on how free the alternator moves, tension to 10 or 12 Nm.

[dirtrider]

2 hours ago, Lowndes said:

Remember, the alt is trying to recharge the batt after the slight drain from starting, but the alt won't "kick in" until it gets up to 2 or 2.5K RPM the first time after startup.  That is to help the engine warm up without extra load.  New belts might stretch or break-in a little, too.  Tighten it up a tiny bit, or just don't blip it.

 

2 hours ago, Lowndes said:

Remember, the alt is trying to recharge the batt after the slight drain from starting, but the alt won't "kick in" until it gets up to 2 or 2.5K RPM the first time after startup.  That is to help the engine warm up without extra load.  New belts might stretch or break-in a little, too.  Tighten it up a tiny bit, or just don't blip it.

Morning Lowndes

 

"That is to help the engine warm up without extra load"--  That is not the reason, that has been incorrectly guessed at for years, long enough that it became believed. 

 

First off, BMW doesn't recommend engine warm-up before riding so why have no charging? 

 

Second, with fuel pump, ign coil, fuel injectors, headlight, taillight electrical system, etc operating that already lowers system voltage considerably. It needs all the fuel injector spray, spark plug spark, & Motronic voltage it can get right after engine starting. Not bringing the alternator on-line right after engine starting is the incorrect direction.

 

Plus, some 1100 (and especially the 1150 twin spark), right after cold-start, idle considerably cleaner, better, & smoother if the alternator is charging right after engine start.  Some riders revv the engine right after starting so they don't notice the initial cold idle difference but the ones that just set the choke then push the starter button (no hand on the throttle) will usually notice a difference. 

 

The real reason that it takes a throttle blip or raised engine RPM after  starting is the charging light on the dash has the incorrect wattage bulb. I don't know if BMW didn't calculate this correctly, or if it's what they had in the system at the time  but in any case the OEM charging light bulb it too low of a wattage.  

 

The alternator regulator uses the input current from the charging light circuit (charging light gets 12v from the ignition switch at key-on. This resisted current from the light  is used to excite the alternator rotor for start-of-charge. If the excitation current is too low then the alternator needs to spin faster to use it's residual magnetism to supplement the low excitation current. 

 

Way/way back some of us figured this out on our own & added a higher wattage bulb to the charging light. I don't know if BMW also figured this out (doubtful) but in any case they later issued a service bulletin to use a higher wattage bulb in the charging light socket to start the charging at a lower RPM. At one time they even changed the bulb part number in the parts book to reflect the new higher wattage bulb as a replacement bulb.  

 

 

[RPG]

14 hours ago, dmsantam said:

Good morning all, my R1100RT 1995 model seems to have the alternator belt squealing just a little if I blip the throttle from idle, when it's cold. After a minute or so of running, it will not happen again. It does not squeal unless I blip the throttle abruptly. Does this indicate that the belt is not tensioned correctly? I did replace the belt about 1,000km ago with a brand new continental brand one, and tensioned it to 8Nm. 

 

cheers,

I had the same issue, except that it would just squeak a bit (at idle) when cold. The belt was just a tiny bit loose.

[dirtrider]

8 minutes ago, RPG said:

I had the same issue, except that it would just squeak a bit (at idle) when cold. The belt was just a tiny bit loose.

Morning Rick

 

Doesn't your 1150 have an elastomer belt?  Those can have their own cold squeal issues even if set properly. 

 

dmsantam's bike has the older Poly-V Belt (non stretchy) belt. 

 

 

[dmsantam]

Thanks everybody for the replies. I will avoid blipping the throttle when cold until i have some time to tighten up the belt. I will try 10-12Nm this time. With 8Nm i could just turn the belt 90degrees at the midpoint so i thought it would be fine. 10Nm may be the go. Once again I have learnt a lot from the replies to the thread, thanks again. 

 

cheers,

[duckhawk64]

On 1/9/2024 at 7:51 AM, RPG said:

I had the same issue, except that it would just squeak a bit (at idle) when cold. The belt was just a tiny bit loose.

Ditto the quote. Ride it 5 years like that with no issue. Maybe better slightly loose than slightly too tight.

[RPG]

On 1/9/2024 at 8:57 AM, dirtrider said:

Morning Rick

 

Doesn't your 1150 have an elastomer belt?  Those can have their own cold squeal issues even if set properly. 

 

dmsantam's bike has the older Poly-V Belt (non stretchy) belt. 

 

 

Morning D.R., I have to say I'm not sure. If you recall, I had the stock clutch removed from my alternator and I installed the appropriate belt mated to the grooved pulley.
The fall, I removed the plastic and torqued the belt to the BMW specs (just to see if that made a difference) and the cold start squeal disappeared. So far, so good.

[King Herald]

On 1/9/2024 at 11:20 AM, Lowndes said:

Remember, the alt is trying to recharge the batt after the slight drain from starting, but the alt won't "kick in" until it gets up to 2 or 2.5K RPM the first time after startup.  That is to help the engine warm up without extra load.  New belts might stretch or break-in a little, too.  Tighten it up a tiny bit, or just don't blip it.

My charge light doesn’t go off if I start it when warm with no ‘choke’ or throttle, but a tiny blip to about 1300 and it goes out. It never used to be that way, but I’ve adjusted the belt a couple of times with no difference. 

[dirtrider]

4 hours ago, King Herald said:

My charge light doesn’t go off if I start it when warm with no ‘choke’ or throttle, but a tiny blip to about 1300 and it goes out. It never used to be that way, but I’ve adjusted the belt a couple of times with no difference. 

Morning King Herald

 

Change your dash charging light bulb to a 3 watt bulb & most likely your lazy alternator start-of-charge will disappear. 

 

The current from the down-stream side of the dash charging bulb is what the alternator uses to initiate charging after starting. 

 

If that current isn't enough for charge initiation (with an LED, or even the original 1.7, watt charge light bulb) then it takes a bump in the engine RPM (alternator RPM) to allow the slight magnetism retained in the alternator rotor to produce enough current to start the charging sequence. 

 

Either that, or just use the choke (fast idle lever) to start it even when hot as that allows a higher RPM right after engine starting.