Rear end operating temp???

[Zot]

I just replaced the bearings on the rear end of my 2000 R1100 RT. Operation was "text book" with no hick-ups.

 

I took her out for a test ride (approx 10 miles) and after parking reached down to feel the temp and was surprised at how hot the rear end was.

Previously I was running Motur 80/90 full synthetic after the rebuild I put in 80/140 non synthetic.

I don't recall the temp being anywhere near as high before.

 

Can anyone tell me if it's normal for the temp on the rear end to be to the point that it's uncomfortable to the touch, after a 10 mile ride.

 

I don't recall it previously being that hot.

Thanks in advance

[ShovelStrokeEd]

Uncomfortable to the touch is pretty broad depending on what you get used to. Hot water in your house is probably not over 120 deg F. Most folks will not willingly hold their hands on 140 deg F. To oil, and bearings, that is not enough to break a sweat. About 1% of the efficiency of power transmission is lost in that 90 degree bevel drive gear due to friction. So, let's say you are averaging 20HP through your gears. 1HP is about 42 BTU/min. 1 BTU will raise a pound of water 1 degree F in 1 hour. You are putting 8.4 BTU/min into your gear oil and probably have a pound of it in there plus the housing and gears so, allowing for radiation from the housing and some heat soak by the mass of the gears, you might see as much as a 60 degree rise over ambient in that 10 minutes.

[Clive Liddell]

Zot,

I like to always, no matter the distance or the ambient temp, be able to comfortably hold my hand on the final drive. Check your brake pads are not dragging and that the wheel is turning fairly freely

[Zot]

Clive,You're right and thats the first thing that I checked and was actually surprised at how cool the rotor was in comparison to the rear end housing.I would have expected more residual heat.

[Zot]

Uncomfortable to the touch is pretty broad depending on what you get used to. Hot water in your house is probably not over 120 deg F. Most folks will not willingly hold their hands on 140 deg F. To oil, and bearings, that is not enough to break a sweat. About 1% of the efficiency of power transmission is lost in that 90 degree bevel drive gear due to friction. So, let's say you are averaging 20HP through your gears. 1HP is about 42 BTU/min. 1 BTU will raise a pound of water 1 degree F in 1 hour. You are putting 8.4 BTU/min into your gear oil and probably have a pound of it in there plus the housing and gears so, allowing for radiation from the housing and some heat soak by the mass of the gears, you might see as much as a 60 degree rise over ambient in that 10 minutes.

 

Thanks Ed, I think that for "peace of mind" I'm going to try the synthetic lube again for a comparison.

I don't think that it's "all in my head" but you never know.

[smiller]

Ambient air temp makes a big difference, but in warm temperatures my final drive housing temperature is typically just about at the point that I can't keep my hand on it continuously (usually equates to around 150 degrees F.) As Ed said this is nothing for bearings or a gear oil, in fact it's near the low end of their typical operating temperature range so cooler may not be better. I would consider what you are seeing as normal and wouldn't think twice about it.

[ShovelStrokeEd]

There is yet another factor to consider. Isn't there always?

 

That is the rate of heat transfer between the oil and the aluminum housing and also between the brake rotor and the gear carrier for those bikes so equipped. Different metals conduct heat at different rates and so might different oils, I have no data to back that up. I do know that surface area in contact is all important both for the heat transfer and your perception of the heat you feel.

 

With that in mind, a 10 minute ride may not be enough time for the entire assembly to reach a thermal equilibrium where radiated heat matches heat input and all the components are at the same temperature. As to the touch thing, a casting with a slightly rougher surface might feel quite a bit cooler than another with a smoother surface.

[RSL]

Rather than worrying whether the oil is OK with somewhat warmer temps (should be no problem), I'd be worrying about the source of the extra heat.

 

My rear end bearings are good, and the surface temperature is warm but comfortable to leave the palm of my hand on it.

 

I doubt that one brand of lubricant would be much (if any) different in heat conductivity, so your higher temperature leaves me wondering if the mew bearings are too tight or other mechanical reason for the heat.

 

BTW, who manufactured the new bearings, and where? I hope not China.

[Zot]

All bearings came from the local BMW dealer,and I was very carefull during assembly. I did remove a shim on the large crown bearing due to too much bearing preload,and after reassembly made certain that everything turned freely.

 

After a couple more test rides,other than the heat "issue" or perhaps heat "non issue" everything feels good, there is no binding,noise or axle end play.

I was probably just being paranoid.

[Tominator]

I would suspect the shim removal would be to blame. Understand the fact the Large roller bearing could live with some Back lash but the tapered Roller Bearing could not since any excessive backlash would cause the rollers to run off the raceway. Todays bearings are manufactured to very close tolerances so removing the shim that was installed oringinaly would be how I would reassemble and then compare the tolerance with a Dial indicator which most do not.

 

Do you have the service manual:

Backlash mm (in) 0.07...0.16 (0.0027...0.0063)

Taper roller bearing preload mm (in) 0.05...0.1 (0.0020...0.0039)

Oil grades Brand-name hypoid gear oil, SAE 90 GL 5

 

Oil to some degree disapates heat, but for the most part your heating issue would be due to excessive friction (The roller bearing (RH) in my opinion. I've seen this before and comend you for your attempt. But is the Backlash (Sideplay) is not correct that repair will not last long :-(

 

Let us know what you find!

 

Good Luck

Tomas

[Zot]

I would suspect the shim removal would be to blame. Understand the fact the Large roller bearing could live with some Back lash but the tapered Roller Bearing could not since any excessive backlash would cause the rollers to run off the raceway. Todays bearings are manufactured to very close tolerances so removing the shim that was installed oringinaly would be how I would reassemble and then compare the tolerance with a Dial indicator which most do not.

 

Do you have the service manual:

Backlash mm (in) 0.07...0.16 (0.0027...0.0063)

Taper roller bearing preload mm (in) 0.05...0.1 (0.0020...0.0039)

Oil grades Brand-name hypoid gear oil, SAE 90 GL 5

 

Oil to some degree disapates heat, but for the most part your heating issue would be due to excessive friction (The roller bearing (RH) in my opinion. I've seen this before and comend you for your attempt. But is the Backlash (Sideplay) is not correct that repair will not last long :-(

 

Let us know what you find!

 

Good Luck

Tomas

 

 

Tomas,thanks for the input but I think that you are confusing "backlash" with bearing "preload"

Backlash is the clearance or gap between the pinion and crown teeth and is usually measured as you mentioned using a dial indicator on one of the crown gear teeth while slowly rotating the pinion shaft.

Preload is merely a radial load placed on a bearing (usually a new bearing) to aid wear-in and compensate for excessive side play once the new bearing is wore in.

Usually a high heat situation would arise due to excessive bearing preload and had I reassembled the original shim pack

I would have expected that.(since I could barely turn the assembly with original shims reinstalled).

 

You are right though, if it is a preload problem it won't take long to become obvious. I think I'll go for a couple more short rides tomorrow and pull the drain plug and see if anything is on the magnet.

[Steve W.]

You stated the assembly was hard to rotate after the bearing replacement. So you removed the shim and then it rotated freely? If so then one of two things happened, either you didn't get the bearing fully seated on the shaft or the bearing was somewhat "thicker". From my experience, modern bearings of the same part number are dimensionally identical for all practical purposes. If you heated the bearing and dropped it on the shaft there is a likelyhood that it is not fully seated down on the shaft. I always put the assembly in a press with about 2 tons of pressure while it cools. The heated bearing will contract when it cools and the inner race can be sitting proud of the flange on the shaft. In other words it contracts in all directions. I have seen this on many mounted bearing assemblys, large and small. The bearing needs to be seated by pressing. As mentioned the shim you removed sets the backlash betweeen the pinon and the crown gear. If the drive was hard to turn this should have been a big "red flag". Something is wrong. Not good mechanics to just leave parts out. I wouldn't ride it. If it comes apart at speed you will be the first one to know.

Cheers

Steve

[Tominator]

Yes I meant preload....damn germans (Me). Backlash is when setting up the crown and pinion gear. It was late....I normally place the inner part in the freezer overnight and the bearing almost falls onto the shaft. (Dry Ice also works) Pressing it on also ensures the bearing race is all the way to the end of its travel. (As suggested on the previous response)

 

Tomas

[Zot]

Just a quick update on rear end temp. situation.

 

I have put about 200 miles on the bike(all short trips).

Yesterday I drained the oil out of the rear end to see if there were any "nasties" attached to the drain plug magnet.

 

The oil, 80/140 non synthetic gear lube was clean and there were no "cling-ons" attached to the magnet.

 

Since some had mentioned the possibility that the bearings may not have seated properly during the rebearing procedure,I was starting to question my rebuild,and pulled the side housing apart,removed the crown assembly and checked that all the bearings and cone were indeed in position.

 

All checked out both visually and also by the tell tale dead "thud" sound when seated with a hammer & punch.

 

After basically repeating the original assembly attempt, by first using the "original" shim pack, once again the crown shaft began to "bind" when the housing was torqued to spec.

 

Removing a shim was once again the answer to my binding problem and once again the crown and pinion turned freely.

 

I then switched the oil in the housing to 80/90 full synthetic and went for a half hour ride..

 

Problem solved,half the heat generated compared to the previous oil.

 

Thanks to all that had advice and tips, its always appreciated to have input by knowlegable folks,and although it turned out to be my choice of oil,I now have peace of mind knowing that all "the innards" will remain in place.

 

Zot

[Tominator]

Many run other blends...I always go with 80/90.

 

Glad it worked out!

Tomas