Jump to content
IGNORED

FD taper roller bearing preload, how to....


Stan Walker

Recommended Posts

Stan Walker

Attached please find adjustment procedure out of BMW shop manual for the R1150RT. This discussion will initially be about that procedure.

 

Things to be aware of in evaluating my comments. I'm NOT a professional wrench. I'm NOT a mechanical engineer. I've only tried this once. I have never seen the actual tools used by BMW in a shop.

 

Things to notice in the two illustrations (marked in red).

 

(1) The type of depth gauge shown can be purchased at a Sears store for a few dollars. It will look virtually identical. It is marked with graduations of 0.5 mm.

 

(2) Since 'a' cannot be directly measured a spacer of known thickness is used. Without that spacer you can use the depth gauge tool twice and arrive at 'a'. First you measure the height of the higher inner ring as shown then measure the depth to the outer surface where the block (2) is resting.

 

(3) Is a BMW tool that I think is mainly used to center and keep the crown shaft from tilting. Assuming the final drive is off the bike you can with a little care balance the crown gear shaft on the taper roller bearing without this tool. The tool has a cutout to allow 'b' to be measured but without this tool you have direct access and this isn't an issue.

 

Now here is the rub. The tolerance specified is 0.05 mm. That's 10 times as good as the sears depth gauge. With 3 measurements to take, the total of the errors will swamp the precision needed. Plus that's an odd number of measurements and any tool inaccuracy will not cancel out (it does in the 'a' - 'b' two measurement approach). In short, a better tool or a different approach is needed.

 

----------------------------

 

An alternate approach. NOT TRIED. NOT TESTED. NOT GUARANTEED TO WORK!!!!!

 

Install the FD cover on the final drive without the 'O' ring that seals it and without the crown gear shaft. Use the bolts to snug it down then back them off. Measure the gap between the cover and the case of the FD.

 

Now do the same thing but with the crown gear including the shim installed (still no 'O' ring). Once again measure the gap between the cover and the case of the FD. The difference between these two measurements is the preload.

 

Assuming it is within spec you can now install the 'O' ring and button it up for good.

 

The bad news is if it isn't within spec. You now have to remove the crown gear from the cover (requires heat) to replace the shim with one of the correct size.

 

I said we didn't try this. It's not entirely true. I did try this but I didn't think about removing the 'O' ring until later. I think that is important as it acts like a spring and prevents making an accurate measurement.

 

OK, time for all you real wrenches to speak up and add your two cents......

 

Stan

702704-FD_shim.JPG.f29dd8ff31008e18b9621d70b3b601f5.JPG

Link to comment
Now here is the rub. The tolerance specified is 0.05 mm. That's 10 times as good as the sears depth gauge.
Most common dial calipers are good to at least .001" or better (good enough to resolve .05mm) and include a depth gauge (check the probe at the bottom of the calipers.) A cheap but adequate example. Would this work?
Link to comment

Several points.

 

- A standard quality vernier caliper can measure accurately down to 0.0005" (or 0.0125mm), with some interpolation skill. With the type of measurement shown, skill will be required to ensure the caliper stands perfectly upright and so on, but assuming a quality pair of calipers is used, and there are only 2 (not 3) measurements being taken, this level of accuracy is attainable by someone that has experience in working with these tools.

 

- Item 3 (the crown gear "stabilizer") may be able to be dispensed with, as you say, if there is a lot of care being used. But it will make life difficult. Remember that you are bringing the caliper up against the bearing, so this will aready have a tendency to tilt the crown gear assembly. It would be better to jury rig up a means of clamping the crown gear and shaft firmly against the taper roller.

 

- The BMW instructions seem a bit vague with respect to the "a - b" thing. They say that "a - b = shim thickness". What is more clear is "Distance "a" minus distance "b" equals the thickness of a shim that will result in zero preload".

 

The ACTUAL shim thickness must be "(a - b) + desired preload distance", that is, "(a - b) + 0.05~0.10".

 

- As another poster has suggested, a dial gauge would be a useful measurement alternative, although "getting in there" with a dial gauge may be somewhat troublesome.

 

- The alternative method suggested will work in theory. The problem I see is that the case gap being measured will be subjected to some tilting, which will make the gap somewhat uneven all around the case, and make determination of the actual gap uncertain.

 

Finally, this is just the procedure for determining the shim thickness next to the big ball bearing. There is ANOTHER shim next to the taper roller that is intended to adjust the crown-to-pinion gear lash. If you are replacing the taper roller, this other shim thickness must FIRST be selected and installed so the correct gear lash is obtained. You cannot replace the taper roller and expect to use the same shim, because the axial tolerances on the taper roller are large enough to require re-shimming.

 

By the way, many thanks for the page from the manual! Maybe you have access to BMW's suggested method for determining the correct thickenss for the gear backlash shim?

 

Bob.

Link to comment

By the way, many thanks for the page from the manual! Maybe you have access to BMW's suggested method for determining the correct thickenss for the gear backlash shim?

 

I second that thumbsup.gifthumbsup.gifthumbsup.gif

Thanks again Stan

Link to comment
Stan Walker

A standard quality vernier caliper can measure accurately down to 0.0005"

 

The base of the dial caliper I had wasn't wide enough to span the gap.... no joy there.

 

I have done some homework and today I placed an order for a "depth micrometer". This is the tool that I think is needed. It has a specified accuracy of 0.001" which should be good enough for the task at hand. And it has a wide base similar to a my standard "cheapo" depth gauge and so will be able to span the gaps as needed. I ordered it from Grizzly; catalog number G5622 for $32.95 plus shipping. They also have digital units with even better accuracy for around $100 that I <sigh> passed over.

 

Finally, this is just the procedure for determining the shim thickness next to the big ball bearing. There is ANOTHER shim next to the taper roller that is intended to adjust the crown-to-pinion gear lash. If you are replacing the taper roller, this other shim thickness must FIRST be selected and installed so the correct gear lash is obtained. You cannot replace the taper roller and expect to use the same shim, because the axial tolerances on the taper roller are large enough to require re-shimming.

 

True, it's all covered in the manual. You need to use a dial gauge to measure backlash and in this case you will need the centering fixture to hold the crown gear shaft. I suspect the cost of that tool (unknown) probably moves this out of the reach of the shade tree wrench like me.

 

Stan

Link to comment

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...