Front hollow axle: wider part jamming in fork

[tmcafe]

I just removed the front wheel for a new tire. The hollow axle this time was almost stuck with its wider part in the fork leg (of course pinch bolts loosened). I never encountered this problem before when I had to remove the axle. Eventually I managed to remove it by inserting a screwdriver in the diametrically opposed holes and pulling and twisting it. I looked at the wider part and it appeared to be ever so slightly bulging out, while its outside seem to be smaller as if it tapered off very slightly. For a visual, I found this image of a Ducati axle, which looks similar except for the holes near the threaded end. On my bike the wider part is on the left, the threaded part and the spacer are on the right. I don't know why this happened. It wasn't a fork alignment problem, I remember I had made sure that the axle slid in smoothly. I don't think the pinch bolts were too tight, I torqued them evenly on both fork bottoms.

 

Anyway, I am not sure what to do. Should I sand that part very carefully to reduce the diameter?

 

 

[gstallons]

You can use a ScotchBrite scuffing pad to clean it up with. Use a micrometer and take some measurements to see if you have a diameter problem. with the wheel off install the axle shaft (bolt) to see if it slides in and rotates without any difficulty. Lubricate these parts with a small amount of oil upon reassembly.

[HaydnR]

" I looked at the wider part and it appeared to be ever so slightly bulging out, while its outside seem to be smaller as if it tapered off very slightly " a photo would help.

If you mean that the edge towards the centre of the length of the spindle I would guess that the spindle has been overtightened, mushrooming the spacing part not contained within the bottom of the fork. Also check that the spacer on the opposite has not been deformed.

 

I would fit the spindle back in place without the wheel if the spindle no longer slides into the bottom of the fork leg with ease I would suggest a new spindle is needed.

 

 

Torque values

Front wheel spindle 90-100 nm /66-74 ft lbs

Fork pinch bolts 10.4 nm / 7.5 ft lbs , which is bugger all, just a nip up with a standard allen key

[tmcafe]

Thanks for the comments. I'll try to take a picture and post it. The wider part won't fit in the fork bottom unless some force is used, and the very slight irregularity/bulging is apparent to the naked eye. I'll try some measurements. The spacer appears to be ok. I didn't go over the book torque value for the spindle nut. HaydnR, how did you get the torque for the pinch bolts? Thanks again.

 

 

[HaydnR]

The pinch bolt torque is on the tech drawings of the forks in the workshop manual. The spindle nut,I would say would be at the lower end of the specified value due to it being hollow, I couldn't find any different values for the different spec of spindle.

[tmcafe]

The pinch bolt torque is on the tech drawings of the forks in the workshop manual. The spindle nut,I would say would be at the lower end of the specified value due to it being hollow, I couldn't find any different values for the different spec of spindle but would assume the hollow one to be squishier

Thanks. Now that you mention the torque value for the axle, I realize that the one they give in the manual may have been meant for the non-hollow type of axle . Oh well. A guy in service when I took the wheel in said that maybe the heat contributed to it, though I can't see why it would have gotten that hot.

 

Anyway, I looked carefully and the slight bulge is pretty much where the axle faced down in the fork bottom. You can see the shape of the opening lightly imprinted on the surface. It also corresponds roughly with the half-circle indents on the edge, which are a bit tapered off. I'll try to sand the area very gently to reduce the micro extra. Sorry I can't post a pic yet.

 

 

 

[HaydnR]

Google ohlins pinch bolts and you will get lots of results on Aprilia and Duc forums with woes of over tightened bolts cracking the fork lowers resulting in big money to replace.

[tmcafe]

I've tried to sand a bit the offending bulge with a sheet of 150 grit I had. Not much luck. I'm thinking of using a finishing sander very carefully.

 

I'm sure I didn't torque the axle above 100Nm, but I may have torqued the pinch bolts to 25Nm, which is the value for the same size bolts on the fork clamps. Yes, not smart to assume they need to be torqued the same. I couldn't find a torque value for the pinch bolts anywhere in the shop manual, and I can't find the Ohlins fork info right now.

 

Pics aren't great, taken with an older gen iphone. You can see the very mild curvy outline, and how far the axle would go in before it hits the thicker area.

 

 

 

 

 

 

 

 

[HaydnR]

So its the area that should be within the bottom of the fork leg that has distorted, that would occur due to over tightening of the pinch bolts. I take it that part has oval'd too.

[emry]

Have you tried a nice whack with a rubber mallet? Many models experience deformation of the lower fork leg due to the pinch bolts, they are intentially used to "oval" the mounting area to clamp the axle. Since the bolt that retains the cartridge is in the center of the fork bottom that area is not in contact with the axle. The outer areas of the clamp will deform over time, which provides a tighter clearence during removal and installation. A decent tap will normally set the axle back into place, and the pinch bolt will happily hold the axle from rotating itself free. Your original posting for the Duc axle is an excellant visual of the areas that are clamped.

[Baldini]

In your photos head looks out of parallel with shaft, irespective of 'bulge' - probably just the camera, but have you checked it using a straight edge? If cost reasonable, think I'd be looking to replace axle. Forcing it isn't going to do fork lowers any good & your going to have problems everytime you take it out.

I always grease axles liberally.

Hope you get it sorted.

 

KB

[HaydnR]

I think it may be in the design of these spindles to squish if the pinch bolts are overtightened as a cheaper option to replace the spindle rather than the fork bottom.

The shape really needs re-forming rather than shaping,by removing material you are making the spindle weaker,I'm not an engineer but would think that this could be done by clamping in a split aluminium block bored to the correct diameter.

I think it would be better to source a replacement. You may find a used item at somewhere like Reboot. Or a new replacement par no. GU01614180 (would need to confirm correct one)listed at stein dinse 35 euro but not in stock:

[tmcafe]

I could whack it back in with a rubber mallet--after all that's how I started it out from the other end, but I don't feel too comfortable with the idea of forcing the axle which should slide into the fork bottoms smoothly. While I understand that pinch bolts and fork bottoms somehow act against the round section of the axle in order to hold it fast, I wonder why only the wider section has this problem, since all pinch bolts were torqued the same.

 

I think the lack of parallelism is more of an optical illusion due to camera distortion and framing, esp. in the second pic.

 

I also feel that removing material isn't the best option since it's going to weaken the axle at least in theory. I'm going to look into replacing it, though I'm not sure if they're available. For now I'll try to grease it as usual and see if I can fit it back in with some 'coaxing' and patience.