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inner clutch hub drilling mod

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I did this a few months ago on my 07 YZ250F and it seems to be working. The clutch seems much more consistent. I had tried the washer mod, and different springs, cables, plates, etc. but the clutch was never consistent. I probably only have 6 or 7 hours on it, but in my opinion it's worth the effort.

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Hello, I had problems with clutch dragging and hard time finding neutral. Tried everything and after assembling the clutch it behaved perfect for 30min and then bad again. Once manually oiled and put back in - perfect for 30min. I ended drilling extra holes in my new inner hub. Mine is 09 yz250f and it already had one hole at each channel. So I drilled 2 more holes at each line (somewhere just 1 because I didn't want to weaken the construction) and my clutch problems disappeared. If you decide to do it I suggest going to a machine shop because I tried drilling holes with normal drill in home and the result was bad (used my old already ruined inner hub for testing) 🙂

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Edited by nk_dimitrov

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How were the results bad. I have already drilled my holes. I was worried about balance more than anything. I did this at the same time I did a 290 kit. It does seem to have a vibration with my bike in gear and clutch disengaged. But I have not actually rode the bike since this work. Before I worry to much I would like to ride it first an see if this goes away. I used my drill press and layed out the holes evenly to avoid any balance issues

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This is a very common mod for the CRF150r. On this bike the oil flow is greatly reduced when holding the lever in like at the starting line. Look at any of the aftermarket clutch hubs, covers and you will see more holes, some larger then you would think. Key is to drill slowly which will help to remove the same amount of material.

 

For the ones that have issues,  I bet you will find dry plates inside if you would pull it apart. This will stick the plates as well as build heat which will make performance inconsistent. I had clutch issues on a Beta and the best quick fix was 0wt synthetic oils.

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Of course when you do this it will drop your oil pressure.  I'm not saying your motor will blow, but in theory your oil pressure to the rest of the motor will drop. 

I guess I would try it if you really had a problem, but I would try different oil or clutch disks first.  IMO.

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Do these motors have a pressure valve/relief?? Other brands do and I would have to assume these also because the pressures/flow would be very different at 14,000 rpm vs idle. In any case pressure would be lower but flow would be higher. Also aftermarket would have had known issues arise from their parts which advertise more oil flow via holes.

 

To mass produce these holes for model lines would be very expensive. The benefit of aftermarket are the holes, tighter tolerances and better overall material/finishing which can not be done in production at a marketable cost. I ran a Hinson hub on our CRF150r and never had any clutch or motor issues.

Edited by weantright

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I don't think the clutch is pressure fed. Just the crank, piston cooler, and cams are pressure fed. Clutch should be splash oil. 

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I don't think the clutch is pressure fed. Just the crank, piston cooler, and cams are pressure fed. Clutch should be splash oil. 

It's pressure fed.  That is why drilling holes gives it more oil.  Most modern 4strokes are pressure fed.

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It's pressure fed. That is why drilling holes gives it more oil. Most modern 4strokes are pressure fed.

Pressure only because of centrifugal force on the inner hub. It picks up oil by "splashing" and the spinning forces it through the holes and lubricates the discs. I am pretty sure there are no pressurized oil ports into the inner hub.

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Pressure only because of centrifugal force on the inner hub. It picks up oil by "splashing" and the spinning forces it through the holes and lubricates the discs. I am pretty sure there are no pressurized oil ports into the inner hub.

 

Oil comes through the center of the main shaft, around the push pin, lubricates the push bearing, and lubricates the clutch.  It floes through the main shaft in much the same way the upper connecting rod bearing and piston oil ring are lubricated.

 

The clutch is mounted higher then the crankshaft.  It doesn't splash or dip into the oil.

 

You'll notice that the posted article states that drilling too many holes will starve the top end of lubrication.  This is because you could loose the pressure needed to get oil to the top end.   

Edited by speedtoad

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Do these motors have a pressure valve/relief?? Other brands do and I would have to assume these also because the pressures/flow would be very different at 14,000 rpm vs idle. In any case pressure would be lower but flow would be higher. Also aftermarket would have had known issues arise from their parts which advertise more oil flow via holes.

 

 

I don't know of any pressure relieve.   I'm thinking that as RPM's increase the resistance to oil pressure decreases and the demand for more oil increases effectively regulating oil pressure, but I'm just thinking out loud.  The holes in the shafts at lower RPM's would be open less often at lower RPM's reducing the amount of oil that can enter.  At fast rpm's the holes would be open more often.  At high RPM's they wouldn't be open as long but since oil can't compress as long as they were open long enough to allow the cavities to be filled it wouldn't matter.  I hope someone who knows could chime in.  There is a technical forum for these types of questions though.

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Oil comes through the center of the main shaft, around the push pin, lubricates the push bearing, and lubricates the clutch. It floes through the main shaft in much the same way the upper connecting rod bearing and piston oil ring are lubricated.

The clutch is mounted higher then the crankshaft. It doesn't splash or dip into the oil.

You'll notice that the posted article states that drilling too many holes will starve the top end of lubrication. This is because you could loose the pressure needed to get oil to the top end.

Who wrote that article? I reviewed a bunch of oil schematics from yamaha manuals and none of the sow the inner hub being lubricate from the pressurized system. I do agree that oil does travel through the gear shafts but that's mainly to oil the drive gears. And i'll agree that oil the will travel past the disengaging rod and throwout bearing but the inner hub has no affect on oil pressure as it in not a sealed system. Every time you pull the clutch the pressure plate separates and leaves about a 1/4 in gap all the way around the assembly. I could still be wrong but I don't see how the clutch is lubricated through the pressure system.

Pictures are from this site and my own manual.

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I also thought about the oil pressure thing and did some research.  I've heard drilling holes in the hub changes oil pressure from other places also.  So I went outside, although it was 0 degrees out there, to look at some inner clutches.  You are right.  There are so many places for the oil to escape besides those holes.  The most obvious is around the clutch springs.  Also for that to affect pressure the whole inner hub would have to be filled with oil.

I still believe that the clutch does not splash in oil, but the oil comes from the main gear.  It must be centrifugal that forces it out the holes.

Here is two pictures from the inside of two different inner hubs.  One is stock.  The other is a rekluse 3.0 hub.  Theres a huge difference in the number and size of holes. It should be noted that I have not had any lubrication problems with my top end, as suggested in the article.

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