Locker Shaft

I've decided the locker shaft needs a section all its own.  As I learn more about these bikes, I see interrelated issues in which the locker shaft is involved. 

A 7mm hole runs through the primary (clutch) gear shaft.  This allows air, and possibly fluid, to pass through the hole.  The presence of a locker shaft makes draining the oil more difficult.  

• Early bikes (2011 - 2012) had no locker shaft.  Thus the through-hole is 7mm in diameter.

• Middle bikes (2013 - 2014) used a locker shaft that came out with the gearbox.  This design had a 3mm through-hole.

• Late bikes (2014 - 2015) had a locker shaft held captive in the engine cases.  This shaft was solid with no through-hole. 

The model years I associate with early, middle, and late are only approximate.  They may vary by geographic region as well.  According to an OSSA press release, a lot changed in 2013.  Some early bikes in the USA were updated before being sold.

NB: I've recently been made aware of a 2012 Explorer that has a captive locker shaft with a through hole and a 14mm ID bearing.  I'm beginning to think no two bikes are identical!

 2nd Gear Pinion

Along with (or perhaps before) the addition of the locker shaft, the second gear pinion was changed to provide a longer engagement region.  

Notice the adjacent photos.  Instead of just being the gear alone, a bearing surface was incorporated at the end.  This bearing surface has an outside diameter of 20mm.  The inside diameter of the gear and bearing surface is nominally 14mm.  It is an interference fit (approximately 0.00075 inch) on the 14mm shaft.  

This necessitated changing the shaft's support bearing in the crankcase to one with a bigger ID.

Primary Shaft Support Bearing

Models with the updated 2nd gear also have a different shaft support bearing.  The early bearing is a 6201 which measures 14 x 32 x 10mm and lacks seals.  In later bikes, two different bearings were used - both of which measure 20 x 32 x 10mm.

The bearing in my late 2014 (2015 specs?) bike is marked “FAG 3804-B-2RSR-TVH Japan.”  This is a double-row, angular contact bearing.  The writing is very small and its seals are marked 6804 (which is a bearing measuring 20 x 32 x 7).  This was initially a source of confusion for me.

The bearing in my early 2014 bike is a 63804.  This is a deep-groove bearing. 

Both bearings are an interference fit in the crankcase (more on this later).  A snap-ring is also used to keep the bearing from moving towards the gearbox.  When installing the snap ring, the sharp edge side must face toward the gearbox.

Final (Captive) Locker Shaft Design

I was surprised by an undocumented change to the locker shaft.  Upon attempting to remove my late 2014 gearbox for the first time, it would not budge.  Usually after removing the five shoulder screws and assuring the gearbox is not in neutral, the gearbox will come out with a light tap from a soft hammer on the countershaft.  

Upon further inspection, I noticed the locker shaft was solid (there's no 3mm hole down the center).  Removing the locker shaft's left-hand nut allowed the gearbox to come out easily.

This later locker shaft is very different from the one in my early 2014 bike.  The locker shaft has the same basic shape as a 4T valve.  The “head” of the early locker shaft is 19.9mm in diameter and can pass through the center of a bearing with a 20mm ID.   Whereas the head of the final locker shaft is 23.9mm in diameter and cannot.  The final locker shaft also lacks the cross-drilled holes found in the earlier version.

I'm not sure when the change occurred.  The 2015 parts book does not list a different locker shaft.  In fact, the only item in the 2015 parts book that ends in “15” is the crankcase itself.

Gearbox Puking Oil

The fact that the final locker shaft design has no through-hole may explain why my late 2014 bike pukes oil out of its gearbox breather.  Neither my 2011 TR280i (no locker shaft) nor my early 2014 TR250i (locker shaft with through-hole) do that. 

The official fixes for the oil-puking problem are to route the breather so that it lubricates the chain or to extend the breather up near the headstock.  I used the latter method with a piece of clear plastic tubing so I could see the oil percolating.  It is described below.

Bearing Fits and CTE

Firstly, I apologize for not doing this calculation in metric but I am far more familiar with thousandths of an inch for bearing fits.  A 32mm OD bearing nominally measures 1.2598 inches.  I measured my bearing OD at 1.2594 inches.  My case bore measured 1.2585 inches.  Both measurements were made at the same ambient temperature of around 60° F. 

1.2585 - 1.2594 = -0.0009 (or slightly less than 1 thousandth of an inch interference).

This is considered a light press fit.  To easily install the bearing, there must be clearance between the bearing and the cases.  This involves shrinking (by cooling) the bearing and expanding (by heating) the crankcase.

The linear coefficient of thermal expansion (CTE) for steel varies from 6 to 7 micro inches per inch per degree F depending on the alloy.  Let's call it 6.5. 

My freezer is about 10° F.  This provides a 50° delta from room temperature.  Thus, the bearing will shrink about 0.0004 inches.

1.26 * -50 * 6.5e-6 = -0.0004

The linear CTE for aluminum varies from  11.7 to 13.3 micro-inches per inch per degree F depending on the alloy.  Let's call it 12.

Assuming the case is locally heated to 200° F provides a 140° delta from room temperature.  Thus, the case will locally expand by about 0.0021 inch.

1.26 * 140 * 12e-6 = 0.0021

Taking the shrinkage of the bearing and the expansion of the case together provides about 0.0025 inches of clearance.  This will be adequate if we can keep that much clearance for the duration of the bearing installation.  Unfortunately, the cases will rapidly conduct heat to the rest of the engine, thereby cooling and shrinking.  Similarly, as soon as the bearing contacts the hot case it will warm and expand.    

So the key is to work quickly and have an alignment/installation tool that can be struck with a hammer to seat the bearing.  Ideally, the case would be heated in an oven but because the work was performed in situ, I used an electric paint stripping gun.  Where fire is not a concern (e.g., a wheel bearing) I use a propane torch for heating.  I also literally keep the bearing on ice until the cases are hot.  An infrared thermometer is practically a necessity.  If in doubt, strive for a greater temperature differential /  larger clearance. 

For those who want to perform the calculation in metric, the CTE for aluminum is 21 to 24  micrometers per meter per degree C.  The CTE for steel is 10.8 to 12.5 micrometers per meter per degree C.

Finally, for completeness, I will mention what happens when using heat for bearing removal.  When you heat the aluminum crankcase with a bearing installed, both the crankcase and the bearing expand.  Because the CTE for aluminum is roughly double that of steel, aluminum will expand more than steel for each degree of temperature rise.  Because the aluminum is on the outside, clearance will form between the crankcase and the bearing making disassembly easier.  If however, an aluminum shaft is inside a steel bearing, heating will only make the fit tighter and more difficult to separate.