[55firearrow]

I took it to a machine shop yesterday to have the shafts measured.  The guy who I hoped would be there wasn't and this guy didn't check the temp or anything.  It was a little cooler that day so I would say the crank was 60 to 70 F when he measured it.  Anyway he got .9995 where the inner drivers side bearing would ride, .9996 where the outer bearing would be on the drivers side, and .9991 on the timing side.  The guy didn't seem to think it was any big issue but then again he doesn't know anything about these motorcycles.  What are your thoughts?

[Arizoni]

I say live with it.

The roughly 18 degree temperature difference will only cause the journal to appear to be .0001 smaller than it actually would be if measured at the correct temperature.  Actually, if the measuring equipment and its calibrating gage blocks were at a similar temperature they would also be that much smaller so the reading you got would be still be accurate.
As I mentioned before, the .0003 tolerance (1.0000-.9997) is for a brand new journal size.  It is anticipated by the designer that there will be some wear during the course of the journal's life and these hardened steel journals can not be "built up" to enlarge them.
For that reason a limit lower than the original new size is allowed before scrapping the crankshaft would be required.

The service  limit of .9994 I suggested in my previous post will effect the radial clearance in the bearing assembly by allowing it to be .00015 looser than a brand new journals lower limit.  The oil film between the rollers and the journal will eliminate any perceptible play in the bearing even with this added clearance.

I'm assuming the journal that measured .9991 diameter is on the lightly loaded side of the crankshaft?  If so, it should still work for many miles as long as the engine is not run hard.

As a side note, if this wasn't a surface with rolling element bearings running against it, it could be repaired by "thin dense chrome" or "electroless nickel" plating.  These repairs could be used on a shaft that was going to have a full bearings inner ring pressed onto it, for instance.
These methods of repair cannot be used with your engines design because the direct contact between the rollers and the journal would rapidly chip off any plating that was applied to the crankshaft.

As I said, live with what you've got.  Run the engine easy and it should last for many years.

[55firearrow]

I say live with it.

The roughly 18 degree temperature difference will only cause the journal to appear to be .0001 smaller than it actually would be if measured at the correct temperature.  Actually, if the measuring equipment and its calibrating gage blocks were at a similar temperature they would also be that much smaller so the reading you got would be still be accurate.
As I mentioned before, the .0003 tolerance (1.0000-.9997) is for a brand new journal size.  It is anticipated by the designer that there will be some wear during the course of the journal's life and these hardened steel journals can not be "built up" to enlarge them.
For that reason a limit lower than the original new size is allowed before scrapping the crankshaft would be required.

The service  limit of .9994 I suggested in my previous post will effect the radial clearance in the bearing assembly by allowing it to be .00015 looser than a brand new journals lower limit.  The oil film between the rollers and the journal will eliminate any perceptible play in the bearing even with this added clearance.

I'm assuming the journal that measured .9991 diameter is on the lightly loaded side of the crankshaft?  If so, it should still work for many miles as long as the engine is not run hard.

As a side note, if this wasn't a surface with rolling element bearings running against it, it could be repaired by "thin dense chrome" or "electroless nickel" plating.  These repairs could be used on a shaft that was going to have a full bearings inner ring pressed onto it, for instance.
These methods of repair cannot be used with your engines design because the direct contact between the rollers and the journal would rapidly chip off any plating that was applied to the crankshaft.

As I said, live with what you've got.  Run the engine easy and it should last for many years.

I'm not sure what you mean by lightly loaded side, it's opposite the clutch/drive sprocket side.
I think I'll take your advice and just go with it, replacing only the rollers and cages.

[Arizoni]

By "lightly loaded side" I was talking about the force the bearing must resist to keep the crankshaft centered in the engine crankshaft bores.

Usually, driving the camshafts and the ignition gears doesn't require much horsepower so the force that the crankshaft must produce to rotate the gears is not very large.  This sideways force on the crankshaft produces the "load" that the bearing must resist to keep the crankshaft centered, hence the term "lightly loaded".

The clutch side of the crankshaft must deliver the full power that the engine can produce to the clutch thru the primary drive chain.  This produces a large sideways load on the crankshaft which its bearing must resist so I refer to this side as the "heavily loaded side".  Because the force needed is large, the bearing on that side will be "heavily loaded".

[55firearrow]

That makes sense, thanks.

[Arizoni]

55firearrow

I've been doing a bit more reading and if you really have a 1955 250cc firearrow it should be basically the same lower end as the old 350 bullet and the transmission is mounted on the rear of the engine in a similar manner.
I'm not sure where I got the idea that the bearing rollers were running directly on the crankshaft but according to what I've read, the bearings have a hardened inner race which is pressed onto the crankshaft.  Of course, I could be wrong about this.

If the bearings have inner races that are just pressed onto the crankshaft journals, you could have the one(s) that are undersize plated to bring it up to spec.

The processes I'm familiar with are called "electroless nickle plate" and "thin dense chrome plateing".

Both of these plating processes can be applied so they will only increase the steel or iron journal a  tenth of a thousandth of an inch or two in the area that is undersize.
Because it is a slow process where the plating fluid is applied directly to the metal with a soaked wand or stylus, there is no machining involved or required.  (Actually, these plating processes can add up to .0005 per surface without a problem).

The difficult part is finding a plating company who can do the process and will work for someone who does not work for a large company that will give them a production order.

If you are beyond this level in your rebuild, don't worry about it.
As long as the bearings inner race is a press fit on the crankshaft journals you have no problem.

If one of the bearings inner races is a slip fit, not requireing a press to install it you can clean the surfaces of all oils or preservatives and apply locking compound specially made for this type of application.  If you can't find any of this, good old Blue Loc-Tite will work.

[55firearrow]

55firearrow

I've been doing a bit more reading and if you really have a 1955 250cc firearrow it should be basically the same lower end as the old 350 bullet and the transmission is mounted on the rear of the engine in a similar manner.
I'm not sure where I got the idea that the bearing rollers were running directly on the crankshaft but according to what I've read, the bearings have a hardened inner race which is pressed onto the crankshaft.  Of course, I could be wrong about this.

If the bearings have inner races that are just pressed onto the crankshaft journals, you could have the one(s) that are undersize plated to bring it up to spec.

The processes I'm familiar with are called "electroless nickle plate" and "thin dense chrome plateing".

Both of these plating processes can be applied so they will only increase the steel or iron journal a  tenth of a thousandth of an inch or two in the area that is undersize.
Because it is a slow process where the plating fluid is applied directly to the metal with a soaked wand or stylus, there is no machining involved or required.  (Actually, these plating processes can add up to .0005 per surface without a problem).

The difficult part is finding a plating company who can do the process and will work for someone who does not work for a large company that will give them a production order.

If you are beyond this level in your rebuild, don't worry about it.
As long as the bearings inner race is a press fit on the crankshaft journals you have no problem.

If one of the bearings inner races is a slip fit, not requireing a press to install it you can clean the surfaces of all oils or preservatives and apply locking compound specially made for this type of application.  If you can't find any of this, good old Blue Loc-Tite will work.

Sorry I dropped off the face of the earth for almost a month.  Things have been crazy here.  The transmission is mounted at the rear of the motor.  And I do know there is an outer race that is pressed into each of the case halves, but I don't think there is an inner race pressed onto the crankshaft.  Here is a parts blowup of a 1956 look on page 7 of the pdf or 11 of the manual:
 http://www.klassiekrijden.nu/techniek/re-1956-clipper-sparepartslist.pdf

I believe it's virtually the same engine and it doesn't appear to be any kind of inner race except for the crankshaft itself, which is what it looks like to me when I look at mine.