Cam bearings

[mattcfish]

I just got a hold of a used 336 cam on eBay. The front cam bearing has way to much longitudinal (front to back) play. I need to replace the bearing.
I have 3 other 308 cams with good bearings on them. I noticed , however, that the 336 and 2 of the 308's have aluminum front bearing carriers, while one from a 77 or 78 bike has a cast iron bearing. This one has the tightest fit and has the least (if any) amount of ware. Are these cast iron ones superior? ....or is the softer aluminum one preferable because it wares out before the cam does?

Also, the 336 has some signs of ware on the rear bearing surface (I can just feel it with my finger nail) . If it wasn't a 336 I would get a different cam, but in this case I'm hoping I can polish this out without decreasing the diameter beyond tolerances. Can/should this be done?

[Max Headroom]

I just got a hold of a used 336 cam on eBay. The front cam bearing has way to much longitudinal (front to back) play. I need to replace the bearing.

If the excessive clearance is longitudinal, then correcting it is simply a matter of pressing the cam sprocket on a bit more. End clearance should be between 0.002" - 0.004" from memory.

I have 3 other 308 cams with good bearings on them. I noticed , however, that the 336 and 2 of the 308's have aluminum front bearing carriers, while one from a 77 or 78 bike has a cast iron bearing. This one has the tightest fit and has the least (if any) amount of ware. Are these cast iron ones superior? ....or is the softer aluminum one preferable because it wares out before the cam does?

The cast iron cam bearing comes with a bronze bush, and is superior to an alloy cam bearing. It can maintain a tighter clearance when hot because cast iron is thermally more stable. BMW said at the time that it was done to keep the cam timing (and indirectly the ignition timing) more consistent. I deliberately chose to use one when I rebuilt the engine in my bike.

Also, the 336 has some signs of ware on the rear bearing surface (I can just feel it with my finger nail) . If it wasn't a 336 I would get a different cam, but in this case I'm hoping I can polish this out without decreasing the diameter beyond tolerances. Can/should this be done?

Unless the grooves are really bad, the cam should still be quite serviceable if you can "just" feel the ridges, 'specially if you can clean the journal up with some emery tape.

[mattcfish]

If the excessive clearance is longitudinal, then correcting it is simply a matter of pressing the cam sprocket on a bit more. End clearance should be between 0.002" - 0.004" from memory.

I need to remove the single row sprocket and replace it with a double anyway. I'm using a bean can cam on a1975 bike.
I plan to seal the hole for the points/advance nose and run my crank mounted ignition alone.

The cast iron cam bearing comes with a bronze bush, and is superior to an alloy cam bearing. It can maintain a tighter clearance when hot because cast iron is thermally more stable. BMW said at the time that it was done to keep the cam timing (and indirectly the ignition timing) more consistent. I deliberately chose to use one when I rebuilt the engine in my bike.

Thanks for the information on that. Strange how older cams and newer cams use the aluminum carrier. Was the cast iron only on a few years or is it only used on rebuilds?

Unless the grooves are really bad, the cam should still be quite serviceable if you can "just" feel the ridges, 'specially if you can clean the journal up with some emery tape.

That sounds good. I'll check with a dial indicator to make sure.

[kreece]

Motoren-Isreal offers a phosphor bronze cam bearing that is very nice. Worth a look.

http://www.motoren-israel.com/products/ ... echse.html

Ken

[Max Headroom]

Motoren-Isreal offers a phosphor bronze cam bearing that is very nice. Worth a look.

http://www.motoren-israel.com/products/ ... echse.html

Ken

Very nice find . . . and welcome to BW!

[mattcfish]

Motoren-Isreal offers a phosphor bronze cam bearing that is very nice. Worth a look.

http://www.motoren-israel.com/products/ ... echse.html

Ken

Very nice find . . . and welcome to BW!

Thanks, I love looking at the MI stuff, but I have yet to find something I can afford.
That looks just like the cast iron bearing I have. It's in excellent shape, so I'll use it.