So I bought a supposedly serviceable crank off Ebay
Posted: August 6th, 2008, 8:33 am
And when I measured thrustwasher-counterbalance clearance, I found that it measured .043". The service limit is .040". I also noticed that the drive sprocket collar had a sizeable groove in it, indicating that the crank has more hours on it than advertised, which will doubtlessly cause spooge issues. I wrote to the seller, a 'Dr. Ilja Hermann', and he responded by saying:
Hello JT,
Thank you for the message. I am sorry for the delay in response - I have
been on a short hike with family since Friday.
About the crank:
All critical dimensions were indeed inspected myself before listing
(metrology is my background, earning my living with in R&D for a major
test equipment manuf. in the silicon valley), and privately I keep
service protocol for every riding hour with my bikes (Rode/raced/passion
built my CR 500's from scratch for 18+ yrs). By experience I know that
there is always room for subjective interpretation wether a part needs to
be reworked (if possible) and/or replaced. However, I am also well aware
of handbook clearances, but after working with brand new cranks and
rebuilding used CR 500 cranks myself, I know that the mentioned clearance
is hard to judge objectively as long as you do not characterize the wear
of the axial bearing thrust washer itself + overall counter balance
width. Just to give you an example for a used, never serviced crank - the
latter can vary by up to +- 30 microns around the nominal width 68.00 mm,
so that a clearance can be easily <0.04 (0.038 in particular case) in
even for a crank with obviously worn thrust washer (radially varying
thickness). I would clearly indicate this with immediate service need
(rod replacement) as the axial bearing lubrication would not work anymore
reliably and the entire crank would fail soon. This was not the case for
your crank, and if otherwise, I would have replaced it (still would if I
should have sent you not the one on the picture by mistake). Regarding
the collar I would like to say that the probability of leaking is zero
with new seals as long you have uniform circumferential wear trace as the
loss in normal pressure is caused mainly by wear of the gasket lip and
not the metal counter part. Usually, those collars last 2-3 lower engine
rebuilds with 120+ hours of total use, and though inexpensive (new
roughly $10), you still can have a used one performing like new if your
wear track is not too wide (<0.06in), so that you may install the seal
slightly off the original position not compromizing function and
performance at all. I also could send you another one, though I think you
won't have any problems with this one as well as the crank itself. Please
let me know what you think though. Thanks again.
While the seller (who I am not bad mouthing) had a lot to say about why the crank he sold to me is actually serviceable, his claims seem contrary to real world experience documented on this site and 'that other site'.
Whatcha'll think?
Hello JT,
Thank you for the message. I am sorry for the delay in response - I have
been on a short hike with family since Friday.
About the crank:
All critical dimensions were indeed inspected myself before listing
(metrology is my background, earning my living with in R&D for a major
test equipment manuf. in the silicon valley), and privately I keep
service protocol for every riding hour with my bikes (Rode/raced/passion
built my CR 500's from scratch for 18+ yrs). By experience I know that
there is always room for subjective interpretation wether a part needs to
be reworked (if possible) and/or replaced. However, I am also well aware
of handbook clearances, but after working with brand new cranks and
rebuilding used CR 500 cranks myself, I know that the mentioned clearance
is hard to judge objectively as long as you do not characterize the wear
of the axial bearing thrust washer itself + overall counter balance
width. Just to give you an example for a used, never serviced crank - the
latter can vary by up to +- 30 microns around the nominal width 68.00 mm,
so that a clearance can be easily <0.04 (0.038 in particular case) in
even for a crank with obviously worn thrust washer (radially varying
thickness). I would clearly indicate this with immediate service need
(rod replacement) as the axial bearing lubrication would not work anymore
reliably and the entire crank would fail soon. This was not the case for
your crank, and if otherwise, I would have replaced it (still would if I
should have sent you not the one on the picture by mistake). Regarding
the collar I would like to say that the probability of leaking is zero
with new seals as long you have uniform circumferential wear trace as the
loss in normal pressure is caused mainly by wear of the gasket lip and
not the metal counter part. Usually, those collars last 2-3 lower engine
rebuilds with 120+ hours of total use, and though inexpensive (new
roughly $10), you still can have a used one performing like new if your
wear track is not too wide (<0.06in), so that you may install the seal
slightly off the original position not compromizing function and
performance at all. I also could send you another one, though I think you
won't have any problems with this one as well as the crank itself. Please
let me know what you think though. Thanks again.
While the seller (who I am not bad mouthing) had a lot to say about why the crank he sold to me is actually serviceable, his claims seem contrary to real world experience documented on this site and 'that other site'.
Whatcha'll think?
Gonna be needing alot of bearing and seals when I go thru my motor this winter!!!
