I'm hoping someone out there can help me figure out why my 120R has been eating cam plates since it was new. The rotors on the oil pump eat into the cam plate in a half moon shape. (See photo.) We first discovered the problem when the motor had about 1200 miles on it. We took it apart for some cam work, and found the unusual wear.
The dealer investigated things and put the second cam plate in for me. At the same time we thought maybe the crank was the culprit so we had the crank trued, welded, plugged, and a Timken conversion done at Darkhorse. After the motor went back together the dealer put another 11 miles on it, re-checked it and found it had bad wear on the second cam plate.
They tore it back down, and investigated some more but still couldn't find anything wrong, so they put the third cam plate in it. By the time I got the bike back it was just before Memorial Day Weekend. The dealer didn't think it was fixed, but they said it's summer time, get out and ride, and we'll see what happens. We have been riding it all summer and by the time we got back from Sturgis (about 8,000 miles on this cam plate), the motor was still running strong, but had very low oil pressure and ran VERY hot! The dealer took it apart and found the cam plate and oil pump were both worn out. (Not really a surprise.)
They have re-checked the crank runout and it is showing about .0018". While it is not perfect, it's still not bad runout, and Darkhorse agreed that it's still within acceptable limits and shouldn't be causing these kinds of problems.
I'm on my fourth cam plate now. The dealership is stumped, so along the way they called Tech Services for a little help. Tech Services agreed that it definitely sounded like there is something wrong with this motor, but since it's a 120R they had to refer it to the Screamin' Eagle group. After a couple of weeks the answer came back from Screamin' Eagle: It's a high torque motor, the crankshaft could flex and cause the oil pump rotors to eat into the cam plate. It's "normal" for one of these motors.
Not the kind of help we had hoped for. The mechanic who is doing the work has been doing this stuff for over 20 years, and has previously built a very reliable motor for my 2007 SERK. It went through 3 crankshafts and numerous oil leaks while under the factory warranty. After the warranty expired we had Darkhorse do the crank and Timken work, and the motor has run strong and reliably (knock on wood!) ever since.
I'm hoping someone out there has either seen this kind of problem before and knows what might be causing it, or maybe someone can tell me what we can check to figure out what is causing this problem. So far, the dealer has stood behind the motor in spite of the MOCO's unwillingness to back them up, but I don't think they can continue much longer. The time has come to either figure out the problem and fix this motor or replace it.
Thanks in advance for any help you all can provide!