- Joined
- Jul 30, 2009
- Messages
- 191

I rebuilt my 74 850 recently. After covering about 200 miles the primary started making an odd noise. I decided to check the primary chain tension. I found the chain was very dry and there was almost no oil in the primary. I had managed to seal the primary very well, and I hadn't noticed any leakage at all. At first I thought maybe I had forgotten to put any oil in. Further reflection and I remembered putting the oil in. I put the oil in quite a while before the top end was back on the engine and I remember taking out the level plug filling the primary with ATF and then replacing the plug, with a new Dowty type seal. I remember being very pleased that the O ring was holding the oil in perfectly. I attributed the perfect seal to the coating of Ezyturn grease that I had used. Also I think if I had forgotten to fill the oil then the primary would have made some bad sounds sooner. After I re filled the oil the primary sounded fine again and I have covered about another 40 miles now. I never had to adjust the primary chain. I think I must have caught the problem just in time.
I am pretty sure that the problem is my new reed valve breather that I installed on the side of the engine. I think I bought this thing about 5 years ago from Grandpaul. I think it is working really well and I am getting a strong vacuum in the crankcase. I have gap less total seal rings, and after the rebuild I checked the leak down and it is insignificant. I think the primary oil is getting sucked into the engine. I had this same problem on my Vincent, to solve it I put the seal in the other way around (with the spring on the outside) Has anyone else had this problem with too much vacuum in the crankcase causing the primary oil to go into the engine? Some of the breathers with reed valve like the ones designed by Jim Comstock must cause that problem as well?
I am pretty sure that the problem is my new reed valve breather that I installed on the side of the engine. I think I bought this thing about 5 years ago from Grandpaul. I think it is working really well and I am getting a strong vacuum in the crankcase. I have gap less total seal rings, and after the rebuild I checked the leak down and it is insignificant. I think the primary oil is getting sucked into the engine. I had this same problem on my Vincent, to solve it I put the seal in the other way around (with the spring on the outside) Has anyone else had this problem with too much vacuum in the crankcase causing the primary oil to go into the engine? Some of the breathers with reed valve like the ones designed by Jim Comstock must cause that problem as well?