Cam Bearing Journals

[genejohnson]

I ran this through another forum and got no response! I have a spare, partially apart 1986 Rebel 250 engine. The two inboard cam journals look to be beveled. The bearing surfaces in the head and rocker assy doesn't look like it could have worn the journals to this shape. I can see that the two end journals are supported by slipover bearings pinned in place by the rocker assy but I am at a loss to understand what I am seeing unless there are parts missing that shroud the inboard journals incorporating the bevels in the process! I don't have a manual yet so I need someone to enlighten me. I am sure some of you have had the top end apart before. Does anyone have any idea what I am looking at? Thanks, Gene

[GearJammer]

http://houseofmotorcycles.bikebandit.com/parts/Honda/CMX250C+REBEL+/1986/209028

http://houseofmotorcycles.bikebandit.com/parts/Honda/CMX250C+REBEL+/1986/209296

I'd never torn down the top-end on either Reb, but am wondering if these diagrams offer any insight ?

For future reference, you can just go to www.bikebandit.com, click on OEM Parts, click on Honda, click on 1986, click on CMX250C and you'll see the list of various schematics......

[genejohnson]

Yeah GJ, I looked at those diagrams before but they don't show enough to answer my questions. They appear to be beveled but I just don't get it. Thanks for the reply. Gene

[GearJammer]

Did a search on www.google.com for "beveled camshaft motorcycle" and got some hits, but kinda skimmed thru the scant info. One page that covered older Nortons mentioned OHC with "bevel-driven camshaft". Not sure if this helps explain anything or not............had a rough evening here, but next thing I'd Google would be "bevel-driven camshaft" & see if you can get more detailed info ? At least from what I was able to concentrate on, it seems that the bevels are the correct design. Just exactly how they work, I dunno..........yet ;)

[genejohnson]

GJ, these journals support the shaft and don't drive it. The camshaft has four supporting journals. One on each end, encased in bearings and two other inner journals along the spanse of the shaft. These inner journals are what I am concerned with. Gene

[GearJammer]

Gene.....in the second diagram link in my first response, there's the "camshaft holders".....Would these have anything to do with what you're seeing there ?

[genejohnson]

Yes, in a way they do! But my problem is trying to understand how it holds down the inner cam journals because they are beveled. Gene

[ole Ed]

Gene I think what you are looking at are not actual bearing surfaces. Yes they do make some contact with the journals but only in times of extreme camshaft flex. And as for the beveled edges, they are for side to side movement of the camshaft and for splash oiling and oil runoff. I have never torn a 250 engine down but I will bet there are no oil passages in these areas. The beveled edges allow for oil from valve train to splash up to these surfaces and then run off again. The 2 true bearing surfaces on each end of the camshaft are the support bearings and oil passages where the oil is pumped up through to oil the valve train.
However, I must add that I am by no means an expert but simply a small engine mechanic experienced in Briggs and Stratton, Tecumseh, Honda, Kohler and other small engine makers. Haveing never torn one of these engines down I am only making an educated GUESS here.
Hope some of this was helpful.

[genejohnson]

Thanks Ole Ed, I think you are the only person that knew what I was talking about. What you say makes a lot of sense now. I couldn't seem to get anyone centered on my concern. Maybe it was the way I was trying to describe "The Beveled Journal" that no one could understand. Thanks again, Gene

[GearJammer]

Right on, ole Ed! ;)......Checked out the 450 Reb manual & it says that upon reassembly, to "fill in the pockets in the head with engine oil until the cam lobes are submerged in oil".....(confirming your input on oil splash).