Motorcycle Repair: 1971 Honda CB250 Euro, cylinder head gasket, honda cb250

Question
I recently purchased a 1971 Honda CB250, which had been imported to the US by a soldier in Oregon (I live in Seattle).  The bike has a bit over 8000km (approx. 5500 miles).  I'm told the bike is similar to the CB350 that was produced for the US market, except that my bike has unique turn signals, fenders, etc. (not to mention kph instead of mph...which gets confusing).  

My question:  The bike has electric start, which works great (when the choke is on).  However, once I ride the bike for a while I see oil slowly coming out of top of the engine.  It's not a large amount of oil, but every day I check below the engine I see a small pool of clean oil sitting there.  Any idea what could be causing the leak?  Before I purchased the bike the oil was changed, carbs were cleaned/synched, new OEM pipes were added, plugs were changed, battery was replaced, rear wheel/tire replaced, etc.  Overall the bike is in great condition for being 34 years old, I just don't want to see my engine sieze if this problem is serious.  PLEASE HELP!

Thanks!  

Answer
Dustin, even with low miles, the seals and gaskets are 34 years old and subject to deterioration and failure. These bikes are directly related to the CB350s here in the US.

I am not clear about your description of "oil coming out of the top of the engine" however. Oil leaks are possible from the cylinder head gasket, the cam cover parting line, camshaft seal, tach drive seal, cylinder head sealing washers or oil breather tube.

If the oil breather tube is cracked or loose at the top back of the head, then it needs to be reattached firmly. It is normal for oil vapors to be present at the crankcase vent tube, but if it is a LOT then there are potential issues with ring sealing, perhaps. Check to be sure that the tube is not pinched further down and causing the joint/tube area to expand and weep oil.

You will have to remove the fuel tank to see more clearly where the oil is coming from and determine what the needed repair is from that point. If there is a big mess, then you will have to clean the whole area off, ride the bike and recheck it again.

Bill Silver