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Hello,

My 250 narrowcase has been in storage for the last 4 years.
I don't remember what kind of engine oil I used last time it ran.
I was wondering what is the best way to proceed.
Do I need to change the oil before trying to start it again?
Or do I need to do something more drastic (eg. dismantling)?
What type of modern oil is recommended?

Thanks
-Adriano

I'm worried about "dry spots" in the engine.
Is there a way to make sure the top end gets some lubrication before I try to start it? Do I need to pour some oil through the bevel gear cover?

Also, what oil is recommended for the NC singles?

Thanks

To lubricate the top end.

1) Remove spark plug.
2) Remove bevel cover on right hand side of cylinder head.
3) Kick engine over repeatedly until oil flows continuously from centre of camshaft on right side.

You could even take off the rocker covers and squirt some oil onto the camshaft and rockers as well as the above.

As for oil, I believe a 10/40 or 15/40 would be OK. Just make sure it's a pretty good one.

I use Bel Rey 20/50 semi-synthetic in my narrow case bikes. However, any 20/50 motorcycle oil will be fine. You can use car oil but it may make the clutch drag.
Check for spark.
If it's got spark and you've pumped some fresh oil through the motor, go ahead and see if it starts. As long as it runs OK, you're home free. If it doesn't run well, pull the carb apart, soak it in lacquer thinner (after removing all rubber items, etc. then blow it out with compressed air. Remove all jets and make sure they're clear, especially the pilot jet.
The clutch plates may be sticking after so long in storage, if the clutch won't release, push start the bike then ride it with the clutch pulled in while pressing down on the rear brake pedal, this will, eventually, free up the clutch plates.

Thanks for the tips.
I'm curious why is a 20-50W oil preferred over a 10-40W oil?

-Adriano

If it were a modern bike, with nice tight clearances everywhere, and a close-tolerance oil pump that pumped out plenty of oil at all rpm, and if it were a liquid-cooled engine with stable temperature control, etc., 10/40 might be okay. However, your Duc is fifty years old, oil pressure is controlled by a brass bushing that could be worn, a pump that is in who-knows-what condition, an engine with 50-year-old metalurgy, an air-cooled engine, etc.
Stick to 20/50 motorcycle oil. Narrow case big ends are fragile enough as it is. Also, change the oil every 1,500 miles or so.
Also, the big end bearings on early Duc singles don't like a lot of putt-putting around at low rpm. Too much of that and you risk blowing the big-end bearing before its time.