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This is my first thread on the forum and I'm hoping for some advice. I recently was given a '78 CB400T II that is in need of some TLC. I had a Honda Ascot VT500 which was an awesome little bike, and sold it, and have been regretting the decision ever since. I'd love to get on this 400 and be back on two wheels, but it needs to run well first, and I think it's going to take a little more than cleaning the carbs.

The main problems:
- Runs consistently on only one (right) cylinder
- Blue smoke from exhaust
- Leaking a lot of oil, from almost every engine gasket, so far as I can tell.

My work so far:
- Fresh gas, oil, oil filter, fuel lines, battery
- Compression test: 150psi for each cylinder
- Checked for spark: both plugs fire, looks weaker on left cylinder
- Cleaned carbs but not thoroughly enough, probably (I will return with monofilament to "floss" the jets and everything)

Other weird stuff I can't explain
- Air box had about a cup of gas sitting in the bottom of it, probably from the crankcase breather.
- Left plug is getting fouled by gas or oil or both.
- A medium sized, possibly brass washer was sitting in the bottom and front of the right crankcase, near a vertical chain that might drive the oil pump? The washer had a tool mark near the center of it as if somebody put a flathead screwdriver across it and struck it with a hammer. Otherwise it's bent slightly but not really chewed up.

The bike only has 9,000 miles on it, but since it's a '78, that might be more bad news than good news if it sat around for a really long time. The blue smoke, possibly oil burning, is what concerns me most. It does not smoke when I start it, but five or ten seconds later it does start to smoke and does not stop when the engine is hot. Maybe the rings are frozen? Valve guides? I had the right exhaust pipe off and the valve did look a little oily, but I don't know what exhaust valves are supposed to look like. Also I don't know how to troubleshoot the one cylinder that is not firing. The pipe on that side gets hot enough that you can't keep your hand there, but not nearly as hot as the other side.

Thank you for your help! I like a good project, but I like a running motorcycle even more. With wrench in hand, I thought I'd ask what I might try to do next. This is an awesome forum. Thanks!

JL
 

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Discussion Starter #2
One mystery solved: I was checking the service manual for maintenance on the oil pump, and it says to use a copper washer to prevent the pump gear from turning while removing the bolt on the gearshaft. Apparently somebody was working on the oil pump and never took it out, so it ended up in the bottom of the crankcase...
 

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I have a Honda 400N Superdream, the same year as yours ... mine is the later 400N Euro styling, I love that old bike and it runs beautifully .. they do go well when running right.

Sorry to hear you are having these issues, the blue smoke can be anything from worn rings/pistons/bores to stuck rings or hardened and worn valve seals ... you say also the gaskets are leaking so at this stage you need to buy a complete top end gasket set and strip down and examine the top end, remove the head, the cylinders and pistons for cleaning and examination ... then if alright put it back together with all new gaskets and seals.

My 400N had a leaky cylinder base gasket when I got her many years ago and I just stripped down and rebuilt the top end with new gaskets, after that she was perfect and never missed a beat :)


Good luck with it all and keep us informed :)


Jules
 

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Thanks Jules, that actually was another question I had: Can you cut your own gaskets for top end stuff? I used a sheet of gasket material, along with an exacto knife and some patience, to cut my own float bowl and crank case gaskets and have had no trouble so far. I was hoping to do that for as many other gaskets as possible. Will that work for the top end despite engine pressures and heat?
 

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I would say cutting your own gaskets for low pressure areas like covers and carbs etc is probably fine but definitely not for the Cylinder head gasket ... if you look it's a much thicker, higher temperature resistant material with steel inserts around the cylinder cutouts and some other areas ... I think the base gasket had reinforced areas too ... for the top end I would go with a quality top end gasket set or face having to redo it all again when it blows or worse ruins the engine...

Good luck!!

Jules :)
 
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