[PeterV]

I'm about to embark on a repair odyssey which, to many of you, would be a walk in the park on a sunny day with a beautiful girl and an obedient dog. For me, it's something else.
I'm a new rider and a total novice, mechanically speaking. Heck, I live in Oregon where we're not even allowed to pump our own gas! OK, I have changed oil and headlights and some spark plugs and stuff like that so I do know which end of the wrench is which. But I'm notorious for going up the ladder without the tool I need. Throw in a dose of male-pattern ADD and you have a recipe for a pile of CM400 parts for sale on Craigslist, cheap.

Not this time. This time will be different!

I bought this 1980 CM400E about a month ago for what was probably an extortionate amount of money.

It was apparent pretty quickly that it had problems in spite of the PO's assurances to the contrary. The head gasket appears to be leaking as evidenced by the oil on the engine. Plus, it sputters a lot and backfires under engine braking.

So the job is to pull the head and inspect everything. Fix or replace what needs fixing and replacing and put it all back together shiny and new. There’s a local shop that specializes in vintage Japanese bikes so I’m probably going to have them check out the cylinder and piston do any work that needs doing in that area.

I checked the compression and it's 145 left and 150 right. Per the manual, it should be 185 psi +/-14 psi. I've been riding gently to and from the coffee shop and not much more. The other day, it suffered a sudden and severe loss of power. Luckily, I was only blocks from home and I managed to chug the rest of the way.

I re-checked compression and it hadn’t changed. However, one plug was super oily. The other was dry and sooty black (more so than expected as I replaced them a couple weeks ago). Oddly, when I put the plugs back in and restarted, it had returned to its former glory (if anyone knows what that’s about, I’m all ears). I'm still not going to ride it until I have the work done, though.

I ordered my gasket kit from this site’s illustrious sponsor Speed Moto Co and that should arrive today. I read in another recent post that buying piston rings in advance wasn’t a good idea as I may end up needing oversized ones depending on what’s going on with the cylinder.

I’ve spent the last few weeks acquiring knowledge, supplies, and gumption. The best information seems to be in the factory service manual and right here on this site so thank you to all the questioners and answerers.

I’ll update this thread with my progress as I go (with pics aplenty). And please feel free to tell me if you see me doing something completely ridiculous.

Thanks for reading,
Pete

 

[Franchesco_94]

nice bike seems to be complete and in fairly nice shape, this might help for the spark plugs
Spark Plugs

 

[cdr]

Nice bike. How many miles are on the odometer and how long did the bike sit before you purchased it?

 

[J-T]

Bike looks great. I suspect you'll have it on the road without too much trouble.

 

[PeterV]

Nice bike. How many miles are on the odometer and how long did the bike sit before you purchased it?

It had 12,630 on the odometer. PO says he road it regularly in the spring and summer months so it was probably dormant through the winter. Starts like a champ and it wants to go! You can kind of tell.

 

[PeterV]

nice bike seems to be complete and in fairly nice shape, this might help for the spark plugs
Spark Plugs

Thanks for the link. That helps. I have a feeling I'm going to find worn piston rings on one side at least.

 

[longdistancerider]

Before tearing the engine down I would clean the engine really good and ride it for a 100+ miles and see if there actually is an oil leak. These engine can leak from the outer rear head bolts, the timing chain run area in the center or the valve cover gasket. That's the only place oil is present. If you spot what looks like a leak throw baby powder on it and run it for a bit. If there's a leak it'll turn into a gooey mess.
I would also adjust the valves and while in there re-torque the head bolts. Again ride it 100 or so miles and recheck the compression