[aeron]

Ok, I copied and pasted some of this from the new member introduction thread. I just figured I shouldn't plug up that department with all the work I'm planning to do on this bike.

This is my first dive into the inner workings of a 2 wheeled motorized vehicle. 4 wheels, boats....all very familiar to me. These machines? Well, other than riding them and doing basic maintenance, I have hardly turned a wrench on 'em.
So, here it goes! A new adventure begins...

A 1979 CM400T caught my attention. It was also nearby, which is a challenge since I live in the nether reaches of rural Idaho.
Upon inspection and a quick ride, I paid the man the money, loaded it on the trailer and brought it home. Haven't ridden it since because my driveway is still frozen over with ice and snow.
During my inspection I noted that the valve cover gasket had a small leak, as does the Upper head gasket (below the valves, above the pistons). Gaskets have been ordered and should be here this week along with a clymer manual.
I also noted the petcock on the fuel tank leaks a bit when in the off or reserve position.
Other than these things, the bike is in pretty great shape.
Hopefully I can learn a lot from the forum, and I can also return the favor at some point.
Now, time to go get my hands dirty and relish in the smell of petrol products!

 

[aeron]

Here is my official "to do list."
Bike runs pretty good, but there is a bit of oil where oil shouldn't be, and a bit of gasoline where gasoline shouldn't be.

1. Replace the valve cover gasket.
2. Replace the Head gasket (just the upper one, not the one between the cylinder head and the crank case. That one is dry, so I'm gonna leave it be).
2a...inspect and freshen up the valves if necessary. Also depends on the ratio of "need" to "pain in the rump" to do the job.
3. Replace or rebuild the fuel petcock. It leaks in the off position and the reserve position.
4. Upgrade the headlight to something brighter than a jack-o-lantern candle.
5. Maybe freshen up the tank and the side covers with some new paint.
6. Ride it until something else comes up!

 

[aeron]

Day One!
Drained the oil.
Removed the Valve cover.
Removed the exhaust. I hate exhaust. Those stupid little flanges at the bottom are NOT my friend! But it's done.
Ordered a Clymers manual from Amazon. Should be here by the end of the week. Downloaded the Shop Manual from here earlier last week, but I like to have paper in the shop to write on and make notes and get all greasy and grimey.
Ordered a gasket kit from partsgiant.com. Price was right and free shipping. That CMNSL, or whatever it is, charges more for the shipping than the whole lousey gasket kit!
After reading a zillion posts here I settled on an athena gasket kit. This way I have the gaskets I NEED, and a few extras for when other things need some sealing up.
Have not ordered a new petcock. Not sure what one to order yet. Didn't order a new petcock repair kit either, since there seems to be two different types. I will deal with this in the next couple of days. I did drain the fuel tank though.

Oh, I forgot that I had to install a new battery when I brought her home. Up to that point it was only kick started. Since the new battery was installed I was able to start her up with no problems.

There was a slightly elevated amount of exhaust 'smoke' coming out of the left exhaust pipe before I started to break it all down. I suppose looking at the valves when I pull the head will be in order. It wasn't much, but it is something I noticed. Could I live with it? Probably. Should I? Who know's right now.

Pics are of today's accomplishments...
Alright, that's it for tonight. Time to go pull the elk roast off of the smoker and have some dinner!

 

[DD23]

Hi aeron,

If she is still a runner, perform a compression check.

Don't forget about the oil filter "washer" usually stuck to the bottom of the filter. Much glitter or black bits in the engine oil ?

Maybe oil leak is due to improperly fitted cam cover seal. I like to glue them to the cam cover.

It's good you know of CMSNL.com for the exploded views.

Problematic head bolts, sometimes they are a nightmare !
As you have noticed, the inner head bolts are "naked" and exposed to all the outside world throws at them. Have come across quite a few that have " corroded" themselves in place, even some that have burst Thier holes with have the threaded hole sitting on the sump floor !

You have not come across some you tube videos yet showing these bolts well and truelly stuck needing Oxy acetylene heat to remove them. Some outboard motor bolts ( Volvo penta achemiedies anchor ) suffer same fate.

Continue your research until your manual arrives...

Yeah, exhausts, but at least those header nuts have come off ok.

Enjoy

Ps, take your oil filter bolt ( or measure ) to a fastener supplier to get a flywheel puller ( pusher really ) bolt. Also research the clutch nut peg socket, there is a how to make one on here...

Exhaust smoke, is it blue ish, slightly 2 stroke like ?

Do a compression check before strip down...

 

[aeron]

Oil looks good. No sparkles, no chunks. Got the oil filter o ring, but thanks for the reminder. The bike was well maintained and never ridden particularly hard. The guy sold it because he is 85 years old and doesnt feel safe to ride anymore. He also has a nice shop where he works on his classic corvettes, so i have a good feeling he is being straight about the bikes history. Ill probably do the compression check this evening. I dont expect any problems as she was running pretty strong. Hopefully my expectations are not un met, but only one way to find out. Exhaust smoke was difficult to determine color. It was VERY faint. Really only noticeable if looking for it. Hopefully the compression check and plugs will give me some clues. Thanks for the heads up about the head bolts! I will keep my fingers crossed on that one. Alright, back to my paying job for now.

 

[Rockatanski]

Before you order a new petcock or petcock kit, just disassemble the one you have and check the rubber. You may just need to replace a 50 cent 'o' ring. A local store sells 'o' rings and I just match them up. Fuel petcock repair kits are a last resort for me for they overcharge you for crap you need and contain crap you don't.

 

[DD23]

Oil filter o ring ?

The rubber o ring in the oil looks like the sealing o ring that fits in a groove in the oil filter bolt.

See CMSNL view of oil filter, spring and thin steel washer...

Hope oil leak is just a badly fitted cam cover seal ring...

You know of balance shaft "dot" and its relevance ?

Compression check results and pictures of spark plug electrodes ?

If I remember correctly the fuel tap is rivetted and the seal is more washer like ?

I would go for a similar new tap with a sediment trap. A small fridge magnet magnet would fit in the sediment trap...

 

[aeron]

Oil filter o ring ?

The rubber o ring in the oil looks like the sealing o ring that fits in a groove in the oil filter bolt.

See CMSNL view of oil filter, spring and thin steel washer...

Hope oil leak is just a badly fitted cam cover seal ring...

You know of balance shaft "dot" and its relevance ?

Compression check results and pictures of spark plug electrodes ?

If I remember correctly the fuel tap is rivetted and the seal is more washer like ?

I would go for a similar new tap with a sediment trap. A small fridge magnet magnet would fit in the sediment trap...

Compression check will be done tomorrow...stupid job (that pays for all of this stuff) is getting in the way of my time in the shop!
I will certainly report back with the results and the the pictures of the plugs.
"balance shaft dot?" ....ummmm... no. Have not come across that yet.
I will also get back to you about the oil filter o-ring in the pan. The one on the bolt is still on the bolt...the one in the pan may be from another project. I will report back tomorrow night on that!

 

[aeron]

Pulled the plugs and took pictures. Not too bad...a bit wet. Hopefully its a valve issue, not a piston ring issue. Couldn't do a compression check because my compression gauge has too big of a fitting for the spark plug hole. I will pick up an adapter tomorrow at NAPA.
Pulled the fuel tap. Riveted. Time to shop for a new replacement, or drill out the rivets. Probably prefer to find a replacement.
I have three days off this weekend, hopefully between St Patricks day celebrations and other shenanigans I will get the compression done, order a tap, and replace those gaskets on the head.
btw, the bike has 17,000 miles on the odometer.

 

[aeron]

Compression results are in! Took a while since I did not have an adapter for the 12mm sparkplug threads.
Both cylinders are reading very close to each other at around 140 psi. Added oil and they only jumped a bit to 145 psi. The specs are 185 +/- 14 psi for this bike. The results are a bit low, but I have not adjusted for the altitude or the hose length(doubt the guage is accurate enough to worry about hose length though). I am at about 3500' so the results would seem to be pretty decent for an old bike. Not really feeling like it would warrant a full tear down to the cylinders right now.
Gaskets also came in the mail yesterday, so I will probably start taking the top of that motor off this afternoon or tomorrow. Probably check the valve clearances first. Then look at the valve seats and seals once I have it apart.
Still need to find and order a new fuel petcock/valve...An easy fix I would like to get out of the way.

 

[mike in idaho]

Likely, it will run just fine at 140 psi, no sense tearing up a good engine in search of that mythical 185psi compression figure that some people bandy about. In the real world, dynamic piston ring seal (Inside a running engine) is what really matters. Unless there is evidence of excessive amount of blowby out the breather pipe or oil smoke out the exhaust, ring seal is as good as it's going to get.

 

[aeron]

Likely, it will run just fine at 140 psi, no sense tearing up a good engine in search of that mythical 185psi compression figure that some people bandy about. In the real world, dynamic piston ring seal (Inside a running engine) is what really matters. Unless there is evidence of excessive amount of blowby out the breather pipe or oil smoke out the exhaust, ring seal is as good as it's going to get.

I agree about the compression. It was running just fine before I began the tear down. I like to walk that fine line between "not fixing what isn't broke" and "may as well do it while its all opened up."
Since the whole purpose of the upper end tear down is to just replace some mildly leaking oil gaskets, I see no reason to go deeper into the engine at this time.
Soooooo...Today I will begin to remove the cylinder head! I am looking forward to seeing what sort of condition the valves and such are in. Hopefully it will all look good.

By the way Mike, what part of Idaho are you from?

 

[aeron]

Teardown complete! Now I just have to clean it all up a bit.
One odd thing that I ran into was one of the inner head bolts would not slide out of the cylinder head very easily. It turns out, after I finally wrestled it out of there that the threads are covered in a baked on crusty carbon-oil gunk. All of the other bolts were clean. Has anyone else run into this? Any ideas as to why this ONE bolt was so gunked up?

Carbs removed

Left cover removed. Sprocket looks like its in good working order.

Head bolts all loosened up in the correct sequence.

A picture of the Gunked up bolt. All the others seem alright.

Gotta keep everything in order and organized.

Rockers ready to come off.

Rockers off, cam looks like its in good order.

Sprocket and cam removed, chain wired up to keep it from falling into the crankcase. Doesn't look like too much elbow grease will be needed to clean this side of the cylinder head.

 

[aeron]

The rest of the pics from the teardown this afternoon.

The head popped off nicely with one good whack of a rubber mallet. Some dumb&^# forgot to remove the engine mount bracket on the rear of the head though, and that NEEDS to be off in order to get the clearance needed to remove it from under the frame.
Once the head was removed it was pretty clear that the gasket was likely the main culprit making all of the mess here.

Fairly happy with the condition of the cylinders. The left one had a bit more oil left in it from the compression test yesterday. Cleanup doesn't look too bad.

This looks like where the elbow grease will be applied to clean things up a bit before re-assembly.

That right exhaust valve looks a bit more gunked up with carbon.

A close up look at the pistons again.

May start the cleaning and scraping and such later this afternoon. Any suggestions for making the job a bit easier and less messy? I am thinking of soaking the head in a bucket of degreaser or something to loosen some of that carbon build up on the valves.
The head gasket popped off fairly easily. There isn't too much to clean off of that at least.

 

[aeron]

Overall the breakdown was fairly smooth using the clymer book that finally arrived. Great pictures in it, great step by step instructions. That, combined with the dozens of other project posts here, made the process fairly painless. The hardest part was not allowing that chain to fall into the crankcase while removing the head. Could probably have used another set of hands. May have to enlist my wife's help with that during the re-assembly.

How many of you install the gaskets dry vs. using glue?