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Admitting the problem is the first step to solving it. Make sure the plugs are good, the wires are good, and the points are good (though if they fire one side, they should fire the other if this is a 360 degree crank.) Make sure you have fresh fuel and fuel filter(s). Make sure you have fuel going to both cylinders. Is one plug fouled with fuel or oil? Valve adjustment was mentioned. Look up as much info as possible on the bike. Most repair manuals will have some theory and troubleshooting info. Find one (your library is a good start, and maybe someone can point out an online site.)
 

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OK,
Lets think about this logically. The symptoms are:
1. Weak performance
2. The right exhaust is not as warm as the left
3. There is oil in the right header pipe.

What problem can account for all of those symptoms?
Tight valves won't cause the oil in the pipe.
Ignition problems won't cause the oil in the pipe.
Carb issues won't cause oil in the pipe.
Leaking valve guide seals might cause some oil in the pipe but usually that oil will be partially burned, not pooled.

Stuck or broken rings will account for all the symptoms and will be confirmed by a compression and/or leak down test.

There is no need to confuse Spacemanspiff with other issues that can't be the cause of the issue. It is a simple diagnosis problem that can only be confused by becoming parts changers and using the hotgun approach to it.

Ken
 

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Guess I should have read more thouroughly. Yes, get stuff together for a rebuild. Learn by doing. That is how I did it back in 93 with my old CL175. Either that or buy another motor.
 

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quote:Originally posted by kenessex

OK,
Lets think about this logically. The symptoms are:
1. Weak performance
2. The right exhaust is not as warm as the left
3. There is oil in the right header pipe.

What problem can account for all of those symptoms?
Tight valves won't cause the oil in the pipe.
Ignition problems won't cause the oil in the pipe.
Carb issues won't cause oil in the pipe.
Leaking valve guide seals might cause some oil in the pipe but usually that oil will be partially burned, not pooled.

Stuck or broken rings will account for all the symptoms and will be confirmed by a compression and/or leak down test.

There is no need to confuse Spacemanspiff with other issues that can't be the cause of the issue. It is a simple diagnosis problem that can only be confused by becoming parts changers and using the hotgun approach to it.

Ken

For what its worth, I agree completely. Proper, logical diagnosis is the most important skill any of us can learn.

This begins with one simple paradigm:

1. Eliminate the cheapest (or free) options first.

Before you do anything, check the plugs. They can tell you a hell of a lot. Then, perform a basic tune up. Clean the plugs, adjust the timing, check the filters, charge the battery, adjust the valves, check wires and connections and beg or borrow a compression tester.

Money spent so far = damn near zero.

The weak cylinder could be caused by something as simple as a fouled plug or as shitty as a huffed piston/ring. Logic (and as Ken said, oil in your pipe) says its both.
 

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I think for what it would cost to rebuild it and any machine work needed. Just find another engine. These CM400 and CM450 engines are pretty cheap. They vary between 100-200 from what I've seen. There's one by me for 125 picked up I was thinking of picking so I could keep one bike running.
 

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Pinche,
You don't learn anything by swapping engines except to be a parts changer. Tear it down and find out what is wrong. It could be as simple as a hone and new rings if they are stuck. Rings and a gasket set are not that expensive and the experience is worth it. Anybody that is going to live with old bikes better be able to work on them all the way to an engine rebuild or find a newer bike. Parts changers need not apply.

Ken
 

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True...true Ken. I guess it just comes down to how much he wants to spend. So say if it's a ring that's bad. He'll need new rings, hone out the cylinder(hone tool, head gasket, torque wrench(if he doesn't have one) manual to know how much to torque the head bolts down to, yada yada. Yeah it's cheap if you have the tools. Not to mention if the cylinder can just be honed or if it needs to be bored or and fitted with an oversized piston/s if it's spitting out that much oil and leaving a puddle. Now if he doesn't have a hone tool, ring compressor, torque wrench, manual, etc. Compared to at the most 200 for another engine to get his bike on the road. I guess it just determines if this is something he see sticking with for awhile...as in a hobby or buying the tools just to use once for an engine that cost just a few bucks more and he could be on the road. Know what I mean?
 

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I started tearing down my 350 motor, until I found a (mostly) complete running cb350 for $85, including carbs, which I also needed. I still have the engine I started tearing down, and will probably finish that job at some point, however, how can you really beat $85 to get the damn thing on the road?

I also bought another complete running motor & a whole bunch of other shit I needed for a project for about $120.

I have (successfully, and otherwise) done diagnostic work on other bikes, and also done some fairly complex repair jobs (I know the top end of my '72 Bonneville more intimately than I know my own wife), and I appreciate the need one has for that kind of knowledge when one owns old bikes... However, sometimes it just makes more sense to change the offending part.
 

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By the way, the bike in question (in my case) is one I have assembled from parts, And therefore didn't have a motor to diagnose in the first place, and even though I did get it running using a motor I bought as a "complete running engine", which it was, I haven't gotten it running well enough to know what shape the motor truly is in, and I still expect to have some diagnostic work and fine tuning to do.


Fuck me, that's one hell of a run-on sentence.
 

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Discussion Starter #72
thanks everyone, especially ken. if it is the rings, i need to:

1. tear down topend
2. replace/service rings on both cylinders.
3. potentially replace both pistons.
4. potentially hone both jugs.

anything im missing here? i want to know what i might be in for before i get started, and i want to price all the parts i will need. dont worry, i will do a compression test before i buy new pistons :). just need to buy a tester. i think checker sells one for $25, and another with a longer, steel braided cable for $40.

thanks.

Jarrett
 

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Jarrett,
You really won't know until you take it apart. It could be as simple as a stuck oil control ring, in which case you could get away with honing the cylinders and replacing the rings and a head and base gasket.It could be as major as broken rings and a scored cylinder, which would require 2 pistons and rings and bored cylinders along with gaskets. I would go ahead and do the compression test before you tear it down, but I am pretty sure that motor is going to come out and get torn down.

Remember, tearing it down is free. After it is apart, you may want to consider finding a replacement motor, but a 25 year old motor may need work too.

Ken
 

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While you have it apart it would not hurt to clean and relap the valves. I think they may be stellite-faced if they are like other Hodas of the era, so no cutting or grinding. You can rent the valve spring tool from an auto parts store, and the valve lapping compound is so cheap there is no reason not to. Then port the head, mill it, got a big bore kit...
 

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I'm looking at a CM400E. Do you know the difference between the E and the T?

I really like how yours looks so far! Nice work.
 

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Pinche,
sarcasm.
 

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My middle name is gullible. As for the models I believe the E is like the base model with wire wheels and drum brakes front and rear while the T has the five spoke "comstar" mag wheels that uses a disk up front and still a drum in the rear. It also has a tach while the "E" model doesn't.
 

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Discussion Starter #79
So, finally caught up with all the free-lance ive been doing at home. ugh...but the debt commands me to work extra hours!

anyway, did a compression test. left: 150psi, right: 140psi. not bad. manual spec is 171-199, but i dont know if it EVER made that

onto the valve seal test. the wells for each cylinder's intake valves are sealed off from the rest of the little compartments in the head. i fill the well in question with some 10w30 and in a few minutes it is empty again. so, im thinking i have my problem solved. valve seal, right?

i might as well replace all 6, and maybe a valve job. definitely gonna hold off on pulling the jugs, considering the compression is ok.

a little help on where to get parts would be appreciated, or if you think my diagnosis to be wrong, let me know!

i can get 6 seals from bike bandit for about $60
or an entire engine gasket set from oldbikebarn for about $80

anybody else?

Jarrett
 

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Jarrett,
You have to pull the head in order to replace the valve guide seals, so you might as well get the complete gasket set for the head gasket and the exhaust gaskets. You might as well pull the cylinders then too since it will be all unbolted. I am surprised that leaking valve guide seals would put that much oil into a cylinder and exhaust pipe. How does it run if you run it for a while and then put a brand new set of spark plugs in it when the engine is warmed up? I wonder if you have an oil fouled spark plug in the right side?
But, since you are going to have it apart, I would inspect the pistons and rings, hone the cylinders, lap the valves and replace the gaskets.

Ken
 
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