81 xs400 complete engine rebuild

sdhadley94

sdhadley94

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I just bought a 81 xs400 special about a month ago. I have no clue if it's a sohc or dohc as i have not dug into it yet. But the point of this post is that my oil
1.) Reaks of gas
2.) Had almost 5 quarts of oil in it before changing oil.
Somewhere on the site I read that my bike requires 2.4q of oil. I'm suspecting my rings are bad but it runs beautifully once warmed up, other than an obnoxious acceleration ticking/knock after a fresh oil change at the full level on the side window on the clutch cover. Seems as if it may be the upper end, maybe the cam? I'm curious if anyone has come across this problem and could fill me in on a rebuild how to and or a diagnosis. Any and all info is much appreciated.
 
Carbs probably flooded the engine over time. That'll be the extra fluid and the source of the gas smell.
Don't tear it apart if it runs well.
Dry/wet compression tests would be a good idea. Do a compression test normally, then pour a couple teaspoons of oil into the cylinder through the spark plug hole.
Test again.
If the dry reading was poor and goes up significantly with the oil you're likely looking at worn piston rings.
If it doesn't go up you may have a valve sealing issue.

Welcome to the forum! An 81 would be a SOHC. First three VIN digits would narrow down the exact model.
Photos help too. :)
 
What would your guess be on the almost 3 extra quarts of oil in the engine? I found it hard to believe that the bike had just about as much oil in it as a typical 4-6 cylinder car without worn rings. I have a feeling the person who owned it prior to me put the extra oil in it to compensate the compression loss, if the rings are worn out. Side question (kinda stupid) but would a normal compression test be the same procedure as it would be on a car?
 
How gassy do you figure the oil is? It's possible for the entire gas tank to drain into the motor if the petcock is leaky.
The extra could all be gas.

Haven't actually done a comp test on a car but I'm sure it's close.
Screw the compression tester into a spark plug hole and turn the motor over a few times, holding the throttle wide open.
Should only take a few cranks for the reading to stabilize.
Hopefully somewhere near 150psi.
 
Ya basically the same procedure, but I could probably run a two stroke off of my oil lol. I use 20w50 in the spring (currently high 40's) and the oil still has a great stringy viscosity which is weird because it smells like I'm sniffing my gas take. So you'd think it would lose it's thickness if it's being diluted with gas so bad but it hasnt. But I've also only put about 50 miles on it since the oil change. Prior to the oil change it didn't make the ticking noise. That's why I'm thinking it's top end and bad rings. Gas is forced into the top of the piston and if I don't make up for the lost compression with the 4 3/4q of oil I get dry cylinders because the 2.4q cant lube the walls properly causing some kind of piston slap possibly. Or maybe the oil pump can't get enough oil into the cam upon acceleration. Coasting in neutral is fine though. I settled for Castro motorcycle oil and a k&n filter. Maybe the filter is restricting the flow. Sorry if I seem all over the place, I like to think of all possibilities. Never know unless you ask.
 
Start reading the manual on maintenance. Do a valve adjustment. Use oil that is designed for wet clutches. Did you drain the sump of the bad oil also? Check the oil with the bike on its center stand. How many miles on the bike. Post some pics of the bike. We love pics.
 
I don't quite know what you mean by sump, but I checked it on the center stand and in the vertical operating position. I'll get some pictures up here in a few. And she's got 15,000
 
A little dent in the tank but it adds character
 

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It may have been neglected at one point and the tick was created because the engine was run briefly with low oil.

The owner probably didnt add oil the proper way and added too much, or knew about a lifter tick and added until it went away, OR added an additive to stop the ticking.

Replace oil and filter first. I think you should adjust the valves cold, not sure at the moment... After they are adjusted, go for a ride and see what happens.

I urge you to refrain from opening up the engine unless you absolutely have to... If compression is OK and the ticking goes away after the adjustment, RUN IT! lol
 
The sump is on the bottom of the motor. There is a plate with six small bolts that holds it into place. When you remove it there is about 8 oz of oil left in there even with the motor drained. There is a screen in there that needs to be checked/cleaned. When you replace the gasket for it, smear a bit of grease on it so when you remove it again it will come off easy.
 
NewHavenMike said:
It may have been neglected at one point and the tick was created because the engine was run briefly with low oil.

The owner probably didnt add oil the proper way and added too much, or knew about a lifter tick and added until it went away, OR added an additive to stop the ticking.

Replace oil and filter first. I think you should adjust the valves cold, not sure at the moment... After they are adjusted, go for a ride and see what happens.

I urge you to refrain from opening up the engine unless you absolutely have to... If compression is OK and the ticking goes away after the adjustment, RUN IT! lol
Click to expand...

Before I changed the oil there wasn't a tick, it was afterwards when I used the correct amount of oil is when I started hearing it.
 
These sohc bikes do make a fair amount of top end noise. The extra oil could have masked some of it. If you did a proper valve adjustment you should be fine. When doing one make sure your motor is in the correct stroke and NEVER turn the crank back to get the timing marks lined up, always foreword . That will put slack in the cam chain giving you a bad adjustment.
 

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