Major Oil Leak

[74Novs]

Hello,
Can anyone help diagnose what kind of a major issue would cause oil to leak out of this square hole in the crankcase? It's located close to the oil filter and oil pump pickup. I'm not even sure what its called or what its for.

I've never seen something like this so any help diagnosing would be helpful. I'll be digging into it so I will update anything I find internally.

I was riding along at about 65 MPH without issue and all of a sudden I felt the oil splash under me. Once I got the bike home I cleaned everything up and refilled the bike with oil to find the leak. Nothing leaked until I started the bike and it probably lost a cup of oil in 10 seconds.

First post myself but I've used the site for helpful tips and tricks through the years so thanks for that! I've loved riding this '82 XS400 for the past 15 years and this is the first issue.

Thanks for the help,
-Kyle

 

[amc49]

The round oil filter cover could have blown seal or cracked right there to look like oil is coming out of the square hole. You have full pressure there, that accounts for oil coming out so fast.

 

[74Novs]

After digging into it I was able to confirm there is a hole in the crankcase way inside this square tube. Still don't know what caused it but should know more once I split the crankcase and get inside.

 

[74Novs]

Well, I've discovered the square tube forms a mounting brace for the chain tensoner. Lucky enough when I took the engine apart the whole piece was still sitting in place. I'm checking to see if something caused the break but so far everything inside the engine looks good. It may just need a new crankcase and go back together!

 

[amc49]

Well, that's the odd duck isn't it?

FYI, there really should be NO single case, you generally change both as they are machined in pairs and changing just one can easily shred your new engine when the bearing bores are not round, what the matched case pair thing guarantees. It allows the bearing bores to wander off spec a slight bit to make far more pieces good off the machine line, the bores then do not have to be perfectly halved in two which is almost impossible to do over hundreds of cases. If you are unlucky and pick a case that is slightly under a half hole and your top case is the same way then your bearing is pinched and destroys in only a minute or two.