Spun bearing

[Bax]

3Phase I know a good set of dogs when I see one. Better to avoid any troubles so I'll be sure to stay off of Lake street and change my commute to the uphill both ways route.

[3Phase]

Those are some fine dogs!

There are lots of fnu and adventures in store for you once you get that 'Special up and running so you need pictures.

[DiverRay]

That was Special Ed, NOT me! I just helped with the repair....
Mine was the trans lock-up at 85mph leaving Yosemite a few years ago. about 250' black stripe, and a tire almost through the cords in just one place...

[3Phase]

Yep, you had to ride down with a spare final drive for Ed and put it on right there on the street. I think that was a year after you'd hung his bike from the rafters and done the 2nd Gear fix!

[2WheelFun]

Off topic but thanks for the picture of the 2nd gear fix. Mine will be hanging like that soon. I really wasn't looking forward to a backache working it with both wheels on the ground. Great idea hanging the bike!

I can't wait to actually have a second gear.

[3Phase]

Having 2nd gear is nice! It can be aggravating trying to put the gear set back in the case after you fix the gears or just change them out for used ones that aren't quite as worn as your worn out gears.

I had to fix my XJ when I bought it used, then loaded up and took off for a trip but didn't get to the end of the block before the gears started skipping.
I was angry but it was actually a lucky break because I pulled the engine and split the case, then discovered a rod bearing was about to go on my 'new' used bike.
I hate spun bearings!

[2WheelFun]

Are there oiling issues inherent to the XS that cause this or would spun bearings be placed in the owner abuse (over-rev/oil not changed/low oil) category?

[DiverRay]

The XS engine usually does NOT have any oil related problems. RC Engineering back in '79 ran all season drag racing an XS without looking at the crank!

[Bax]

2WheelFun I'd suspect most of the spun bearings, not due to improper maintenance, on these XS engines would be from cylinder blow by on excessively rich running carbs quickly thinning out oil that went too long between changes. Add in float issues that would leak gas to the cylinder during inactive periods having same thinning effect on the oil, something along these lines seem likely. Big picture here, we are on a forum about enjoying 40 year old bikes and keeping them going, inherent oiling issues would probably make for a very small membership 5 years after the last XS bike produced.............

---Bax

[3Phase]

The oil system in the XS11 is fantastic but there are a couple of issues that can mess up the engine: cold starts and oil that is too thick.

The oil pump itself and the oil filter housing cast into the engine case both have oil pressure regulator/bypass valves.

The oil pump pressure regulator maintains oil pressure and prevents excessive oil pressure by dumping oil straight back into the oil sump when the oil pressure reaches the regulator's upper limit.

The oil filter pressure differential bypass valve in the engine case makes sure the oil flows to the crankshaft main bearing oil gallery even if the oil filter itself is plugged up solid by bypassing the oil filter.

During cold engine starts, oil does not want to flow through the oil filter so the oil filter gets bypassed until the engine oil begins to warm up and go through the filter without restricting the flow.

During cold engine starts, oil does not want to flow from the oil pump to the oil filter housing and the pressure regulator dumps oil back into the sump.

During cold engine starts, revving the engine before the oil warms up forces the pressure regulator/bypass valves to open and return oil to the sump and bypass the oil filter.


Now we move on to oil that is too thick and basically acts like the engine oil has not warmed up.
Cold starts are even tougher on the engine because the regulator and bypass valves stay open longer.

Even after the oil is warmed up it's still thicker than the regulator and bypass valves were designed to use so they dump oil and bypass the filter at lower engine RPMs and stay open longer like when you pass a vehicle or just run it up to put the standard XS!!00 BSEG on your face.

Now, oil that is too thick not going to instantly destroy the engine but you have to be careful during cold starts and warmup.
The usual start-engine-then-rev-it-a-couple-of-times-after-it-fires will spin the crankshaft 'dry'. Lubrication at that time is only provided by the additive package in the oil before oil can flow and build pressure and that will wear out and spin bearings, especially the outer main crankshaft bearings and the connecting rod bearings.

[2WheelFun]

Stuck float valves and vacuum operated petcocks can sure cause some some bad problems, as well as poor tunes. I ask because there have been some issues with oiling on my generation Kaw, some mods have been developed to fix the issues. Most don't have a problem but some throw the #3 rod thru the case. I don't think about it and use the bike like it was meant to be used, full range of the tach usually once or twice every time I ride it.

Thanks for the explanations. You folks sure have some great insight!

[3Phase]

Heh, gas in the oil from leaky carburetor float valves is an entirely different situation and it's the closest thing to instant death for an otherwise perfectly fine engine.

It only has to happen one time because scuffed bearings can't heal like scuffed knees so always check the oil level in the sight glass before you start the engine.

When the bike is on the side stand the gas will flow out the back of the carburetor air intakes if the float valves leak and leave a puddle next to the bike.

When the bike is on the center stand the gas will flow into the cylinder head and then down into the oil sump.

Yeah, you can lose a full tank of gas overnight as it slowly drains into the engine and totally overfills the oil sump.

You can get around that problem by putting a small block of wood under the front wheel when you use the center stand so the intake valves are higher than the carburetors and gas will flow back out the air intakes but that is easy to forget and the next thing you know you've got up to five gallons of gas in your oil.