Motorcycle Repair: 98-03 suzuki 800 crankshaft, worn bearings, viscosity oil

Question
what seams to be the problem with the suzuki 800 crankshaft?im a bike mechanic myself and have replaced several 800 cranks and was wondering why that the front rod on every engine seems to break or spin a bearing and is there something i can do tostop it from happening to my bike?

Answer
Hi Dave,

Once the initial problem starts there is no fix but to replace the crankshaft.
The way it starts is with missed shifts or over-revving the engine
one too many times. The crankshafts tend to twist under all the force applied.

Once the crankshaft is twisted the bearings start to wear off to the side
of the crankshaft rod journals. This abnormal and off centered wear wipes
out the rod bearings and/or causes them to spin or turn in the rod.
The rest of the story is broken or bent rods and twisted cranks etc.

To stop this from happening the rod bearing contact or wear pattern
should be checked before assembling the engine.
You can tell this by looking at the worn bearings and see if the
wear or contact area is off to one side of the worn rod bearing.

A good crankshaft will wear the bearings out from nearer the center
or evenly across the bearing surface. If you see the bearing has had
a hard contact near one side of the cranks rod journal  then the crankshaft
may be twisted. This crank would not last long until it again wiped out the
bearing and rod.

The front rod just happens to be affected the most
when over-revved for some unknown reason.

The solution is to keep engine speed reasonable if you have
a good crank and be sure to check any cranks for bearing wear patterns
when you do rebuilds. Keep the oil clean and don't use overly heavy
oil that the oil pump can't circulate easily when cold.

People make the mistake of thinking heavy viscosity oil
is good but the engine runs dry until it starts pumping
that thick stuff. Multigrades can help with that in cooler
areas. I would use 10W-40 unless you are in warm climates.
20W50 is another alternative in the hot countries.

Keeping the idle higher also saves engines as slow idles
don't circulate oil very well even if they sound cooler.

WS
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