BC490 Cub Cadet


Old 08-09-16, 05:51 PM
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BC490 Cub Cadet

This is a 4 cycle string trimmer, labeled more so as Brush Cutter by Cub Cadet.
It will start and run without any issue however, it spits oil out the breather tube from the crank case to the air filter, which soaks the air filter (even though it is foam) and eventually causing running issues, not to mention, leaking oil.

I drained the oil which was at the correct level, replaced it with Cub Cadet oil (10W30 basically) and left it at the add mark according to the owners manual.

There is no head gasket or separate head on this engine, it is part of the cylinder.

The IPL shows no parts inside the crank case, only a short block.

I searched and searched and found others with the same problems posting all over but never an answer to one, so....I intend to post an answer to the problem here....

Ideas? Anyone seen this?....etc.

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Old 08-10-16, 04:16 AM
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Just input more than anything else.

That type of thing happens a lot to some degree in fixed positioned engines, like lawnmowers, etc. You've probably seen the shield and wire mess in crankcase breathers. They stop a lot of it but the crankcase venting has a lot of oil vapor created by the crank shaft/piston churning things up. It's almost a given something is going to be blown up the vent tube. The PCV lines/valve in automotive applications are very well shielded, but you find oil being drawn into the intake.

There would be an additional problem with a weed trimmer with crankcase oil since the engine isn't upright all the time. The routing through the air filter would have to do with emissions control, but the crankcase gas with the oil vapors wouldn't have to be filtered. That gives rise to the notion of sending the venting back through the intake, but bypassing the filter itself.

What you have there, since it's seems to be a common problem likely has to do with the design of the breather apparatus plus the crankcase oil in that application. Putting a mesh screen in the tube itself wouldn't be advisable since you need the volume of the air tube to vent.

It may be a workable solution to go from the tube where it enters the filter and bypass the filter with a small tube to vent everything directly into the air stream of the carb.

This is just thinking out loud.
Old 08-10-16, 07:19 PM
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I agree marbobj, I think it is a lack in train driver development. This thing only holds 2oz of oil to begin with. There is simply not enough volume in the crankcase to keep parts lubed and not blow oil out some place.

So this unit was under extended warranty from a chain store, not an IR. The chain store does not provide any service, only the extended warranty. We are an authorized IR so it came to us.

IR Dealer tech support says that there must be some sort of valve that is in the crankcase to which they nor I had access to any drawings of, only the short block. So their determination was the fix would be a new short block plus labor....IOW, cost effective was to give the customer a new unit.

Old 08-10-16, 11:48 PM
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More evidence to support my belief that a 4 stroke has its' places and at the end of a trimmer pole isn't one of them.
Old 08-11-16, 03:55 PM
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I agree! Not only are they twice as heavy but they just seem to be plagued with issues. Then they put this "Easy start" thing on them, which has two coiled springs, one light one for the pull then it releases and spins the second one....have to remove the nightmare of a recoil system just to adjust the valves....
Flippin train drivers.... No doubt these ideas come from a plethora of high dollar college educations, when all they need to do is go ask any kid who mowed lawns for a few summers what REALLY works. I know alot of it is driven by EPA and emissions type stuff too but...

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