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Thread: Valve shims
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post #11 of Old 10-14-2018, 08:24 PM
2nd Gear
Join Date: Jun 2017
Posts: 320
Originally Posted by pdwestman View Post
I'll suggest to not be so stingy with the air filter oil.

I use enough air filter oil that I can squeeze at least a few driplets back out between my fingers. If one can't squeeze some oil back out of the foam, some areas of the foam are not oiled well enough.
If you would care to use a dab of grease under a fair sized flat washer on the air filter center bolt, it would be like most real dirt bikes I've owned or serviced.

A thoroughly oil foam air filter is the absolute best defence against dust ingestion for an internal combustion engine. I doubt that one could find a single competition dirt bike in the current market place which comes from the OEM with any other type.

High pressure compressed air can actually open the pores of paper type air filters and then allow slightly larger particulates to pass thru. They are intended to be used once & then disposed of!
One can thump and bump and tap the worst of heavy deposits out of paper filters as a quick & dirty short term 'fix', but replacement is best.

OEM motorcycle paper disposable filters are always pricey, aftermarket brands are less expensive, but people still attempt to re-use. Not a good plan, in my opinion.
Certainly you have to be careful using compressed air to clean a paper element. If you keep the nozzle 6” or so away from the paper, you will remove the loose dust on the external part of the filter and extend its life a fair bit with no damage to the filter. I have done this for 40 years without issues and most paper element manufacturers allow it.

I have to disagree that an oiled foam element is the “absolute best defence” against dust ingestion. Many tests have shown just the opposite. Oiled foam is the worst element at catching dust. It has less restriction so provides more performance and will withstand getting wet, but it is a much poorer filter of particulates. Here is just one test that shows this quite clearly.
ISO 5011 Duramax Air Filter Test Report

If you race and thus value performance over engine life, then oiled foam is the way to go. Similarly, if you ride or drive where the engine may ingest water, then foam is better. However, under all other conditions, a good paper element is the best dust and dirt filter you can get for a car or bike.
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