10 micron or 30 micron Harley Engine Discuss 10 micron or 30 micron in the Harley Tech & Harley How-to forums; I`ve got 94` Heritage I`m kind of confused to what filter to run? Should I run the 10 micron my dealer gives me? Or should I run the 30 micron ...

[jc94]

I`ve got 94` Heritage I`m kind of confused to what filter to run? Should I run the 10 micron my dealer gives me? Or should I run the 30 micron a buddy tells me I should run? Can anybody tell me what to run and what`s the diff. between the to if a whole lot? Thanks Jc!!! P.S I run 15~50 Mobile one If it`s any help to ya!!!

[humpbackbob]

Using the Syn Oil I would stick with the Dealer recommendation of 10 mics. The New "Definitives" filtration system provides a 5 mics filtration, specificly for Synthetics. They make a filter to fit your yr/model bike.

[whylee]

The 10 micron will filter smaller particles, but it will allow more unfiltered oil to bypass. The 30 micron wont filter the smallest particles but will allow less oil to bypass the filter. By going with a lighter weight oil also helps more oil to be filtered without bypassing the filter. Either will probably work fine.

I rember this question being asked alot when H-D first came out with the 10 micron filter.
I went straight to the horses mouth with this one, a well respected lead mechanic at a local H-D dealership.
I learned from him:
10 micron is for Twin Cam only.
The gearotor pump In Twin Cams can easily push the oil through the finer filter media.
The spur gear pump on EVO's and earlier models just does not have enough power to push the oil through it.
The oil is filtered on the return for EVO and earlier.
The engine would suffer from a oil flow backup.
The use of the finer micron filter would show up as way excessive oil blow by in the air cleaner or whatever breather system is installed on the bike because the pump cannot return the oil fast enough.
The use of a 30 micron filter on a Twin Cam would be all wrong as they were designed to use the finer filter and yes, the finer filter definately gives beter protection.
Twin Cams filter on the feed side. If there was any flow problem the engine would be starved of oil! So it goes to figure that the relief valve is set to a lower psi than one would think.

I meant oil filter relief, or by-pass valve, not to be confused with the oil pump pressure regulating relief valve.

[BadBenny]

NO oil bypasses the filter. I repeat - NO oil bypasses the oil filter on any Evo or later Harley. dls8 is correct about the different oil pumps on Evos and Twin Cams. Use only the 30 micron filter on Evos and the 10 micron on 2000 - 2006 Twin Cams. There is a new 5 micron filter for the '07-'08 bikes. They need this extra measure of filtration for the nonexistent cam bearings ( they are just holes drilled into the cam plates).

Originally Posted by BadBenny

NO oil bypasses the filter. I repeat - NO oil bypasses the oil filter on any Evo or later Harley. dls8 is correct about the different oil pumps on Evos and Twin Cams. Use only the 30 micron filter on Evos and the 10 micron on 2000 - 2006 Twin Cams. There is a new 5 micron filter for the '07-'08 bikes. They need this extra measure of filtration for the nonexistent cam bearings ( they are just holes drilled into the cam plates).

Benny, possibly what he means by bypass is the built-in bypass on the filters. All filters (with exceptions) have a pressure relief valve that will allow the oil to flow (unfiltered) and avoid engine seizure.

[whylee]

Yes oil does bypass the filter, the last tech article I read states that about 1/3 of the oil bypasses the filter on every pass thru the system.

Yes I meant the relief valve built into the oil filter itself.

[BluesFan]

dls8 said it well.

One thing though, don't get all hung up on bypasses.

Some of my cleanest oil systems only filter a tiny part of the oil flow on every pass.

So what? The bulk oil ends up clean and that is what matters.