Friday, August 7, 2020

Royal Enfield oil filter: Which diagram is right?

Diagram of Royal Enfield oil filter assembly.
There's something funny about this illustration from
the owner's manual of my 1999 Royal Enfield Bullet.
If you own an old-fashioned, iron-barrel Royal Enfield Bullet motorcycle, you know that changing the oil filter is a messy job. Instead of a modern spin-on oil filter, you have a filter "element" that fits inside a housing in the side of the motor.

It is held in place by a spring-loaded cover and associated washers and nut.

Your owner's manual explains how to put all these bits back together. In a blog item here in 2008 I noted one oddity in the diagram shown in the owner's manual of my 1999 Royal Enfield:

The spring in the cap bears directly on a delicate felt washer!

The felt washer in turn is on top of a metal washer that would likely better withstand the pressure of the spring. Shouldn't these two be reversed, to put the spring pressure directly on the metal washer?

If so, is that a typographical error in the manual?

Well, if it is, my dealer didn't balk at it when he changed the oil. That's the way I found the pieces arranged when I did my own first oil change.

And I have done it this way, ever since, despite a friendly warning from a reader that I had it wrong. I have always wondered whether I am right or wrong.

Then, recently, I came across an eBay ad for a 1954 owner's manual for a Royal Enfield 250cc Clipper. Despite its age, the design of the 1954 Clipper is related to my 1999 Bullet.

(Proof that my motorcycle is a true antique, although still only 21 years old.)

Diagram of Royal Enfield oil filter assembly.
This illustration from the 1954 owner's manual shows
the metal washer between the spring and the felt washer.
Sure enough, the oil filter diagram in the 1954 manual shows the felt washer belongs beneath the metal washer, where it is protected from the spring.

Which manual is correct, 1954 or 1999? Does it matter? I don't know.

In 2008 I wrote that reversing the order of felt and metal washers resulted in a leak. But I now question how anything could have leaked past that firmly attached spring cap.

I guess I will have to it try again.

Your comments are invited, below.


  1. The metal washer goes against the spring. The top picture is incorrect.

    1. Makes sense. Yet I vividly recall finding the spring against the felt the first time I changed the filter. It was surprising. But based on that, and the illustration in the owners manual, I've done it that way ever since, and the felt remains intact.

  2. Charles I Fernandes8/11/2020

    Hi David,
    When I purchased my Old Faithful in 1971 (in Bangalore India), it did not come with a detailed manual.
    Watched my mechanic do it and learnt.
    Yes it does not make sense to have the spring bear on a felt washer.


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