On the parts diagram it shows the big rubber oring which goes at the neck of the pump, then below that is the metal washer which sits on the crankcase to stop the pump eating into the case, then it shows another rubber oring which sits right at the bottom of the pump. Just wanting to confirm that this is correct and that a metal washer and rubber oring are at the bottom of the oil pump?

No, it's a poor illustration!

The second O-ring is for use with the later oil pump/cases, that have twin feeds. Look on the underside of your pump, and see if there is a secondary hole (about 2mm in size).

Late MC21s* and all MC28s have the second feed. MC16, MC18, and early MC21s have just the single feed (and therefore just the one large O-ring.

*It's not as simple as just a change of model year, so don't ask when they changed! Just look at the underside of your pump and the crankcase for two holes!

Note: The MC28 parts manual illustration more accurately depicts the second O-ring.
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Andy.
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Also, an oil pump with the added oil feed needs to match up to a set of cases that have the required oil passage to the crank bearing.

If you put a newer pump on an older engine, you will end up with oil all down the engine and on your back tire (don't ask me how I know this).

You can use an "old" pump on "new" cases though. Just plug the extra hole in the cases.
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Andy.
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Thanks for the replies. I took the pump off and guessed that it was for the secondary oil hole as I had a new o ring and compared, thankyou for the confirmation though much appreciated.

Andy wrote:You can use an "old" pump on "new" cases though. Just plug the extra hole in the cases.

Hi Andy, I just discovered the new crank cases I sourced for the rebuild are the later model with the additional oil inlet.....I did order a replacement oil pump....is there a benefit to using the new pump within the additional inlet?
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"If your not first, your last!" Ricky Bobby

Yes. Additional lubrication to the RHS main bearing.
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Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

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Is this still for sale?