Case oil dam identification

Some cases came with an oil dam above the sump plug as shown below. What model
and what years did this happen?

Also - did all Combats have this dam and were all missing the large sump plug?

You're probably already familiar, but here's an article that talks about crankcase changes affecting the 1972 models. Sounds like a one year thing, but I don't know.

The oil dam also came on cases with the large sump plug as in the top photo. Those are the ones I'm most concerned about - what year and what model (if not Combat)?

All 72/73 750's regardless of them being Combats or not had no large sump plug, how the dam fared during this time I do not know but my 72 has the dam. The dam seems to have continued onto the 850's when the large sump plug was re-introduced, my 74 has the dam.

Best to stop referring to 72's as Combats, not all 72's were Combats but the crankcases were common to all 72's eg all 72's were missing the large sump plug.

jseng1 said:

Some cases came with an oil dam above the sump plug as shown below. What model
and what years did this happen?

Click to expand...

I believe it is the 850 crankcases that had both.

jseng1 said:

Also - did all Combats have this dam and were all missing the large sump plug?

Click to expand...

Yes, as kommando said, the sump plug was deleted from 200000-on 750 (750 MkIV) cases so that's pre, during and post "Combat" production and continued until almost* the end of 750 MkV production (or 1973 750 for those who don't think outside of the 'model year' box).
*(Late Edit: 230xxx series MkVs apparently had '850' cases).

LAB said it is the 850 cases that had both the large sump plug and the oil dam. What years or serial numbers did this cover? The combination of large sump plug and oil dam is what I'm trying to nail down.

850 from serial 300000.

Edit: It seems 850 Mk3 cases do not have the dam (but do have the sump strainer). So no dam after serial 325000.

Ok Because I always have questions, What was the purpose of dam? It's located wrong to act as a oil scraper( as in Harleys). So was it there to only hold a larger amount of oil on top of the sump? Have oil scrapers been installed in Nortons and any advantage?

Could it be a baffle?

L.A.B. said:

850 from serial 300000.

Edit: It seems 850 Mk3 cases do not have the dam (but do have the sump strainer). So no dam after serial 325000.

Click to expand...

Plenty of "dam"s in my garage with my mk3, also a few effs and jeff's...

The scraper or dam or whatever you want to call it is a problem - its usless and needs to be removed - it actually causes the sump to fill up with too much oil. I need to know which models, years and serial #s have both the large sump plug and dam as shown below.

Hi,
Can someone please give me some more background on this thread? I’m really battling to get my head around it.
# Do I assume that some 750s had no way of draining oil from the sump. This seems inconceivable. Assuming the bike wet sumped after sitting for an extended period, how would one remove the oil.
# Isn’t checking the residual Crankcase oil for swarf or contamination essential for engine maintenance?
# What was the intended purpose of the oil dam?
# Does this mean that it doesn’t have a strainer on the scavenge pickup? Again, this sound unbelievable.
# Surely Norton must have used extensive engine testing on test beds where the oil starvation problem would have shown up? I presume they would have run some engines to destruction? How could a change be made that allowed for oil starvation during hard use?
# When changing the oil, I always remove the large sump plug from the crankcase to remove residual oil, clean the pickup filter and check for any horrors. Isn’t this standard procedure when servicing?
# Is there a definitively correct breather as standard equipment on a particular Commando Mark? Mine is a 74 Mk2. I’ve not had any reason to believe that it doesn’t work correctly. As 360’ twin cylinder engines have been around since Noah installed one on the bilge pump of the Ark, surely breathers are totally understood and designing one should be relatively straight forward.
I just feel I’m missing something. Such a shame there is not more archival information of what actually went into the design and testing of our excellent bikes. In some ways they fought so much above their weight in the 70s and were still a force to be contended with long after they appeared technically outdated. A shame their name was besmirched by silly and avoidable failures of design.
regards
alan

Alan L said:

Do I assume that some 750s had no way of draining oil from the sump.

Click to expand...

No, those 750s had a drain plug (item 32, below).

850 models had both strainer and drain plug.

Alan L said:

Isn’t checking the residual Crankcase oil for swarf or contamination essential for engine maintenance?

Click to expand...

It should be but somebody at Norton decided otherwise.

Alan L said:

Does this mean that it doesn’t have a strainer on the scavenge pickup? Again, this sound unbelievable.

Click to expand...

Unbelievable as it may sound that is correct.

You can add a sump strainer

L.A.B. said:

No, those 750s had a drain plug (item 32, below).

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

850 models had both strainer and drain plug.



It should be but somebody at Norton decided otherwise.



Unbelievable as it may sound that is correct.

Click to expand...

That was the condition of my ‘72 750 combat engine when I bought it in ‘97. The previous owner suffered the left piston colliding with the exhaust valve sending bits through the oil pump.

HAHAHA yep Breathers in that location, maybe the new offering is causing issues.

Here's on old racing case of mine from the 80s. You can see the dam has been completely removed with a die grinder (I didn't have a mill then). In a vertical engine as in a featherbed frame etc the vent tube must be very tall as the example shown or it will be flooded with oil and not breath properly with a reed valve. The original dam will not allow a tall tube. I used an oil filter.




The original dam shown below