I have NEVER said it was not an IMPROVEMENT or it will blow all to pieces if you don't do it the better way BUT if it can be done BETTER why not??? the 72-73 750 case's need work to the oil pickup anyway so why not take the high road, on the other style pony up for Jim's NEW sump breather for the other type case's

madass140 wrote:I think a reed valve at the magneto position would be an improvement

I definitely like the new style large-sump-plug unit.

OK. Here we go.
I have in the past made inquires to Matt, Fred E. and others about modifying the 72 cases to allow for the strainer type plug. The concensus is that there just is not enough meat to allow for the machining nor the structural integrity to make this possible.

I mention this because the 72, to say the least, was prolific. We (72 owners) are, for all practical purposes, stuck with what we have. We are generally left with good and sound machanical practices to make sure all ways are clear and all things are buttoned up properly when closing the cases.

This does beg the question, do owners of a 200000 - 2xxxxx crankcases need to validate that the thrust washer tab is eliminated and that the oil tunnels are clear? Speaking for myself, I sleep and ride better knowing that this is so.

I am not a purist and it's not that my bike is a bitsa. But there are somethings that just need to be what they are. A 72 Commando needs a 72 Crankcase imho. I replaced an early inferior set with a later improved set. The sump system was, unfortunately, not part of the improvements. If I wanted a 73, 74 or a 71, I would have gotten it. It is what it is and I love it for that sake.

I have run the $5 pc valve breather from autozone low, high, the Mike xs low, high, off the lower back and off the mag boss. I have run 2 reed breathers, one off the lower left and one off the mag boss together. Before "butchering" and after "butchering" the cases. The best senerio that I have personally come up with, and I speak for the 72 only, is the "butchered" case with the reed equiped breather on the mag boss.

Butchery is an art form in itself and to do properly takes years of experience and guidence and proper tools to complete. If anyone chooses to call me a butcher, I will be inclined to say "thank you".
I think the term you seek is "botch". As in "We have thoroughly botched this topic".

The direction this thread is taking I would start to think that a Commando without a breather at all would be near worthless.

And while I realize that the '72 cases can't be machined for a large sump plug I have to wonder if it wouldn't be possible to make up a smaller diameter plug that allowed for screening of the return oil. There is nothing that says it has to be an inch and half in diameter, it just needs to flow enough oil to evacuate the space. Something like this perhaps:

http://www.ebay.com/itm/Oil-Pickup-Filt ... es&vxp=mtr

The funny thing about the Combat breather is that if the sump screen got plugged most of your oil would still return to the tank if you use the stock breather postion for a reed valve rather than blocking it off.


Russ

"The best senerio that I have personally come up with, and I speak for the 72 only, is the "butchered" case with the reed equiped breather on the mag boss."

thats exactly what I'm doing on my 72. I think the little non return valve as suggested in the OldBritts mod is to small for the volume of air it has to handle.

madass140 wrote:"The best senerio that I have personally come up with, and I speak for the 72 only, is the "butchered" case with the reed equiped breather on the mag boss."

thats exactly what I'm doing on my 72. I think the little non return valve as suggested in the OldBritts mod is to small for the volume of air it has to handle.

you could install the reed valve inside , but still accesible from outside .

I once posted a thread about this , but the seach function only goes one year back ..
edit : thanks LAB

ludwig wrote:I once posted a thread about this , but the seach function only goes one year back ..

1 year?

post65357.html#p65357

madass140 wrote:"The best senerio that I have personally come up with, and I speak for the 72 only, is the "butchered" case with the reed equiped breather on the mag boss."

thats exactly what I'm doing on my 72. I think the little non return valve as suggested in the OldBritts mod is to small for the volume of air it has to handle.

Even though comnoz proved this to be incorrect?

I normally do not post to the forum since there are a lot of Norton experts voicing what they believe are true facts and what could I add. However I need to verify several things in this thread.

1st: As I state in my technical article www.oldbritts.com/c_c_case.html if you look at a 1971, 1972 and 850 1983 crank cases, you will see the factory changed the 1972 crank case design and went back to a similar design as in the 1971 cases for their 1973 850 crank cases.

2nd: Old Britts has been doing this modification (not butchering!) for almost 18 years and several other well known shops have been doing it since the late 70’s.

3rd: I will agree a better breather system is called for, but I do not know if fixing the 72 breather problems will also fix the oil scavenging problem.

4th: The modification we perform does allow for the oil to pool at the scavenge port and does it in an area that is under almost zero stress, leaving the crank wall almost as thick as other crank case walls.

5th: I have done this modification to several race engines and have never had a failure where the modification was performed. I have had several failures to other parts of the crank cases, but never at the oil pickup area.

Finally if you have not read the technical article listed above, you might want to do so and actually see what this modification actually does.

Fred Eaton

Sorry a typo in the link to my tech article, see www.oldbritts.com/n_c_case.html.

Fred Eaton

Old Britts wrote:I normally do not post to the forum since there are a lot of Norton experts voicing what they believe are true facts and what could I add.............
Fred Eaton

nice Fred!

I admit it. I did Fred's OB crankcase mods to my 72 the last time I stripped the engine. I can't speak to all the other posts about the pros and cons of different breather systems but after careful study of the tech article on Old Brits I came to the conclusion that the process would benefit my Commando. And it has.

I am not an engineer or a machinist but I know a good looking breather when I see it. Back when I worked on Nortons we were also a BMW dealer. The Airheads have a built in breather at the top of the crankcase. It has a small metal breather disk that opens when the pistons move in compressing the crankcase gasses and closes when the pistons travel out. I knew that the Norton would benefit from this treatment.

The crankcase sump mods also made sense to me although I never considered trash getting into the oil pump a concern. Maybe I should have, I don't know. The results are an oil tight engine (for the most part) and believe me the bike oiled itself pretty handily before the modification. I continue to ride the Beast and I have to say the the last thing I worry about out on the road is the OB crankcase mods.

BTW, It was a beautiful winter day here in Texas with a big blue sky, cool but not cold and plenty of sun. The Norton had a blast and so did I.

Hi

I used the XS breather in the magneto position. Didn't touch the cases, I just cut the allen heads to a v shape. Scribe the magneto hole onto an alloy sheet, measure the bolt centers on the breather (remove the bracket it comes with) & place it so that the breather is upright. I found you can cut the bolt heads so that it fits without shaping the cases.

Chris