Restoration adding modifications, butchery or?

pvisseriii said:

I think the thought here should be to relieve pressure. There are many solutions and maybe too many opinions to keep focus.

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Yeah, but there's more to it. The idea is to create the highest vacuum possible. When I was a kid I had a minibike with a reed valve, crankcase induction, 2 stroke engine. One of the hot mod's was to get a reed cage that tried to fill as much of the dead air space in the case as you can. That way the downward stroke of the piston would be more effective at moving air up the transfers by basically raising the compression ratio of the crankcase. That's the idea behind sealing off the timing chest as much as you can, taking the volume of dead air space of the timing chest out of the equation.

A reed valve at the end of a hose off the timing case is an improvement over a passive vent for curbing oil leaks, but there are benefits to taking it to a higher level.

More power due to less pumping loses from pushing air in and out of the crankcase breather.
Less oil frothing and heating when it's under a vacuum. Keeps the oil cooler and gets it out of the way faster.
Better oil control around the valves and by the oil rings on the pistons. (The holes between the scrapper rings are there to create a low pressure area between the rings that actually vacuums the oil off the cylinder wall.)
A high rev'ing inline four would show it more than a 360deg twin with a 7000rpm redline, but there are less windage losses from spinning parts in the 'rarefied air' of a vacuum.

Everybody from Formula One to dragsters go way out of their way to pull as much vacuum in the crankcase as possible, it's free power and they don't leak oil. What's not to like?

The various add on breathers are much debated on the Vincent forum , just like here. Quite a number have a good result by adding an automotive PCV valve.
One company in the UK even has a hideous attachment called the "Elephant Trunk Breather" that connects onto the mag cover/timing side. It looks as good as its name.

The best solution though seems to be changing to low expansion pistons and....I really hate to say it... Honda Chrome rings.

The quality of them is extremely high. We throw out the cast iron rings that come with the low expansion pistons and replace them with the Honda rings. The Honda rings cost about the same as the low Expansion pistons C/W cast iron rings, but it's worth it not to have to prematurely tear the motor down due to compression loss/ blow by/ Leaky sheiky problems after 15,000 miles or so.
The honda rings seem to do an easy 60 - 75,000 miles, a lifetime of riding for many riders.

If they get seated properly, you are set, the oil leaks just seem to go away.

Did a 3500 mile run to Ca. and home last year, couldn't see any change in the oil tank level.

I wonder if there is a crossover for some Honda ring size to any of the available Commando pistons?

grandpaul said:

bill said:

WELL GP IT LOOKS LIKE YOU WERE WRONG as this is straight from the source

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Well, I admit it.

I just know I couldn't get one off without moving a bunch of stuff and loosening it to BARELY manage to get the 2 bolts off and back on.

Now, I have seen the only pictures available of the CNW breather kit, and it has FOUR bolts; so, not sure how that's all done unless the inner plate is held on by 2 bolts, and the rest of the kit bolts onto that?

Bill, you still didn't say how YOU did it, if you ever actually have installed one...

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Paul,

Take a minute, go to my website, in the parts catalog under 'Engine', scroll down to the breather mod. There is a full description, even a picture (you must not have seen all the pictures available, as you stated). This way you can see how its done.

There is a thin adaptor plate that fits onto the case. Then the breather body fits on that plate. Simple.

Matt / Colorado Norton Works

Matt, I got on your website and saw the catalog listing, but didn't go into the specifics after seeing the same blurb that Bill quoted.

My hands are pretty skinny, and I still can't do it without removing stuff. I don't doubt it can be done, though, as I admitted.

There was even more to this with the outboard boat racers.They would do what they called stuffing the case's . This would involve things like making cork inserts to fill the underside of the piston's and filling EVERY area so there was JUST enough room for the parts to rotate.

As to timing case V crankcase breather I am with Jim and you, The LEAST path's the air has to take the easier it will be to remove the air.some people on here refuse to learn and insist that IT'S GOOD ENOUGH.

As has been said you either get on board the train or watch it leave the station. Looks like one on here will be watching it leave.

rpatton said:

Yeah, but there's more to it. The idea is to create the highest vacuum possible. When I was a kid I had a minibike with a reed valve, crankcase induction, 2 stroke engine. One of the hot mod's was to get a reed cage that tried to fill as much of the dead air space in the case as you can. That way the downward stroke of the piston would be more effective at moving air up the transfers by basically raising the compression ratio of the crankcase. That's the idea behind sealing off the timing chest as much as you can, taking the volume of dead air space of the timing chest out of the equation.

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so all those later 750's and 850's that have the breather at the magneto position have serious problems?

madass140 said:

so all those later 750's and 850's that have the breather at the magneto position have serious problems?

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No, not that I'm aware of, but that's not to say that the standard breathing arrangement can't be improved upon.
Only the 850 cases have the timing case breather.

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

Outboard power boat racers? Moto GP? Formula One? Time space continuum? Matter, anti-matter? Holy smokes! We're just a bunch of back yard machanics trying to stop some leakage, not create nuclear fission within the confines of a commando crankcase to reach the 143 mph barrier. (the new ton) new ton......Newton.....get it?

Let us all practice a little "KISS" here and not scare away all the noobs waiting in the wings to jump in.

madass140 said:

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

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It most certainly is.

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 said:

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

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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.

ludwig said:

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

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1 year?

post65357.html#p65357

madass140 said:

"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.

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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 said:

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

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nice Fred!