Date: Wed, 24 Jun 1998 22:28:02 -0700
From: Ben English
Many Commando riders have been seeking solutions to problems related to crankcase pressure that the standard breathers do not relieve as intended. You have to cruise at 3500 rpm and above to run into these problems- which come down to oil going everywhere it shouldn't- after all the usual leaks, motor oil fills the primary case and blows through the breather and oil tank and thence out the air filter (if you connect the tank breather to the filter as the factory did; many don't). If your bike really needs new rings like mine, it's all the worse.
Those of us with Combats are probably the most deeply into this frustrating
subject.
This has been a long running discussion in many forums. Basically we all seek ways to allow pressure OUT of the crankcases (on the pistons' downstroke), and preventing air from being pulled back IN (on the upstroke). Steven Schoner has an elegant solution, which centres around a power brake check valve in the main breather line- an item I tracked down based on a mention by a fellow from Dutchess County, New York who was on the Brit-Iron list briefly.
Steven's refinement was based on work pioneered by Bob Patton, who has been on and off both the NOC and B-I lists over the years. It was to pipe a 1/8" hose off the main breather (before the big check valve) into a tee on the intake stub balance hose (a stock Mark III part), including a .041" restrictor and a small check valve in this line.
This past week I attempted to duplicate Steven's scheme. After getting myself into trouble by trying too many modifications at once (and especially leaving carburettor main jet holders loose), I have at last assembled all the right parts and followed the plan without screwing up anything else. And I have just come back form a four mile ride with speeds ranging from 15 to 80 mph.
It runs. It runs fine. I will have to do some fast road work to discover the eventual effect on the crankcase pressure and oil control problems, but I have this initial report:
First the theory: The .041" restrictor in intended to limit the amount of crankcase air sucked into the intake side of the motor. Its effect must be most pronounced at high engine speeds- the maximum amount of air that can get through it must be reached soon, and then can never be exceeded. But at low speeds, the restriction effect is relatively minimal.
Now the practice: Sho' nuff. At high speeds, there is no sign at all of leanness. But at idle- hoo boy! I had to do major rework on my idle carb adjustments. Idle speed was WAY up- a definite sign of extra air. I had to seriously richen the mixture screws, and run the slide stops WAY out. And it still stumbles just a tad with a quick blip off idle.
And what is really surprising, although it certainly shouldn't be, is that a pipe from the crankcase to the intake stubs seems to meter air a whole hell of a lot better than a pair of worn out Amal Eccentrics. My idle was steadier than it has ever been, even screwed down to 1000 rpm. This is under one condition- mildly warmed up in humid, 80oF weather. We shall see how she does when she is thoroughly warmed up, and when it is 45oF and dry, and all sorts of other situations.
Will I luck out and avoid the necessity to have my Concentrics sleeved? Can tricky breather plumbing really carburate better than carburettors?
Ben English
1972 Norton Commando Combat Roadster #201695
1982 Honda FT500 Ascot / 1972 Olmo 10 speed
Amtrak National Timetable / Pocket full of bus tokens / Good shoes
USNOA 1395 / NOC 06Z06.2530 0 / MGNOC 15713
Scowling Street Terrors 2 / Skinny Tire Motorcycle Club 3
Lower East Side Egyptian Cobras 4 / Hells' Vegetarians 5
Denizens of Doom 304
Date: Thu, 25 Jun 1998 10:54:04 -0400 (EDT)
From: Steven R. Schoner
Reply to message from Ben English of Thu, 25 Jun
>
>Many Commando riders have been seeking solutions to problems related
to
>crankcase pressure that the standard breathers do not relieve as intended.
>You have to cruise at 3500 rpm and above to run into these problems-
which
>come down to oil going everywhere it shouldn't- after all the usual
leaks,
>motor oil fills the primary case and
>blows through the breather and oil tank and thence out the air filter
(if
>you connect the tank breather to the filter as the factory did; many
>don't). If your bike really needs new rings like mine, it's
all the worse.
>Those of us with Combats are probably the most deeply into this frustrating
>subject.
These same symptoms can be caused by gasket failure at the two studs beneath the cylinder head exhaust ports. These should be torqued to 30 foot lbs., and there are various schemes to do it. My method involved using a short extension to my spring bar type torque wrench and calculating the proper indicated torque by dividing the original length by the length with the extension. This number (in my case .81) is then multiplied by 30 foot pounds to come up with the proper torque for the long nuts. It works very well.
Now as to what usually happens on these heads after long miles is that the studs begin to pull. So you have to keep tightening them. But that can only go so far before they completely pull out. And if they were helicoiled before, they will stop pulling out once the helicoil butts against the head gasket. Then you'll torque it up to 30 foot pounds thinking it has finally settled, but alas the head is not seated at these points. Result-- you get a blow by that goes into the push rod galleys and increases the crankcase pressure, which you would interpret as "blow by". When this happened to mine, the engine puked oil at 70 to 80 mph, all over my boots, the engine-- every place where oil could be puked it puked it. It is amazing that it ran in that condition.
So, off with the head, and I discovered the reason even with the breather system that I had installed. Pulled studs beneath the exhaust ports. Big gaping holes where the helicoils from the previous fix once was. So fix time again-- this time using steel inserts rather than helicoils. Result, it worked for about 3000 miles then pulled again!
Dismay! I had invested quite a bit of funds to have Phil Radford rebuild this head with 130,000 miles on it, so I had to do something to save it. It seems that with age and heat, the aluminium casing under the exhaust ports weakens. It is a pretty bad place to have studs anyway as I imagine the heat is very high there. Could be as much as 400 deg. F, maybe even more. At high temps aluminium weakens, so that would explain why the studs tend to pull out here. So after some research on a tip by Knut, I chose to use silicon bronze inserts to repair the holes rather than steel ones. This is because the coefficient of expansion for the steel is half that of aluminium, and the coefficient of expansion for silicon bronze is .85% that of aluminium. The reason that the stud inserts pulled, was because the coefficient of expansion was too great between the steel and the aluminium and this under the high heat conditions beneath the exhaust ports stressed the metal.
So, I got the silicon bronze in the form of 2" x 5/8 11TPI bolts from Copperstate Nut and Bolts in Tucson, AZ (they are used for electrical applications) These are strong and the tensile strength is almost that of steel, and much stronger than cast aluminium. Then I reamed out the holes in the head, tapped them for 5/8" 11TPI, then on my lathe cut the bolts to make the inserts the proper length, drilled and tapped them. Finally, I set them in the head with high temp loctite at 35 ft lbs.
These are the largest stud inserts that you can get into the head, any larger and the head is trash. So I kept my fingers crossed, hoping that it would work.
On assembly I used the type of gasket that the bike was originally equipped with-- copper. I double annealed it, and coated it with coppercoat. Then put everything together. I thought that a copper gasket would allow better heat transfer in the area beneath the exhaust ports. Phil had also fly cut the head, and the cylinder barrels were absolutely flat, so I hoped that there would be no compression leaks as copper gaskets are prone to these. (Double annealing helps. Heat to cherry red and drop edgewise into cold water. Makes it real soft).
Result with the breather system and the above fix-- no leaks-- none from the engine at all. Now I have to work on my transmission which leaks a bit.
With regards to the stud nuts, they don't budge a bit, and there is no compression leaks past the copper head gasket, and I have put many thousands of miles on it since.
It's weird having to actually spray the cylinder barrels with WD-40 to keep them from rusting.
Steven R. Schoner (Meteorite Man and Seeker), dm550@cleveland.freenet.edu
___________________________________________________________________________
Compared to the Infinite we know next to nothing. What good we
do with
the little we do know is the key to wisdom.
Date: Thu, 25 Jun 1998 20:02:40 -0700
From: Ben English
Steven R. Schoner, replying to my discussion of how I copied his breather setup, intending to reduce crankcase pressure and thus to reduce oil leaks, wrote:
> These same symptoms can be caused by gasket failure at the two
studs
> beneath the cylinder head exhaust ports.
[snip]
> Now as to what usually happens on these heads after long miles is
that
> the studs begin to pull. So you have to keep tightening them.
But that
> can only go so far before they completely pull out.
[snip]
> Big gaping holes where the helicoils from the previous fix once
> was. So fix time again-- this time using steel inserts rather
than
> helicoils. Result, it worked for about 3000 miles then pulled
again!
[snip]
> I chose to use silicon bronze inserts to repair the holes rather
> than steel ones. This is because the coefficient of expansion
for the
> steel is half that of aluminium, and the coefficient of expansion
for
> silicon bronze is .85% that of aluminium.
[snip]
> Then I reamed out the holes in the head, tapped them for 5/8" 11TPI,
> then on my lathe cut the bolts to make the inserts the proper length,
> drilled and tapped them.
> Finally, I set them in the head with high temp loctite at 35 ft lbs.
Sounds familiar. One of those studs had been helicoiled ->crooked<- by the DPO on my head. In American thread. I found a common auto industry stud that fit perfectly and tapped American threads into the normally blank end of the nut. Because the stud was crooked, I had to rattail file the barrel to get the head on. Ugly.
The helicoil lasted for over 50,000 miles but the other stud pulled out of the head. Actually fell out one day. I put another in, and IT fell out. 5,000 miles later the head gasket blew (nowhere near the pulled stud, believe it or not). This was only about three years ago. I took the head and a BSF tap to a hotshot machinist who made bronze inserts. Not thinking of Stephen's threading idea, I asked him to make them a serious interference fit into the head. Reassembled with a copper gasket and a judicious application of Kopper-Kote sealer or whatever the groovy goo is. I still get oil blowing out around the pushrod tunnels, but much less than previously.
I have never had the barrel or head surface professionally checked for flatness (they look pretty good to me with a straightedge). I am too terrified of having to have material removed and boosting the compression ratio up yet more.
So I'm riding it for now. Until 1999, more likely 2000, when she comes off the road for a thorough rebuild including new powdercoated frame, a set of them new factory alu-min-ium cylinders, etc. I figure aluminium cylinders will solve 90% of the head gasket problems. I sure hope those bronze inserts still look solid when I lift the head again.
Ben English
Date: Sun, 12 Jul 1998 16:40:48 -0700
From: Ben English
Jeff Schneider wrote:
>The time has come to finish the breather upgrade I began as per the
>tech notes by drilling the holes in the crankcase. Now comes the tubing
>I will need. I have a '71 [Commando] 750 that has no plumbing of this
>sort. My crankcase breathing was done with the timed breather only.
I have to
>start from scratch. Is the best way to go to buy the factory
pieces for
>the install?
Yes. Obtain a 06 4200 breather tube from your favourite Norton parts supplier. On a stock 850, this screws into a threaded hole in the timing cover. To adapt to your 750, drill a hole the tube will pass through (9/16") in the blanking panel where the points were on M20 models. Then acquire suitable SAE fine 9/16"-18 nuts (I used a thin jam nut on the outside and a full size nyloc inside the timing case) and a fibre or copper sealing washer to bolt the tube in the backside of the timing cover nice & tight.
A standard 850 Commando 1/2" ID breather hose (part #06 2619) attaches to the tube. You may route that hose right up to the 1/2" to 3/8" adapter (part #06 2617, used on late 750s and all 850s). From there 3/8" hose goes to the same oil tank pipe that all breathers go to, the rear one at the filler cap.
A check valve may be inserted in that run at any convenient point, but it is probably better to situate it as far as possible from the motor. The auto power brake valve I was touting last year substitutes very nicely for the 1/2" - 3/8" adapter.
Recently I implemented Steven Schoner's trick (based on work pioneered
by Bob Patton, who has been on and off both the NOC and B-I lists over
the years). It was to pipe a 1/8" hose off the main breather (before
the check valve) into a tee on the intake stub balance hose (a stock Mark
III part), including a .041"
restrictor and a small auto distributor vacuum line check valve in
this
line.
The purpose is to utilise intake vacuum to pull pressure out of the
crankcase, thus reducing oil leaks, motor temperature and "pumping
losses",
i.e. more power.
After getting myself into trouble by trying too many modifications at
once
(and especially leaving carburettor main jet holders loose), I have
at last
assembled all the right parts and followed the plan without screwing
up
anything else.
It runs. It runs fine.
Ben English
Date: Sun, 12 Jul 1998 22:15:37 -0700
From: Ben English
Regarding my version of the Patton/Schoner breather modification, John
Mead wrote:
> On automobile race engines the lines go to the exhaust headers and
this
> way the extracting of the crankcase volume does not upset the intake
> mixture.
Michael Moore has compiled posts from 1996 breather threads on the Thumper and Vintage Racing lists into a document he forwards on request. There is extensive discussion of the exhaust connection.
However, determining exactly where the negative pressure pulses might lurk in one's header pipes and then drilling holes and welding fittings on them is not an attractive proposition to me. If it doesn't work right, you're stuck with ugly pipes. Cutting up pieces of rubber hose to squeeze in check valves from auto supply stores is E-Z to experiment with... and entirely reversible.
And the weird thing about my setup is that rather than "upsetting" my intake, it is much improved. The oddball plumbing carburets better than the carburettors!
Ben English
6.2 Wet Sumping and Crankcase Breathing
Date: Tue, 18 Aug 1998 07:19:39 -0700 (PDT)
From: Robert Smith
At 08:51 AM 8/18/98 +0000, Richard Bates wrote:
>What are the hazards of wet sumping? Doesn't the oil just get pumped
out of the
>crankcase once the engine's running? I've never bothered to drain
the crankcase
>after the bike's been idle for a while, but perhaps I should.
Too much oil in the crankcase will significantly raise the crankcase pressure. If the breather can't cope with this pressure (it may be a more of a problem on earlier models with the smaller diameter timed breather, perhaps), the oil will try to find another way out. Frequently this is the drive-side crankcase seal, and the primary fills up with engine oil.
This is a definite problem if you're running a different grade of oil in the primary, and a weak or ruptured seal is going to pressurise the primary, forcing oil out there too.
If you think this may be happening to your bike, keep an eye on the oil level in the primary.
Cheers,
Date: Mon, 24 Aug 1998 09:34:59 -0400 (EDT)
From: Steven R. Schoner
Well folks,
Another season of riding my Norton is almost over, and I am reporting on the fix mentioned below for the leaky head problem. It really works.
Also, instead of steel inserts in the head for the pulled studs, I used special silicon bronze inserts. And instead of the studs and longnuts I used capscrews with fine threads (24 TPI), they were a bit tricky to get in, but much easier to torque to the right 30' pounds with the special attachments that I made for my torque wrench.
Then with the crankcase breather system mentioned below, and after 8,000 miles-- no oil leaks, and my oil consumption is down, too.
The fix is a complete success!
Steve Schoner
>Reply to message from ??? of Fri, 12 Dec
>>
>>Dear Paul,
>>> Are there any comprehensive technical notes on the subject?? To
>>> judge from the recent interest in the subject there is a need for
>>> more than a couple of Chapters.
>>>
>>We had a thorough discussion of this topic earlier this year, I will
>>try to dig out the relevant contributions with significant
>>contributions by the undersigned, and mail them to you. You should
>>also look up the NOC web page and enter the tech topic, an abstract
>>may be avaiable.
>>
>>As for venting the c/case by manifold suction, this method is not
>>recommended. I discussed the venting subject with the honourable
Mr.
>>Les Emery of Fair Spares recently (he is THE Norton guru, as you
will
>>know). The information he came up with indicates that scavenging
by
>>the gear pump (6 start version in this case) will eventually fail
due
>>to suction being too low to overcome the low crankcase pressure.
>>(With a 3-start pump the problems are likely reinforced.) The result
>>is overfilling of the crankcase, increased oil drag, increased oil
>>consumption, carbon build-up, a smoking exhaust, new leakage's
and -
>>in the worst case - a starving top-end and increased wear of the
c/s
>>big-end.
>
>I have incorporated a combination system where a PCV valve is
>installed between the oil tank and the crankcase. Then, between
the
>PCV and the crankcase I have a tee which then runs a line to a tap
>into the carb manifold (low pressure side). This give the additional
>vacuum boost that you speak of.
>
>Early in this project, I too thought of the ramifications of oil
>scavenging, and tested the system to see if the pump was indeed
>being impaired in this vital function. The manual calls for
200cc
>of oil to be present in the crankcase after all the excess oil has
>been returned to the oil tank. In practice this varies
somewhat.
>It can go as low as 150 cc. I ran the engine at idle for several
>minutes, turned it off, then drained and measured the amount of oil
>present-- 200 cc. Then I put the oil back into the oil tank,
restarted
>the engine (drain plug in) ran it up to 3500 rpm for a minute or so,
>turned it off and drained the crankcase again. Result-- 170
cc of
>oil present in the crankcase. At higher rpms the result was
the
>same.
>
>On the road tests, I would go 10 miles or so, up hill, down hill,
>straight, stop and check the oil in the oil tank. Having noted
the
>level before hand, it did not change to any great degree.
>
>These tests were done 3,000 miles ago, and my engine runs fine--
>and with not a drop of oil on the head or anywhere else.
>
>I doubt that the manifold vacuum boost will adversely affect
>the scavenging ability of the oil pump-- Unless the pump is bad or
>worn in the first place.
>
>Steve Schoner.
--
Steven R. Schoner (Meteorite Man and Seeker), dm550@cleveland.freenet.edu
___________________________________________________________________________
Compared to the Infinite we know next to nothing. What good we
do with
the little we do know is the key to wisdom.