Discussion: crankcase modifications for oiling

There have been numerous discussions surrounding the various crankcase modifications that alter the oil return from the sump. There are several variations on the theme most often related to the well-documented version on Old Britt's website. There are also a few variations of the additional drillings to assist oil return to the sump gallery.
Also, there are some variations of breathing through the timing chest, with additional drillings to either assist in oil draining, breathing between the two cavities, or both.

There are pros and cons to any and all mods. Everyone has an opinion.

I believed the issue of cutting out the wier lip at the back of the early crankcase sumps was more or less settled in the minds of the majority that this was a GOOD thing, until a recent reply to one of my posts on an ongoing build of a '72 Combat engine.

I have done a couple of searches and gleaned this list of threads that discuss the topic to some degree. It's not a definitive list, but it covers most of the discussions that have surrounded the topic.

post85701.html?hilit=crankcase mod#p85701
post79009.html?hilit=crankcase mod#p79009
post57832.html?hilit=crankcase mod#p57832
post54589.html?hilit=crankcase mod#p54589
post50761.html?hilit=crankcase mod#p50761
post33277.html?hilit=crankcase mod#p33277
post33008.html?hilit=crankcase mod#p33008
post15458.html?hilit=crankcase mod#p15458
post15415.html?hilit=crankcase mod#p15415
post4837.html?hilit=crankcase mod#p4837
post112320.html?hilit=crankcase sump mod#p112320

There are several technical issues surrounding these mods, mostly related to the following:

1. Improper Oil return from the sump at higher engine speeds causing starvation

2. Crankcase breathing being affected by collected oil being forced up the rear breather on earlier models

3. Crankcase breathing through the timing chest to a reed valve

An additional remotely related issue is wet sumping, which is also discussed in some of the above threads.

Let's have some extended discussion on this topic, with appreciated input being experience in implementing these mods on multiple bikes, significant mileage covered thereafter, and any oil-related failures or other issues experienced in conjunction.

Thanx.

What is the rear breather on the earlier models? Does that have anything to do with the timed breather out the left side of the cam?

I am, as we speak, modifying the oil tank breather on my 69 which has the infamous hole in the front of the central oil tank that leaks oil all over the inside of the filter and drips down on the gearbox to oil the whole bottom end of the bike. I tapped a 5/16-24 bolt into the hole, drilled the center out and cut the head off, making a 5/16-24 nipple. I'm attach a hose to that and run it through a hole in the front ham can air filter cover, and let it drip down on the ground instead of the gearbox (or perhaps a catch bottle). At least I should be able to contain the leak to something I can live with.

Dave
69S

Paul,

I modified my 72 Combat several years ago working with the photos on the Old Britts site. The only thing I've seen much variation on is how the old pick-up hole is plugged. I think the original Mick Hemmings article of many years ago said to plug it up with Araldite. Hope I have that right, but that's where I first heard of this. Phil Radford told me he welds the holes up. I tapped mine, got it surgically clean and loctited a small internal hex bolt in it. What some refer to as an "allen screw". Long after I had my cases buttoned up, I read a comment from someone who drilled a series of small holes for the new oil pickup, instead of milling the case away to uncover it. I think this person referred to it as a de-facto filter, but I only read the description, never saw a picture. Only other thing I did was to add a magnetic drain plug. I can't report on any real differnce, since this was a bike I aquired with a flat cam, and kinda clapped out top end, so everything was re-done. I drilled the holes in the timing case exactly where they were pictured in the MKII version of the INOA Tech Digest, made an alloy plate to cover the old breather, and made another plate to cover the old magneto cover, rather than cutting that one. Initially, I just mounted a half-inch hose from a spigot on the plate to the oil tank, then moved to a Motormite valve, and finally mounted one of those aftermarket XS 650 things on a newly designed plate where the mag cover plate was. Even with no valve, it's always been fairly oil-tight, and nothing unusual to report on anything. I figured since I had the engine apart for the cam, I might as well do this mod as well. Bike is mostly riddern moderatly fast on the street with very little contiuned high RPM operation, so I was probably not the intended audience for this mod. I run an oil pressure gauge, and all seems to be good at higher rpms. But I'm not doing laps on a track, either.

Don W.

You shouldn't have much oil spillage from that pipe unless you are pushing excessive oil out your breather pipe and/or pumping it out on wet sump start-up.

It isn't much but after a while it accumulates and drips off the bottom of the GB and cradle. I've always had this problem and nearly everyone I know experiences the same issue. I think it may be possible to add baffles or traps in the top hat to help prevent the oil from coming out the oil tank breather, but it is always subject to oil vapor which will condense and drip. I'd rather have it drip where I can contain it, than in the air filter and on top of the GB. In just 100 miles, I could see where it was splashing on the inside of the chrome cover, dripping down through the filter off the bottom of the oil tank, on top of the GB and then on down to the bottom of the GB and cradle where the wind splashes it from there back.

I did test to see how much comes out of the timed breather, and about 1oz of oil comes out after about 2 minutes from a cold start overnight, and that supposedly should be trapped back into the tank.

I don't think what I'm doing is going to hurt anything and if I can contain the oil or keep it off the bike, that's what I want.

I hope I'm not hijacking your thread, I'll shut up now.

Dave
69S

I think the issue is that Fred posted it about his race bike which will see very high rpms for an extended time, whereas no street bike will see that kind of abuse (even the self-professed boy racers).

Based on the more recent findings by comnoz it appears that the breather in the back with a reed valve is actually the optimum location.

I, for one, would never consider milling the crankcase unless I was racing. Then I might look into it.

Otherwise reed valve close to the crankcase for me.

Paul, I think you move the breather just so you can use the Triumph reed valves you sell.

DogT said:

It isn't much but after a while it accumulates and drips off the bottom of the GB and cradle. I've always had this problem and nearly everyone I know experiences the same issue. I think it may be possible to add baffles or traps in the top hat to help prevent the oil from coming out the oil tank breather, but it is always subject to oil vapor which will condense and drip. I'd rather have it drip where I can contain it, than in the air filter and on top of the GB. if I can contain the oil or keep it off the bike, that's what I want.
Dave
69S

Click to expand...

Dave, sounds like you simply need to fit a catch bottle to the outlet hose. I don't know the space limitations in a 69 battery / oil tank area, but I find on the 850 a number of plastic containers are suitable i.e. I use a rectangular ex-battery acid bottle that fits nicely alongside the battery. The oil tank vent goes into that at one end about 1" deep to allow plenty of room for mist to condense, and on the opposite side an outlet hose goes down the back of the gearbox to the lower right frame away from the tyre track. No drips, no mess. OK back to crankcase mods.....

Mick

For the sake of newer owners and for those who are not as mechanically astute, let's be clear here. There are "2" type of wet sumping.

1. Oil seep into the crankcase while sitting by gravity through the oil pump.

2. The type of wet sumping we are talking about here. Here is the explanation by Fred.

"History:

In 1972 Norton made some good changes to the crankcases, but blew it when they changed the oil scavenge pickup. Prior to this the oil scavenge was through a sump plug and screen in the back of the crankcase. The Commando engine started out as the Atlas engine and was mounted straight up in the frame. In the Commando the engine is leaned forward, and I guess the engineers at Norton figured that since the existing scavenge pickup was not the lowest part of the crankcase, moving the pickup to the center of the crankcase (the lowest point) would be an improvement. This, however, was not the case, for with the counter clockwise rotation of the flywheel flinging oil to the rear and the lack of a place for oil to pool, at higher RPMs, the oil builds up in the rear of the crankcase and the scavenge pickup cavitates. This causes the engine to wetsump and starve the upper end of oil. "

This situation is exclusive to 72 and early 73 crankcases and should not be misconstrude by the general membership as a performance tip for anything BUT the 1972 and early 1973 crankcases. Better said is that this not a performance tip but a service note to bring proper functionality to these motors.

I have performed these modification on a 210XXX set this last winter. I now have more faith to wind her up and along with the oil pressure gauge, red line is tickled from time to time.

http://s814.photobucket.com/albums/zz67 ... 0Breather/

Pics of what I did to my '73 750; it works great so far, after about 1000 miles.

One pic is of the two breathers, Norton left, XS650 right.

Other pic is of the adapter plate that I made to be able to bolt the XS650 breather to the stock cases.

I did it this way because I could do it in situ and having no reason to split the cases to do it the right way - CNW's excellent product.

I neglected to take pics of the notches that I had to cut in each side of the XS650 breather to make clearance for two Norton breather hold down bolts. The bolt notches I cut came within 20 thou of breaking through the sides of the XS650 reed housing - not good. I also had to weld up/fabricate a U shaped clamp assembly that bridges the sloping sides of the XS650 reed housing and gives the new longer hold down bolts a square clamping surface.

I do not like the fact that I have now have two 1/4" x 1 1/2" bolts that unavoidably are too close together and clamp a tall stack of adapter and breather to a small bolt pad on the cases. It is not stable/durable enough and it does present a risk of failure and in the event of failure the liability is likely to be great. Given the location of the breather assembly, in front of the rear wheel, both rider and bike are risk if an oil leak develops. I watch it closely. The CNW design obviates these issues.

If I ever have cause to split my cases, then I will send them to CNW for their mod.

The rear bottom flange in DS Combat case only goes to the seam and nothing on TS case to block oil flowing / blowing back around it. I just put some holes in it to help more get to the drain faster. I plugged the front hole with can ya believe it JBWeld, in such a way could be drilled out if needed. I've run my pre modified Combat into 2S cam breathing range ie: over 68000 for some intervals and it blew oil oil about every seam and vent. Stayed pretty clean after wards and rev'd it even higher and way longer/hotter as rebuilt to take it, better.

If something breaks it gets chewed up to size chips that can plug drain and sump inlet and its cogs, so some type screen over drain would be good idea but good luck doing it.

hobot said:

The rear bottom flange in DS Combat case only goes to the seam and nothing on TS case to block oil flowing / blowing back around it.

Click to expand...

Paul, can you snap a pic of the TS of the case you are working on?

I'll be working on the T/S case half next week. I've got a rally/bike show to prepare for (they put me in charge of this stuff every time I miss a meeting).

grandpaul said:

I'll be working on the T/S case half next week. I've got a rally/bike show to prepare for (they put me in charge of this stuff every time I miss a meeting).

Click to expand...

I'm suppose to lead the ride for tomorrows club meeting. Sure, ask the guy with the least miles on his bike to lead the ride! :roll: