Crankcase Breather Help

Dirt2Oil · Aug 31, 2014

I am attempting to modify the crankcase breather after reading some material on here. I have the reed type engine breather valve from XS650 direct. So I assumed there was something inside the original I could remove and took the top cover off ( the part the hose attaches to). I was suprised to find there was nothing inside, there is a metal screen top and bottom but nothing else. IS THERE SUPPOSE TO BE SOMETHING BETWEEN THE TWO SCREENS? The manuals I have does not show this breather.

Also there is a hole on the back side of the timing cover that is currently plugged with a bolt. I was thinking of opening that up and joining it into the hose coming out the crankcase breatherport with a T before it goes into the new reed type breather valve. IS THERE ANY REASON I SHOULD NOT DO THIS?

(I have the bolt removed here)

I was thinking two openings would allow the crankcase to breath better. BUT I have been wrong before so NEED your feedback.

I did finally get to go for my FIRST ride on the Commando and it was a blast!

CanukNortonNut · Aug 31, 2014

Dirt2,
I think originally there was a foam piece that went between the screens.
I would attempt to do the CNW 72 breather and blank off the vent holes on the timing side. Do a search on Comstock breathers or check out CNW website.
Cheers,
Thomas
CNN

Fast Eddie · Aug 31, 2014

As CNN says, best thing would be to do this 'properly'. This is a bit of a bigger job though.

If you're looking for a quick fix, then these valves are supposed to work better mounted as close as possible to the source of the pressure. So, blank off your timing cover breather completely and mount your reed valve in the line that you connect to your crank case breather, and mount it close to the engine if possible.

Take out any obstructions in that current crank breather assembly.

Bob Z. · Aug 31, 2014

Check your lower timing crankcase for the grub screw that blanks off the drilling for the internal oil pump pick-up.

If your bike has this screw, you should seriously consider getting the engine cases apart this winter and doing the internal engine oil pick-up and breather modifications.

vidar hjelm johansen · Aug 31, 2014

Hi
That how I did it

Vidar

Hobot · Aug 31, 2014

Lots of ways to lower case pressure some w/o a valve involved at all. Elegant reed valve install Vidar. There is some pumping loss to vent out via TS volume so not a bad idea to open up and create some new vents to crank volume which tends to lower pumping loss and increases volume so piston decent pressure spikes just never get as high as prior. To move oil drain to rear drill/mill into TS case to expose the passage way enough to drain all it can, then blow out swarf with air or spray via front hole before closing it off permanently. No need to mess with the DS baffle.

CanukNortonNut · Aug 31, 2014

Vidar,
I still like it on the crankcase side of the engine. Jim Comstock figured that out. But you are bringing it as close to the pressure pulse as possible. Do a Search for Ludwig's Crankcase mod here on the Access Norton. You can see what he did to get to the Crankcase side of the timing chest.
Uh enough tapping on the computer....time to take out the norton for a snort. :lol:
Cheers,
Thomas
CNN

pete.v · Aug 31, 2014

Mine.....

Dirt2Oil · Aug 31, 2014

Thanks for all the information folks.
I did track down a schematic showing the stock breather assembly.

As a quick fix for this season I will plug off the timing case hole and install the reed valve as close to the crankcase as possible. I understand the CNW valve is the best bet and will probably buy it over the winter when I will likely be replacing the piston and rings as well.

Nortiboy · Sep 1, 2014

Dirt2Oil said:
IS THERE ANY REASON I SHOULD NOT DO THIS?

No reason. I have had the combat breather and the 850 breather both opened to atmosphere with a small catch tank next to the battery. Bike (73-750)has always run very well, no leaks anywhere. I get about a teaspoon of oil from the catch tank every 1000 miles or so. Been working well for 10 years of high speed cruising. There are more sophisticated systems available.

Hobot · Sep 1, 2014

i've kept Trixie Combat as factory issued & did not get any mess or oil tank vent drips getting into 2S cam zone upper 6000's as long as rings sealing well, so the better the case pressure venting the more ya can get away w/o a ring job on your mind. My buddy Wes '71 with cam timed breather does not weep oil either and pulls as hard or harder than a Combat up to 90's with no aftermarket vent gizmos but he's had to put new rings in regularly about 2-3 yr intervals when it did begin to weep oil, until I gave him foam filter material to wrap up the cutie pie k/n crude filter. One thing these Cdo's have taught me in spades is similar to my neurological practice, where the signs and symptoms show up usually ain't the source so tease patients about their other Dr.s being as smart as a dog sniffing at your finger that's pointing to the coon in the tree leaving droppings on the ground.

Dirt2Oil · Sep 1, 2014

hobot said:
One thing these Cdo's have taught me in spades is similar to my neurological practice, where the signs and symptoms show up usually ain't the source so tease patients about their other Dr.s being as smart as a dog sniffing at your finger that's pointing to the coon in the tree leaving droppings on the ground.

I think you have hit the nail on the head Hobot, the real problem is likely the rings really need to be done.

L.A.B. · Sep 1, 2014

What nobody appears to have picked up on so far, is that the timing case breather spigot looks like the factory job, and that type of breather wasn't used on the 750 models.
I think we came to the conclusion in a previous discussion about this bike, that the crankcases have probably been replaced at some point in its history, but it seems perhaps not as a matching pair, as the drive-side case is the usual '72 - '73 750 type, but the timing side case seems to be '73 - '74 850.

CanukNortonNut · Sep 1, 2014

L.A.B. said:
What nobody appears to have picked up on so far, is that the timing case breather spigot looks like the factory job, and that type of breather wasn't used on the 750 models.
I think we came to the conclusion in a previous discussion about this bike, that the crankcases have probably been replaced at some point in its history, but it seems perhaps not as a matching pair, as the drive-side case is the usual '72 - '73 750 type, but the timing side case seems to be '73 - '74 850.

I saw that too L.A.B. but it didn't click. Good point.
CNN

ashman · Sep 1, 2014

I throught the same as LAB when looking at two breathers on your motor, I also run my breather into a catch bottle since I have had my Motor in the Featherbed frame (34 years now) and works very well, I don't get any leaks in my motor at all, but I didn't like the suck and blow with the breather and did put a Yammy Reed valve on the breather line to stop air from going back into the crank case, I have been lucky as my motor has always been oil tight since new.

You could connect the 2 breather hoses together and connect a Reed valve, only a throught and probly be the way I would go.

Ashley

swooshdave · Sep 1, 2014

xs650-breather-exposed-t7345.html

1. Block/plug the hole on the back of the timing chest.
2. Place reed valve as close to engine as possible. Mine (also a 72) is attached to the stock breather with about 2in of hose, maybe less.

Don't forget to drill a drain hole next to the reed. See my post.

Nortiboy · Sep 2, 2014

L.A.B. said:
What nobody appears to have picked up on so far, is that the timing case breather spigot looks like the factory job, and that type of breather wasn't used on the 750 models.

"I have had the combat breather and the 850 breather both opened to atmosphere"

I should have been clearer. Both breathers are on the one bike. (MK5 750) Works well.

Cheers

pete.v · Sep 2, 2014

Dirt, just to be clear, the XS 650 valve will not be incorporated to the breather on the bottom of the left crankcase. This breather should be concidered as a manifold whereas the hose from said manifold will fit the large port of the 650 valve, and the smaller hose from the oiltank will fit the smaller port of the 650 valve. This is the correct orientation and its placement between the manifold and the oil tank is, for me anyways, half way, where it makes a convenient 90 degree turn up from the manifold and on to the tank.

I am also in the 2 breather camp where I have the XS650 valve off the crank breather which dumps to the oil tank and Grandpauls reed machined into the mag boss which although seems to produce less volume but is none the less quite active (audible) dumps to atmosphere.

Dirt2Oil · Sep 2, 2014

Bob Z. said:
Check your lower timing crankcase for the grub screw that blanks off the drilling for the internal oil pump pick-up.

If your bike has this screw, you should seriously consider getting the engine cases apart this winter and doing the internal engine oil pick-up and breather modifications.

I don't see the grub screw you are talking about so assume that is a good thing. I have the reed valve installed just after the stock breather.
Just noticed oil leaking out the back side of the primary case where the stator wire comes through. Have to deal with that and Hopefully that will stop the leaks.

The left cylinder is smoking considerably now so I think I will attempt the piston and rings. Was hoping to get a little more riding before winter but doesn't look like that's possible.

Well I did buy this bike to work on and there has been lots of work but little riding. I will keep telling myself NEXT SUMMER!

Crankcase Breather Help

Dirt2Oil

CanukNortonNut

Fast Eddie

Bob Z.

vidar hjelm johansen

Hobot

CanukNortonNut

pete.v

Dirt2Oil

Nortiboy

Hobot

Dirt2Oil

L.A.B.

Moderator

CanukNortonNut

ashman

swooshdave

Nortiboy

pete.v

Dirt2Oil

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