1970 Commando oil tank vent restricter.

Peter Restaino · Tuesday at 10:10 AM

Good morning guys. Ok I want to install the JS reed valve he sells that is designed to be installed at the left front of the engine cam port that all the early engines have. Cases are split right now so JS says to omitt the rotory valve and spring so I was wondering if I should drill out the restricter that seems to be part of the oil tank vent elbow. Not shure if the elbow unscrews from the tank. Dont want to break it.

NPeteN · Tuesday at 10:23 AM

Peter Restaino said:
Good morning guys. Ok I want to install the JS reed valve he sells that is designed to be installed at the left front of the engine cam port that all the early engines have. Cases are split right now so JS says to omitt the rotory valve and spring so I was wondering if I should drill out the restricter that seems to be part of the oil tank vent elbow. Not shure if the elbow unscrews from the tank. Dont want to break it.

Just follow the instructions for the breather and leave the tank alone.

marshg246 · Tuesday at 10:39 AM

Peter Restaino said:
Good morning guys. Ok I want to install the JS reed valve he sells that is designed to be installed at the left front of the engine cam port that all the early engines have. Cases are split right now so JS says to omitt the rotory valve and spring so I was wondering if I should drill out the restricter that seems to be part of the oil tank vent elbow. Not shure if the elbow unscrews from the tank. Dont want to break it.

Please provide a link to the JS breather. I think I know all he offers but do not know of one that screws into the engine at the end of the cam the drive side. A picture of the restrictor would be good too - I can't visualize what you are talking about.

You should become a VIP member so you can easily post pictures.

NPeteN · Tuesday at 10:59 AM

marshg246 · Tuesday at 11:11 AM

NPeteN said:
View attachment 122711

OK, I see. I have no idea how much oil will come out there but since the timed breather works with the central oil tank this probably will too. Personally, I would not spend the money and would get the more expensive sump version and correct the oil tank vent problem - then I know all is well including evacuating excess oil.

Peter Restaino · Tuesday at 12:32 PM

Im not a fan of the sump reed valve because of the same issue as Gregs 69 had with oil being injected into the air filter. I have the Andover sump drain kit so draining excess sump oil is easy and by the way I have an evo Harely with the same wet sumping issue when left dormant for a while so Im used to the ritual. As for the restricter the elbow coming out of the oil tank has a brass tube in the opening of the elbow makint it half the size opening.

marshg246 · Tuesday at 12:42 PM

Peter Restaino said:
Im not a fan of the sump reed valve because of the same issue as Gregs 69 had with oil being injected into the air filter. I have the Andover sump drain kit so draining excess sump oil is easy and by the way I have an evo Harely with the same wet sumping issue when left dormant for a while so Im used to the ritual. As for the restricter the elbow coming out of the oil tank has a brass tube in the opening of the elbow makint it half the size opening.

Then I suggest that you remove the breather timer, and install no reed valve. If too much oil is entering the air cleaner - figure out why - there should not be much if any. The most likely causes are:

Too much oil in the tank
Hole in the pipe to the air cleaner

I have no clue what elbow you are talking about. The central oil tank has none related to the pipe to the air cleaner.

marshg246 · Tuesday at 12:44 PM

If you don't want to post pictures here, email to me. I'm trying to help but I really am not following you!

marshg@gregmarsh.com

Richard Tool · Tuesday at 1:21 PM

My catch bottle

https://www.accessnorton.com/attachments/uqeopy-webp.76153/

NPeteN · Tuesday at 3:16 PM

Maybe Peter can use this photo to explain his issue. Poor quality but the only one I've got of the area.

marshg246 · Tuesday at 5:53 PM

NPeteN said:
Maybe Peter can use this photo to explain his issue. Poor quality but the only one I've got of the area.
View attachment 122719

The breather is attached to the top of the tank, not to the stub on the side of the tower - good! That's the tank that has no trouble with the breather. The bottom red circle is where the oil tanks vents, from the tower.

If he's saying there is a restriction on your type of tank at the top - it needs to be gone. If he's saying that there is a restriction on the vent to the air cleaner, it needs to be gone and what is causing too much oil to be fixed.

I bet he doesn't have your type of tank since he tested putting water through the breather and it came out the air cleaner vent - doesn't happen with the good kind of tank. Both picture grabbed from eBay - not sure why I don't have pictures of the two kinds - that was a long fight to figure it out.

Bad kind:

Good kind:

Peter Restaino · Tuesday at 8:32 PM

Sorry for the mix up guys, I dont any problems with my bike because I bought it as a basket case but now Im starting to put it together and always wondered what that restricted elbow was for. So I have the tank that NPeteN shows with red circle around the vent outlet. Mine has a brass elbow with a restriction in it screwed in to that hole pointing down, so I guess somebody put that there. I was afraid to try and unscew it cause it looked kinda braised in but I will try and unscrew it. So I guess If last person that operated this bike may of had a little oil going into the air filter and tried that elbow restricter. So in conclusion will try and remove the elbow and with the JS reed valve it may be ok. You guys are very helpful. thanks.

jseng1 · 2025-12-03T11:01:22-0700

That early central oil tank is missing a breather return line fitting. Its not easy but you have to install a return tube to the top of the oil tank. This means boiling out the oil and brazing in a tube or finding a way to thread in a fitting and using JB weld on the threads to prevent leaks (funky). People who use the pre 71 sump breather or the left side cam vent breather need to do this. The original rotating breather valve should be removed at the first opportunity when using the left side reed breather.

pre 71 reed breather shown below

left side cam vent breather below

marshg246 · 2025-12-03T12:07:44-0700

jseng1 said:
That early central oil tank is missing a breather return line fitting. Its not easy but you have to install a return tube to the top of the oil tank. This means boiling out the oil and brazing in a tube or finding a way to thread in a fitting and using JB weld on the threads to prevent leaks (funky). People who use the pre 71 sump breather or the left side cam vent breather need to do this. The original rotating breather valve should be removed at the first opportunity when using the left side reed breather.

pre 71 reed breather shown below

left side cam vent breather below

The two early Commando central oil tanks I showed both have a breather connection. One to the top of the tank (good for reed valve) and on the tower (bad for a reed valve).

If there's a third type, please post a picture.

Peter Restaino · 2025-12-03T13:23:41-0700

Im going with the Js cam vent reed valve leaving out the vent rotor and spring and my 69 oil tank with the froth tower vent. I seen Jims video of reed valve in action and it looks promissing but I dont understand what you mean by the tank is missing a return line fitting. I thought the hole on the air box side of the tank is where it vents out.

marshg246 · 2025-12-03T14:31:50-0700

Peter Restaino said:
Im going with the Js cam vent reed valve leaving out the vent rotor and spring and my 69 oil tank with the froth tower vent. I seen Jims video of reed valve in action and it looks promissing but I dont understand what you mean by the tank is missing a return line fitting. I thought the hole on the air box side of the tank is where it vents out.

OK, I've explained in every way I can come up with so I'm out after this post.

The JS breather output will connect to your froth tower input. Your oil tank is vented by the tube from within the froth tower to the air cleaner. No issue with any of that. However, if the JS breather returns oil with the crankcase air, you will have oil dripping out the bottom of your air cleaner just as I did in my write-up.

Peter Restaino · 2025-12-04T01:04:46-0700

Ok ill will end this insanity and say your 69 had the bottom engine sump reed valve thus blowing huge amounts of oil into the air cleaner so if using the cam port breather JS reed valve I should be good. Thanks for bearing with me. Over and out.

jseng1 · 2025-12-04T17:32:37-0700

The tower must vent to the atmosphere. Do not run a tube to the tower unless you leave it open (to rarely drip on the chain etc).
You've got an engine oil line in and an engine oil line out.

You also need a breather line into the top of the oil tank (above the oil) and this can be missing from the central oil tanks. This is where you want to vent your reed breathier to.

1970 Commando oil tank vent restricter.

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