'70 camshaft breather not working - tach drive leaking? (2014)

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freefly103

freefly103

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Been putting a few miles on the '70 since the top end rebuild. Bike is running well, but have noticed a leak from the tach drive that's more annoying than anything else. Not a lot of oil leaking from there, but enough to have to clean it up after a ride.

The '70 has a camshaft breather. Upon inspection, the hose shows no signs of any blow back to the oil tank i.e. the hose is clear and the breather appears to be functioning but the pressure and leak is manifesting itself at the tach drive and not being released via the breather. I changed the oring in the tach drive body and installed another between the nut where the cable meets the drive body, but that has made little difference. I'd like one of Jim's reed breathers but to dismantle the engine and send the crankcase to the US to have it machined and installed is a bridge too far at this stage. An electronic tach with the analogue drive port blanked off will be the next step. That doesn't solve the inherent problem though, just the current symptoms.

Should the camshaft breather be an effective solution to the crankcase pressure build up or is it a useless design feature?
 
You need to invest in a reed type breather valve system. The later tach. drives were unscrolled so this helps if you can find one to purchase. You can machine the body I.d. enough to fit in a modern rawhide seal. Easy - peasy stuff. :|
 
If the camshaft breather isn't working the disk is not installed incorrectly. I'm not sure that you can fix it without splitting the cases. The tach drive needs an oil seal to keep the oil from leaking.

Greg
 
You could get the case machining done without having too send them to JIM.

But if you check Jim's product line you will see he does a sump plug breather that does not need cases to be machined...though you also need to check your frame, as there are clearance problems on early frames.

Or, as a simpler approach, mount an alternative breather on the timing chest....650 XS sttyle reed would help.....not as efficient as Jim's as all threads on the subject here will clarify....but probably better than a functioning timed breather...though it actually sounds like yours is not functioning!

The tach drive will probably leak whatever.....get a tach drive housing that has an oil seal fitted instead of the O ring...or blank it and use an electronic one..
 
I'm not sure the timed breather can be installed wrong?? If you pull the angle fitting you can see it work. I had Fair Spares machine my tach drive and no problemo and yes, if it's a 70 and has the center stand off the frame, the frame tube will not let you put the sump breather on. My only leak is the crankcase flanges which I didn't seal properly.
 
Timed breather disc could be missing, spring could be missing, disc tabs could be damaged; but none of that would explain why it's not breathing through the hose, unless it happened to get damaged, then stuck in the "closed" position... (not very likely)
 
I have noticed oil leaking from the tach drive on my recently revived '71 Roadster, which has 23,000 miles on it, mostly from the 1970s. I plan on installing the seal, as discussed at length on this and other threads, but I also want to address the breather issue. I also have some weeping from rocker covers.
Questions:
1. Is there a way to verify that the left side timed breather is functioning?
2. Assuming it is working, would it help to add a PCV reed valve in that breather line?

Thanks in advance for any shared knowledge on this.
 
That breather timing disk is a ruse at best. I wouldn't count on it.
 
NickZ said:
I have noticed oil leaking from the tach drive on my recently revived '71 Roadster, which has 23,000 miles on it, mostly from the 1970s. I plan on installing the seal, as discussed at length on this and other threads, but I also want to address the breather issue. I also have some weeping from rocker covers.
Click to expand...

I give a bit of advice about early models because I've owned a 70 commando for 40 years. If your bike leaks oil, then your crankcase pressure reducing system (timed breather) could be blocked, but probably more likely it's just insufficient. If it's blocked then the pin that holds the fixed timing disc could have broken or fallen out, so now the disc may spin a bit and not always align with the timing of the piston's descending. That would increase the pressure in your crankcase and you would notice a significant increase in leakage.

NickZ said:
1. Is there a way to verify that the left side timed breather is functioning?
Click to expand...

yes, unscrew the elbow in front of the breather, and you can look into the port and see if the outer disc is still fixed, and the inner disc spins when the cam turns. You can put your finger over the port and feel the pressure as you kick the bike over.


NickZ said:
2. Assuming it is working, would it help to add a PCV reed valve in that breather line?
Click to expand...

Yes, you can buy a reed valve from Jim Schmidt that screws into the early model breather port and it works pretty well. I have Jim's timed port breather on my own bike along with the more well known plate mounted Mike'sXS reed valve breather on the back of the timing chest on the other side of the bike. My bike doesn't leak now with 2 reed breathers mounted on it. I went with the Jim Schmidt port reed breather to increase the vacuum effect on the piston up stroke because the original timed port breather isn't really as efficient as a reed valve. By lowering your crankcase pressure, your bike will leak much less.

unfortunately our bikes have a different frame than later bikes and the lower cross member on our bikes preclude us from mounting one of Jim Comstock's sump plug breathers, which breathes well AND pumps any oil that sits in your crankcase from "leak down" when the bike is at rest for a long period of time..
 
I measured the sump pressure on my Atlas having the timed breather and found it to be 18 inches of water negative pressure.

Next, I placed an XS650 breather in series with the timed breather port, and measured the sump pressure again.

I was astonished to find, the pressure with the XS650 breather in series was exactly the same 18 inches of water. This result suggests the timed breather is about as efficient as it gets. Placing an XS650 breather on the timed breather port, even with the rotating disc removed, is not likely to show any improvement.

I now have a Comstock sump breather, and I intend to make aother pressure measurement, but as yet have not gotten a round tuit. I expect, but may be wrong, the Comstock breather will show increased negative pressure.

Slick
 
texasSlick said:
I measured the sump pressure on my Atlas having the timed breather and found it to be 18 inches of water negative pressure.
Click to expand...

how did you do that? did it change with RPM? or is that just a static measurement based on turning the engine over with the kicker?

texasSlick said:
Next, I placed an XS650 breather in series with the timed breather port, and measured the sump pressure again.

I was astonished to find, the pressure with the XS650 breather in series was exactly the same 18 inches of water. This result suggests the timed breather is about as efficient as it gets. Placing an XS650 breather on the timed breather port, even with the rotating disc removed, is not likely to show any improvement.
Click to expand...

Of course it's the same. The volume differential hasn't changed inside to engine so a single stroke measures only the change in volume, not the efficiency at speed of each kind of valve. On a single rotation test there is no measurable difference in vacuum pressure because valve efficiency is based on how fast the valve can open and close which becomes more significant as the RPM's increase.

If you think about a "perfect one way valve" which has the ability to open and close instantaneously no matter how fast the engine spins that valve would draw the greatest vacuum and have the least pressure exerted on the gaskets and seals. All valve types that were demonstrably less efficient would also reflect that efficiency with a lower measured vacuum pressure and greater pressure on the gaskets and seals. All the air compressors I have had in my lifetime have all had reed valves to pump air. Is there such a thing as a "timed disc" compressor? A) probably not...

texasSlick said:
I now have a Comstock sump breather, and I intend to make aother pressure measurement, but as yet have not gotten a round tuit. I expect, but may be wrong, the Comstock breather will show increased negative pressure.

Slick
Click to expand...

Unfortunately, we're talking about an early commando which has a frame crossmember which blocks the use of Jim Comstocks breather. It's too bad, because modifications are a pain in the ass, and a top notch "bolt on" breather like his takes the headache out of curing the crankcase pressure/oil leak/oil sumping problems.
 
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o0norton0o said:
how did you do that? did it change with RPM? or is that just a static measurement based on turning the engine over with the kicker?

I put a pressure tap in the rocker box by replacing one of the spindle cover screws with a hose barb connector. I assumed no phase lag between the sump and rocker box. Even if there was a difference in rocker box vs sump pressure, I was looking for changes. The negative pressure increased with rpm, reaching 18 inches water at approx 2K rpm and stayed there up to 5K. No measurements were made over 5K rpm. I used a Magnehelic differential pressure gauge to measure the pressure. The inherent slow response time of the mechanical gauge averaged the pressure measurement.

Of course it's the same. The volume differential hasn't changed inside to engine so a single stroke measures only the change in volume, not the efficiency at speed of each kind of valve. On a single rotation test there is no measurable difference in vacuum pressure because valve efficiency is based on how fast the valve can open and close which becomes more significant as the RPM's increase.

I did not think the rotary disc was a "perfect one way valve", and was subject to leak back. I expected the XS650 valve to stop such leak back, resulting in a negative pressure improvement. Since no such improvement occurred, I concurred the rotary disc is actually very efficient.

If you think about a "perfect one way valve" which has the ability to open and close instantaneously no matter how fast the engine spins that valve would draw the greatest vacuum and have the least pressure exerted on the gaskets and seals. All valve types that were demonstrably less efficient would also reflect that efficiency with a lower measured vacuum pressure and greater pressure on the gaskets and seals. All the air compressors I have had in my lifetime have all had reed valves to pump air. Is there such a thing as a "timed disc" compressor? A) probably not...



Unfortunately, we're talking about an early commando which has a frame crossmember which blocks the use of Jim Comstocks breather. It's too bad, because modifications are a pain in the ass, and a top notch "bolt on" breather like his takes the headache out of curing the crankcase pressure/oil leak/oil sumping problems.
Click to expand...
 
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When the cases are split - remove the disc and spring from the original rotary breather and install one of these. Make sure you have a hollow cam.

'70 camshaft breather not working - tach drive leaking? (2014)
 
Well Slick, my intuition tells me that maybe your readings are wrong. Seeing as you have the timed disc still in place, perhaps it restricts the amount of air that the pistons could displace on the downstroke, so even if it sealed or not both readings could only measure that limited displacement which as long as the disc is in place, does not change.

In my own case, I have 2 reed breathers. and after I added Jim Schmidts timing port breather, ALL leaks stopped. I believe it's because the timing disc breather leaked air into the crankcase which reduced my vacuum. Because I had 2 reed breathers, I didn't have a restriction on exhausting air on the downstroke like a single breather in series with a reed breather would have. So the only possible improvement that helped my bike become leak free is that the timing port reed breather sealed better than the rotating disc...

I'm open to your criticism on my logic. I noticed a difference, and connected the logical dots to explain why.
 
@oOnortonOo

I only reported what I found/measured.

We both agree that if the timed disc leaks back, it will reduce the vacuum. Then a reed valve in series should stop/reduce the leak back and improve the vacuum. I did not find any such improvement, although I fully expected I would, because I fully expected the rotating disc to leak back. I doubt the added flow resistance of the reed valve in series was significant to these results.

There is another factor to consider in the timed rotary disc breather system. Air expelled from the sump must pass thru four 1/8" holes in the cam. These holes may (may means I do not know it for a fact) create a flow restriction that results in a phase difference between sump pressure and the phasing of the rotating disc. By phasing of the disc, I mean the position of the disc opening relative to the port may not be optimal. Removing the disc removes any such phase error, and with a reed valve, might then show an improvement in vacuum. If this can be demonstrated, it implies that phase shifts are happening in the system.

Slick
 
o0norton0o said:
In my own case, I have 2 reed breathers. and after I added Jim Schmidts timing port breather, ALL leaks stopped. I believe it's because the timing disc breather leaked air into the crankcase which reduced my vacuum. Because I had 2 reed breathers, I didn't have a restriction on exhausting air on the downstroke like a single breather in series with a reed breather would have. So the only possible improvement that helped my bike become leak free is that the timing port reed breather sealed better than the rotating disc...
.
Click to expand...

I'm not sure I understand what you mean when you say you have 2 reed breathers. I assume one is the Jim Schmidt that you added to the left side timed breather. Where is the other one?
 
o0norton0o said:
Unfortunately, we're talking about an early commando which has a frame crossmember which blocks the use of Jim Comstocks breather. It's too bad, because modifications are a pain in the ass, and a top notch "bolt on" breather like his takes the headache out of curing the crankcase pressure/oil leak/oil sumping problems.
Click to expand...

Mine is a '71 with the center stand mounted to the engine cradle, so I think that means I could use the Jim Comstock sump breather.
 
Has anyone tried putting an in line reed valve in a tube venting from the intake rocker cover? I think I read somewhere that this been used as a potential solution.
 
old school and does NOTHING for the crankcase. the passages are to small to do any good.

NickZ said:
Has anyone tried putting an in line reed valve in a tube venting from the intake rocker cover? I think I read somewhere that this been used as a potential solution.
Click to expand...
 
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