Easy and cheap modifications I would do again

No, you can keep the timed breather in place as that should, at low revs, enhance the reed valve but as the engine revs increase it becomes less effective as it is really too small. So you need another route for the reed breather and the sump mount won't work with the frame crossmember in place on the 70 frame so that leaves the timing case or a less effective one using a rocker cover. The rocker cover is a long distance from the pulses so less effective but at least spare rocker covers are easy to come by.
I agree with kommando
I have the original camshaft timed breather
And a reed valve on the plate where the aborted starter motor should sit on the back of the timing cover
I use a 125 Yamaha so called (egr valve) with half the housing removed
I don't have any extra holes drilled from the inner timing cover into the crankcase
It works well for me,it's teed to the camshaft rotary breather then into the oil tank
It returns a lot of oil to the tank and never emulsifies

 
I agree with kommando
I have the original camshaft timed breather
And a reed valve on the plate where the aborted starter motor should sit on the back of the timing cover
I use a 125 Yamaha so called (egr valve) with half the housing removed
I don't have any extra holes drilled from the inner timing cover into the crankcase
It works well for me,it's teed to the camshaft rotary breather then into the oil tank
It returns a lot of oil to the tank and never emulsifies


I have a 70 commando with a similar timing side reed breather. I've owned it for 48 years...

Here's the evolution:
First all I had was the stock camshaft rotating disk breather - The biked leaked oil as was standard back in the day, so clearly the stock disk breather was insufficient or the bike wouldn't leak

Some years later, I did the timing side plate breather mod - I drilled 2 holes from the timing side cavity into the crankcase. A 3/8" diameter hole between the cast webbing up high for air to travel out of the crankcase and a 1/4" hole under the oil pump boss to lower the oil level in the timing side cavity, so the other holes would be free to pass air into the timing chest. I added a "mike's XS" style breather on the blanking plate on the timing side to meter the air pulses. I used the stock breather and the timing side modification together for many years. I still occasionally got a little weep of oil at the tachometer drive port.

A few years ago, I added the Jim Schmidt reed breather on top of the camshaft disk port breather. I think it helped make the port breather more efficient at sealing off return air on the piston upstrokes so I no longer got any weeping at the tachometer drive port.

Last season I decided I was going to drill a 1/4" hole right down the middle of the disks while they were in place on the bike.... mostly because people said NOT to do it... I pumped the end of the port full of automotive grease to catch chips, and made a threaded centering device on the lathe to screw into the port and center the 1/4" bit. I bought 4 brand new bits, because you don't want to have any powdering or flaking when you drill. You want curls only as you drill so you can collect them as they are generated by drilling. I drilled the disks, vacuumed out the grease and chips, the followed up with many passes with a rare earth magnet on a stalk to pick up any chips that the grease didn't capture. The magnet did pick up a chip or two, so clearly the grease didn't contain all the chips, so clearly there are safer ways to do this.. but what's done is done as they say.

If you look at the camshaft breather design, the camshaft is hollow and has a wheel shaped part of the casting in the center that has 4 1/8" holes drilled to draw air into the camshaft to go out the port. I think that is one of the inherent weaknesses of using that port as far as pushing a volume of air and the rotating disk doesn't seal as well as a reed valve, so I think the results of only using the timed breather port is the weakest design... and there's certainly better performing options now... those being, going weakest to best performing:

1)Crankcase sump drain plug breathers- Jim Schmidt now makes one to fit the early bikes as Pete mentioned already. The original Comstock design hit against the cross member of early frame bikes*
2) Double breathers Jim Schmidt camshaft breather and timing side breather modification used together
3) Timing side modification and stock rotary disk breather together
4)Timing side modification
5)Jim Schmidt camshaft breather on the camshaft port alone with removed disk port mechanism
6)Jim Schmidt camshaft breather with the disk mechanism left in place. *I think it improves the efficiency of the port seal to resist backward flow of air on the upstroke.
7)The stock rotating camshaft disk system which as Kommando said, works a little bit, but doesn't seal well or have the capacity to remove the volume of air at high rpms...

this is just my opinion..... and not written in stone as fact..
 
Only time I think like this is during the winter when I can't/won't ride a bike that has way too much "why?" done too it.

I have a garage full of stuff that didn't work that well on one vehicle or another. Some of it from the OEM factory.
Actually, I was cracking a joke by saying that I might not have done my modifications if I only knew better. I love making shit, and making it work better too. It's a sickness I've had from when I was a kid. My only regrets on my modifications was that they were all more expensive than I thought they would be as they developed because I had to make extra parts and keep doing extensive testing, besides spending days of time working on the lathe, welding stuff, and test fitting and testing variations of every modification.

If it's true that every modification reduces the value of a classic bike, then I'll have to pay someone to take it when it's time to sell it... 😏
 
I have a 70 commando with a similar timing side reed breather. I've owned it for 48 years...

Here's the evolution:
First all I had was the stock camshaft rotating disk breather - The biked leaked oil as was standard back in the day, so clearly the stock disk breather was insufficient or the bike wouldn't leak

Some years later, I did the timing side plate breather mod - I drilled 2 holes from the timing side cavity into the crankcase. A 3/8" diameter hole between the cast webbing up high for air to travel out of the crankcase and a 1/4" hole under the oil pump boss to lower the oil level in the timing side cavity, so the other holes would be free to pass air into the timing chest. I added a "mike's XS" style breather on the blanking plate on the timing side to meter the air pulses. I used the stock breather and the timing side modification together for many years. I still occasionally got a little weep of oil at the tachometer drive port.

A few years ago, I added the Jim Schmidt reed breather on top of the camshaft disk port breather. I think it helped make the port breather more efficient at sealing off return air on the piston upstrokes so I no longer got any weeping at the tachometer drive port.

Last season I decided I was going to drill a 1/4" hole right down the middle of the disks while they were in place on the bike.... mostly because people said NOT to do it... I pumped the end of the port full of automotive grease to catch chips, and made a threaded centering device on the lathe to screw into the port and center the 1/4" bit. I bought 4 brand new bits, because you don't want to have any powdering or flaking when you drill. You want curls only as you drill so you can collect them as they are generated by drilling. I drilled the disks, vacuumed out the grease and chips, the followed up with many passes with a rare earth magnet on a stalk to pick up any chips that the grease didn't capture. The magnet did pick up a chip or two, so clearly the grease didn't contain all the chips, so clearly there are safer ways to do this.. but what's done is done as they say.

If you look at the camshaft breather design, the camshaft is hollow and has a wheel shaped part of the casting in the center that has 4 1/8" holes drilled to draw air into the camshaft to go out the port. I think that is one of the inherent weaknesses of using that port as far as pushing a volume of air and the rotating disk doesn't seal as well as a reed valve, so I think the results of only using the timed breather port is the weakest design... and there's certainly better performing options now... those being, going weakest to best performing:

1)Crankcase sump drain plug breathers- Jim Schmidt now makes one to fit the early bikes as Pete mentioned already. The original Comstock design hit against the cross member of early frame bikes*
2) Double breathers Jim Schmidt camshaft breather and timing side breather modification used together
3) Timing side modification and stock rotary disk breather together
4)Timing side modification
5)Jim Schmidt camshaft breather on the camshaft port alone with removed disk port mechanism
6)Jim Schmidt camshaft breather with the disk mechanism left in place. *I think it improves the efficiency of the port seal to resist backward flow of air on the upstroke.
7)The stock rotating camshaft disk system which as Kommando said, works a little bit, but doesn't seal well or have the capacity to remove the volume of air at high rpms...

this is just my opinion..... and not written in stone as fact..
Originally I had an oxy acetylene torch flashback arrester on the back of my timing cover
It's basically a small reed valve
This worked well but I have to remove it when I fitted an Alton kit as it was in the way
I immediately started getting a cylinder base leak and it looked oily around the rocker covers
So that was when I thought I'd better refit a valve and the Yamaha one fitted the bill
 
Actually, I was cracking a joke by saying that I might not have done my modifications if I only knew better. I love making shit, and making it work better too. It's a sickness I've had from when I was a kid. My only regrets on my modifications was that they were all more expensive than I thought they would be as they developed because I had to make extra parts and keep doing extensive testing, besides spending days of time working on the lathe, welding stuff, and test fitting and testing variations of every modification.

If it's true that every modification reduces the value of a classic bike, then I'll have to pay someone to take it when it's time to sell it... 😏
Yeah, I got the joke part. I was trying to agree in my unusual way.
 
I use Suzuki GS exhaust gaskets. They work. The Norton ones I got don't. Since I have a couple Suzuki GS1100Es, it was free to try since I have tons of spares. What a relief, not once has that thing backed off and rattled since I changed. My breather on the N15 is stock and has never given any problems, I just put it all back together. Maybe I'm living on borrowed time.
 
Perhaps not considered a cheap modification but in my experience a visit to a well run dyno is good value for money.

A carefully planned programme to test ignition timing and carb tuning can deliver a increase in power and much nicer running engine.

The trick is to find a sympathetic operator who has the skill and imagination to work with older machines.
 
"Perhaps not considered a cheap modification but in my experience a visit to a well run dyno is good value for money. "

Absolutely right! And re that, I'd like to see those "Torque Wings" on an objective Dyno test. ;)
 
Not the easiest thing to do but worthwhile. I drilled the inlet rocker arm shafts through and eliminated the external oil feed to left hand side. This allowed me to use left side line fitting in the head to feed an oil pressure gauge.
 
I use Suzuki GS exhaust gaskets. They work. The Norton ones I got don't. Since I have a couple Suzuki GS1100Es, it was free to try since I have tons of spares. What a relief, not once has that thing backed off and rattled since I changed. My breather on the N15 is stock and has never given any problems, I just put it all back together. Maybe I'm living on borrowed time.
You're good with a stock cam and the timed breather.

Only reason I have a reed breather is I bought and installed a SS cam in my P11 cases in 1990's. (Wasn't a bolt in and go affair.) That SS cam did not support the timed breather. I made my own convoluted breather setup that threaded to a plate attached to the magneto hole on the timing side and used it for 3 decades. Found out about the smaller thinner cNw breather for the 72 cases after joining here and installed that in the same location on the timing side as the one I made. It doesn't actually work any better, but it looks a lot better. Later when I did the engine with the JSM JS2 cam that supports a timed breather, I eventually hooked up the timed breather and run both now. It does work and as was mentioned is better at very low RPM with the timed breather added.
 
I have a 70 commando with a similar timing side reed breather. I've owned it for 48 years...

Here's the evolution:
First all I had was the stock camshaft rotating disk breather - The biked leaked oil as was standard back in the day, so clearly the stock disk breather was insufficient or the bike wouldn't leak

Some years later, I did the timing side plate breather mod - I drilled 2 holes from the timing side cavity into the crankcase. A 3/8" diameter hole between the cast webbing up high for air to travel out of the crankcase and a 1/4" hole under the oil pump boss to lower the oil level in the timing side cavity, so the other holes would be free to pass air into the timing chest. I added a "mike's XS" style breather on the blanking plate on the timing side to meter the air pulses. I used the stock breather and the timing side modification together for many years. I still occasionally got a little weep of oil at the tachometer drive port.

A few years ago, I added the Jim Schmidt reed breather on top of the camshaft disk port breather. I think it helped make the port breather more efficient at sealing off return air on the piston upstrokes so I no longer got any weeping at the tachometer drive port.

Last season I decided I was going to drill a 1/4" hole right down the middle of the disks while they were in place on the bike.... mostly because people said NOT to do it... I pumped the end of the port full of automotive grease to catch chips, and made a threaded centering device on the lathe to screw into the port and center the 1/4" bit. I bought 4 brand new bits, because you don't want to have any powdering or flaking when you drill. You want curls only as you drill so you can collect them as they are generated by drilling. I drilled the disks, vacuumed out the grease and chips, the followed up with many passes with a rare earth magnet on a stalk to pick up any chips that the grease didn't capture. The magnet did pick up a chip or two, so clearly the grease didn't contain all the chips, so clearly there are safer ways to do this.. but what's done is done as they say.

If you look at the camshaft breather design, the camshaft is hollow and has a wheel shaped part of the casting in the center that has 4 1/8" holes drilled to draw air into the camshaft to go out the port. I think that is one of the inherent weaknesses of using that port as far as pushing a volume of air and the rotating disk doesn't seal as well as a reed valve, so I think the results of only using the timed breather port is the weakest design... and there's certainly better performing options now... those being, going weakest to best performing:

1)Crankcase sump drain plug breathers- Jim Schmidt now makes one to fit the early bikes as Pete mentioned already. The original Comstock design hit against the cross member of early frame bikes*
2) Double breathers Jim Schmidt camshaft breather and timing side breather modification used together
3) Timing side modification and stock rotary disk breather together
4)Timing side modification
5)Jim Schmidt camshaft breather on the camshaft port alone with removed disk port mechanism
6)Jim Schmidt camshaft breather with the disk mechanism left in place. *I think it improves the efficiency of the port seal to resist backward flow of air on the upstroke.
7)The stock rotating camshaft disk system which as Kommando said, works a little bit, but doesn't seal well or have the capacity to remove the volume of air at high rpms...

this is just my opinion..... and not written in stone as fact..
Very detailed explanation. Now I really dont what to do. Only fooling kinda. So I understand that the stock breather port on the 70 case is to small by itself to handle the flow of air so adding a second teed in at the right rear will do the trick. does that mean a reed valve at both locations. thanks
 
For the MK3, switching from the $180 UK supplied starter sprag to the $17 Chinese sprag made my e start into a reliable unit.
The Madass big disc 6 pot front brake didn't cost much and transformed braking, especially when riding with gusto in the mountains.
A complete Dunstall 2 1 2 exhaust system was given to me for use on the 920. I believe there are some replicas of these available today, at great expense.
Don't bother.
I tried it out on my 850 first.
The Dunstall ad back in the day claimed the system would boost standard Commando performance so much that it would be capable of quarter mile times in the high 11 second range.
I found that the Dunstall system had the opposite effect, on Dyno Hill, it slowed the bike down vs standard type pre 1974 open peashooters on standard skinny separate headers.
 
Last edited:


Write your reply...
Back
Top