What's Wrong With My Engine?

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Bonwit

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Overall, I've got a lot to be happy about with this bike. It's gorgeous, starts on the first kick, is generally reliable and goes like stink. On the other hand, there are a couple of things that are bothering me, and I wonder if they might in any way be related.

First, I'm still getting poor milage. I moved the Mikuni's e-clip up a notch which improved performance and turned the plugs from dark soot to light gray, but still, I'm seeing only around 35 MPG. average (mostly highway).

Second, and more worrisome is its oil consumption. It's high. I didn't think I was burning it, but last weekend when riding with a friend, he commented that when behind me, he smelled burning oil, though he saw no smoke. Sure enough though, after idling a bit and then gunning the throttle, blue smoke emits from the pipes. The previous owner had a top overhaul done a year or so ago (black diamond valves and rings), but had only put a couple of hundred miles on it before I bought it in September, i.e. the bike sat a lot before I came along. I'm thinking that perhaps his break-in was insufficient. I've already put about 1,500 miles on it in the last couple of months, so if it was going to break-in you would have thought it would have done so by now. Also, I don't remember seeing blue smoke when I gunned the throttle in the past. . . Black, yes (because of the rich mixture), but not blue.

I'm also seeing a slight amount of oil in the (belt driven) primary and have ordered the Yamaha PCV valve, hoping to relieve crank case pressure.

Is there a possibility that any of this could be related? Any ideas on what to do about the slight smoking off idle short of pulling the head and barrel?

Thanks, as always
 
Bonwit,
if you have a compression guage, try the following steps.
1. run a standard compression test, make sure to note & record the readings.
2. do a "wet" comrpression test. make notes.
3. do a "leak down" compression test.
A. build up to the recorded pressure, & try to use the timing marks to establish a point from which to make readings.
( this is a real pain using the kicker, but you will get it eventually)
B.wait say 5 minutes,burp the guage, then record readings.
4. compare the readings L vs. R
( my preference is not more than 10 lb/psi im-balance between the two.)
if you see readings that are more than 15%, from high to low, or left to right, it should point you in the right direction without having to pull the jugs to inspect the bores pistons & rings.
hope this helps.
 
recklessridr said:
Bonwit,
if you have a compression guage, try the following steps.
1. run a standard compression test, make sure to note & record the readings.
2. do a "wet" comrpression test. make notes.
3. do a "leak down" compression test.
A. build up to the recorded pressure, & try to use the timing marks to establish a point from which to make readings.
( this is a real pain using the kicker, but you will get it eventually)
B.wait say 5 minutes,burp the guage, then record readings.
4. compare the readings L vs. R
( my preference is not more than 10 lb/psi im-balance between the two.)
if you see readings that are more than 15%, from high to low, or left to right, it should point you in the right direction without having to pull the jugs to inspect the bores pistons & rings.
hope this helps.
Click to expand...
Thanks for your comments. The only compression tester I own is a differential gauge set which I use to test compression on my Lycomming. In the aircraft engine application you can listen for pressurized air leaking from the exhaust, air intake and oil tank to determine whether the leak is from the exhaust valves, intake valves or rings, respectively. Can I utilize this differential method on my Norton?

My original question refereed to whether any of these issues could be related. I'm wondering if the over rich condition could have caused excessive wear in a couple of thousand miles, or if any carbon build up from this condition could have fouled the valves. I think I'm going to try adding a bit of Marvel Mystery Oil to try and clean up the top end to start with.

Thanks again for taking the time to spell this out for me.
 
I am also getting engine oil in my belt primary, my valve should be here tomorrow in hopes it will stop this leaking.
If it does not, I am NOT looking forward to pulling the primary apart to put in a new mainseal.

As for your gas mileage, I have never bothered to check mine, but 35mpg seems quite low.
You said this is with highway riding, we all can assume just cruising and no high speed, rpm, runs included of course.

Often a friend behind me will say that he smells oil from my Norton. My bike, like yours, starts and runs very good.
If it works, don't fix it. Let's just ignore some oil burning and not so great gas mileage, especially given the amount of
time and hassle trying to do something about it. I despise the thought of taking my head or cyclinders off.
Better to consider these minor "features", than problems that just have to be dealt with !

By the way, I am thinking of trying some strong velcro to attach the PCV valve to the back of the air cleaner plate.
I am looking forward to its arrival and tinkering with, I love to cut hoses up!
 
highdesert said:
I am also getting engine oil in my belt primary, my valve should be here tomorrow in hopes it will stop this leaking.
If it does not, I am NOT looking forward to pulling the primary apart to put in a new mainseal.

As for your gas mileage, I have never bothered to check mine, but 35mpg seems quite low.
You said this is with highway riding, we all can assume just cruising and no high speed, rpm, runs included of course.

Often a friend behind me will say that he smells oil from my Norton. My bike, like yours, starts and runs very good.
If it works, don't fix it. Let's just ignore some oil burning and not so great gas mileage, especially given the amount of
time and hassle trying to do something about it. I despise the thought of taking my head or cyclinders off.
Better to consider these minor "features", than problems that just have to be dealt with !

By the way, I am thinking of trying some strong velcro to attach the PCV valve to the back of the air cleaner plate.
I am looking forward to its arrival and tinkering with, I love to cut hoses up!
Click to expand...
Highdesert, I think we ordered our valves at the same time. Let me know how your install goes. I tend to agree with you, I'm not in a hurry to tear apart an engine that runs so well. I think I'll do the compression test to see what it tells me, add some Marvel and see if that cleans it up and then go from there.

Velcroing your pcv valve may be a very good idea. The heavy duty stuff hold like crazy and the added cushion will hold down vibration.
 
Hortons Norton wrote:
Maybe an intake valve seal?
Curious, what points you toward that conclusion?
Click to expand...

With signs of crankcase pressure I don't think it's a guide seal, but a mate had one pop off and the little bugger acted like a pump.

Cash
 
Highdesert, 35 mpg is roughly the fuel consumption of my Matchless G15 which is a pretty standard Atlas motor but with raised gearing for quick acceleration. It may be the case with your Commando (you do say its quick) that the sprockets have been changed. My old 850 Commando was returning 50 - 55 mpg and that was screwing it, but on acceleration its no where near as fast as the G15.
 
When referring to 'gallons' it is often a good idea to say if they are Imperial or US gallons.

1 Imperial gallon = 1.2 US gallon.

1 US gallon = 0.83 Imperial gallon.
 
Highdesert,

If you have a camera handy, I would love to see a few photos of the setup for the PCV valve that you settle on. I've got one myself that I'm planning to mount this weekend.

Thanks,
NWM
 
Assuming its in US gallons, 1 = 3.78 liters this bike is avergaing 14.89 Kms per litre. I run a Mikuni VM 34 on my 850 and average 22Kms per litre or 51 Miles per US gallon. Somethings not right. Better check the compression and the carb float level. The general spec for a Mikuni VM34 is -

Main Jet 240

Needle Jet P2 or P4

Needle 6DH3 or 6DH4

Pilot Jet 30-35

Air Jet 1.0

Slide 3
 
ML said:
Assuming its in US gallons, 1 = 3.78 liters this bike is avergaing 14.89 Kms per litre. I run a Mikuni VM 34 on my 850 and average 22Kms per litre or 51 Miles per US gallon. Somethings not right. Better check the compression and the carb float level. The general spec for a Mikuni VM34 is -

Main Jet 240

Needle Jet P2 or P4

Needle 6DH3 or 6DH4

Pilot Jet 30-35

Air Jet 1.0

Slide 3
Click to expand...
To what extent do you suppose low compression would affect MPG? I'm thinking if I'm burning a bit of oil the compression is probably down too. Would that be enough to reduce milage 15 MPG! Too, I'm wondering if my speedo is off a bit, making it look worse than it is. There's one other thing. Our fuel is 10% ethanol. My experience (at least in my car) is that you never get as many miles per tank full when there's alcohol in the fuel.
 
You can still get excellent MPG with low compression. In Britain and most of Europe and elsewhere after the war, the bikes in the 1940's and 1950's ran on 72 octane fuel. It was common for 350 and 500 singles to get 70 or 80 MPG and the Vincent V twin 1000cc could achieve up to 60MPG. These bikes had low compression, i.e. BSA A10 650 was 7.25-1 and the Vincent Rapide 6.5-1. What made the difference was a much smaller bore carb and consequently smaller main jet. Power was down but torque was the chief benefit the designers sought. A stock (used in good condition) 850 Commando should read around 140 to 150PSI cold. My only other thought is that maybe one of your cam lobes is wearing badly?

Mick
 
140-150 PSI from a COLD engine?

That surprises me.

What then would good compression levels be for the engine tested after warmed up?

Thanks.
 
BrianK said:
140-150 PSI from a COLD engine?

That surprises me.

What then would good compression levels be for the engine tested after warmed up?



I can only ever get about 80-90PSI but my gauge only has a 1/2'' long adaptor, does seem high for lower compression motor.
Click to expand...
 
Bonwit said:
Overall, I've got a lot to be happy about with this bike. It's gorgeous, starts on the first kick, is generally reliable and goes like stink. On the other hand, there are a couple of things that are bothering me, and I wonder if they might in any way be related.

First, I'm still getting poor milage. I moved the Mikuni's e-clip up a notch which improved performance and turned the plugs from dark soot to light gray, but still, I'm seeing only around 35 MPG. average (mostly highway).
Click to expand...

I have no experience with a Mikuni, but my 74 Roadster gets 55-57 mpg US with Amals. One ride this Summer at average 45 mph I got 60 mpg. I think I'm a bit lean on the needle.


Second, and more worrisome is its oil consumption. It's high. I didn't think I was burning it, but last weekend when riding with a friend, he commented that when behind me, he smelled burning oil, though he saw no smoke. Sure enough though, after idling a bit and then gunning the throttle, blue smoke emits from the pipes.
Click to expand...

Oil consumption while under power is usually rings, smoke while blipping at idle is usually valve guides or seals. Do both cylinders smoke the same?


The previous owner had a top overhaul done a year or so ago (black diamond valves and rings), but had only put a couple of hundred miles on it before I bought it in September, i.e. the bike sat a lot before I came along.
Click to expand...

Did he do guides too?


there a possibility that any of this could be related? Any ideas on what to do about the slight smoking off idle short of pulling the head and barrel?

Thanks, as always
Click to expand...

You really need to do a compression test and leakdown test. Low compression from bad rings could definitely affect gas mileage.
 
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