Various problems after rebuild 1973 commando 850

dimitri said:

@Rohan: Thanks for the advice. I really appreciate any input. I would not let my bikes idle for extended periods if it was not for adjusting reasons. But in my experience, i follow Hobot on this one. I am not talking about Commando's in particular, but i had air-cooled engines idle for much longer with temperature sensors connected. They should not overheat that fast. In fact, when properly adjusted and under normal conditions, the temperature stabilizes at a certain point. If the Norton does overheat (and i don't say it can't just by idling, you guys know better than i do), it would be caused by a wrong setting or the particular design of the engine. And that's one of the things i'm trying to find out ;-).
Just for fun: many of the stuff manuals warn you for are disclaimers, legal stuff and product placement. My Commando 961 manual says i can only use fuchs oil. And funny enough, there is a wrong procedure to measure oil level, causing overfilling when owners don't have experience with dry sumps .

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I can see I'll have to find the road test of an - admittedly near new - Commando that boiled its oil sitting in a traffic jam.
It was a hot summers day though.
How does that sit with this 'temperature stabilisation' business. ?
Perhaps hobot could actually show us his data for his claims ??

There is also the minor matter that the cylinder walls don't get much oil while idling for long periods,
and the cam in a Commando doesn't get much oil while idling either.

But its your engine, you and hobot can do what you like with it.... !
Cheers.

Allright,

After fitting a new rocker feed line, new correct spark plugs, plug caps and wires (now, the complete ignition system is new) i had the chance to go for a ride today.

The bike is driving very good, but not perfect yet. Especially idle is not perfect. For the test drive, i did set the idle at 1000rpm. It does not stall and the gas response when accelerating is very good and linear. But...

Problem 1: it idles too rough.
When i set the air screw on the mikuni at 2 turns out, it makes the highest revs. It idles smoothly, but the idle is fluctuating a bit (lets say it goes up and down 50-100 rpm). Also, the spark plugs are indicating a lean mix.
At 1,5 turns, i have to set the idle screw higher to stay at 1000rpm. It idles roughly (does not stall) and the spark plugs have a nice tan.
I guess it's just very sensitive on the air screw.

Problem 2: speedo on speed
Are there common causes on a commando for a speedo that will indicate 220 when doing 50? Also, it is just going crazy up and down. Is it the cable winding up, the speedo gear or the speedo itself? Or can all of these fail on a commando?

Probem 3: Primary oil leak. I hoped to get it more or less tight for the moment with some liquid sealant. It didn't work. The funny thing is, it is only leaking when hot. I guess the cases warp a little when hot, as the oil in the primary should not really heat up that much? I tried the search, but did not find the answer. Can anybody give me some advice on shimming the inner case? Do i need parts to replace? Crankcase to primary gasket? Anything else? I need to remove a shim, because the outer case has a gap in front.
Also, do i need special tools to remove the clutch/inner case?

Rohan said:

The Owners Manual for various bikes warns about idling them standing still for more than 5 minutes, max.
I certainly wouldn't idle my bikes for more than that.
And would believe it over anything you say any day.
You can feel them getting HOT, in the cylinder head dept.

Especially if the idle mix hasn't been dialled in yet.
Thats a quick way to blue the pipes...

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How do you get through cities, with traffic jams? I let mine for as long as I need to let it idle. It's a road vehicle. Nothing melts!

Yes, mixture should be dialled-in.

A 35 pilot jet should be fine with air screw out about 1 1/2 turns. I run a 2.5 slide with a 159 P-5 Needle Jet. F -5 Needle 2nd notch from bottom. Main jet is a 250 .NGK BP6 plug. .My pipes are Emgo peashooters. I'm getting great fuel mileage with very good performance and terrific throttle response......Skip

Triton Thrasher said:

How do you get through cities, with traffic jams? I let mine for as long as I need to let it idle. It's a road vehicle. Nothing melts!

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The road test report said their test commando boiled its oil in a long hot traffic jam.

I've had bikes that started 8 stroking.
When its down to 12 stroking, you know its really hot.
Assumed it was the fuel boiling in the carbs.
Either escape at that point and get it into the breeze, or shut it down.
If its watercooled, the electric fan has cut in way before that...

Its been pointed out to me that some car makers print a warning about long periods of idling too.

But we digress...

On the still air or tail wind heating issue, if this is routine situation, its foolish not to fit a heat temp and oil temp quage and thermo stat cooler to save some groin tension and carbonized engine,

Bleedy Plimary .

If ye canaye get the spacer behind , CUT THE SIDE out of one , So YOU can slip it over the bolet .

WITHOUT the SPACER , if you lightly tighten the cover ( NEVER highly tighten it :x ) itll pull back , so NEVER seal .

If you want to throw the chain , run it empty & tight . Can get red hot and self diassemble . So ALWAYS see it Lubed .

MAY just be oil running down the back , from clutch mainshaft . They all do that . unless Modified .

It called a Oil Bath , as its a Oil Bath , For The PRIMARY CHAIN . This is called Lubrication . If you don't want oil , fit a belt drive .

Removeing & cleaning to ' O ' Ring , and GROOVE , might help things - they tend to stretch when aged so need a bit of technique to refit .
Or cut 7 fit with the join ( compressed ) at the TOP .

But Put a Bleedy Spacer in behind , or we'll have something to say about it . :wink: . say a U section with the Ends PARRALLEL . Please .

For the primary leak first make sure the three bolts holding the primary case to the engine are present and tight.

dimitri said:

Problem 2: speedo on speed
Are there common causes on a commando for a speedo that will indicate 220 when doing 50? Also, it is just going crazy up and down. Is it the cable winding up, the speedo gear or the speedo itself? Or can all of these fail on a commando?

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My guess would be the speedo end of the cable protruding too far out of the cable housing and pushing too far into the speedo. Should be about 7/16 inch. On some replacement cables, the speedo end is way too long and needs to be trimmed. Make sure you check it and don't run the speedo for too long like this or you will need a rebuild in short order.

tpeever said:

My guess would be the speedo end of the cable protruding too far out of the cable housing and pushing too far into the speedo. Should be about 7/16 inch.

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7/16" for instruments used up to around 1970, on the units that have (or originally had) the 'brass caps' (on the right in the photo).
9/16" for later instruments (left).

Thanks for the input!

I took the speedo off and checked with a screwdriver. It was doing the same strange stuff that way so i opened it (not my first time, but the first time with a smiths speedo). Everything was looking good except for the worm gear that was pushed too far down. Probably, like you guys say, from driving with a cable that was too long.
I adjusted it, reassembled and went for a drive. It is working as new again. I did order a new bezel kit, because the bezel was opened before and shows some tiny cracks.

I got the primary leak fixed (for the moment) by following the instructions of someone else here (i used a 5,7mm o-ring cord). It is just temporarily, because it definitely needs to be shimmed. But now i can do some test driving. Make sure i can cover all issues at once if i take the primary off.

Also set the mixture screw a little richer and getting close to what i want. It is very drivable at slow speeds (better than the 961 ). But not perfect yet.

hobot said:

On the still air or tail wind heating issue, if this is routine situation, its foolish not to fit a heat temp and oil temp quage and thermo stat cooler to save some groin tension and carbonized engine,

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If there is no airflow, oilcooler(s) don't help much.
Unless they have a fan/electric fan blowing through them.
But we digress...

Good to hear its all coming together.

Rohan said:

hobot said:

On the still air or tail wind heating issue, if this is routine situation, its foolish not to fit a heat temp and oil temp quage and thermo stat cooler to save some groin tension and carbonized engine,

Click to expand...

If there is no airflow, oilcooler(s) don't help much.
Unless they have a fan/electric fan blowing through them.
But we digress...

Good to hear its all coming together.

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When I raced, there'd be occasions where you'd be held in the start up area longer than planned. It did not take long for a race engine to get very hot and very uncomfortable, 8 stroking, back firing, etc.

Once we were released, one gentle 'sighting lap' later - and having air flowing around the engine brought it right back into its comfort zone again.

There seems little doubt to me, that an air cooled engine does need flowing air to function correctly.

Plus, the vast majority of our engines internals are lubricated by splash, splash is caused by revs. Ticking over like a stationary engine cannot be good for all those parts that rely on splash.

My final case: a mate had an 860 Ducati, years ago, stationary and in his workshop, fiddling with the slow running, whilst using a colour tune plug, he blew the motor! We never found out if it seized or holed or whatever as he practically gave it away in an act of despondency !!

Let's agree that idling for too long is not good .

Got a little further today. I noticed at a plug chop (i made the mistake of only reading one plug at a time, single carb...) the plugs were different in color. That's why i could not get it adjusted. The reason seems a little overlap in the 2 intake manifold gaskets, causing a very small, but 'real' air leak.
Maybe it is covered already, but the gaskets delivered in my VM34 kit needed some trimming. I didn't notice it upon installation.
I trimmed them and went for a quick ride. Both plugs are now the same light tan color. But i need to do the basic setup all over. I'm getting there!

Also fixed the warning lights and light switch. Everything is working now.

Let's agree that idling for too long is not good .

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No!

We will NOT agree on anything, and that's the way we like it around here....

1up3down said:

Let's agree that idling for too long is not good .

Click to expand...

No!

We will NOT agree on anything, and that's the way we like it around here....

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As long as my pressure guage shows some pressure, around 7 to 10 psi hot, I feel pretty safe.

Usually i feel pretty confident about the idling thing. But in this case, i have to admit, it could have gone wrong. One cylinder getting false air and the other one being tuned properly.

Anyway... i found the cause of the primary leak after a new test drive. At my first highway testdrive all of a sudden at 130km/h the bike started shaking very hard. I got off, and inspected. Seems like all 3 bolts that bolts the crankcase to the cradle were loose. The 2 ones at the back lost their nuts (probably that was already the case, causing the primary to stress). And during my ride yesterday, i think the lower bolt at the underside (the thinner one) snapped. So the crankcase was only hanging on the isolastics and the primary.

Scary...
Anything particular i should check for damage? I took the primary cover off. I can't find visible damage there.

I think that your Pazon, like most digital ignitions will require 5kOHM resistor plug caps, otherwise damage can be caused to the electronics. If the Pazon is like the digital Boyer, it has tickover stabilisation, which basically uses ignition timing to catch a stall at low revs, these means that checking the timing at tickover revs will have you tearing your hair out.

Small update:

So the engine bolts came loose causing the engine vibrating like hell. But i don't have much experience driving a commando so i thought it was normal. Ordered some nuts and one new bolt. Fixed the engine and went for a new ride. I did not know these isolastics worked so good. It is basically vibration free now. I went for an hour drive and when i got back, i was waiting for the drips under the primary. I knew they woud come... so i waited... and waited. But not one single drip. It will start dripping again in a while... i cleaned the underside. But good thing is i know now my primary leak was caused by a loose engine.
Also the fluctuating idle is gone. I don't have an explanation, but it had a perfect idle now.

Only problem it developed today is a non working speedo. The speedo itself is good. It seems that the gearbox was shot. Needle is moving when i turn the cable at the rear wheel.

dimitri said:

Small update:.........So the engine bolts came loose causing the engine vibrating like hell. ......... I did not know these isolastics worked so good. It is basically vibration free now. ........Also the fluctuating idle is gone. I don't have an explanation, but it had a perfect idle now. ....Only problem it developed today is a non working speedo.

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Glad to hear that it's coming together for you