A Good Ride Spoiled

Saber

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Looks like some leakage to the pushrod tunnel but would that equate to a blowout or sudden loss of power?
 

baz

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Looks like some leakage to the pushrod tunnel but would that equate to a blowout or sudden loss of power?
That was my thoughts also
I've never blown a head gasket on a commando,but I was expecting to see worse than that?
I've blown a gasket on a t140 but that blew a section out between the bores and compression was gone
 

Derek Wilson

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Before you pull the barrels, how do the cylinder walls look? Is there a major ridge at the top? As soon as you pull them off, you will be into a deglaze and new rings as a minimum.

As your principle problem is your head gasket, unless there is good reason to pull the barrels (previous oil consumption, low on power, etc.), I would be inclined to let sleeping dogs lie.

My $0.02 - FWIW
 

maylar

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I don't use copper head gaskets any more because they leak oil, but I've never blown one. I have blown 2 flame ring gaskets over the years but was always able to make it home. And both of those instances were while seriously flogging the motor. It's hard to believe that a copper gasket would blow under normal cruising.

Were the head bolts loose?
 
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About 15 years ago my Commando had a similar sudden power loss, however it had been at a sustained 6600 rpm in top gear for several miles. All of a sudden RPM dropped to 6000 and oil appeared on the cylinder fins.
What happened was the head joint started to leak after two of the studs pulled out. The bike did manage to limp for 25 miles or so back to home.
Helicoils and a new composite gasket solved the problem. It's been dry ever since. I don't do the sustained 6600 thing anymore though!
I know you take it pretty easy so it would be surprising if the any of the threads have pulled, but you might check them.

Glen
 

Tornado

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Bike has 14.7 k Miles if clock is to be believed. Obviously engine has been into by a previous owner since gasket is not stock. Gearbox tear I did revealed similar evidence as locktite was present on some bolts and bushings.
The lower front sleeve nuts are rear nut were no longer at proper torque when I removed them yesterday. Top side bolts had descent torque on.
The image of HG were pushrod tunnel is shows carbon built up but looking closely at left side shows copper is narrower and thinner compared to right side. Question is is that sufficient for sudden power drop and smoke appearance or is there possible ring damage?
 

Derek Wilson

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Again, I would be having a close look at the cylinder walls. If you have a broken ring and worn cylinders, that should be noticeable. But yes, power drop and smoke are in line with you have indicated: I am guessing that the you are seeing compression loss on both cylinders (looking at the head gasket and compression test numbers), and you would be drawing in some oil through that same area on each intake stroke. It doesn't take much oil to create a significant smoke show, especially when you have a sustained source of oil like you head gasket leakage has created.

And again - my $0.02 - I am not there to see what you see, just trying to read the clues you have provided.
 

Fast Eddie

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Yes, that gasket is goosed on the one side and would definitely suffered compression loss and also oil burning.

So that’s a yes to your question, it could be the source of your sysmotoms.

But it’s also equally possible it could be the rings.

Honestly, without a 100% clear certainty, you simply cannot not lift the barrels at this stage of the game.

From where you are now, it’s a 10 minute job !!
 

Tornado

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Lifting barrels pretty much means new rings? Have never done any of this before so im a little daunted to replace rings or even to try refitting old ones back into barrel. Watch a few videos on this and head refit, so im humbled.
 
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My inclination would be to do as Derek suggests.
We can clearly see the head gasket has been leaking in a big way.
You could clean things up and put it back together with a composite gasket.
Do test the threaded holes first. If they hold at the prescribed torque, great, if not you will need to helicoil or similar.
Once buttoned up, you could do a leakdown test. If there is a broken ring, it will fail the leakdown test. In that case I would not run it, just take it back down and fix that.
As Derek says, once you lift the barrel off, the old ring seating is pooched even if things look great.
Eddie's way is not wrong either, just more involved and you could end up doing some work and spending $ that is not required.
It's a bit of a crap shoot as to which is best.


Glen
 
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Just to be awkward (moi?) mine smoked heavily one side, lifting the barrels revealed a broken ring on the opposite side!!! But no evidence of scoring in the bores either.... (Turned out to be head/valve related)
BUT.. agree with all regarding lifting barrels to investigate, just make sure the crankcase is well protected against possible falling debris...
 

Tornado

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How best to test stud holding? I'm thinking using a block of lumber, drill to pass the stud through, then fit some washers and the head nut, torque away to she if she holds. Sound like a plan?
 

baz

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If it were mine I would absolutely have to lift the barrel
You can check for camshaft wear,check the followers
Check and replace the rings
Check the bore and the ring gap
I'd check the head is flat and check the holding down studs
I'd lightly lap the valves in (after checking they are not badly worn) replace the guide seals
Check valve spring length
And put it back together with a composite head gasket
Cheers
 

baz

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How best to test stud holding? I'm thinking using a block of lumber, drill to pass the stud through, then fit some washers and the head nut, torque away to she if she holds. Sound like a plan?
You could do that
Not sure if timber would have any give?
Maybe just bolt the head back on to test
You won't need to fit the push rods
 
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Well in for a penny in for a pound.... Whatever makes you feel assured that you've done what's best for your scooter and allows you to rest easy when you climb on it...... I would piss on the penny at this fork in the road and pull the jug just because I don't know if I can't see it. Rather not try kicking my own down the road for not looking when I had the opportunity whilst crying over a greater problem..... My time is coming with 25,000mi on the guesstimated clock +.
 
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Torque is torque. If you have some hardwood and build up to big flat washers against the wood, you should be able to get to the prescribed torque. It's not much. The wood will crush a bit but so does metal, just by a smaller factor. Shouldn't matter as long as the Torque wrench clicks before the threads pull.
Or as Baz suggests, head on acid test.
Not difficult sans pushrods.


Glen
 

Tornado

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Torque is torque. If you have some hardwood and build up to big flat washers against the wood, you should be able to get to the prescribed torque. It's not much. The wood will crush a bit but so does metal, just by a smaller factor. Shouldn't matter as long as the Torque wrench clicks before the threads pull.
Or as Baz suggests, head on acid test.
Not difficult sans pushrods.


Glen
With head on, would I need to worry about not having the gasket in place or micro grit getting mashed into head? Would have to do all the fittings to torque, not just the three studs, or risk warpage, correct?
 
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