oil build up in crankcase on commando 850 bleeding through cylinder barrel gasket

ashman · Nov 24, 2022

concours said:
There is no base gasket used on an 850.
12oz. in the sump is not excessive.
The "sporadic" recovery to tank is as-designed, the scavenge pump has more volume than the supply, thus, slugs of oil,

concours said:
There is no base gasket used on an 850.
12oz. in the sump is not excessive.
The "sporadic" recovery to tank is as-designed, the scavenge pump has more volume than the supply, thus, slugs of oil, slugs of air.

My 74 850 mk2 brought new and on first rebuild had a base gasket fitted from the factory but when replacing with a base gasket make sure it don't cover that oil return hole same with using gasket sealer, in over 46 years I have never had a base gasket leak, before starting the new rebuild did you prime the oil pump before starting, I also fill the oil pump up with oil before fitting and turning to see oil come out of the holes while filling it.
I have been caught out a few times with gaskets kits some gaskets not cut or fitting right, always check first but mostly timing cover gasket near the lower points cover to be cut wrong, 2x this has happened to me and had to get another timing gasket.

Ashley

concours · Nov 24, 2022

Tornado said:
Reviving old thread.
I have seepage at two places of the 850 mkII barrel base. This was last fitted by a classic bike shop a year ago. Seems to have a gasket and some sealer evident around edges. Thinking to remove head and lift barrel enough to clean up, apply locktite sealer and torque. Trying to avoid full block lift off as I've never done ring fitting before and don't want to risk it.

Does this sound like a reasonable approach?

No.

Fast Eddie · Nov 25, 2022

Tornado said:
Reviving old thread.
I have seepage at two places of the 850 mkII barrel base. This was last fitted by a classic bike shop a year ago. Seems to have a gasket and some sealer evident around edges. Thinking to remove head and lift barrel enough to clean up, apply locktite sealer and torque. Trying to avoid full block lift off as I've never done ring fitting before and don't want to risk it.

Does this sound like a reasonable approach?

IMHO that will be way more fiddly than doing the job properly.

And you run a big risk of not doing a good job, and having another leak.

Make a board like the one shown below, ensure the barrel has a good taper (will almost certainly need making bigger if it’s been rebored), and use good ring clamps.

Do the above and it’s really not difficult, and is a piece of cake compared to the head !

I’d put money on your through bolts being loose. They cannot be re torqued, so must be done up RFT. The base gasket is not a problematic joint IF a) the engine is breathing right b) surface prep is right c) good sealer is used d) bolts are tight.

I have to say… as your posts add up in my head, it seems clear that shop you used should be avoided in future…

Onder · Nov 25, 2022

That photo is worth a thousand words. You run up a piece like that then dropping the jugs on is straightforward. However, you will notice why alloy barrels are an attractive option.

concours · Nov 25, 2022

Onder said:
That photo is worth a thousand words. You run up a piece like that then dropping the jugs on is straightforward. However, you will notice why alloy barrels are an attractive option.

I put the piston rings in the bore, then invert the barrell, then wiggle in the wrist/gudgeon pins

Thomasa · Nov 25, 2022

It's been so long since I did this operation that I don't remember the details except that the head juggling act is much harder. One needs at least 11 fingers. I do, however remember that it was imperative NOT to let the rod/piston assembly fall front or back, nicking the rod(s). From that nick a crack can develop. If the previous shop nicked the rod you should file out the nick, being careful not to get any filings down into the case.

Onder · Nov 26, 2022

Agree about nicking the rods. And putting in the pots first is a good idea as long as you have figured out how to keep the jugs at the right distance above the cases so there is no wiggling of the jugs as you worry in the gudgeon pins. Those jugs weigh a ton.

Tornado · Nov 26, 2022

I believe Mr Comstock has a viddy on his channel showing his method. Holds the barrels up on deep sockets while fettling in the wrist pins and circlips.

Perhaps this is a way to avoid removing pistons entirely, lift barrels off with pistons/rings still inserted.

baz · Nov 26, 2022

Tornado said:
I believe Mr Comstock has a viddy on his channel showing his method. Holds the barrels up on deep sockets while fettling in the wrist pins and circlips.

Perhaps this is a way to avoid removing pistons entirely, lift barrels off with pistons/rings still inserted.

No you wouldn't remove them like that
The reason you fit them that way is to avoid breaking the rings lowering the barrel on to pistons

Tornado · Nov 26, 2022

baz said:
No you wouldn't remove them like that
The reason you fit them that way is to avoid breaking the rings lowering the barrel on to pistons

Is the reason b/c the pins cannot be pushed out with pistons still inserted?

baz · Nov 26, 2022

Tornado said:
Is the reason b/c the pins cannot be pushed out with pistons still inserted?

Nope
The sole reason you would fit the pistons into the barrel first is to avoid breaking the rings
IE with the barrel on the bench you can fit the pistons individually without breaking the rings
Then lower the block and pistons together onto the Conrods and fit the gudgeon pins and circlips
Personally I use plastic 3" rainwater clamps to clamp the rings tight to the pistons then tap the barrel down with my palm
Then remove the clamps and fully lower the barrel
These work fine for a 750 I'm not sure about an 850 though

Tornado · Nov 26, 2022

baz said:
Nope
The sole reason you would fit the pistons into the barrel first is to avoid breaking the rings
IE with the barrel on the bench you can fit the pistons individually without breaking the rings
Then lower the block and pistons together onto the Conrods and fit the gudgeon pins and circlips
Personally I use plastic 3" rainwater clamps to clamp the rings tight to the pistons then tap the barrel down with my palm
Then remove the clamps and fully lower the barrel
These work fine for a 750 I'm not sure about an 850 though

Understood. But was wondering if possible to leave piston/rings inserted and remove barrels, to avoid having to risk rings on re-installing. Recall i'm only trying to address leaking barrel base, not needing to do cylinder/piston work.

baz · Nov 26, 2022

Tornado said:
Understood. But was wondering if possible to leave piston/rings inserted and remove barrels, to avoid having to risk rings on re-installing. Recall i'm only trying to address leaking barrel base, not needing to do cylinder/piston work.

Well you could try
I reckon you'll need an assistant with it because of the weight of the barrel
You could probably remove the circlips from the pistons
Then using external circlip pliers you may be able to pull the gudgeon pins out
But honestly I don't think it's worth the bother

texasSlick · Nov 26, 2022

Tornado said:
Understood. But was wondering if possible to leave piston/rings inserted and remove barrels, to avoid having to risk rings on re-installing. Recall i'm only trying to address leaking barrel base, not needing to do cylinder/piston work.

I see no problem with your proposed method. IIRC, I did that technique myself at one time.

Jack up the barrels far enough to get the outboard circlip out, then push out the pin. Hold the barrels up with wood shims while you are fiddling with the circlips. Put rags around the connecting rods to keep them off the case lip. Reverse to assemble.

Slick

Fast Eddie · Nov 27, 2022

IMHO, just because Comnoz does something (who has built hundreds and has well honed knacks) doesn’t mean it’s the best way for a first timer.

I believe you stand more chance of damage, and injury, using the above methods vs a stout board and ring clamps.

baz · Nov 27, 2022

texasSlick said:
I see no problem with your proposed method. IIRC, I did that technique myself at one time.

Jack up the barrels far enough to get the outboard circlip out, then push out the pin. Hold the barrels up with wood shims while you are fiddling with the circlips. Put rags around the connecting rods to keep them off the case lip. Reverse to assemble.

Slick

Did you do this on an 850 ? Just wondering if there's enough room between the pistons to "push out the pin"

baz · Nov 27, 2022

Fast Eddie said:
IMHO, just because Comnoz does something (who has built hundreds and has well honed knacks) doesn’t mean it’s the best way for a first timer.

I believe you stand more chance of damage, and injury, using the above methods vs a stout board and ring clamps.

I agree
But each to their own I guess

baz · Nov 27, 2022

For me I would absolutely have to remove both pistons from the barrel to inspect the pistons
Inspect the rings
Check the ring gap and the fit of the rings in the piston grooves
If the bike has been running rich for any reason I'd be looking for sharpness on the rings etc

Fast Eddie · Nov 27, 2022

baz said:
Did you do this on an 850 ? Just wondering if there's enough room between the pistons to "push out the pin"

Depends how thin and strong your fingers are !

Or you make up some kind of puller ?

Counter productive IMO though. Requires more effort than it saves.

baz · Nov 27, 2022

Fast Eddie said:
Depends how thin and strong your fingers are !

Or you make up some kind of puller ?

Counter productive IMO though. Requires more effort than it saves.

This is why I suggested external circlip pliers
Maybe you could put them inside the gudgeon pins, expand the pliers and pull them out keeping the barrel perfectly level so you can get the one out

oil build up in crankcase on commando 850 bleeding through cylinder barrel gasket

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