Help with tuning.

Could the reed be in backwards not allowing the crankcase to vent?
As Greg said, rocker spindles could be oriented wrong.

Bike looks GREAT btw. Combat Long Range Fastback will be a FUN ride when sorted!!
 
When the bike was running did you happen to check the return flow to the tank? 20 oz of oil in the sump is way too much. After the bike has run a minute or two there should only be a couple of ounces in the sump even if it was wet sumped to start with. A sump full of oil can definitely make an engine smoke, though usually on both sides. It sounds like for some reason the scavenge side of the pump is not returning oil to tank sufficiently. The AMR mod is on the feed side and shouldn't affect the scavenge. Did I see where you mentioned you modified the drain in the sump? Can you be more specific.
 
MichaelB said:
Could the reed be in backwards not allowing the crankcase to vent?
As Greg said, rocker spindles could be oriented wrong.
Click to expand...
htown16 said:
When the bike was running did you happen to check the return flow to the tank? 20 oz of oil in the sump is way too much. After the bike has run a minute or two there should only be a couple of ounces in the sump even if it was wet sumped to start with. A sump full of oil can definitely make an engine smoke, though usually on both sides. It sounds like for some reason the scavenge side of the pump is not returning oil to tank sufficiently. The AMR mod is on the feed side and shouldn't affect the scavenge. Did I see where you mentioned you modified the drain in the sump? Can you be more specific.
Click to expand...

Michael, Dont think you can put the reed in backwards. I will check it, easy once the barrels the starter are off.

HTown, The oil return has a good flow. Here is the drive side revision notes. Included is the explanation from Jim Comstock.


Brian,
The combat engine had a scavenge problem that caused the engine to wet sump the cases at highway speed. Then they would blow oil out of every seam.

The factory had moved the scavenge pump pickup to the front of the case thinking it would work better since it was the lowest spot. They did not take into account the fact that the windage from the spinning crankshaft pushes the oil to the rear of the case where the pump could not pick it up.

To fix it you need to plug the original hole and use a mill, a burr or a 1/4 inch rat tail file to open the oil passage near the rear of the case.

I have attached a picture.

Another mod that is necessary on that engine is to remove the locating tab from the camshaft thrust washer -if it is still there. Otherwise it will break off and go into the oil pump -breaking it. If it was missing make sure it is not stuck in the scavenge passage leading to the oil pump. Jim
 

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Were the valves & guides renewed? Sucking oil down through guide(s) from rocker side into combustion chamber could explain this problem fully, no?
 
Anything is possible. I dont suspect the head, having recently , (milagewise) been completely reconditioned.
Hot dye test, replace guides, cut seats. kibblewhite guides, black diamond valves, conical valve springs, teflon seals. JCC pistons and Hasting rings.

There is 30-40 miles on this engine, yes miles.
Tornado said:
Were the valves & guides renewed? Sucking oil down through guide(s) from rocker side into combustion chamber could explain this problem fully, no?
Click to expand...
The oilway through the barrel is clear, and through the crankcase, no sealant on the head gasket and the base I used a spray on light film.

The rings are intact, I will take them off tomorrow and measure the end gaps in the barrels. The bores are unscored. No contact marks on the piston tops. I think I have 95 thou combined with the base and head gaskets.
 

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You say the oil way through the barrel is clear, but in the picture it looks like the barrel has left a mark that shows the barrel hole was misaligned and was ‘eye-lidding’. Is this the case? And if so, could this have slowed down the draining sufficiently to have caused the head to fill?
 
Fast Eddie said:
You say the oil way through the barrel is clear, but in the picture it looks like the barrel has left a mark that shows the barrel hole was misaligned and was ‘eye-lidding’. Is this the case? And if so, could this have slowed down the draining sufficiently to have caused the head to fill?
Click to expand...
Thanks, I see that. Looks like about 90% open, I'll check the gasket against the barrel tomorrow to see if it lines up. I can open it up a little on reassembly.
 
At the risk of being POWERFLAMED, I am not a fan of modifying the oil drain holes from the timing chest.

I know, racing legends have tested, proven the process, and others have mimmicked this racing mod.
I'm not 100% convinced this is good for a street plonker.

As an aside, have you VERIFIED the crankcase venting SYSTEM? Plumbing? Etc?
Hose routing?
The symptoms described, images shown, scream to me:
A dry sump engine with a flooded crankcase. Figure out why.


JMWO
 
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Check also for overlapped oil ring spreader ends.

It has happened to me before on one set of rings. Easy to do, as it will sometimes jump to an overlap condition when you install them.
I am super careful now, and check for adequate piston tension in the bore.

If the spreader is overlapped, a perfectly clean head will look like yours in no time at all.
 
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brian4.2 said:
Spitting oil out the exhaust port and leaking at the exhaust nut and the header to muffler joint was weeping a lot of oil. I drained the sump and out comes 20oz of oil.

How does a wet sumping condition put oil in the exhaust ports?
Click to expand...

Because the oil gets past the piston rings.
 
concours said:
As an aside, have you VERIFIED the crankcase venting SYSTEM? Plumbing? Etc?
Hose routing?
Click to expand...
Thanks Concours, I appreciate your input, I will verify this today.
elefantrider said:
Check also for overlapped oil ring spreader ends.
If the spreader is overlapped, a perfectly clean head will look like yours in no time at all.
Click to expand...
Thanks ER, I am not quite understanding this. Are you talking about the (clocking ) of the rings in relation to each other?
 
Fast Eddie said:
You say the oil way through the barrel is clear, but in the picture it looks like the barrel has left a mark that shows the barrel hole was misaligned and was ‘eye-lidding’. Is this the case? And if so, could this have slowed down the draining sufficiently to have caused the head to fill?
Click to expand...
Good call Eddie, Looks like a bad stamping of the base gasket. I didn't catch it on install. This is significant blockage.
 

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brian4.2 said:
Maybe so, it was sold to me as a 750 gasket.
Click to expand...

750
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk

06-7869 GASKET - CYLINDER BARREL BASE - COMMANDO 750 - NM24249 - British Motorcycle Parts - Auckland

www.britishmotorcycleparts.co.nz www.britishmotorcycleparts.co.nz
Help with tuning.


850
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk

You searched for 06-3812-gasket-cylinder-barrel-base-commando-850 - British Motorcycle Parts Ltd - Auckland NZ

www.britishmotorcycleparts.co.nz www.britishmotorcycleparts.co.nz

Help with tuning.

Also a gap between the gasket and barrel spigots in your picture.
 
elefantrider said:
Help with tuning.
Click to expand...
I once had something similar happen on a 750 commando I once owned
The very tip of one the oil control expanders was missing/broken off
This caused it to partially overlap like the phone above
This was causing really excessive smoking
 
brian4.2 said:
Michael, Dont think you can put the reed in backwards. I will check it, easy once the barrels the starter are off.

HTown, The oil return has a good flow. Here is the drive side revision notes. Included is the explanation from Jim Comstock.


Brian,
The combat engine had a scavenge problem that caused the engine to wet sump the cases at highway speed. Then they would blow oil out of every seam.

The factory had moved the scavenge pump pickup to the front of the case thinking it would work better since it was the lowest spot. They did not take into account the fact that the windage from the spinning crankshaft pushes the oil to the rear of the case where the pump could not pick it up.

To fix it you need to plug the original hole and use a mill, a burr or a 1/4 inch rat tail file to open the oil passage near the rear of the case.

I have attached a picture.

Another mod that is necessary on that engine is to remove the locating tab from the camshaft thrust washer -if it is still there. Otherwise it will break off and go into the oil pump -breaking it. If it was missing make sure it is not stuck in the scavenge passage leading to the oil pump. Jim
Click to expand...
I Thought it was more of an issue with Race motors.
However I did do it along with the case mods you did with a modified JSM rear breather.
I have no iissues. I did it because it was a part.
There are thousands of Combats out there that haven't done the mod.
Unless you are running hard, don't think this is the issue.
brian4.2 said:
Good call Eddie, Looks like a bad stamping of the base gasket. I didn't catch it on install. This is significant blockage.
Click to expand...
Yup, that'll cause an issue.
Don't think I'd be splitting the cases for the pick up mod.
But then again, maybe you're more ambitious than me....:)
 
If you had good return to the tank the pickup mod is working. Perhaps the gasket covering the drain hole is part of the problem. Did you check to see if the oil seal on the intake valve on the smoking side is correctly installed?
 
L.A.B. said:
750
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk

06-7869 GASKET - CYLINDER BARREL BASE - COMMANDO 750 - NM24249 - British Motorcycle Parts - Auckland

www.britishmotorcycleparts.co.nz www.britishmotorcycleparts.co.nz
Help with tuning.


850
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk

You searched for 06-3812-gasket-cylinder-barrel-base-commando-850 - British Motorcycle Parts Ltd - Auckland NZ

www.britishmotorcycleparts.co.nz www.britishmotorcycleparts.co.nz

Help with tuning.

Also a gap between the gasket and barrel spigots in your picture.
Click to expand...
DING DING DING!!!
We have a winner!

Well spotted L.A.B.
 
Last edited:

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