MK3 Wetsump

Still doing lots of work try to help a local guy with his Mk3 bike. We now have his kicker starter working again (chipped edge on the ratchet pawl).

Now we turned to the non working electric leg. Found the anti backfire device completly loose in its mount...could rotate the adjustment nut by finger. So it had backed off when encountering a back fire or just too much engine rotation resistence. Further inspection revealed a newly installed 18 roller sprag completely blown to bits.

Discovered more than 1.5L of oil in the sump...so I imagine this triggered backfire device, which ultimately unwound the adjuster nut. Then the sprag was unable to cope with the wetsump pressure and blew up.

We still had his older sprag in reasonable condition (also 18 roller type so not original) and are working to setup the backfire device as per book 50ftlbs release torque...need to figure out a way to make adaptor to hold shaft while torquing

What are the usualy reasons for a mk3 to wetsump and solutions?

Tornado said:

What are the usualy reasons for a mk3 to wetsump and solutions?

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Just because the Mk3 has an anti-wetsump valve in the timing cover doesn't mean it won't wetsump eventually especially if the valve jams open. Solutions, have the O-ring conversion done to the oil pump.

The anti-backfire device nut must be staked after it is set so was it?

L.A.B. said:

Solutions, have the O-ring conversion done to the oil pump.

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Interesting, can you provide more details on what that is about / how it works?

L.A.B. said:

Just because the Mk3 has an anti-wetsump valve in the timing cover doesn't mean it won't wetsump eventually especially if the valve jams open. Solutions, have the O-ring conversion done to the oil pump.

The anti-backfire device nut must be staked after it is set so was it?

Old Britts, Overload backfire device assembly and adjustment

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Yes there was evidence of debris in the kick back device shaft groove and a notch on the nut edge, presumably where the peened over bit was ripped away when it let go.

2WheelsUp said:

Interesting, can you provide more details on what that is about / how it works?

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Even if the anti-sump valve shuts completely, oil can still find its way along the pump shaft from the feed side to the scavenge where it can drain to the sump. The mod (AMR Nortec) ads O-rings to the pump shafts.

I have a MK3, so you are saying for my bike I only need to get them to do the O-Ring mod to improve wet sumping over what the factory already did for the MK3.

Tornado said:

We still had his older sprag in reasonable condition (also 18 roller type so not original) and are working to setup the backfire device as per book 50ftlbs release torque...need to figure out a way to make adaptor to hold shaft while torquing

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For a friend's Mk3 we welded a piece of 1/2" key steel to the side of a medium set of vise-grips so a torque wrench could be attached.
Then wrapped some thin (1mm?) aluminium around the spline (for protection) and clamped the visa-grips very tightly on the spline.
Put the other end of the assembly in a bench vise (soft jaws!)
Then applied the torque repeatedly while tightening the nut.
When 50ft.lb was achieved, staked the nut to the shaft (centre-punch) and... Bernard's yer Aunt!

Could also buy the special tool if you choose.
I reflected afterward that, using a "spare" spline nut and some 1/2" key steel, I could make my own special tool
Cheers

robs ss said:

For a friend's Mk3 we welded a piece of 1/2" key steel to the side of a medium set of vise-grips so a torque wrench could be attached.
Then wrapped some thin (1mm?) aluminium around the spline (for protection) and clamped the visa-grips very tightly on the spline.
Put the other end of the assembly in a bench vise (soft jaws!)
Then applied the torque repeatedly while tightening the nut.
When 50ft.lb was achieved, staked the nut to the shaft (centre-punch) and... Bernard's yer Aunt!

Could also buy the special tool if you choose.
I reflected afterward that, using a "spare" spline nut and some 1/2" key steel, I could make my own special tool
Cheers

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As per the old brits article LAB linked above, an extra splined washer/spacer can be tack welded to a suitable sized socket to make the torque wrench adaptor. We just need to order the washer and then arrange for visit to another local brit bike club member to perform the welds...and Bob's your Uncle, EH!

Tornado said:

As per the old brits article LAB linked above, an extra splined washer/spacer can be tack welded to a suitable sized socket to make the torque wrench adaptor. We just need to order the washer and then arrange for visit to another local brit bike club member to perform the welds...and Bob's your Uncle, EH!

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Yep - I was just offering a "quick and dirty"
Cheers

2WheelsUp said:

I have a MK3, so you are saying for my bike I only need to get them to do the O-Ring mod to improve wet sumping over what the factory already did for the MK3.

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That would leave you with a spring loaded plunger in the cover instead of the AMR ball, the plunger does hang up in the hole and then not stop the oil flow. The ball is less likely to hang up but the plunger is best left alone IMHO, a polish of the OD of the plunger and increasing the chamfer width on the pump end of the plunger would much reduce the hanging up.

This pic is from the wrong end but its looks like the pump side has next to no chamfer unlike the spring side.




a pic from the pump side would give more info on that other chamfer. I would like to see the spring side chamfer on the pump side too.

Install a sump reed valve breather so the oil pushes into the oil tank instead of pressurising the crank cases.

Is this a plug?

Or install a Holland Norton Works anti wet sump valve and all the problems associated with wet sumping are no longer relevant! Just like on a velocette. Graham. This may look like a plug!

Certainly if the owner wants to spend the money on a sump reed breather I would support him.
On the velocette, wet sumps are dealt with a sprong loaded ball check valve on feed side...just like we hear horror stories about from Commando owners, 'cept it is a factory original part on the velo.

This was my solution. Use at your own risk.

Moose3869 said:

This was my solution. Use at your own risk.

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I have similar on my mk2
..but with an ignition defeat switch tripped by the tap handle. 8yrs and zero issues from it.