LCGB Forums

Doing a leak test using bike inner tube and foot pump. Its not holding any air despite new seals and gaskets.Soapy water everywhere and no bubbles. Tested tube and pump in water but and no leaks there.Cannot find any leaks,but it must be large.I have the stator out and sprayed the crank seal where it sounded like it was leaking but no bubbles. At my wits end any ideas?

I had a big leak that I couldn't find with soapy water. Used a lighter in the end and found it that way.

drive side seal ?

How do you apply the soapy water ? I use an old detergent spray gun (which partly atomises the soapy water).

You can't be as daft as me can you?
I looked for 10 mins before I realised I hadn't put the plug in

Have you tested the valve of the tube when the pump is connected,I had to disconnect my pump to stop the valve from leaking.

For the drive side I fill the bearing with gear oil, it will still bubble. The last major leak I found on a motor was a new SIL mag that had been badly machined on the gasket surface and leaked through the stud holes.

Ill test the valve again but it seemed ok when I put the whole lot it the waterbut. Spraying the soapy water on.I have the chaincase off and sprayed the front sprocket.The main drive bearing is one with a seal on the inside no need for halite washer//gasket.( I think) but it had one in it when I replaced the drive side seal.Over enthusiasm when I built it years ago.Goint to make some plates up so I can test without barrel and/or mag housing.Was going to call this thread leak test denefit or curse lol

the best way is to test with a spray, and to use hot soapy water, and spray everywhere, mag housing, base of cylinder, inlet manifold as well as seals, good luck.

When I built my last engine, I couldn't find the source, everywhere I checked was sealed tight. Colin Jenkins called it when he said check Drive Side and sure enough, it was bubbling.

I personally still fit the halite gasket even with the sealed bearing, the space is still there to take gasket so I think better in than not, more sealing the better.

In the spanners manual it says fit the seals with spring side to the crank webs which I have done.I seem to remember there was a debate whether this was the right way round, or is my memory playing tricks?

Fit (lubed) seals with springs to face the greatest pressure that requires 'maintaining', is the general rule.

In the case of the crankcase bottom end, both Ø25 mm crankshaft seals have their springs facing the webs.

Similarly, the smaller magneto seal encounters it's greatest pressure from within, so the spring faces toward the inside (also with spring facing the web)

Elsewhere, the crankcase transmission has seals fitted with springs facing toward the inside even though there is a breather.

The front hub is debatable (as you may wish to periodically add grease via a grease gun ) but I always fit with springs facing toward the inside or junk them for 2Z bearings.

I hope that explanation helps....