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Electra Oil Leak



I intended trying out my recent Electra purchase (first foray into British bikes) before going too deep into the oil leak(s) however I have decided the leak is too severe to allow this.

Back story tyres replaced with correct sizes, new fork stanchions (one bent) and a new slider (cracked at pinch bolt and previous repair meant a new one was the best option, gulp..the expense already!).

So, back to the leak .. I am wondering if I am the right path?

There was a leak from where the wiring exits the generator (much reduced to prove a point with a liberal application of silicone) however there is still a leak with motor running noted from below the engine in the area of the gearbox sprocket (unable to identify exactly). It is steady stream.

I thought it maybe the seal between the casing and engine but could it be the output seal mentioned? 

Any thoughts on the most likely culprit or the best way to tackle this ? 

I have some technical knowledge but do not consider myself an expert by any means..


Regards Andrew 



Hi Andrew,

You observe oil coming out of the primary chain case at the point where the three wires exit the inner chain case.

Is the rubber grommet that seals the three wires present? You mention using silicone sealer so I presume it is not. You need the proper sealing rubber part if you can find one. 

If oil is coming out of this hole I suggest the primary chaincase is too full? because the crankshaft oil seal, behind the crankshaft sprocket is defective? and the bike has stood so long that the crankcase is holding all the engine oil? and the the level in the chaincase matches the level in the engine? The primary chaincase is not pressurised unless the crankshaft oil seal has failed.

Excess oil in the engine crankcases is partly blown up to the oil tank by the crankcase breather system, and mostly by the oil return pump. Excess oil gets there if the bike is left standing, unused, for a month or more.

Your bike has stood a long time and I'd suggest the crankcase breather system is ruptured where the rubber pipe fits on the stub tube coming out of the engine above the gearbox sprocket. Oil is being forced out of the engine breather stub tube when you start your engine and going all over the floor. You need to renew the breather pipes (engine to oil tank / oil tank to top of chainguard) as they perish easily and also can be attacked by a slack drive chain. They also have a habit of blocking solid with water/oil emulsion, so best to check they are clear.

Access to this region around the gearbox sprocket is rubbish and easiest when primary inner chain case is removed. You might be able to do it without removing engine sprocket/alternator/clutch. Please use the proper pullers or secondary damage from hammers, screwdrivers and levers will leave your Electra irrepairable. Replacements are not generally available, unlike the more modern stuff you are used to.

I'm sure you will get there in the end. 


Hi Peter,

Thanks for your detailed response.

The rubber grommet that seals the 3 wires is present however not sealing at present.

I think the case needs to come off for a decent investigation.

The breather (at this point looks OK).

Maybe the crank seal as you suggest? I noted the oil was present at point of purchase (tray under bike). Is this a simple fix when casing removed?

I see also the stator insulation covering is poor ..please see photos.

Thanks again for your help.




My Navigator leaked in exactly the same way as your when I first got it.   I found that the crankshaft oil seal had hardened with age and was leaking engine oil into the primary chain case over filling it, causing the clutch to slip and pressurising it causing oil to leak past the oil seal behind the clutch and emerging round the gearbox sprocket.   Although both seals are available from the NOC shop for a few pounds unfortunately their replacement requires stripping the whole primary side which requires a special puller to remove the crank shaft sprocket.   Whilst doing the job it is worth replacing the gearbox output oil seal behind the final drive sprocket which if it isn't leaking yet probably will do once you start using the bike!   Remember the nut holding the sproket on has a tab washer and a left hand thread.   Good luck - once these jobs are done it will be oil tight.......from there!     Nick



Thanks for your input.

This all sounds very likely and thanks for the tip Regarding the left hand thread.

Regards Andrew


I'll be interested to see where the leak is and what needs to be done to cure it.

I've been chasing leaks on my Navigator.  Rather than use a proper sealant with the gaskets, whoever built the engine used silicon sealer, just about every joint leaked!   That and poorly prepared joint faces.   I've sorted out the easily accessible joints, tappet covers, timing cover and so on without dismantling the engine,  but I'm left with a bad oil leak around the final drive sprocket.  One of three places then, oil seals either side of the sprocket or the engine breather?

I'm going to ride the bike some more then dismantle the engine, something I intended to do anyway for peace of mind but now a necessity.


Hi Andrew,

Some good suggestions from Nick. 

In the photos you posted 24/7/20.

Insulation on stator. It doesn't look bad to me but I can see you are concerned about the tape coming unwound. On a similar problem on my 1964 Electra I cleaned the stator in petrol. Do it outside for safety. Then got some thick thread, almost quality twine, intended for buttons, and took a few turns around the affected coil. Knotted. Cut off tails. Then using a polyeurethane varnish made sure everything was stuck down neat and dandy. You could use epoxy resin instead of varnish, but keep it thin so that the heat can get out of the coils.

Stub pipe, oil breather, at rear of engine. In your photo the pipe looks as though it is brass. The original would have been zinc plated steel and looked grey. Also the original breather pipe was black rubber, not the vastly better blue silicone pipe shown. I'm just a bit suspicious that the brass tube is a sleeve over the steel pipe, and why? and is it a leak source?

Generally, the state of the nuts, bolts, gasket faces, presence of correct tab washer on crankshaft nut indicates that your Electra has been well maintained and looked after over the past 55 years. 

Lucky you.



In reply to by peter_holland1


Hi Nick,

I like your ideas regarding the stator repair - I will look into this.

I will look closely at the breather as a possible leak source bearing in mind what you have said.

Yes I think someone has loved the bike and hope it to be good when issues are sorted.

Thanks again.



In reply to by john_crocker


Hi John,

I will report back with issues found.

i do have other leaks to solve however I am starting with the biggest !

Regards Andrew 


I was surprised to see the primary chain case was unvented, that is to say no breather.  I think the gearbox may be the same.  I don't think that would cause oil links but no harm done in rectifying the omission. 

I've made a filler cap for the chain case with a breather, suitably baffled so it doesn't dribble oil. 

If there isn't a breather for the gearbox I will sort one out for it.




Lovely bit of machining John!   From experience if the crank, clutch and alternator wire oil seals are in good fettle the Jubilee and Navigator and therefore I suspect the Electra don't suffer from pressurisation of the primary chain case so long as you don't over fill it - you need to check but if my memory is right the Electra primary side takes 1/2 pt, just enough to lube the chains and no more - I have settled with straight 20 grade which reduces clutch slip and drag whilst still providing ample lubrication.   Mine has remained oil tight for three years and almost 4000 miles but I always use silicone gasket goo instead of the rediculously thin and difficult to seal paper gasket - the Electra's may be better.   If you look very carefully at the round gearbox inspection / filling plate on the off side of the bike you should see a very small breather hole slightly off set from the centre.   This is all the breather the gearbox needs, but I find it is better to position the inspection plate with the hole upper most otherwise with spirited riding I do get aslight weep from it.    Final top tip is make sure the engine oil tank isn't over filled - the level should be 2" below the mouth of the filler cap.   You need to check that the rubber engine breather pipe vents into the lower of the two pipes short pipes on the top of the tank.   The upper pipe feeds a thin rubber tank breather pipe which routes through a small hole at the top front of the chain guard so any condensed drops of oil lubricate the final drive chain.   I have been surprised just how low 2" is below the filler and how even 1/4 Pt too much oil 'to be on the safe side' means that as you corner the excess oil spills down the breather pipe and appears to be an oil leak from either the primary chain case or gearbox output seal!    Good luck and keep us informed on how the Electra is getting on - Lightweight Twins are remarkably good, reliable and quite sporty little bikes once properly sorted!  



Have a look at Dave Cormeau's narrative on gearbox breathers - a good piece of experimentation. End result is breather isn't needed as gearbox vents via the clutch cable amongst other 'vent'points. 

Regards, George. 

In reply to by john_crocker


Hi John - I think the primary chain case is vented but it’s (VERY) difficult to see it!  There’s a small breather hole in the inner chain case just below the rear top securing screw, I think you have to have the clutch assy off to able to see it though!


I've looked for a breather hole in the filler, none there, I'll look for the other hole when I dismantle.  How big is the hole and can its exit been seen while the engine is still in the bike?

I have found and read the article by Dave Cormeau on gearbox breathing.  I'm not sure its a valid experiment, he is not duplicating the conditions the gearbox runs in. 

I would agree that allowing the gearbox to breath is not a cure for a leaking box,would most likely have little or no effect on leakage. There is a good reason to allow air to move freely in and out of the box, he seems to have ignored that.



Hi guys,

Just to say my observations and experience have been the same as Nicholas Clarke and Bruce.

The primary chain case of a Lightweight is vented through a tiny hole in the inner case near the csk securing screw behind the clutch. 

The gearbox is vented through an equally tiny hole in the inspection/filler cap.

When all other seals are sorted the bike runs nicely, and enjoyably, without leaks from chaincase or gearbox. The engine breather that finds its way to the top of the chainguard, via the oil tank, is a fairly generous mist on my Electra, so I don't often feel the need to remove and immerse the chain in LinkLyfe (Remember that!!) .Maybe my Electra is a slightly heavy breather after 36,000 miles on original bore and pistons, but what's a slightly misty rear rim after a few hundred miles.

When replacing the oil seal in the primary chaincase, take care to support the thin wall around the seal when doing it. 

If you rest the inner chain case on it's sealing face and bash the new seal into place, the thin wall containing the seal is belled downwards, so that the seal is closer to the clutch than it should be, and the seal may not even seal on the last part of the sleeve gear, being too far towards the clutch and always leak. Use a straight edge to check the case is reasonably flat in area behind clutch, and correct with light hammering with wood between hammer and inner side of chaincase.

The other two seals mentioned in above replies are in more robust housings.

Hope this is useful Andrew and John.



Useful info Peter, thanks.  I've found the breather in the gearbox filler cap, small hole isn't it!  No doubt adequate to allow air to move in and out of the box but less than ideally positioned, can water get in? 

I'll look for the primary chain case breather when I dismantle the engine.

I've been considering the crank case breather, that may be the cause of the leakage?  I have some ideas for improving crank case breathing. 


John, the crank case breather on the Electra and late Navigator (like mine) is the same and consists of a metal pipe several inches long, emerging from the rear of the left hand crank case well above the gearbox final drive sprocket.   A rubber pipe runs from it up to the lower (forward) of two small pipes emerging from the top inner side of the oil tank.  Providing the pipe is in good condition I have not known it to be a source of a leak.   As I described in my post above the rubber oil tank breather pipe should be attached to the upper (rear) of the two small pipes and routed down to a hole in the front of the chain guard just above the gearbox sprocket.    With a healthy engine and correct oil level only hot oil mist from the engine should vent via this oil tank breather tube.   Similar to Peter in my experience it is just enough to keep the chain lubricated but not enough to produce anything like the oil leak you describe - they are almost certainly down to leaking crankshaft and clutch oil seals or the gearbox oil seal.    The other possibility is over filling the oil tank as I did explained above - or having the engine breather pipe incorrectly attached to the upper oil tank pipe and the oil tank breather attached to the lower oil tank pipe which has a similar effect.   It took me several months of experimenting and head scratching to fathom it out but I'm not very bright! 

Good luck and let us know how it goes!  Nick      


Nicholas, I'm just speculating as to where the (bad) oil leak is. Its in the sprocket area but I think you are right, unlikely to be the breather.  I did notice a small amount of oil in the clear tube I fitted to the  breather so oily air is passing up through the breather. I've got the breather and vent pies the connected the right way round.  

I think the breather arrangements can be improved, at the crank case and something to encourage separation of the oil and air at the oil tank end as some other manufacturers did. 

But first I need to find where the oils coming from.


I planned on replacing both the crank and gearbox output shaft (in gearbox) seals (awaiting parts delivery from the NOC shop) however I am now nervous regarding their removal. 

Any advice on best removal process?

I favour the seal marked below as the culprit of my leak not the ones mentioned.

Regards Andrew 





The seal should have a metal backing on the outer face and a sprung seal on the inner face. Have the replacement to hand before you start so you can weigh the job up.

First, offer the inner case up and check the sleeve gear is actually through the seal. Refer to my notes above on belled cover.

A flat blade screwdriver like the one you used for the case screws can be placed on the inside of the seal, outside the spring, and gently tapped with hammer to push seal outwards. Repeat in small steps moving the screwdriver position to push seal out evenly.

Use a socket or tube to tap the new seal into the cover. Keep it flat as it goes in or you risk damaging any rubber on the outside of the new seal. Or deforming the thin metal of the seal.




Thank you for the information.

I have a concern regarding the seal in the primary case and ensuring good contact with the sleeve as you mentioned.

There seems a lot of play (over 3mm) and my concern is position of the sleeve may render the seal useless.

I have attached two photos of the sleeve, one pushed in and he other pulled out - I would appreciate views on this and whether I ought to be concerned.

Regards Andrew 





The sleeve gear play you observe is greater than if the drive sprocket and securing nut are in place.

Repeat your test with the drive sprocket on the sleeve gear and the securing nut and washer (not tabbed or fully torqued) in place. 

Another tip for oil leaks. The hardened ring that is visible in your photos, and forms the inner oil sealing surface for the gearbox oil seal. Remove this hardened ring and put gasket sealer on the inner flat face and inside the ring before refitting. Although the oil seal stops leaks between the gearbox housing and the ring outer face, there is nothing to stop gearbox oil leaking slowly past the face where the ring presses against the gearbox bearing inner, and under the ring.

A design flaw perhaps, but metal to metal joints like that will often allow oil to pass.


Hi Peter,

I have already tried (and now checked) with the nut nipped up however the play appears the same.

I did wonder ought there be a spacer fitted before the sprocket (see photo) ? - none fitted on disassembly (and there is a spacer built in to the rear of the sprocket face).

 Thanks Andrew 


In reply to by andrew_boulton


Hi Andrew,

The ball bearing, part #7 in the diagram above, is usually a tight fit in the gearbox housing. The action of tightening the sprocket nut should trap the sleeve gear in the inner part of the bearing.

And you still get considerable end play on the sleeve gear? Unexpected.

If the sleeve gear is poking through the clutch seal under both extremes of end play it will seal. One of your earlier photos of the sleeve gear displayed a good polished area in the region of the seal. Should be OK then.



Hi Peter,

Yes OK thanks.   

I  also discovered there was a problem with starting mechanism - although pre strip down it did seem to operate ‘OK’.

Of the three pins fitted to the pawls - one had sheared into two pieces (historic failure I think) - one bent - the other was OK. See photos.

Have now started the bike for a short time and the good news is there seems to be no primary leaks (using oil to hand, SAE30).

Bad news is there seems to be a new wiring/charging issue ! Stator now removed for investigation.  

Regards Andrew 





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