GT380 Oil leaking from alternator cover.

[Willgo]

The GT running, gear change sorted and nice very happy. But!
Up to now most of the runs have been 20 to 40 miles.
I just got back from a nice 180 mile trip most of it at a study pace of 40-60mph
Nearly home I thought I let the bike have its head and it shot up to 90 easy.
For the rest of the journey home 10 miles the engine run perfectly and idled nicely, But looking her over once home I found some oil leaking out the alternator cover,
removed the cover and yes it has to be main bearing oil.
The bottom end is new, bearings and seals. So do they weep or is the near side oil seal shot.
I would have thought if the seal was faulty it would effect the running but as I said it’s running really well.
Again any advice appreciated.
Bill Dag

[tz375]

Are you 110% sure that it's coming from that alternator cover - ie could it be from just behind there? The only oil that could get to the alternator is out of that end crank seal, but the cover behind that has a pushrod seal that tends to leak trans oil.

[Willgo]

Yes as sure as I can be it’s a deep red like the engine oil

[tz375]

Bill, When you say "engine oil" I presume that you mean injector oil and not transmission oil yes?

[Willgo]

Yes the oil that’s pumped to the main bearings and inlet ports. The one I have used has a deep red tint and the oil I found inside and coming out the alternator housing is that deep red. The transmission oil is a full synthetic and a light yellow.

[Willgo]

I don’t have much working experience of two strokes, but have an amateur understanding of how they operate.
That’s what I find puzzling the engine seems to run well. I don’t have anything to really compare it with but it matches and out performs Brit twins of the same era I ride with. It pulls well from 2k to 3k in higher gears with a deep moan from the intake, will race though the gears the engine running up to a round 6k pulling and accelerating strongly, In fact as I would expect. Most times it starts 1st/2nd kick cold or hot and as I understand it difficult starting is a sign of faulty crank case seals.
Bill

[Coyote]

Is it possible to install that crank seal backwards?

[Willgo]

If I recall its plan face to the alternator that is the spring round the lip is on the inside of the engine

[tz375]

That seal does appear to be leaking. if it's just one seal, the motor will still start and run OK on the 2 good and one slightly weak cylinders.

I'd pop the alternator off and see what you can see. Clean and dry it and run it again to be sure that it wasn't just a freak post assembly leak. If it is still there, remove the carbs and the left pipe and plus the intake and exhaust and use a modified spark plug to pressurize the bottom end to around 6 psi and see if it holds it. If not, listen for where it leaks out and if it leaks from that seal, the crank has to come out again to replace that seal.

[Craig380]

Have a check & comparison of the spark plug colours, is the left cylinder's plug paler / whiter than the others?

To be honest, the bike sounds like it is running well as it is. Assuming the plug colours aren't showing signs of excessively weak mixture on the left cylinder (porcelain isn't white and the centre electrode has some brownish deposits), I wouldn't worry.

[tz375]

That's what is puzzling here. It sounds like it's running fine and yet it's weeping oil out.

Where does the oil feed go on that bike? Is it possible that the oil is leaking but the seal is still OK? That would explain why there's oil and not fuel there.

[Willgo]

Have now removed the alternator and yes the oil is from the seal, the oil is round it and a small spot on the bottom of lip where the shaft passes though and a streak down to the bottom of the cases.
I cleaned all the oil out of the casing and from around the seal, then run the engine for some 20minutes. I revved it up a few times but mostly it was idling in fact it was a steady idle for 15 minutes before I switched off the engine.
Not a sign of any oil?

So I have put every thing back and intend taking the bike for a run in the morning, then check for signs of oil.
As I have said it runs really well??
If on inspection I find oil traces it would seem to be a faulty seal. If it’s dry maybe it was just some freak occurrence.
Either way I may well do a crank case pressure test like you say.

Having now looked at the assembly if a seal is needed I am considering pressing in a new seal.
I could turn up some tools to guide and press a new seal in using the thread in the crank shaft.
Looks very possible to me I would do it on a 4stroke.
Any one have thoughts?
Bill.

[Willgo]

I just been a pulled the outer plugs both on the damp side.
I had checked the ignition timing before I went on my last run, I do remember they looked fine then.
Nice light brown porcelain.
Maybe the prolonged idling accounts for the damp appearance. I will see tomorrow after a run.
Bill

Yes Magic is also in the number 1971 GT380 to

[Willgo]

Thanks to all for the help once more.
Just got back from a 40mill run and theirs oil in the alternator casing.
So although the bike goes well I will be fitting a new seal, apart from anything else the oil cant do the alternator any good gooing up the slip rings.
I am going to turn up some tools to press the new seal in with out splitting the engine.
As I see it the most I can loose is the price of the seal.
If it works I let you know
Bill.

[Willgo]

I have now fitted a new seal.
Went for a 40mill run on mixed roads let it run up to 80 a couple of times and some acceleration up to 6k and making engine pull in high gyres, but most light cruising.
Got home let her cool down and took off the alternator cover no sign of oil, then removed the alternator windings,
There was a trace of oil in-between the winding casing flange at the bottom?
Hoping it’s what might have been caught up in the windings. Will give her a good run and check again.

For anyone interested I turned up a piece of alloy with a taper to match that of the shaft on its inside and the same O/D as the shaft, it slips on the taper of the crank shaft butting up to the parallel part of the shaft were the seal runs, so it would have a smooth a transition as pos going onto the shaft. I also turned up a piece of alloy just under the seals I/D bored so that was a close fit on the piece over the taper so it would run square I machined out the pressing face to a depth of 4-5mm so there was only a 3mm face to bear on the seal. I then pressed the seal in by tightening a bolt in to the end of the crank shaft. Worked really well.
Bill.