Rear main or not.

My project has an oil leak. Appears as though it's been ignored for some time. I'd say classic rear main except that the  oil drops are clean. I've read other forums on this topic so it must not be unusual. There is oil from middle of sump to suspension linkage.

Is it engine or gear oil? You’re familiar with Guzzis I believe so you’d be aware that the 2V CARC models use essentially the same clutch and operating system as all the other big blocks since time immemorial. That includes the two cone seals on the pushrod from the thrust mechanism and they can leak gear oil into the centre of the clutch and thence the bell housing. O rings and front seal are also potential gear oil leak points.

If it’s engine oil it can be the rear main, although this is unusual, the Viton seals used are very robust and reliable. The other likely places are the two bottom bolts of the rear main bearing flange, (Rare on engines of this vintage.) or, more likely, the welch plug at the rear of the camshaft bearing. If it does turn out to be the welch plug it is best not to remove it as they are a bastard to reinstall. Simply clean the area thoroughly and then seal it with epoxy. The last place is the rear main bearing flange gasket itself but this is extremely rare. If in doubt though? Remove the flange and replace the gasket and seal it with the thinnest smear of threebond 1211.

The oil appears clean and fresh. It only takes a few minutes of running before drips appear to form. Both engine and gearbox have correct oil levels. The bike appears to have been well maintained in the past. There is a strange rattle coming from either gearbox or clutch. My Breva is faultless so have little to compare with. I know well the rattles when the clutch is pulled in. It would appear that some sort of additive has been added to the gear oil. Could this be a possible cause of seal failure.

Unlikely. Have you sniffed it? Even synthetic gear oil has the phosphorous stink to it.

Any undue knocking from the gearbox is likely to be due to poor throttlebody balance. Nobody has moved the throttlestop screw/s or messed with the linkage rod ball joints have they?

Actually, think ing on it further it occurred to me last night that if it’s an early 1100 it may be suffering from the collapsed shock absorber washer tower issue in the gearbox. Is it ‘Clacky’ and shuddery under load on take off from a standstill?

I haven't ridden the bike. It went straight from trailer to work bench. I noticed it has an after market rear shock fitted as well. Your knowledge and advice is sound, I'll look at all this as I work my way through the bike. Thanks.

Will,

I've moved your topic to the GRiSOLOGY section as that is the best place to receive help for technical issues. The Who You Is section is the best place for folks to introduce themselves.

Cheers!

Pete (Street)

After removing the motor from the frame, giving everything a good wash I discovered the oil was coming from 2 places. The oil/sump breather line had degraded causing it to weep. Also, there was a weep from between the bell housing and the gear box. Enzed fixed the hose and an application of JB gasket silicone fixed the bell housing. I replaced the front gearbox seal just in case while I was there.

It is wise with gearbox leaks to also replace the o-ring, part number two in the diagram below that in fact sits outboard of the bearing rather than inboard and acts as a crush seal on the shaft to prevent oil migrating up the splines of the shaft and out of the hub.

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Also the two cone seals on the pushrod are considered by some to be leak prone and although I’ve never found them particularly troublesome if you have a gear oil leak and have the box off it’s very cheap insurance to pop a couple of new ones in. Parts number seven in this diagram.

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I didn't find any evidence of other leaks other than those mentioned. The main seal looked iffy so I replaced it. The bike is almost reassemble, I'll run it and see what happens. If I have to pull it apart again, so be it. Thanks for your advise.