The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Hornsved on 15.08. 2019 11:34

Title: Oil leak from primary chain case
Post by: Hornsved on 15.08. 2019 11:34
I am new to this forum and have just recently acquired a beautifully restored A10. It is a 1960 swing arm with a 1955 engine.

The engine have been rebuild some years ago with 6v electronic ignition, an SRM oil pump and possibly other mod's that I am yet to discover. It runs great and starts on first kick. However when the engine is running it has a very bad oil leak from the primary chain case.

The crankcase breather hole seems dry and not the least bit oily.

The oil seems to be coming from the (loose) bolt in the picture (taken from below the bike) and possibly from the front sprocket axle of the secondary chain.

The gear box is not loosing any oil. The oil return to tank looks very healthy and once the engines drips off the oil level in the primary chain case is constant. With the oil level gradually dropping in the return tank I believe that the oil somehow must make its way from the crankcase into the primary chain case and onto my garage floor.

Any idea on where the leak is coming from and what spareparts I will need to fix it?


Title: Re: Oil leak from primary chain case
Post by: bsa-bill on 15.08. 2019 12:55
Hi Horsved - that  looks like one of the two bolts that hold on the sliding plate behind the clutch, this plate retains a felt seal that stops oil from the primary case escaping, the plate has to slide to allow the gearbox to move in order to tension the primary chain this in turn means the bolts cannot be drum tight. from your observations, it is possible the oil seal on the driveside of the crank is leaking, perhaps it wasn't renewed when the engine was rebuilt, (should have been).
to avoid an engine teardown you could change the primary case oil to  RED atf and see if it gets discoloured with engine oil of a different colour (or if you can find a highly coloured engine oil and leave the primary case oil alone this would be more conclusive)
Title: Re: Oil leak from primary chain case
Post by: RogerSB on 15.08. 2019 14:33
Here's a couple pics to illustrate bsa-bill's comments.

In photo with clutch the yellow arrow points to the felt seal behind the sliding plate, red arrow to the sliding plate bolt (the other side of the leaking nut in your picture). Unless something else has been fitted the two sliding plate bolts are shouldered to prevent over tightening.

The other picture show the oil seal for the crankcase bearing in the inner primary chaincase.
Title: Re: Oil leak from primary chain case
Post by: Hornsved on 15.08. 2019 15:52
Thanks to both of you - I was concerned that it might be the crankshaft seal. Looks like I need to get the primary chain case off and make sure.

Is there any way to install a new seal without tearing the whole engine apart?
Title: Re: Oil leak from primary chain case
Post by: RogerSB on 15.08. 2019 17:54
Once the outer primary case is off you'll have to remove the engine sprocket nut (it will be very tight), remove shock absorber (cush drive) spring, sleeve, engine sprocket, bearing, shims if fitted and a distance piece. Then you'll end up with it like it is in the photo. You don't need to remove inner cover as it has a big hole in it that fits over the boss on the crankcase, with a spacer disc and gaskets in between. The oil seal butts up against the main bearing (also can be seen in photo). If you do this take note which way the distance piece is fitted, the concaved side needs to be fitted to face inward.

There's lots on here about the cush drive and engine sprocket removal and fitting, etc.  Mine shown in the photo has SRM's upgraded nut. You may find you have an original castellated one, which means you'll need a big, strong 'C' spanner to remove it without damage.  Some use a centre punch or chisel but that will invariably damage the castellations.
Title: Re: Oil leak from primary chain case
Post by: bsa-bill on 15.08. 2019 17:58
Quote
the two sliding plate bolts are shouldered

Well done RogerSB I had completely forgotten that
Title: Re: Oil leak from primary chain case
Post by: Greybeard on 15.08. 2019 20:09
... You may find you have an original castellated one, which means you'll need a big, strong 'C' spanner to remove it without damage.
Or buy the special tool
Title: Re: Oil leak from primary chain case
Post by: RoyC on 15.08. 2019 21:29
Another way that oil leaks is through the sliding plate.
Rub a band of sealer around where the two parts of the sliding plate join.
Title: Re: Oil leak from primary chain case
Post by: chaterlea25 on 15.08. 2019 23:59
Hi All,
There were also clutch centre adaptors floating about a few years ago that had the scroll cut in the wrong direction  *eek*
Roy beat me to it about the crap replacement sliding plates  *razz*

SRM adaptors do not have a scroll, they supply a further felt washer to fit between the adaptor and sliding plate
This seems to work OK

I found that the available large felt discs also "wicked " the oil out  *sad2*
I made a cork disc to fit instead (thickness is fairly critical to seal and allow the plate to slide)

John

Title: Re: Oil leak from primary chain case
Post by: RoyC on 16.08. 2019 07:59
I found that the available large felt discs also "wicked " the oil out  *sad2*
I made a cork disc to fit instead (thickness is fairly critical to seal and allow the plate to slide)

John

I replaced my felt seal with a foam seal from Dave Flintoft Engineering. david-flintoft@sky.com

Title: Re: Oil leak from primary chain case
Post by: Hornsved on 16.08. 2019 08:31
Thanks to all of you for these comprehensive and very well illustrated replies. Looks like I will be busy with the spanners...
Title: Re: Oil leak from primary chain case
Post by: Swarfcut on 16.08. 2019 09:39
Hi Hornsved, Just read your first post again, and a drop in oil level in the oil tank is mentioned. This is a bit of a worry on a newly acquired machine. On standing for a few days, the level will drop as oil makes it way down from the tank into the engine sump, but on start up this is returned to the tank and the level restored. This is a normal characteristic of these engines, and varies in severity from engine to engine....some do, some don't.

 A continually dropping level is due to oil being lost via the bores, guides etc indicating the motor is not as good as initially thought, or being transferred somewhere else, in this case the primary chaincase, and  loss via the clutch felt seal.

 Oil is retained in the engine cankcase by the crank oilseal, and also by a good seal on the chaincase/crankcase retaining bolts, the wired ones in the pictures above from Roger, and the circular plate between the inner primary case and crankcase. With the primary cover off you may find the oilseal compromised, the case retaining bolts loose one missing or  some other easily seen assembly error. This could account for the dropping tank level and subsequent leak from the primary case, as it becomes too full for the seal arrangement to handle. Well worth a look. The length of these bolts is critical....too long and they catch on the crankshaft web!.

Swarfy.

Title: Re: Oil leak from primary chain case
Post by: muskrat on 16.08. 2019 10:43
Wot he ^^ says.
Cheers
Title: Re: Oil leak from primary chain case
Post by: RogerSB on 16.08. 2019 11:20
Hi Hornsved,
Before stripping anything down, if it were me, I would carry out a test to see if engine oil is definitely making its way into the primary chaincase by first draining it, then pour in a measured amount, i.e. for A10 Swinging arm it's 8 fl oz  (225 cc). When you notice the oil level in the oil tank has dropped again, drain the primary chaincase again and measure the amount of oil that comes out. If it's obvious that it's a lot more than you put in it'll, at least, tell you if the engine oil is making its way into the chaincase. I imagine (as I've not tested it myself) that it'll have to be a considerable amount of extra oil in the chaincase to reach the level of the sliding plate bolts or the felt seal and to dribble out without the bike being run.

(Edit): My 1960 G/Flash wet sumps and it takes about 2 weeks for the oil tank level to fall by about 1/2". I make sure I start it within that period (summer and winter) to get the oil back to where it belongs before the sump gets too full. I find that more convenient than having to remove the sump drain plug to drain the oil out. When I acquired my GF it didn't wet sump at all because it had an anti-sumping valve fitted to the oil supply pipe.  It was great  *smile*, but I got worried in case it got stuck closed and the consequential lack of oil would destroy the engine  *sad2* - so I removed it and now have to do my 2 weekly ritual.
Title: Re: Oil leak from primary chain case
Post by: bsa-bill on 16.08. 2019 11:50

I suggested replacing the engine oil with some sort of coloured oil that would show up in the primary chaincase not knowing if anything like this is available that would suit an A series engine or any kind of dye that could be added to the existing oil.

For future reference does anyone know if either exists
Title: Re: Oil leak from primary chain case
Post by: KiwiGF on 16.08. 2019 12:32

I suggested replacing the engine oil with some sort of coloured oil that would show up in the primary chaincase not knowing if anything like this is available that would suit an A series engine or any kind of dye that could be added to the existing oil.

For future reference does anyone know if either exists

Lawnmower oil sae 30 (made by Briggs and Stratton amongst others) is red and can go in the primary to show up leaks from there, but I find it goes blackish fairly quickly and is then tricky to tell from an engine/primary oil mix. Alternatively ATF can go in the primary, its red but it’s thin and makes leaks worse!

Edit: if the crankshaft oil seal has failed or has popped out of position then you will get pressure fluctuations in the primary case, some filler caps have small holes in, that will “show” this pressure, or one can remove the cap and see if it’s “puffing”.