Timing case breather

[Sakura]

Hi, the previous owner of my RGS has drilled a hole in the back of the timing case adjacent to the mag and fitted a breather pipe. It looks awful to my eyes. Is this a recognised mod? I intend to remove it and plug the hole. There is an inlet tappet cover breather and presumably the timed breather so I really don't see why it's necessary. The previous owner did say the mag had oil in it so presumably that's why he did it.

[Worty]

Hi, the previous owner of my RGS has drilled a hole in the back of the timing case adjacent to the mag and fitted a breather pipe. It looks awful to my eyes. Is this a recognised mod? I intend to remove it and plug the hole. There is an inlet tappet cover breather and presumably the timed breather so I really don't see why it's necessary. The previous owner did say the mag had oil in it so presumably that's why he did it.

Never come across this.  Seems like the oil in the mag belongs to a different issue and he's chosen the wrong solution.  I'd sort the mag issue and plug the hole.

[RDfella]

Point is, is the engine breathing heavily? Only reason to fit an extra breather and perhaps try to relieve oil getting into the mag.

[Sakura]

Never come across this.  Seems like the oil in the mag belongs to a different issue and he's chosen the wrong solution.  I'd sort the mag issue and plug the hole.
[/quote]

I agree entirely and that's what I intend to do. I did find a picture from E D Cranks where they do this for their offset crank conversion because that makes the normal engine breather out of phase. I guess we live in a different world now where a drop of oil on someone's immaculate riven sandstone drive is a world shattering event

[muskrat]

G'day Sakura.
Is the "top hat" breather still in the motor between the cam pinion and cover? If it is yes plug that hole.
Is your "hole" where the arrow points in the attached pic? There is supposed to be a plug in there.
Cheers

[Sakura]

Hi, only just bought it and haven't pulled the timing side apart yet. I'm fairly certain the timed breather will be in place. The drilling plug is in situ. So your suggesting to do away with the timed breather and just rely on the modified added breather? You obviously have a reason for this, what would that be? Replacing a timed breather which will blow and not suck with an open breather which will do both in that area seems a backward step but I'm sure you have a good reason for it. Please explain! Always ready to learn from others experience, particularly when the breather is already there. I must say it doesn't look pretty going around the mag but it might be possible to improve that. Going on from my experience in the distant past with car engines, should it have a check valve in the pipe to stop it sucking in air?

[muskrat]

So your suggesting to do away with the timed breather and just rely on the modified added breather?  Going on from my experience in the distant past with car engines, should it have a check valve in the pipe to stop it sucking in air?

G'day Sakura.
No, plug the "extra" drilling. Leave the timed breather in place. Theoretically the breather in the tappet cover negates the timed breather to an extent, 99% of the breathing is outwards due to blow by the rings.
My breathing on my highly modified A10 Cafe is reply #14 here https://www.a7a10.net/forum/index.php?topic=15161.msg127571#msg127571
Cheers

[Sakura]

Hi Musky,
your reply makes total sense, l misunderstood your first reply. I have plenty of top hats and a tappet cover breather is already fitted. Rather than alter the breather tower first,  I think I will add a breather to the oil tank cap as a temporary try out. I like the unobtrusive layout of your mod rather than the crude looking arrangement there is there now.

[berger]

Sakura the oil tank should have a breather pipe on it at the back.

[Sakura]

Hi Berger, Musky is suggesting an additional breather outlet. In from the engine breather, using the oil tank as a catch tank, out to atmosphere with a check valve. In through the tappet cover, out via oil tank, using check valves to ensure negative pressure in engine. At least that's how I understand it!

[muskrat]

G'day Sakura.

How bad is it breathing and does it wet sump?
To start with I'd just run it as is and monitor how it behaves. If your worried pipe the normal breather outlet (in front & above of the front sprocket) to a small catch bottle. I think your making work for yourself before you know if you need it.
My modifications were because I was road racing it up to 7.5K rpm @ 14:1 compression.
Cheers

[Sakura]

Hi Musky, you're right in all areas! I have only just bought the bike back (for the third time since 1970!) so I don't know how it breathes. It's only done about 1000 miles since I sold it in 1997 and there were no with breathing or wet sumping then, nor should there have been as it had a complete engine overhaul about 7000 miles before selling it. The po said he put the breather in because there was oil in the mag. The mods you are suggesting would only be carried out if I find problems after using it. However, they are interesting and a simple solution as I already have a breather in the Dow tappet cover and a pipe on the engine breather so your system would be easy to carry out. I will strip the timing side, block the hole, retime the mag  and see how I get on. Anybody know the advance ignition timing in degrees, not stick down the plug hole?

[groily]

If there is still oil in the mag, probably a good idea to check the oil seal is OK as that's where it would be coming in (unless down the HT leads from a leaky top end). It's probably gone a bit hard after 25 years, just guessing!

As for the timing in degrees  - lots of threads on here, but low- to mid- 30°s BTDC. I always found 34 seemed a good number on mine, which was a flat-top piston and late iron head job. At some point that had also had a breather on the tappet cover - but it didn't need it so it was removed.

[Sakura]

Hi Groily, mag has supposedly been reconditioned, but I will check the seal.  About 34 degrees seems to suit many engines. 13/32 seems to be recommended for SR's but I do prefer a degree disc which can be used to check points opening on both cylinders.

[muskrat]

G'day Sakura.
As Groily said, check the mag seal.
I too prefer to use a degree disc and strobe for timing even with a magneto. Depending on the compression, 9:1 and over is 34-35 degrees, 7.5:1 is 32 degrees. Make a degree disc to live under the cush nut and fashion a pointer off the cover screw holes. Pic is my plunger one.
Cheers