Author Topic: S6 crankcase pressure venting (Read 14731 times)

Ian Dabney · « **on:** 01 Jun 2015 at 09:36 »

I have a persistent oil leak between the magneto and timing cover, which then runs onto the hot cylinders. The leak seems to be caused by crankcase pressure within the timing chest. The magneto drive shaft is very slack in the timing cover, which needs investigation. It may also be worn rings/bores; however the bike starts and runs well. Before I start stripping the engine, I am keen to ride it this summer and hence I am first seaking advice on some other sources of the issue.

Can you advise where is the pressure release/venting on the S6 crankcase, as I would like to check it is not blocked. I cannot see anything obvious (e.g a one way valve and a pipe)

Can you advise if there is any seal inside the timing chest and on the magneto drive shaft that should assist in stopping the oil?

My concern is even if I do seal the mag/timing cover joint for some time, the pressure may just force the oil into the magneto.

help much appreciated
Ian

eddie · « **Reply #1 on:** 01 Jun 2015 at 11:38 »

Hi Ian,
Firstly, the magneto on the S6 can be removed without affecting the timing - it has a dog drive to the shaft in the timing chest. The oil that is escaping will be finding it's way past the shaft and it's bearing bush. As a temporary fix, you could try inserting a light spring between the mag armature and the drive shaft - this would preload the shaft against the shoulder and reduce the leakage.
The crankcase breather is a timed disc driven by one of the cams and running against the timing gear outrigger plate. The breather port then goes across the back of the crankcase to exit in the joint between the drive side crankcase and the primary chaincase. In the chaincase, there is a spout which directs any oil so that it drips onto the primary chain (with the gases venting out of open back of the chaincase).

Hope this helps,
Regards,
Eddie.

Ian Dabney · « **Reply #2 on:** 01 Jun 2015 at 19:54 »

Eddie,
Many thanks for your explaination and great idea. I will try the spring to see how it improves the situation, also look to improve the shaft/bearing fit hopefully after a Summer's riding.
thanks again
Ian

Ian Dabney · « **Reply #3 on:** 08 Jun 2015 at 11:45 »

I have removed the timing cover and what I believe to be the disc venting the crankcase does not seem to rotate with the cam gear. See attached picture. Can you confirm that this is the disc and it should be rotating. I am somewhat confused as to why the disc would rotate at half crank speed? If this is the disc, it may well be the source of my timing cover oil leaks.
many thanks
Ian

eddie · « **Reply #4 on:** 08 Jun 2015 at 15:08 »

Ian,
The breather disc is an alloy casting that has 2 ports in the face that abuts outrigger plate, so it opens twice for every turn of the cam (in other words once for every turn of the crankshaft). On the opposite face there should be 2 lugs that take the drive from 2 holes in the recessed face of the cam gear. The disc is spring loaded against the outrigger plate - this load also pushes the cam towards the crankcase wall and can cause wear of the thrust face of the cam bush, resulting in shallow engagement of the lugs. This can also result in the cam followers rubbing the back of the gear. Sometimes the lugs actually break off!
As you now have the timing cover removed, make sure you tighten the crankcase through bolts correctly when replacing the cover. The first stage should be to tighten the bolts so that they clamp the crankcases and primary chaincase together before attempting to fit the timing cover. If you fit the timing cover before tightening the through bolts, the blocks that carry the cam followers may not be properly clamped in place and may end up just floating around on the bolts. Also, the extra load on the timing cover usually results in the cover cracking under the load (usually across the bottom 2 bolts).

Regards,
Eddie.

Ian Dabney · « **Reply #5 on:** 09 Jun 2015 at 12:01 »

Edie,
Many thanks. Yes, on inspection the breather disc alloy casting has worn lugs and part of the front end has broken, allowing it to skew on the shaft, disengaging from and not rotate with the cam gear. Two of the springs has also become dislocated and bend/faltenned.

I will post a message to see if anybody has a spare. I will also see what are the options to build up the worn/broken sections or turn something equivalent out of alloy bar,
many thanks for your help
regards
Ian

eddie · « **Reply #6 on:** 09 Jun 2015 at 12:29 »

Ian,
I made one from alloy bar for a fellow LDMCC member sometime last year, but haven't heard any feedback regarding it's effectiveness. The breather you have is the 2nd type designed for the S6. The earlier type may have been just a prototype (and not fitted to production machines), but it featured different breather timing which I thought looked preferable to the later version.
Regards,
Eddie.

Ian Dabney · « **Reply #7 on:** 09 Jun 2015 at 13:56 »

Eddie
Do you have a diagram of the early type. Is it the location of the holes?
much appreciated
Ian

graeme · « **Reply #8 on:** 10 Jun 2015 at 00:57 »

Hi Ian

I too suffered the broken alloy pillar on my S6, and I have a spare engine where the same thing has happened. Can I suggest you also do what I did, and make up a plate that also mounts on the other two studs, a much more robust set up.

Cheers, Graeme

Ian Dabney · « **Reply #9 on:** 10 Jun 2015 at 05:49 »

Graeme,
Thanks for the advice, that is the approach I will take.
regards
Ian

Dewey · « **Reply #10 on:** 07 Aug 2016 at 10:19 »

Graeme,
Can you elaborate on the plate you mentioned? I'm trying to visualize it but it's not working. I have the Fulton H32 (S6 derivative) up & running and the one bothersome bit is the amount of oil being expelled out the breather onto the primary chain. It's not pumping out badly, but more than I'd like to see. The timed disc has been repaired in the past but does turn with the cam. Is this normal?

hoejmark · « **Reply #11 on:** 07 Aug 2016 at 12:22 »

Hi Ian
A few years ago I also had the problem about oil leaking out of the magneto drive on my T6. I didn't manage to find any drawings or sketches showing the drive system, so I had to design a new sealing. The magneto drive system has been oil tight for 3 years now.
I attach a photo of how the old sealing was looking and two photos of my own design (the compression nut is not included in these two photos. I also attach a sketch of my new sealing system.
Regards
Hoejmark

graeme · « **Reply #12 on:** 07 Aug 2016 at 23:38 »

Nice setup Hoejmark.

Dewey, if you look at the picture at the top of this thread you will see the original plate locates on the two RH studs and the central cast pillar. The one I made up also locates on the two LH studs as well. And yes the timed breather disc should rotate with the cam.

Cheers, Graeme

Dewey · « **Reply #13 on:** 09 Aug 2016 at 01:15 »

Thanks Graeme. Ok, now I see what you did, and why. What do you see as normal amounts of oil being expelled onto the primary chain. Are there supposed to be any sort of baffles to catch droplets of oil downstream of the breather disk? All I have is a passage going first thru the timing cover, then thru both case halves and finally being directed to the primary chain at the bottom.

Dewey

graeme · « **Reply #14 on:** 09 Aug 2016 at 10:39 »

Hi Dewey

There are no baffles in the vent tube on my bike, whether there are supposed to be I don't know. If the timed breather is working correctly, and presuming the rings are doing their job and not allowing blowby, I imagine a mist is what is supposed to go up the breather tube, which obviously condenses to a small amount of oil getting onto the primary chain. Being a machine "of an era" the oil then eventually leaks out of the primary case!

Cheers, Graeme

Dewey · « **Reply #15 on:** 10 Aug 2016 at 00:04 »

Graeme,
So there's just a straight, as in no restrictions, path to the primary chain? Not even a screen placed somewhere to collect droplets?

Dewey

eddie · « **Reply #16 on:** 10 Aug 2016 at 06:52 »

Dewey,
I would check out the rotary breather valve. Make sure it is seating correctly on the back of the outrigger plate, so that gases can't bypass the valve. Also check out the thickness of the sealing washer between the outrigger plate and the inside of the timing cover (an extra thick timing cover gasket may result in a leak past the washer). As in Ian's photo (above), the breather valve should have a deep groove around it, covered with a gauze and a steel sleeve with holes. When spinning, the gauze should catch the majority of the oil droplets and throw them back into the timing chest. Check also that there isn't a leak between the crankcase chamber and the breather port, as this could provide another escape route.
Just another thought - have you had the barrels rebored?, and were they bored to size? It was common practice in the prewar years to make the bores to 'size' (say 68mm) and provide the running clearance on the pistons. If your barrels have been bored to 68mm + the clearance, the problem could be excessive leakage past the pistons.

Regards,
Eddie.

Bert · « **Reply #17 on:** 11 Aug 2016 at 10:52 »

This thread reminded me that I hasn't looked inside my T6 timing case since buying it last year, and had been intending to do so before the Australain Douglas Rally in Mildura. I've found similar issues as described above. My inlet cam bush was slightly loose with the spindle plate slightly ovalled, causing it to move horizontally which I suspect would affect the tappet gap. The timed breather was on its last legs and would have stopped turning soon. I hunted through my spares and found two others (one useable but I think I'll make a new one) the other is quite different as per the photo.
Does anyone know what the breather with the holes bisecting the circumference is from?
Also, why the stepped face on one of the breathers that would allow pressure to pass during its complete cycle?
None of my breathers have springs to create the contact on the spindle plate so I would also like to know what they look like. Are there four and do they fit in the machined holes at the rear of the breather?
A question to Graeme- with your replacement spindle plate, did you have a high curvature to avoid contacting the oil pump gear? And my crank cases have also had the original pillar destroyed ( and repaired with a huge amount of weld).

Bert · « **Reply #18 on:** 11 Aug 2016 at 11:10 »

First time attempting to upload a photo.

eddie · « **Reply #19 on:** 11 Aug 2016 at 11:34 »

Bert,
The breather upper left looks to be the right one for the S/T6. The other face should have 2 lugs (to match the slots in the face of the inlet cam) and 4 shallow holes for the springs. From memory, the springs are a neat fit in the holes and about 1/4" long. The snapped off (and welded up) pillar inside the timing chest is the result of incorrect tightening sequence of the crankcase through bolts. These bolts should first be tightened from the left hand side - so that they clamp up the crankcase halves and primary chaincase. Then the timing gear (with the outrigger plate) should be assembled (with the outrigger plate secured to the through bolts with locknuts). Finally, the timing cover can be fitted. If this sequence is not followed, it is possible to have the whole lot clamped up, but with the through bolts loose in the crankcase - the end result being that the operation of the cams rocks them backward and forward until the spindles work loose in the crankcase, and also shake the outrigger plate about until it breaks the alloy pillar (the last remaining rigid fixing for the outrigger plate). The final part to give up will be the timing cover, as this will now be trying to hold the crankcase halves together (they usually split across the 2 lower mounting holes).

Regards,
Eddie.

graeme · « **Reply #20 on:** 13 Aug 2016 at 00:04 »

Bert,

Yes the plate I made has the curve as you describe to clear the oil pump gear

Dewey · « **Reply #21 on:** 07 Sep 2016 at 00:00 »

Bert. In your post above you mentioned that you were able to repair the outrigger post by welding. Could you elaborate on that? Procedure? Filler used?

Dewey

eddie · « **Reply #22 on:** 07 Sep 2016 at 06:25 »

Dewey,
If the outrigger plate is modified as Graeme has done to pick up on all 4 crankcase studs, then the alloy pillar becomes redundant as a structural member. The crankcase can then be machined back at the point of breakage and counterbored to accept a 'loose' pillar that uses the existing banjo bolt to clamp it to the back of the outrigger plate. The joint with the remachined crankcase can then be made with an 'O' ring - the oil pressure in the pillar is only about 6psi (enough to lift the oil pressure indicator). This method would reduce the chance of further crankcase damage due to distortion from excessive welding.

Regards,
Eddie.

Dewey · « **Reply #23 on:** 07 Sep 2016 at 22:51 »

Thanks Eddie. I don't have a broken pillar but early on went thru hell trying to weld a crack that caused external leakage. The bearing boss of the idler & generator drive however, had been successfully welded sometime in the past and for my own knowledge wanted to know how they might have achieved that success. The one thing that stands out is the filler was quite bright and formed with large puddles. You guys must have dealt with cracks in the S6 and its derivatives at some point so I was hoping you could enlighten me as to the approaches you use.

Dewey

Bert · « **Reply #24 on:** 08 Sep 2016 at 00:35 »

Hi Dewey,
I didn't have the welding done. I found that it had been done when I removed the timing cover. Whoever did it must have had problems trying to get the weld to adhere to the oil impregnated crankcase as the repair is not a neat low build job. However it isn't seen and seems to work. I turned up a new breather and the following photo shows my attempt at a 4 point mounted outrigger plate. It was a bit fiddly to get it to sit square (machining the rear two studs to the correct height) so that the breather sat square to the plate. If I still have excessive mist at the primary case outlet I think i'll make a reed valve to sit on the top of the crankcase opposite the oil pressure indicator rod.

Bert

Dewey · « **Reply #25 on:** 11 Sep 2016 at 22:59 »

Nice job on the plate. Rather artistic looking.

Getting back on the welding, I've been trying to figure out how they were able to successfully weld the area I described when I had so much trouble on this 2xxx alloy. I think they used pure AL filler and reverse polarity to minimize heat to the case, but that's only a wild guess. I had a Ducati in my youth and a local welder fixed it with resulting appearance to what I see here. Unfortunately I never asked him how he did it and he's long gone now, but the repair held up fine.

Dewey

eddie · « **Reply #26 on:** 12 Sep 2016 at 07:15 »

Dewey,
As you probably know, aluminium is TIG welded with AC current - the principle being that the current in one direction does the cleaning and the current in the other direction does the welding - the ratio of positive to negative being controlled from the welding set.
I am lucky enough to know an 'ace' welder, and when I questioned him about certain alloys being 'unweldable', his advice was to adjust the amperage low enough that it would heat the material but not actually weld it, and then do a couple of runs over the joint area. You can then see where the 'cleaning' phase of the arc has done it's job. Next, scrub the cleaned area with a stainless steel wire brush ( a plain steel brush will contaminate the area again) to remove any loose particles of dirt. Then adjust the amperage and weld as normal. As I understand it, pure aluminium rod is used on commercial pure aluminium sheet and sections - rod with 5 or 10 % silicon is the norm on alloy castings, etc.

Hope this is of some help,
Regards,
Eddie.

Dewey · « **Reply #27 on:** 13 Sep 2016 at 10:48 »

Thanks Eddie. I suppose this should be a separate thread by now but interesting regardless. I've TIG welded AL starting back in the 70s after the Ducati incident and some was on larger castings but had never been exposed to the CU-AL alloy until this project came along. I've also welded AL castings using DC straight (DCEP) with good success. It's not as pretty but just as strong. 4145 is great for those tempermental alloys due to its extremely high silicon content - 18% I believe. There have been times tho when I had to experiment because the norm just wasn't working. I had a 1929 Indian 101 transmission case with a broken off mounting ear. 4340, 4370 and 4145 just didn't want to play. I didn't have any 1100 on hand so I stripped the insulation off some URD AL cable and the results were nothing short of amazing. The manufacturer reports the wire to be 1350. Had the Fulton bike not been of historic value I might have tried something like that.

Your "ace" weldors technique of heating for cleaning is good info and I've done similar approaches on dirty castings. The stainless wire brush is also of merit to anyone else reading this thread that has an interest in AL welding and is thinking of embarking on that journey. The ones I really admire tho are the guys who can weld sheet AL with a OX/Acetylene torch.

Dewey

eddie · « **Reply #28 on:** 17 Sep 2016 at 11:29 »

That's easy - well, I find it easier than TIG welding! The secret is not to be afraid of it, and use a large, soft flame that is slightly fuel rich - messing about with a small, fierce flame usually results in the molten pool being blown onto the floor!

Eddie.