S6 Engine/crankshaft

[fbjelland]

Hi all, question about putting together an S6 engine.
1. Should there be any trust washer, or shim on the timing side? Crankcase has wear marks showing contact between case and shaft.
2. How should the crankshaft be shimmed? Found mine put together with only an springwasher between crankase and crankshaft on drive side.
3. Thinking about to modify bearing on driving side from two ball bearings to one roller bearing together with shimming. Any experience out there?

[cardan]

Hi,

Interesting problems. I'm not experienced with the S6 engine, so treat the following as general advice. No doubt I'll be corrected if I get it wrong.

If the timing side bush is as designed, it was a bad design. Mostly the bush here would be a "top hat" design, with a flange inside the crankcase. The flywheels would normally bear against the flange of the bush, and the thickness of the flange determines the alignment and end float of the crank. You can't (ok, you can but you shouldn't!) put a shim on the timing side between the flywheel and the bush. Shims should never go between parts that rotate relative to each other.

Because the engine is now really old, all manner of things may have happened to it over the years. The best you can do is to put it right as best you can.

1. Make sure the con rods are straight - not bent or twisted. The human eye is very useful if you don't want to dismantle the crank.

2. Make sure the main shafts are round, particularly the timing side where it runs in the bush. Wear here can be pretty bad.

3. Put the crank in the cases with the two races and the current timing bush is place, and no shims anywhere. Presumably there is a thin paper gasket between the crank case halves?

4. The crank should be a sliding fit in the inners of the ball races, and free with little measureable play in the timing side bush. Check for end float. I hope there is lots - maybe a mm or two.

5. Measure as accurately as you can the centrality of the rods in each cylinder opening.

6. Hopefully there is enough end float, and the alignment is such that the timing side bush can be replaced with a top hat design, with a flange thickness chosen to give a little end float (0.010"/0.25mm or so). When you make a new bush, remember to chamfer the inner diameter where it bears on the flywheels so it doesn't bind. Pay attention to oil holes and distribution channels.

7. The two-ball-race setup on the drive side is fine. If you need to shim, do it between the cases and the bearing outer. Make sure your races have appropriate clearances: they are probably interference fit in the cases (heat cases to put them in and take them out) and sliding fit on the main shaft, so 00 fit is probably OK - your bearing man will know.

Good luck,

Leon

[eddie]

I would suggest that the scoring inside the timing side crankcase could have been caused by something silly - like too large a tab on the bigend tab washer!!

  Regards,
                 Eddie.

[Kalle]

Hi

In my S6 engine there is a SKF with double ball bearings see picture  (Spherical ??) that aligns with the position of the crankshaft
Regards Kalle

[fbjelland]

Hi, Kalle
From your pictures you got an shim on crankshaft timing side. My plan is to do the same on my engine to prevent subbing. Made a 1mm shim. With shim installed, con rods are in centre. Bushing on timing side are in good condition. On driving side i replaced the steel sleeve and spring washer with an aluminium sleeve with oil and felt seal. Hope it works.

[Kalle]

Hi
It will be nice with shims and I think your solution on sealing must be better than the original.
I have the lathe turning crankcase to fit a modern seal and shrink on a sleeve on the crankshaft for the seal
Regards Kalle

[Kalle]

Hi agan

Forgot photos
I also have a spacer ring in the crank case
Regards Kalle


Duplicate image removed - Dave, 10 Oct 2020

[fbjelland]

Hi,

measured play in my timing side bush to 0,004". Is this within acceptable limits, or is it too much?

[Kalle]

Hi
I will send the question to the forum to get radial play for the crankshaft and bushing on the pinion side and the wear tolerance,
I have a task of the play on other motorcycles but I think we hear what the forum gives for results
Regards Kalle

[cardan]

Hi Kalle,

Let me answer here.

I don't know if there is a spec for the timing side bush clearance. And I can't say how much clearance I would use myself, but I think it would be more like 1-2 thou than 4. That said, 4 thou doesn't seem too bad, and would probably work.

If you want to replace it, I suggest: check with a micrometer that the main shaft is round (to better than 0.001"); fit a new phosphor-bronze bush a couple of thou undersize; use an adjustable reamer - with a pilot in the main bearing on the drive side - to open out the bush until the shaft just fits; take one more light cut; done!

Sorry for the clumsy answer. Maybe someone knows better?

Cheers

Leon

[eddie]

I have never seen any information regarding clearance on main bearing bushes for prewar machines, but Mr Douglas specified 3 thou clearance on the postwar models - any less, and the bearing is prone to 'nipping up'. What has to be taken into account is the fact that these engines run on about 6 - 9lbs psi oil pressure, and there has to be enough clearance to allow the oil to flow, and do it's job!
   Personally, if I had an engine fully bedded in with just 4 thou clearance, I would leave well enough alone!

  Regards,
                  Eddie.

[fbjelland]

Thanks for inputs. Decided to replace bush. Compared with other engines, 4 thou clearance is a bit much. This could also result in poor lubrication of crank shaft big ends. Target would bee between 2 and 3 thou. Bushing on magneto drive looks to bee the same as crank shaft. Clearance on magneto bush is 2 thou. Oil pump pressure is an other issue. Is there any other way of checking delivery pressure, than look at the tell tail on top of engine?
Thinking of using aluminum broze for bushing. Any experiences with this material compared to phosphor bronze?

Regards,
 
Frode

[cardan]

Hi Frode,

Not sure about aluminium bronze - the spec looks ok? One nice thing is that it is said to machine more easily. I use PB2, which is probably what was used back in the day.

Leon

[dalgrae]

Hi had good success on  triumph tiger cub using lead bronze

Colin

[Kalle]

Hi everyone
Thank you for your answers and I also think that 2-3 hundred clerance is the good measure.
 An old Harley that I renovated has these dimensions and the bushing is changed when the wear is 6 hundred clerance
Regards
// Kalle

[Dewey]

When I rebuilt the Fulton Douglas some years ago with a lot of great help from this site the timing side bush wear was unacceptable so I turned one out of P/B stock and as the first one to reply said, it was of the top hat design. The thrust area was a little thin for adequate end play, but it was there.