Gear box noise and primary gear bearing fixation

[Will van Gemert]

I thought our little Singer could not surprise me with anything anymore and yet she did just last week!
Only two weeks ago Johan and his wife Annejuuk drove her from the Netherlands to our holiday house in Umbria (Italy) crossing the Alps and several mountain passes amongst which the famous Stelvio pass. This trip of over 1700km she completed without any complaints other than a little strange noise coming apparently from the gearbox and the occasional popping out of third gear when going downhill on engine breaking.
Last week my wife and I did some amazing trips thru the Umbrian hills covering at least another 400km. During these trips the noise from the gearbox got worse to a point that it made me worry a bit as also the popping out of gear got worse. I decided to pull the gearbox out for a quick check. Upon dismantling I noticed that the primary gear bearing had been turning in its housing as it had a very shinny outer ring. The bearing itself was not in a too bad condition but also not perfect so I decided to replace the bearing (We always carry our p2p spare and tool kit with us so I had a spare at hand). During reassembly I noted that the amount that this bearing protrudes out of the gearbox housing is less than the depth of inprint in the bellhousing. As a result of this the primary gear assembly can move back and forward about half of a mm (about 0,04 of an inch!) This seems way too much for me I would even expect that the bellhousing would press this bearing with a certain load into to gearbox casing to keep it from spinning in the housing.

My question is: should there be any shims mounted at the bellhouse side of this bearing or sort of a spring plate, like I now is used on Riley gearboxes of the same era, to give this bearing a certain pre load and keep it steady in the gearbox housing?

For now I made up three shims out of a tin can (these are 0,25mm thick) so the bellhouse is pushing the bearing in its place. (I came up with this number as I know that 0,3mm is used on several bearings inside a classic mini’s gearbox as e pre-load.

After having everything assembled again we took her for a spin again only to find out that it did not cure our problem, the noise is still there and she still pops out of gear during descends (on steep down hills >10%).

At this moment I think that the two problems are related and are caused by too much play in the bronze bush bearing inside the first motion shaft as well as too much play in the bronze bearing inside the crankshaft. (I know the first one can cause popping out of gear during descends)

The rattling noise starts at 50km/hr (31 ml/hr?) when cruising at a steady speed on a flat road. At higher steady speeds the noise gets worse and the frequency rises with the rpm. When lifting the throttle the noise completely disappears. During acceleration above 50km/hr the noise is still there but only at higher speeds and way less apparent. When driving in third gear at a steady speed the noise also starts at 50km/hr but has a higher frequency.

My second question is: is there anything else that I should be looking at that could cause the rattling noise?

Sorry for the lengthy text
With kind regards,
Will van Gemert

[mikeyr]

My Honda S2000 started popping out of gear when the shift fork was bent a tiny amount allowing the gears to move around a little until they slipped out of gear, it only did it when decelerating and otherwise shifted fine. I had to replace the shift fork and that was all I had to do to fix it. From my experience, I would say you are on correct path if something is allowing the gears to move on the shaft but I have never had my LM gearbox apart so afraid I can't help except to say "I think you are on the correct path". My only concern is if there were no shims there before, what kept the gears from moving around ? Since my gearbox is out of the car right now, if it will help I can take some pictures or measurements.

[Peter McKercher]

Check the bronze bush that carries 2nd and 3rd gear. The centre collar breaks off and allows the gears to float.

[Will van Gemert]

Since my gearbox is out of the car right now, if it will help I can take some pictures or measurements.

I would very much appreciate that as I am back in the Netherlands now and the Singer stayed in Italy.

If not to much Asked could you take the following measurements for me:
-Diameter of nose of the first motion shaft (part that enters the crank)
-outer diameter of bush bearing in crankshaft
-Diameter of nose of main shaft (part that enters the first motion shaft)
-Outer diameter of bush bearing in main shaft
-Are there any shims or rings in place behind the first motion shaft bearing inside the bell house

With kind regards
Willie van Gemert

[jeans_old_man]

Hi Will,

You don't say what year your car is. Early cars relied on a bronze thrust bearing between the primary shaft and third gear to keep the gears in place, later cars had a nut. The earlier design was prone to jumping out of third when the bearings were worn.

I wouldn't worry too much about shims. The bearings are usually a tight fit. If yours are loose use Loctite 641 bearing fit.

I agree with Peter, the bronze bush that supports second and third tends to break off the collar that separates the cogs. However it will run quite happily until, that is, something worse happens!

bush1.jpg (66.5 KiB) Viewed 6401 times

As for the rattle. I've been chasing the same rattle for years. Your theory that it might be the bearing in the end of the crankshaft seems plausable. My latest thoughts are the shaft that runs across the front of the footboard and connects the accelerator pedal to the carburettors. When the throttle is open there is nothing to stop the butterflies from 'chattering' especially with a loose bearing fit at the carburettor end of the shaft. This at least would explain why the noise disappears when the throttle is lifted and gets quieter at full throttle.

I cannot drive at the moment but if I find the source of the rattle I will let you know.

[ColinB]

Sorry you can't drive at the moment Brian. Are you OK?

[ukmax]

I'm having a similar problem except my LeMans Special Speed jumps out of second gear on overrun and I am currently addressing the problem. I haven't taken my gearbox out yet, I am rebuilding a spare gearbox that I have.

The bush in the gearbox I am building is intact but i can't find what the exact thickness of the central thrust collar part of the bush should be, does anybody know please, or does anybody know what the 2nd and 3rd gear end float should be? I can work out the thickness from this, I am able to turn a new bush if required but I obviously need the dimensions. Is there any reason that the thrust collar can not be a completely separate thrust washer instead? bronze is not strong enough to support the gear if it is not bearing against another fixed surface, in this case 3rd gear. Imagine this is the reason it breaks when it wears thin.

The main shaft bearing will also need replacement but I can't see any numbers on them, all that is on them is "SKF" and "Made in England", can anyone tell me what bearings I need to get please?

Ironically, I am also trying to trace a "Canary like" noise but I will address this in a separate post, when I will post a recording.

Thanks