Clutch rattle and slowing engine

[DCMVan70]

Hi All

I have an issue with my clutch - some history… The engine is an A+ 1275, the gearbox is a standard ribbed case, refurbished and fitted about 1500 mile ago. At the time of fitting the GB I also changed the clutch, release bearing and rebushed the clutch release are and fitted a new bolt.

I have an intermittent (well kind of) issue with a bad vibration when engaging the clutch. Normally the car start up fine, but after a couple of uses the peddle vibrates when the clutch is engaged and the engine RPM drops quite a lot. Seems to be less of an issue at higher engine speeds, so is more noticeable in traffic or when manoeuvring.

The video below (hope it works, and shame we can’t post videos directly here?), show what I mean through the bell housing.

https://youtube.com/shorts/p4pJt7525w0?feature=share

I have now removed the engine and gear box and see that the clutch and release bearing look brand new, but there is quite a lot of lateral play on the clutch release fork. There are scratches on the bolt and the new bush seems worn.

Do you think I can just rebush and reboot the release fork - bad new parts again, or there is something else going on?

There is a little bit of movement on the GB input shaft, but not worse than when I received it, and the little bearing on the end of the shaft seems fine - it is a roller type due to the A+ engine and is new (about 5000 or 6000 miles). I cannot see/feel any crankshaft movement, so think that the thrust bearings are OK.

Regards
David

[philthehill]

The biggest problem with the Minor clutch release arm/clutch is that the release carbon thrust moves in an arc which is not concentric to the clutch cover release pad i.e. when you push the pedal down the thrust bearing moves off centre relative to the clutch cover release pad - the more you press the pedal down the carbon thrust goes further off centre. That causes the thrust bearing to oscillate on the clutch cover release pad. The oscillation can be seen in the video. The only way to mitigate the problem is not to have everything so well fitted. One supplier of modification kits has the clutch release lever mount pivot hole slotted so that the thrust pad can find its own centre. The turning clutch release pad pulls the carbon thrust to naturally centralise itself so getting rid of and cancelling the oscillations. My own modified clutch release lever and roller release bearing is fitted with sufficient play to allow the roller release bearing to find its own centre so cancelling out the oscillations and and any vibrations that may have formed.
The first motion shaft and bearings are not effected by the oscillation and will be ok. The first motion shaft on the gearbox fitted to my Minor is supported by a roller bearing in the rear of the crankshaft and I have not experienced any problems with the bearing.

[DCMVan70]

Hi Phil

Thanks for that, certainly makes sense.
The rattle or vibration is one thing, but probably the more worrying issue is how much the engine slows when the clutch is dipped.
The reduction seems related to the vibration - when starting no vibration, very small reduction in RPM. When the rattle starts the RPM drops to such an extent that the engine will stall - probably a drop of 300 rpm.

It has not always been like this, so wonder where that issue is?

I will try and take a quick video of the play in the release fork - just to check it’s not excessive.

Regards
David

[philthehill]

The engine revs will normally reduce when the clutch pedal is pressed as you are pressing an immovable object i.e. the carbon thrust against a moving object the i.e. clutch. Something has to give and what gives is the engine revs.