idler gear chatter

[AndyB72]

A year or so ago I fitted a 'new' engine to the Mini, rebuilt gearbox, fresh engine, clutch etc. From day one when warmed up it made a rattling noise from the drop gears, so I just assumed I'd set the clearance wrong, I decided to run the engine in and pull it out to investigate. The idler gear clearance was spot on but the primary gear bushes were a mess (I'd had the bushes replaced by a specialist) so I replaced the primary gear with the best used one I could find in my box of bits, end float set and all felt nice and I put the engine back in assuming the primary gear was the source of the noise. Nope, its still there, no change. I need a plan of attack for when I pull it out again, what should I be looking for, would iffy idler gear bearings cause this problem?

[Exminiman]

was the crank tail ok ?

[AndyB72]

Yes the crank tail is fine, the crank has been hardened.

[Spider]

I find the C Clips that slide in to the slots on the crank to retain the Primary Gear are on the soft side these days, you can see the witness mark in them if that's the issue.

Mind you, if you are running a more than a mild cam and a low idle speed, it'll clatter.

[AndyB72]

I'm using a 266 cam, the tick over is around 900-1000rpm, higher than I would like really.

[360gts]

Question.....are you running SC drop gears
..are you using 1:1 ratio or something different?

[AndyB72]

Standard gears and ratio.

[AndyB72]

Just to be clear, it rattles on tick over but stops then I press the clutch.

[CooperTune]

May not apply, but I seem to remember having the same issue many years ago. I seem to recall my carbs were not correctly balanced. Steve (CTR)

[360gts]

Helical gears should not chatter regardless of the cam etc.
Replacing the primary gear is one less item to be concerned about.

So, process of elimination......idler gear bearings....and the other one that is sometimes overlooked is the input shaft bearing
There are three different sizes of these bearings. Sometimes the builder will just replace the bearing and assume the piece in the housing is OK,,,...,(bit of a pain to replace that piece)
I have seen this problem with a mis match of the bearings. If the new bearing is smaller than the piece in the flywheel housing ....you will get noise from the drop gears.

It is normal for the noise to stop when you depress the clutch.

Worth a check.

[Exminiman]

....I wondered if the clearance between crank tail and primary gear bushes might be too much ?

[abs]

I have to same problem with my mk2 with a 266 cam, reconditioned box, NOS primary gear, Jap high spec idler bearings, carb`s balanced and every clearance in spec.
The motor has been out and stripped once already so I`ll be following this one closely.

Funny old thing I have a 100,000 mile late 1275 with clearances like a bucket down a well that is quiet and I`ve owned it for 31 years !

[Spider]

I'm using a 266 cam, the tick over is around 900-1000rpm, higher than I would like really.

I can't see that being the issue.

What condition were the thrust faces of the Flywheel housing and Gearbox like ?

It can also come from further down, a worn Layshaft and / or Layshaft Thrusts can sound similar, though these sometimes have other sounds too.

Worn gears too will also give the same sounds. When in Neutral, all gears except the final drive are spinning and can make noise.

If you were to pull the engine out as you strip it down, once you get the Flywheel off, you can of course, rotate the Primary Gear by hand and get a feel for the geartrain and backlash from there. Generally, the further you need to turn the Primary Gear to take up the backlash, the further along the geartrain the backlash is.

Depressing the clutch pedal of course disconnected the geartrain from the engine, so that everything downstream of the Primary Gear stops spinning or rather, spins slower. Loosing the noise when doing depressing the clutch shows just this.

[Rolandino]

It's almost certain that the two bearings, in the gearbox and flywheel cover need replacing. Had the same problem and I needed to change the flywheel cover as tge face where the shim sits against was completely ruined. Pity you now have to split the engine from the gearbox to reshim the idler gear. Also check the shafts of the idler gear. Good luck!

[BAD942B]

A year or so ago I fitted a 'new' engine to the Mini, rebuilt gearbox, fresh engine, clutch etc. From day one when warmed up it made a rattling noise from the drop gears, so I just assumed I'd set the clearance wrong, I decided to run the engine in and pull it out to investigate. The idler gear clearance was spot on but the primary gear bushes were a mess (I'd had the bushes replaced by a specialist) so I replaced the primary gear with the best used one I could find in my box of bits, end float set and all felt nice and I put the engine back in assuming the primary gear was the source of the noise. Nope, its still there, no change. I need a plan of attack for when I pull it out again, what should I be looking for, would iffy idler gear bearings cause this problem?

What was the clearance on the idler gears & the primary gear out of interest & what grade of oil

[TECH396]

Just a thought. I don't see mention of the type of flywheel used, but in my experience as well as others using ultralight flywheels, combined with a lumpy cam will certainly have the chatter you're speaking of. This is not to say you don't have another issue but even with perfect bearings, and clearances you can certainly get clatter with some component combinations.
Another consideration is the alignment of the transfer case to engine/ gearbox. These were factory machined as one unit. I've seen mismatched components used where it caused the idler, or first motion shaft bearings to bind once installed. Perfect clearances but misaligned.

[Spider]

Just a thought. I don't see mention of the type of flywheel used, but in my experience as well as others using ultralight flywheels, combined with a lumpy cam will certainly have the chatter you're speaking of. This is not to say you don't have another issue but even with perfect bearings, and clearances you can certainly get clatter with some component combinations.
Another consideration is the alignment of the transfer case to engine/ gearbox. These were factory machined as one unit. I've seen mismatched components used where it caused the idler, or first motion shaft bearings to bind once installed. Perfect clearances but misaligned.

For what ever it's worth, I agree with everything you've mentioned here, however, the flywheel housings are not matched and why they were available as a spare part, without a gearbox case & viki-verka.

The factory also stated this;-



I will say though, that considering how poor they do align and the variations I've found with them and given the Idler Gear has a live axle with bearings either side, they should have matched them.

[Smithmaps]

In my experience, there is a simple explanation for this.
Idler chatter occurs when you fit a lightened flywheel. The net result of removing mass, especially with larger engines, is that the flywheel rotates in a series of jerks, as it no longer has enough momentum. This simply rattles the gears at low RPM, and there is no actual fault with your drivetrain. When you press the clutch the whole train stops, so no noise.

I stripped a 1400cc motor 3 times many many years ago, with the same problem, only to be informed afterwards that it was normal on a lightened motor.
So go and drive your car and have fun.
Guy

[mab01uk]

I quite like a little idler gear chatter on tick over....all adds to the various unique noises that add character to old Minis!

[Exminiman]

Great thread this, peace of mind.....have now managed to attribute all the odd noises emanating from my engine to a 649 cam and lightened flywheel...