Bristol Mod Scooter Club

My scoot has developed a bit of a rattle! (No, it's not a loose spotlight or mirror - LOFL!)

I've filmed the 'noise' on this video clip. Even perfect engines sound a bit rattley when on film, but have a listen and tell me what you think. Is it a bearing on the way out? Seems loudest on the flywheel side!

https://www.youtube.com/watch?v=EdutX45N8YI
you might have to right click and open in a new window

Thanx for any help!

See (or rather hear) what you mean Jim.
Could be the big end bearing allowing the conrod to move on the crank and knock against the casing. That would be major surgery I know but if it is that and you run it, it could do some serious damage so I'd let a grown-up have a look soon as possible. The noise speeds up as the engine revs increase so don't think its just something loose and rattling, more likely mechanical.

I understand what you're saying Nick!

I would've thought if the big end was worn and the con rod was touching the crank case, it would be more of a louder metallic clank happening! Plus I would've thought that a worn big end would be pretty noisey on it's own!

The crankshaft and bearings were replaced some years ago, would they wear out that quick, considering the crankshaft that came out was probably the original one!

Thanx for your input Nick.

doesn't sound like Big End bearing on the way out- not a heavy enough sound. Is there any vibration when you ride it?

Possibly:-

1) Small end bearing shot- easy fix
2) broken ring- easy fix if caught in time
3) Piston skirt damaged allowing "slap" replace piston
4) loose flywheel or magnets- Electonic? Indian flywheel?
5) Flywheel side bearing on the way out
6) fan touching F/W housing
7) loose flywheel cover? (the alloy bit in the middle)

Thanx Chris-

Scoot running OK with just the normal amount of vibration - it is a Lambretta after all !

1) Small end bearing shot- easy fix

I've had a few worn small end bearings in my time, and I know what they sound like - a 'click' when the piston changes direction, very recognizable when kicking the engine over slowly! I'm certain it's not this!

2) broken ring- easy fix if caught in time

Maybe, but compression still good and not changed.

3) Piston skirt damaged allowing "slap" replace piston

Might be, but I think this is more flywheel related!

4) loose flywheel or magnets- Electonic? Indian flywheel?

Still running good, old skool points! Indian flywheel!! Definitely not!!

5) Flywheel side bearing on the way out

Was replaced a few years back - would it have worn that quick?

6) fan touching F/W housing

Possible!

7) loose flywheel cover? (the alloy bit in the middle)

Might be!

Hopefully I'm going to have a bit of exploratory diagnostics tomorrow! Where do I plug in my laptop!

mag flywheel side bearing to me ,ask clive PMSL,,, if your gonna take it apart do the full bearing change, give you a chance to check everything, a nice winter job

Jim, I think you`ve answered your own question: `Is it a bearing on the way out? Seems loudest on the flywheel side!`

I think I`d agree with Gerry on this one

to check the flywheel side bearing, remove the N/S rear board and the F/W cover

Then try rocking the F/W, top to bottom and side to side- any wear in the bearing will show as movement against the F/W housing. A very small amount of movement is acceptable

Replacement is "so so". The F/W bearing is a 2 part item- inner track and outer bearing set up.

You have to remove the inner track from the crank- this can be done "in-situ" with the correct tool (which isn't very good anyway). Alternatively you have to apply a grinder carefully. This means removing the crank.

The bearing is a matched item- don't try to fit a new outer to the existing inner track- it will last about 1 month.

Just whipped the fly wheel cowling off to have a closer look (and listen).

Fly wheel alloy cover all good with the round retaining wire in place! Took it off anyway!

There is zero play when rocking the flywheel up / down and side to side, it all feels good!

On closer inspection, the rattle seems to be coming from within the cylinder, so I'm guessing it might well be the small end, or a worn crank / big end!

Here's me rotating the fly wheel against compression - have a listen!

https://www.youtube.com/watch?v=A20hozB ... e=youtu.be

need to whip the top end off- sounds too "light" for the big end (and you've not got any additional vibes apparently).

Small end; damage to piston; ring snapped?

Yep - gonna take the head and cylinder off next!

No other vibes or noises - the scoots going fine apart from this rattle!

I agree, the tapping/ rattle seems too light for the big end! I think you may be right about this being piston or within the piston related !

Could the gudgeon pin ever show signs of wear, or is all the wear taken on the bearing?

only ever seen one pin with wear and that was on another forum- generally the small end takes the damage.

Just taken the top end off. Found a small amount of piston waggle so I guess that could well be a worn small end bearing!

Removed the piston and that mostly looks OK - rings look good with the small nodule which keeps them from moving round all OK in both grooves! However, having said that the piston looks OK, I'm a it concerned about a bit of scoring on part of the piston!

I can also feel this scoring with my finger nail, so my plan is to have a rebore and upsize the piston and obviously re new the small end bearing!

I've heard there is a good place in Bristol - can anyone give me their details - Ta! Would they be able to sell me the bearing, and new circlips?

Have a look at this scoring - I guess you'll always find this on a well used piston!

https://www.youtube.com/watch?v=Tc867TfiYJU

I`ve heard `Piston Broke` are good, might that be who you`re thinking of? they`re in the Easton area of Bristol

Yep - that's them! I'll give 'em a call on Monday!

Thanx Steve!