Flywheel sprockets loose, dangerous to ride on?

[Erik]

Hey all,

It has been a while since I have been working on my bikes. Very busy at work etc…

Today I was finally preparing my two speeder for a rally this Sunday and one of the things I intended to do was changing the drive chains. I noticed there is quite some play in the drive sprockets on the flywheel. As I have little time I wondered what the risk was if I used the bike nevertheless… Will the sprockets come loose entirely? Are there cases known of this? Or would it be ok to use the bike this season and fix the problem next Autumn? And of course keep an eye on it.

If I hadn’t been so busy I would have done the engine this Winter as I intended and would not have been surprised now..

Cheers,
Erik

[jampotrdann]

the trouble with a loose sprocket is you can elongate the holes in time

[Jan Buchwald]

Had three loose rivets and one broken, is now held with four 8mm countersunk screws.

[Erik]

Thanks guys for the input. On my Flyers Flywheel I also use countersunk screws. The holes are probably elongated anyhow by now so I should have some work fixing that.

But…

My question was, would it be very unwise if I just fit the chains and ride the bike as it is? It has just a couple of mm play both axial as lateral. I simply do not have the time/parts to fix it now. And for all I know, I have been riding around like this for years… Or not.

What could go wrong? In the worst case scenario all rivets would sheer off and I would have no drive left. Or could there be casing damage?

Any ideas/experience on that?

Erik

[Anonymous]

Hi Eric,

I’ve not ridden a bike with loose sprockets for any long distance, but thinking about it you may be able to wieght up the risk yourself.

If the sprocket is loose by 2mm, it will be rocking backwards and forwards every revolution until eventually you will start shearing the pins. The pins are there to clamp the sprocket to the flywheel so friction can take the drive – the pins are not for taking the drive through! Pins in single shear bend so are weak. I see two things that can happen. One is the pins will move outward and grind a nice groove in the bearing cup. The second is if a pin or two breaks or bends far enough it will allow the sprocket to move outwards and the chain will chew the crankcase. Worst case here is a pin breaks and jams the chain or sprocket. A “bad thing” if you are giving it some steam at the time.

I’d personally not ride it, the damage will only get worse and the more you ride it the more grief you have later to fix it. If the holes in the flywheel are still round-ish you can quickly strip the bottom end and helcoil the holes to use bolts that will still go through the holes in the sprockets. I think I used 1/4″ BSF on the last one i did but right now I’m stuck in Germany due to the flight cancellations any my notes are in the UK. You can do it in a day no problems if you have the stuff ready. It costs almost nothing so really I’d suggest you fix it soon, but remember advice is worth what you pay for it… and also if you di strip it you may find more work lurking!

Cheers,
Rich

[Anonymous]

Eric, I’ve just realised you are in Holland. I am currently in Hamburg but I’m riding to Rotterdam tomorrow morning to catch a 9pm ferry to the UK as the planes are all grounded. I’ll be in Rotterdam about 2pm and have 6 hours to waste. I’ll PM my email and mobile, if you want to meet up tomorrow afternoon (17th April) let me know.

Cheers,
Richard

[Erik]

I know I should strip the engine. But it’s a shame as it is now nice and watertight at last. As far as I know it is not possible to take out the flywheel with the cylinderblock in place (conrods are in the way).

I is just that I would really like to ride the bike again!

🙄

[dave bushell]

Back in the mid fifties, I must have had a loose sprocket on my 48 Scott as it sheared off completely and I found that I had no drive. Up until that point. I was unaware that anything was amiss. It actually sheared as I was going up a hill when the loading was obviously higher. Fortunately, a guy came by with a flat back truck and with a bit of effort we got the bike on board and back to my place. I had to drill out the rivet holes and fit oversize pins and all was well again.
Dave

[Dripfeed]

Erikunless you are more fortunate than me dont ride it fix it first . Back in the early 1960 s had the same problem with a 1930 flyer and it let go 120 miles from home.I am now old and more cautious.
Regards D. F.

[Erik]

I choose the head and not the heart and decided not to attend the rally. I will rip the engine to pieces soon and fix the problem.

But looking at the splendid weather it sure is a shame 🙁

[Erik]

Well, I took the bike to pieces today. And as to be expected, the loose sprockets were not all that I found…

The sprockets were pretty loose. On the low gear side two of the for rivet heads were missing and the sprocket was very loose. The sprocket had quite some play on the flywheel boss and the teeth were pretty worn. The high gear side was a lot better and might be reusable. But I will change both nevertheless. Now the question is what size sprockets to use? The chain is 1/2″ x 0.205″ and the sprockets that were fitted were 4,9 mm wide. On the HG drum the sprocket is about 5 mm wide (original) and on the LG drum about 5,1 mm (replacement from Ken Lack). So any ideas? 1/2″ x 3/16″ seems so narrow…

The crank assembly was a pain to disassemble. It was driven up very solid… But after disassembly the glands were in a very good shape. The main bearing cups however were bad. Especially the one on the LH side was pretty pitted and will need to be changed soon.

In the RH conrod the bigend bearing ring came loose again. The last time I soft soldered it in place (after nickelplating it failed two times) and this worked well for last season. This time I used silver solder all arround the ring, turned it to size and fitted it again with some Loctite. That bodge at least should hold until the planned overhaul next Autumn.

So, having to wait for the replacement sprockets (I will order as soon as I figure out the correct dimensions), I do not think I will do much riding this weekend 😥

Cheers,
Erik

[Anonymous]

Hi Erik,

I’m sorry to hear the tale of woe, but on the bright side it was going to break if you continued to ride it, so at least nothing else is damaged.

Keep us posted with the rebuild!

Cheers,
Rich

[radicool]

Erik,
The chains driving the 2 speed unit are 1/2″ x .205″ and the sprocket supplied to you
measuring 5.1 mm is .201″ giving .004″ clearance.That’s OK.
I think silver soldering parts of the big end assembly was a mistake as the temperature
required to s/s will have softened it nicely.
The final drive chain dimensions are 1/2″ x 301″
If the rivet holes in the flywheel are worn it’s possible to open up the holes to take 7mm
diameter rivets.

Laurie.

[radicool]

Erik,
One other thing whilst the flywheels out, look to see if the tongues on the glands have cut
into the keyway. If it has get it filled as it can stop the gland setting properly.

Laurie.

[Erik]

Hi Laurie,

Thanks for the input. Also it seems that there are no of the shelve sprocket plate wheels that have the correct thickness. The ones that are available are for 1/2 x 3/16. Those are 4,5 mm wide. Would that be too narrow? Or should I opt for thicker sprockets and thin them down?

Do you really think the ring is now softened severely? I thought that the temp used to harden this part was a lot higher than the temp I used to solder it. I used the same torch that I used when I soft soldered it last year and after a year of hard use the bearing tracks itself still looked fine. I now just used the torch a bit longer of course.

Of course this is a temporary fix. Just to get me through the season.

The flywheel and glands both look like new! No pitting or cut ins. So at least one part that is reusable without work…

Erik

[Author]

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