What's going on here?

[Laverda Dave]

 Hi All.
A mutual friend contacted me last week about a problem he's had with a newly acquired 1976 Honda CB550.
He took it out for a spin and the kick-start lever suddenly flew down and stalled the engine. The engine would not then restart with the kick-start as it had seized solid!

He took the engine out of the frame and removed the sump to find the kick-start gear has seized solid to the kick-start shaft. He eventually removed the shaft by cutting the gear off.

He sent me the attached photo.

It appears as though the kick-start shaft has been spinning so fast it has welded itself to the gear. I know this engine has a ‘tang’ in the crankshaft casting to stop the kick-start shaft rotating. I don’t know if the tang has broken off as I haven’t seen the engine but the owner tells me there was nothing in the sump to indicate something has broken.

My concern though is looking at the burring damage on the journal of the kick-start shaft how did he get the shaft out from the engine without drifting it through and thereby damaging the crankcase bearing?

He’s bought another kick-start shaft as in the photo but that is only going to replace the damaged shaft, the potential cause of the problem and possible crankcase damage remains.

Does anyone know of what may have caused the kick-start to drop down in the first place considering the bike was being ridden at the time and if the ‘tang’ has broken off can it be welded back on to the crankcase and if it can will the crankcase need to be split to do so, I’m second guessing it will and whilst he’s in there it would also be a good idea to check and possibly replace the primary chain?

Thanks in advance for any advice.

[Sesman]

This may assist in the diagnosis.

[Sesman]

And the opposing case.

[Sesman]

I’d say the kick start pawl retraction failed (spring and mechanism) causing the shaft to be permanently engaged.

Regarding the primary drive, I guess it depends on the current condition and intended use. I’ve attached a photo of a new vs 17000 mile example. I’d say the used one had a further 5-10 thousand miles in it at absolute best. And that mileage would be noisy and snatchy. You would also probably benefit from checking and potentially replacing the primary drive Cush rubbers which can go very hard. Though to be fair, mine were fine. I replaced them anyway.

[Laverda Dave]

Thanks for the photos.
I can't see any tang there but looking at the photo of the shaft and the slug of metal left in the centre of the gearwheel after it had been cut off the shaft now makes me wonder how did the gearwheel travel that far down the shaft to seize on the shaft considering when you look at the replacement shaft and the shaft in your photo that should be the position of the ratchet gear, the straight cut gear should be hard up against the journal?

[Laverda Dave]

I’d say the kick start pawl retraction failed (spring and mechanism) causing the shaft to be permanently engaged.

Regarding the primary drive, I guess it depends on the current condition and intended use. I’ve attached a photo of a new vs 17000 mile example. I’d say the used one had a further 5-10 thousand miles in it at absolute best. And that mileage would be noisy and snatchy. You would also probably be fit from checking and potentially replacing the primary drive Cush rubbers which can go very hard. Though to be fair, mine were fine. I replaced them anyway.

Looking again at your photos I can see now where the tang would be adjacent to the main spring and on the outside (as it were) of the crankcase half and maybe therefore it would not require a split of the engine to repair it (if that is what caused the problem). I would guess a failure of these parts is more user error than a design flaw as I've never heard of this happening before. I wonder if a previous PO had been in the engine, caused some damage and sold the bike on before it failed. I know the new owner has only had the bike for a few weeks.

[Nurse Julie]

[ Guests cannot view attachments ]

[Sesman]

?

[Bryanj]

Thats not the bit that normaly fails.
1 the circlip fall off the end
2 excess movement of all the parts alows the gear onto a bit of shaft it shouldnt be on
3 gear siezes to shaft

The pressed steel bit on the end of the shaft has a leg that fits into a cast groove in the casing so it can move longitudinaly and cause the ratchet teeth to either engage or not

[Laverda Dave]

Thanks for the info. I'm going to have a look at it next week and take some more photos.
I am concerned about the potential damage that may have been caused to the crankcase getting what is left of the shaft out. I would assume that should the used spare kick start shaft be loose in the housing as a result of drifting the damaged shaft out the cases are scrap?

[Bryanj]

Dont forget the shaft is held in the clutch cover casting as well

[McCabe-Thiele (Ted)]

Not sure if this helps this was when I assembled mine, at one point with a washer in the wrong place.

http://www.sohc.co.uk/index.php/topic,29348.msg281517.html#msg281517

.
500 kick start by Macabe Thiele, on Flickr

.3rd Oct 2022 by Macabe Thiele, on Flickr

.gear shift levers etc by Macabe Thiele, on Flickr

[Mike_Berkshire]

Not sure if this helps this was when I assembled mine, at one point with a washer in the wrong place.

Are you talking about the washer don't eh shaft that in your picture is behind the circlip Ted? I hope so because in mine it is in front of not behind the circlip although I guess this is your 5500/4?

[McCabe-Thiele (Ted)]

You are correct about the washer it's my 500, that photo was during dismantling as can be seen by the dirt - I put the washer in the right place on assembly with a new  circlip as advised by Ken. Just thought it might help seeing what is where.

[McCabe-Thiele (Ted)]

This is assembly iirc.

.500 casing progress by Macabe Thiele, on Flickr