Rebuilt engine seized

GregMcN · Post by **GregMcN** » Tue Jul 17, 2018 12:14 pm

Al

The chain seemed to turn freely and the sprocket was not turning when the engine was running.

I can not see any problem with the clutch. I just checked and there seem to have been 2 different rotors made but do not know how they differ. I do have one from a newer bike but on checking I can not see any difference.

Greg

GregMcN · Post by **GregMcN** » Wed Jul 18, 2018 4:03 pm

I checked the 2 rotors I have and the depth including the sprag clutch was identical for both but when I put them on the crankshaft they are not sitting the same. The older one I have been using does not seem to have any clearance to the starter sprocket whereas the newer one does.

Greg

honda brian · Post by **honda brian** » Wed Jul 18, 2018 6:52 pm

Hi Greg, I have checked the sizes of 8 starter sprockets and come up with a few variations. The width of the sprocket seems to be pretty much the same on all eight, however there are two distinctly different types. You said that the newer one has clearance. I have measured the height of the roller surface edge to the sprocket side on all of the sprockets. I found two different measurements. Four were between 14.44mm to 14.67mm and four were 13.55mm to 13.77mm. When you visually compare the two sprockets,you will see that the 13.**mm sprocket has a raised surface and gives a clearance at the rotor.
There were also early and late rotors just to confuse the issue further. I seem to remember CB72L is stamped on the later ones but I don't know if they have any physical differences as I only have early types. I think the "L" type had weaker magnets and the plain "CB" was the one to use when possible. A forum search will give you more.
You've done well opening another can of worms mate! Now I need to go and check the engines I've built and make sure I haven't slipped up with the starter rotors and sprockets.
I had some thoughts on your crank build and don't understand how the crank can be wide at the centre as once the centre bearing assembly and inner webs are pushed together, the width is set. The only thing I can think of is that some cranks centres have a spacer washer and it may have been left out on a previous build. I think they are early type but the old brain don't remember like it did.
I hope this helps.
Cheers, Brian.

AlanW · Post by **AlanW** » Thu Jul 19, 2018 4:17 am

Looks like my evil twin has solved it, I too checked 7 sprockets and 1 has the raised face near the edge. I put it back to back with another and a 1mm feeler goes in the gap.
I think your problem is solved, I have that sprocket if you need it Greg and good detective work Bri.
Al.

honda brian · Post by **honda brian** » Thu Jul 19, 2018 5:03 am

We can only hope Al.

G-Man · Post by **G-Man** » Thu Jul 19, 2018 2:20 pm

Hi Brian

From my understanding the webs hadn't been pressed up to the shoulders on the centre section.

G

honda brian wrote: I had some thoughts on your crank build and don't understand how the crank can be wide at the centre as once the centre bearing assembly and inner webs are pushed together, the width is set. The only thing I can think of is that some cranks centres have a spacer washer and it may have been left out on a previous build. I think they are early type but the old brain don't remember like it did.
I hope this helps.
Cheers, Brian.

honda brian · Post by **honda brian** » Thu Jul 19, 2018 5:44 pm

Thanks Graham, that explains it.
Cheers, Brian.