sf750 starter spinning

T

terry66

New member
Location
New Zealand
Hi all, put in a new battery after bike has been sitting for a while, then out of nowhere it sounded like starter was spinning but not catching, took off case and toothed belt was absolutely shredded optibelt ZR 210L, cleaned the remnants out took the belt off and the starter is spinning the chain but it isn't catching. if i push in the cog it catches then releases.
Whats up? is there a sprag bearing or something in there?
 
The generator uses a V belt, not toothed, as standard. Z 19 1/2 or equivalent. Any small puller will remove the sprag clutch after you have removed the reverse thread 24mm nut on the crankshaft.
 
When the springs give up working (and as per old ones I have dug out of the sprag assembly) they are usually a lot shorter as they have been chewed up.
This means the rollers are not pressed fully onto the surface. It only needs one or 2 to break up to cause the symptoms you mentioned.
Dismantle, clean thoroughly, then reassemble with new springs and also rollers if they look chewed as well.
 
hello Terry is your bike standard factory 750 or has it been modified to a non Nipon Denso starter?
CLEM
 
CLEMTOG said:
hello Terry is your bike standard factory 750 or has it been modified to a non Nipon Denso starter?
CLEM
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What makes you ask that, Clem? Just interested. Apart from the bike just needing the usual sprag clutch o'haul, I'm not aware of anyone successfully fitting a non-std ND starter motor. I've considered it, but not gone there yet.
 
Hi so took off the sprag and found one spring and ?pushrod ? gone, rest look ok but I have a complete freewheel repair kit that I dug out of the parts that came with it😁, the empty space looks like the pushrod has sheared off in the hole, how do I take the ?cover? off , I see there?s a hole on the side do I try and prise it off from there?
 
Make sure the back plate if firmly attached to the flywheel - If not get rid of them rivets and either Tack weld the back plat on or drill and tap for bolts. A loose back plate will rattle your dogs to death in a starter clutch.
 
Hi yeah its firmly attached, do i have to drill the rivets out to take this off so i can try and get the broken spring rod out or is there a trick to this?
Do you need to take the plate off usually? seems like a lot to do just to replace springs, rod and rollers, cheers
 
You don't need to remove the rivets - and (sorry Ron) don't listen to Ron - I have never known an SF starter freewheel plate to come apart and I have seen and worked on MANY over the last 45 years.

You may find that the piston/s is/are stuck inside the pesky hole. If it's really bad, it is possible (I have done this recently) to drill form the outside into the cavity and use a prod to remove the dodgy piston an d it's broken pieces of spring that are no doubt blocking its movement. It isn't easy to get the angle right and I used my lathe to align it, using a mill vice on the cross slide, and milled a flat at the drilling point (the curve won't allow a drill bit to bite without the flat starting point). I did it for all 6 pistons. Worked a treat and there for any future probs.

As you've discovered, it's difficult to get them out from the open end. You can try tapping the freewheel against a piece of wood in an attempt to let inertia force the piston out, but be careful not to whack it too hard as it can crack the insert (a replaceable part, but preferable to avoid).
 
terry66 said:
Hi, a bit of perseverance does the trick all old ones out, new ones in and working perfectly, cheers all, ps what should i use to lube it?
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Good result. I assemble them bone dry, I have found that any lube makes them more likely to slip if they get moisture in, and I service it once a year. Others swear by grease or oil of their choice, which will work.
 
Piranha Brother 2: If read what I said you only have to remove the rivets then tig or mig tack weld or tap and bolt the back plate on if the cover is loose. If the back plate is not loose there is no reason to remove it when servicing the unit.

And YES, I have seen two incidents were the back plate of the starter clutch came loose and caused the dogs to rattle and slip in the shaft - mine included ;o)

I had good results using Molly Lube in the starter clutch and starter sprague wheel cluster.

If the shaft has been peened or pounded with bruises, you use a flat file to smooth and finish off with wrap sanding using emery cloth.

You can get springs and dog pin bearings from Wolfgang.

If there is any sign of looseness, denting or warping in the back plate, you will wasting you time if you do not correct the situation.
 
Laverda SF said:
And YES, I have seen two incidents were the back plate of the starter clutch came loose and caused the dogs to rattle and slip in the shaft - mine included ;o)
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Me too ;)

The "loose" back plate locked the freewheel up.
Ended up with a destroyed (beyond repair) starter :(
 
A major issue with the early SF's without the dis-engaging clutch lever switch and not having the starter relay grounded through the neutral tranny switch was that the starter could be engaged while the engine was running causing all sorts of damage if you accidentally hit the starter button. I shredded the internals of a starter to ash when I accidentally did this on a 7000 rpm down shift.


 
Guess some people have issues with starters, most don't. Absolutely, if the backing plate is loose, fix it! I've had a really good run as have all the SFs around me over the years. I too have always run mine dry - seems to work both ways. The moving parts are all tucked out of the way once the motor is running anyway, so the lube really just works on the pegs/pistons.

Glad you got it sorted anyway. Good work. terry. If you can't see a name on the starter, it's most likely the std ND.
 
I use everything from 3/1 to margarine and run of the mill grease.
Margarine was a roadside repair on a 750 SFC. Worked fine.
I use grease when I dismantle a freewheel, otherwise, my freewheels are drilled into each pusher housing so I squirt some 3/1 in there when the belt cover is off.

You can of course use a toothed belt, only no teeth on pulleys.

Paul
 
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