s25 starting issues

[frogeyeman]

Me again. On one of my s25 engines the roto start will not turn the engine. Removed the roto start back plate and the shaft that the OWB sits on just turns as if it is not engaging with the crank pin. if you push the shaft in it engages but on turning the engine it disengages. Removed the backplate assembly and the crank pin looks as if it is too short. Saw a video on You Tube and that crank pin looked about the same. Here are the pictures of the innards of the engine. Hope you can help or is it scrap. A good running engine.

 

[ELWOOD]

@frogeyeman
I WOULD GET THAT PIN AND SPRING OUT TO SEE IF SPRING IS GUNKED
AND THE HOLE THEY SIT IN. IF ALL GOOD I WOULD CAREFULLY STRETCH THE SPRING AND TEST.

 

[frogeyeman]

@frogeyeman
I WOULD GET THAT PIN AND SPRING OUT TO SEE IF SPRING IS GUNKED
AND THE HOLE THEY SIT IN. IF ALL GOOD I WOULD CAREFULLY STRETCH THE SPRING AND TEST.

Thanks for your reply. Will give it a go,,the engine has been standing for a while. Seems a strange set up.

 

[ohsnap]

It looks like it's been sitting for a while with unburnt fuel that has coagulated.
I'm real sure that the gunk is at the heart of your problem.

Pull out the pin and spring and clean the internals with denatured alcohol.
I'm pretty sure that your problem is that the gunk is impeding the pin and springs functionality.

I think that it is premature to stretch the spring at this time as I feel that a good cleaning will resolve your problem. You can always stretch it later if needed - but can't undo overstretching.

Plug up or remove the carb and run some denatured alcohol through the internals and give it a good clean out. Then throw it back together and see how it works.

PS - Yeah, it is a strange set-up...

 

[Gazzman]

like ELWOOD & ohsnap said above it's probably the spring glued up or gone weak. Also pays to turn the pin round as the end which engages the shaft, loses it edge after alot of use. Yours actually looks pretty good.
Just for the record, the spring should be 8mm long & the pin 5mm.
Just could get a new starting pin/pressure spring kit and have done with it. HPI #1433 or a kit for a Force mill, just the same.

Are you sure you got the backplate fully home when you put it back on, silly question I know but for the shaft to engage and then de-engage when rotated, it sounds like to much movement. You could try putting a couple of shims between the backplate and the underside of the mushroom on the starter shaft to reduce the end float. Just a thought.

 

[Vinni]

like ELWOOD & ohsnap said above it's probably the spring glued up or gone weak. Also pays to turn the pin round as the end which engages the shaft, loses it edge after alot of use. Yours actually looks pretty good.
Just for the record, the spring should be 8mm long & the pin 5mm.
Just could get a new starting pin/pressure spring kit and have done with it. HPI #1433 or a kit for a Force mill, just the same.

Are you sure you got the backplate fully home when you put it back on, silly question I know but for the shaft to engage and then de-engage when rotated, it sounds like to much movement. You could try putting a couple of shims between the backplate and the underside of the mushroom on the starter shaft to reduce the end float. Just a thought.

The bug 404 uses a bic lighter spring as cheap replacement 👍👊

 

[ELWOOD]

@ohsnap
" but can't undo overstretching. " , THATS WHAT SHE SAID !

 

[frogeyeman]

It looks like it's been sitting for a while with unburnt fuel that has coagulated.
I'm real sure that the gunk is at the heart of your problem.

Pull out the pin and spring and clean the internals with denatured alcohol.
I'm pretty sure that your problem is that the gunk is impeding the pin and springs functionality.

I think that it is premature to stretch the spring at this time as I feel that a good cleaning will resolve your problem. You can always stretch it later if needed - but can't undo overstretching.

Plug up or remove the carb and run some denatured alcohol through the internals and give it a good clean out. Then throw it back together and see how it works.

PS - Yeah, it is a strange set-up...

That was the problem,gave it a good clean out and flushed out with cleaner. Some oil and all good. Thanks for your help.