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Discussion Starter #1
Hi all, another st1050 starting issue. I cranked my bike to start it the other day, it is normally a bit hard to start, however takes about two 3 sec cranks to start when cold. On about the 2nd or 3rd crank, the starter Motor changed pitch, sort of like 2 pistons were cranking instead of 3, and the bike would not fire. It did a couple of coughs and that was about it after many attempts.

The bike is a 2006 st, 60000 km on clock.

I pulled it apart thinking maybe it dropped a piston, but looking down spark plug holes all pistons appeared to be going up and down normally when cranking, looking into air cleaner ports, valves were also all working. I found that the 3 core plug from recently fitted cmos rr was all charred from poor connection, so did resistance check on rr and all appeared normal. I cut out plugs and reconnected wires with new spade terminals and tapped these all up to keep moisture out. No change to starter pitch or starting.

My thoughts were that the rr would not cause a change in starter pitch etc anyway as battery was fully charged.

I have fitted a new battery only a few weeks prior to this issue, so know that is all good.

About 12 months ago I changed starter cogs near sprag as the 16t one was stripped and a couple of teeth from the large one were smashed off. I recovered all teeth, so this repair was successful and have done about 10,000km since then.

I note that the bike has already had the sprag clutch upgrade to the heavy duty one, and this seemed to be okay when turning by hand etc.

I have just pulled the starter apart and it was a bit dirty, but brushes etc all in good condition and seems to operate normally when operating starter switch.

Not sure what to check next? :| Any ideas would be appreciated.
 

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Discussion Starter #3
Can you post a video?
What voltage on the battery?


Fred
Hi Fred,
Voltage at battery is 12.75v
I will have to do video tomorrow as have just reassembled right side engine cover and need to refill with oil.
But starter still appears to be cranking fast, just a bit higher pitch, like it’s pushing 2 cylinders instead of 3? That was my initial thoughts, there was no clunking or anything, just a sudden change in cranking pitch.
 

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Discussion Starter #5
I put starter back together, now starter is free wheeling, and not turning engine over, have i put brushes in back the front making it spin backwards??
 

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Discussion Starter #6
I don’t have facility for compression test Fred, I doubt it has dropped a piston/ring, it only has 60,000 km on clock? The last ride I had was a 5000 km ride about 3 weeks before issue. Bike went like a dream.
 

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Discussion Starter #9
Thanks for the comments, that compression tester looks legit, tomorrow I am going to pull the starter motor apart and turn the brushes 180 degrees as stater is turning wrong way, so figure that is why. Will give it another crank over and see what it sounds like. If still sounds different I will record it and buy that compression tester next week
 

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Discussion Starter #10
I have pulled starter apart again, looks like there is only one way to put brushes etc back on, starter turns clockwise? If this is correct I am not sure why engine won’t crank? Sprag Issue?
 

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Discussion Starter #11
Here is pic of sprag, it allows gear to spin anti-clockwise only. When I turn sprag with large Alan key all compressions seem similar and it does crank engine? Not sure what I am missing here?
 

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Discussion Starter #12
I have checked and starter motor gear going clockwise is correct on sprint!

I have checked the sprag gear rotation which is free counter clockwise and braked clockwise - also correct!

So with gearing the way it is, it looks correct that starter going clockwise would make sprag gear go counter clockwise hence freewheeling? What engages engine crank?
 

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Is there another gear that goes between that idler gear above the sprag?

Playing with the gears in my head, with the starter working directly on the idler gear the crank would be turned clockwise. Locking the sprag, turning the crank.
 

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Discussion Starter #14
The photo does not show the idler gears, so there are two, one to the gear you see, the larger one to the starter gear, so starter gear goes clockwise, next gear anti clockwise next gear clockwise then sprag anti clockwise?
 

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Since you have it apart you can easily see if the spring has defects. ....... behind the sprag outside the crankcase, not in the middle, or the other side) I think that leaves only one part left. Be interesting to see what you find but this is my best bet as an amateur and the reasons for my guess. I know for me, when it matters personally it can be harder to make deductions so I hope this is of help..

Your post is very difficult to read. Could you please add some line feed in it?


Thx


Fred
 

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Discussion Starter #20
Awesome thanks for the comments, I am also convinced it is the spring, so I am going to pull the sprag off and take a look at it, see if I can buy an after market one to suit.

I would have thought Triumph would have got it right on the heavy duty sprag, and if not sell the spring seperate, mmmmmm my other 3 sprints have been good, this one is testing my patience.

Will keep you all posted.
 
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