2 Questions about starter motor/sprag clutch issue...will starter motor spin in rever - Ducati.ms - The Ultimate Ducati Forum
 
LinkBack Thread Tools
Old Sep 17th, 2006, 10:06 pm Thread Starter
Senior Member
 
Join Date: May 2006
Location: Phoenix, AZ, USA
Posts: 442
2 Questions about starter motor/sprag clutch issue...will starter motor spin in rever

Initial symptom is that the starter motor turns and engine does not. Haynes says: sprag clutch. So I pulled that tonight and inspected. Haynes says if it is:

a. locked up
or
b. spins in both directions

It is bad. Curiously it spins in one direction and locks in the other. I even put it back on the crankshaft and tested extensively. It has the grip to spin the crankshaft in one direction and slips easily in the other.

So I hook up the battery and thumb the starter. The starter motor turns and turns the starter gear on the crankshaft ... IN THE DIRECTION WHICH THE SPRAG CLUTCH SLIPS.

So I have narrowed it down to two possibilities:

1. sprag (one way clutch) is installed backwards.

2. starter is getting the wrong polarity of juice and is spinning backwards...thus spinning the starter gear backwards...thus slipping the sprag...thus not turning the crankshaft.

So my questions are:

1. Is scenario #1 possible? I have not dismanted the sprag yet, but it appears it can only be installed in one direction.

2. Is scenario #2 possible? Will the starter spin in reverse if given the wrong polarity of current?

Thanks all.

-Trent
Desmo Soundtrack is offline  
Sponsored Links
Advertisement
 
Old Sep 17th, 2006, 10:16 pm
 
Join Date: Apr 2004
Posts: 284
I've seen a starter spin in the wrong direction. For some odd reason the "memory" of the starter changed and it did EXACTLY what you are describing. It would spin the starter, and the engine would stay still. This was a 97 GSXR 750 motor. The way I fixed it, was to disassemble the starter and pull the stator out of the starter (thereby removing it from the magnet, and "clearing the memory"), then reassembling the starter and giving it a short with the right polarity to "reset the memory". I know this sounds odd, that a starter could change it's rotation for some reason, and then be re-taught which way it should rotate...but it worked. Try it and give us feedback.

Good luck.

Ps. I believe the reason for the starter changing rotation, was that it had been sitting unused for an extended period of time.
bubbazenetty is offline  
Old Sep 18th, 2006, 12:29 am
Senior Member
 
Join Date: Mar 2004
Posts: 204
The starter clutch (sprag) is supposed to grab in one direction and freewheel in the other. This is normal.

Here's my two cents.......I think the clutch is supposed to be unlocked when spun in the same direction as the starter motor.

Thinking out loud..........looking at the engine from the left side (the side you'd see the starter gear from), the crankshaft spins counter-clockwise (CCW) so the starter should also spin CCW (it's a three gear system).

While the starter is cranking the engine, it transmits torque (CCW) thru the intermediate gear (CW) and then to the crankshaft (CCW) thru the starter clutch..........for it to do this the clutch has to be locked.........so the clutch needs to lock in the clockwise (CW) direction (opposite to the rotation of the crankshaft).

Once the engine starts, the clutch has to unlock so the engine doesn't constantly spin the starter, so it unlocks in the CCW direction (engine RPM overtakes starter RPM).

If my reasoning is sound, the starter should spin in the same direction that the clutch unlocks. In other words, turning the cranckshaft CCW shouldn't turn the starter. The clutch should be unlocked.

Weird? Sounds like it at first. Think about it in terms of what is transmitting the torque when cranking the engine vs. once the engine has started.

Now the question of why does the starter spin but the engine does not?

Has the engine been apart? The clutch might be installed backwards. From the crappy line drawings in the parts catalog, it looks like the clutch can be installed backwards.

If the engine hasn't been apart and the starter motor spins in the correct direction the clutch or it's mating parts might be worn/bad.
paulo57509 is offline  
 
Old Sep 18th, 2006, 1:54 am
Supermoderator - I┤m special!
 
amullo's Avatar
 
Join Date: Oct 2004
Location: Stockholm, SL, Sweden
Posts: 8,171
Garage
Images: 313
Quote:
Originally Posted by paulo57509
The starter clutch (sprag) is supposed to grab in one direction and freewheel in the other. This is normal.

Here's my two cents.......I think the clutch is supposed to be unlocked when spun in the same direction as the starter motor.

Thinking out loud..........looking at the engine from the left side (the side you'd see the starter gear from), the crankshaft spins counter-clockwise (CCW) so the starter should also spin CCW (it's a three gear system).

While the starter is cranking the engine, it transmits torque (CCW) thru the intermediate gear (CW) and then to the crankshaft (CCW) thru the starter clutch..........for it to do this the clutch has to be locked.........so the clutch needs to lock in the clockwise (CW) direction (opposite to the rotation of the crankshaft).

Once the engine starts, the clutch has to unlock so the engine doesn't constantly spin the starter, so it unlocks in the CCW direction (engine RPM overtakes starter RPM).

If my reasoning is sound, the starter should spin in the same direction that the clutch unlocks. In other words, turning the cranckshaft CCW shouldn't turn the starter. The clutch should be unlocked.

Weird? Sounds like it at first. Think about it in terms of what is transmitting the torque when cranking the engine vs. once the engine has started.

Now the question of why does the starter spin but the engine does not?

Has the engine been apart? The clutch might be installed backwards. From the crappy line drawings in the parts catalog, it looks like the clutch can be installed backwards.

If the engine hasn't been apart and the starter motor spins in the correct direction the clutch or it's mating parts might be worn/bad.
What he said +1

Curiosly, me and my brother got this when we installed a light flywheel on his 996S. We installed the sprag the wrong way around, so it didn┤t lock/grab, but free-wheeled when trying to use the starter. So the sprag CAN be mounted wrong way around.

//amullo

2010 Multistrada 1200s - engine mapped by tomtom, Íhlins mechatronics SCU and alot of mods to make up for poor skills
amullo is offline  
Old Sep 18th, 2006, 7:42 am
 
Join Date: Jun 2004
Posts: 852
Images: 40
Red face I've put the sprag in backwards too!

...and if you put it together with grease as an assembly lube (just use engine oil) it WILL fail... At $157, education doesn't come cheap...

But if I save someone else the expense it will all be worth it!
RichD is offline  
Old Sep 18th, 2006, 10:59 pm Thread Starter
Senior Member
 
Join Date: May 2006
Location: Phoenix, AZ, USA
Posts: 442
Sprag was actually installed backwards. It took me a while to figure it out based on the Haynes pictures, but once I got it all apart and started reassembling it, it became very clear. Now I just need some case sealant, a new crankcase bolt and washer, and a few days of sunshine!

Thanks all,
Trent
Desmo Soundtrack is offline  
Old Sep 18th, 2006, 11:02 pm
 
Join Date: Apr 2004
Posts: 284
Glad you got it figured out. Good job.
bubbazenetty is offline  
Old Sep 19th, 2006, 8:00 am Thread Starter
Senior Member
 
Join Date: May 2006
Location: Phoenix, AZ, USA
Posts: 442
I'm glad it was that and not that crazy sh*t you were talking about! I've never taken a starter apart before so I was kind of hoping that wasn't it. On the other hand, I figured it was, because I didn't put the motor together, but I was the one that wired it up, so I figured more than likely it was my mistake! Thanks again all.

-Trent

Quote:
Originally Posted by bubbazenetty
Glad you got it figured out. Good job.
Desmo Soundtrack is offline  
Sponsored Links
Advertisement
 
 

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ducati.ms - The Ultimate Ducati Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Thread Tools



Similar Threads
Thread Thread Starter Forum Replies Last Post
Clutch questions (yet again) Derek999S Superbikes 9 Sep 14th, 2006 9:29 am
Clutch questions Derek999S Superbikes 9 Jun 13th, 2006 4:18 pm
clutch questions JDuc Ducati Motorcycle Chat 1 Apr 17th, 2006 4:37 am

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome