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DC 4127 sprag from AliExpress

Discussion in 'Norton Commando Motorcycles (Classic)' started by worntorn, Apr 24, 2019.

  1. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    I hope everyone who ordered has received one.
    My 2 showed up last week. They appear to be the same as the last one.
    That sprag has done 150 or so starts now, no issues.
    The minute I hear any slippage is when the old will come out and a new $17 unit will go in.
    The $180 Norvil unit lasted about a day, this first $17 unit has done two years of light use so far.
    I did not change the expensive inner and outer drive parts as recommended by Norvil.
    It's all still running on the original stuff, which looked and measured OK.

    Glen
     
    Last edited: Apr 24, 2019
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  2. Esmerela

    Esmerela VIP MEMBER

    Joined:
    Jan 9, 2017
    Hi Glen

    I rebuilt my engine over the winter. My year old £55 sprag never coped with the increased compression of the fresh engine, even with the new £162 gear and sleeve :(

    After reading your previous post I ordered 2 of the AliExpress sprags, comunication from the seller was good and tracking information was accurate.

    I fitted the $17 AliExpress Sprag Good Friday morning :) I Rode out every day over the long weekend and the bike started on the button hot or cold every time:D.

    So far so good. Thank you for sharing.

    Best regards

    Esme
     
  3. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    I'm thrilled to hear that Esme!

    Hopefully these bargain sprags will still be working a thousand starts from now.

    8 more starts for mine today including a lovely operator induced stall and nearly instant restart at a stoplight. Left it in gear, just pulled in the clutch, hit the button and off I go, no chance for horns to honk!

    Glen
     
    Last edited: Apr 24, 2019
  4. HRD

    HRD

    Joined:
    Mar 21, 2011
    I can only agree with the service and communications/tracking info.I have not installed the sprag so unable to comment on working quality other than they look the part.
    Thank you Glen for sharing.
    Paul
     
    worntorn likes this.
  5. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    Still waiting for mine. Communication from seller really good. Still in transit.

    Thanks Glen for the heads up on this, as others I've spent 80-90euro on a single sprag & have had them fail after 20-30 starts and that's with replacing all the other 'bits' with new parts!

    I was hoping CNW would get around to their MK3 ES project with improved parts etc. but I've not heard anything about this project in a while?

    Kevin
     
    worntorn likes this.
  6. Britbike850

    Britbike850

    Joined:
    Dec 9, 2012
    I have heard that the drive gear should be replaced if they are scored or dimpled otherwise it can compromise the sprag...even if new. Anyone check these before replacing the sprag...if so, what are the limits in ripples, gouges...before replacing...anyone have a photo of a bad one or one that is close to the limits...
    Thanks for your time,
    Rod
     
  7. dynodave

    dynodave

    Joined:
    May 28, 2003
    Interesting enough since I was asked by Alton right after the 2011 Norton Empire Rally, Blackthorne Campground, Durham, NY to supply 20 reverse rotation starters for their new MKIII starter mod which AFAIK never came to fruition. I'm now sitting on a pile of parts that will likely never get paid for.

    You discuss buying and replacing one part out of the current system. I have studied and examined many components a fair amount, but I'm not going to stand up and claim to be the expert on a conventional industrial product used in this type of environment.
    Anyone care to opine, in engineering terms on the operation and failure mode of each component and the system ?
     
  8. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    I installed the cheap sprag as a stopgap measure in order to temporarily reactivate the estart ( knee injury)
    The longer term plan was to install the upgraded components that CNW plans to produce.
    For the cheap sprag I intended to try the fix described by Dobba99 who used a bearing race to tighten clearances up.
    After sliding the cheap sprag into the existing original components, I noticed that it had plenty of bite, that is to say, it grabbed the crankshaft firmly long before getting close to overcentering of the dogs.
    I recall that the new Norvil sprag did not look that way when installed. The dogs on that one were nearly tipped to their full length when they gripped the crank. Right from the getgo there was some slippage and after a dozen or so starts the dogs overcentered and the cage broke.This overcentering is what Dobba99 cited as the main cause of sprag failure and why he fits the bearing race.
    Anyway, it looked to me that the cheap sprag would work in the existing original parts, which have a few lines on them from earlier slipping sprags.
    It does work and very nicely at that, but time will tell if the material in this cheap sprag is the right stuff for durability.

    Glen
     
    Last edited: Apr 25, 2019
  9. dynodave

    dynodave

    Joined:
    May 28, 2003
    14 or 18 dogbone/rockers per clutch?? Any opinion on the pre load spring style and stiffness having an effect on the ability to grip? cheap/expensive does not provide much detail for investigation. Which ones last and which ones die. Any length differences in the dogbones?
     
  10. trident sam

    trident sam

    Joined:
    Oct 23, 2012
    Glen,
    I've tried to find these but I'm not exactly proficient with computers !
    Can you post some sort of contact for them.
    thanks
    sam
     
  11. worntorn

    worntorn

    Joined:
    Dec 22, 2006
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  12. worntorn

    worntorn

    Joined:
    Dec 22, 2006

    18 in these sprags.
    Which ones last and which ones die is what I've been posting about.
    Also differences in the dogbone length as posted above.

    Glen
     
  13. Britbike850

    Britbike850

    Joined:
    Dec 9, 2012
    Adding a bearing race...how is it fixed to the starter gear? Any measurements after adding race for proper clearance? Someone must know this measurement for proper operation. Surprised at the limited data on this subject... and no photos of good/useable/not usable condition.
    Thanks to all that have at least added to the limited info available,
    Rod
     
  14. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    The search feature works for that info.
    This thread was for the purpose of getting feedback from those who ordered the AliExpress sprags, just to see if
    a. The product arrived
    b. The product worked.

    I can't agree that there is a shortage of info on estart repairs on this site.
    Ive spent hours searching and reading it all.
    Here is the Dobba99 info, it's been re-posted a few times.

    https://www.accessnorton.com/NortonCommando/mk3-sprag-repair.20855/

    Note that in the above thread Hanksmarx posted this info
    "Just had my fourth sprag failure in 9000 miles Two high dollar 14's, two 18's. The last time I replaced the sprocket as well. It looks like I will be kicking it for a good while"

    There are a lot of us who have had a similar experience to Hanksmarx.
    I tried this inexpensive sprag without following proper procedure of also renewing the gear and drive sleeve( about $300 just for those two bits) and so far it has greatly outlasted the expensive items from England .
    I think this may be because the dogs on the $17 sprag are longer and bite properly without going over centre.
    And when it does finally wear out, it's $17 to replace.
    That's the info I was attempting to share.
    Of course I'm hoping others will have similar success with this inexpensive fix.

    Glen
     
    Last edited: Apr 26, 2019
  15. Britbike850

    Britbike850

    Joined:
    Dec 9, 2012
    Thanks Glen,
    Got to pick my search parameters better... has anyone tested the actual hardness of the starter gear... is there a process for improving the hardening of a stock starter gear?
    Rod
     
  16. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Matt at CNW did some testing of the stock stuff and it did not test well. That was when he got the idea to have higher grade components made up.
    I waited a year or two for that, but I guess he hasn't had time.
    In the meantime I'm finding this inexpensive temporary solution to be better than expected.

    I'm not convinced that there is a problem with the original parts, although they probably could be harder.
    A friend in Australia commutes daily on his MK3 year round. He has a huge mileage on thr bike, over 150,000. He has replaced several sprags, I believe he is on his fourth.
    He keeps track of the sprag life and found the average was lasting 1700 starts. His sprags have all failed at about that same point +-200 starts.
    He has never replaced the other drive parts and still managed 1700 or so starts on the last sprag. I think most of us would be happy with 1700 starts. That would see me out!!

    I'll have to ask if he is using these Aliexpress sprags.:)

    Glen
     
  17. dynodave

    dynodave

    Joined:
    May 28, 2003
    Hey Rod
    yes I have hardness tested several sets of the drive components. I seem to be a lightening rod for starter problem inquiries, though most are behind the scenes. I've looked at it and done some math but again no expert here...
    I have come to a preliminary conclusion of the failure mode. Yes the sprags do funny things upon overload, stress and ultimately failure.
    When some of the sprags grip and some fail to grip, funny things start to happen. Two differing actions must occur for failure.
    One sector of sprags will grip, while at the other side of the sprags they fail to grip. Based on the internal wear and staining of the crank gear, the sprag assy mostly runs with the engine sprocket. The sprag dogs inner end slides over the smaller inner drive race. This will eventually show up as a wear pattern on the sprags. It seems from observation that the inner drive race takes a majority of the stress of starting. While the engine sprockets rarely show deformation, most all the inner races show markings. Some are almost not noticeable and some are extremely beat up.
    Where the dogbones go over center, it's like a runner going for 3rd base and does a double foot plant on the bag, his upper body falls forward doing a face plant...bang... over center
    But for this to happen it MUST on the opposite side of the sprag assy these sprags have laid down like the running to home plate sliding on their butt. If this did not happen the dogbones, wouldn't they have to be crushed and break or the engine sprocket or drive race would burst. Both top and bottom dogbones, if straightened out, would be .00184" of tool steel expansion on the engine sprocket or compression of the drive race.
    I have seen a few types of engagement preload springs touching the dogbones which can be damaged an add to engagement problems.
    So far it seems these clutches are only rated for around 130 ft/lb torque.
    I continue to study why the dogbones fail to grip and have a few idea's there too.
     
  18. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    The other big consideration is kickback.
    My friend with the 4x 1700 starts has eliminated engine kickback with a good ignition , proper timing, strong battery and fully functioning charging system.
    Any one of the above can be the weak link to cause kickback and sprag breakage.
    The antikickback mechanism is there to attempt to deal with it, but best is to eliminate it.
    I eliminated kickback and low voltage to the ignition during starting. I installed a tiny, isolated second battery that feeds full voltage to my ignition on cold startup.

    The starter also needs to be fed with lots of power.
    Some Hinckley Triumph triples had starter sprag issues. The owners manual warns against attempting to start the bike with a low battery. Triumph suggests that it is necessary to have a strong battery for proper sprag engagement.
    A lazy gentle turnover does not lock the dogbones in securely and slippage occurs.
    Slippage causes rapid wear.

    I can't see why it would be any different with the Commando sprag. The operation is the same.

    Glen
     
  19. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    Got my sprags today:D

    Back in 2016 I got the 'Ken Merrick' mod done. Because I was dealing with other Norton related issues I never got around to fitting it but it's on my 'list'!!

    I searched my digital archive and came across this article I kept. It might be useful to others with more engineering talent than me!!

    It's an article that Ken published, I think, in the Roadholder Norton Owners Club publication.

    (Article written by Ken Merrick)

    There is, however, a further weakness in the starter system and that is the spragg clutch. This clever little device is a form of “free wheel” which engages the main shaft via a reduction gear drive from the starter motor. The sprag clutch transmits the drive to the main shaft when the starter button is pressed then free wheels once the engine fires up. Early sprag clutches had 14 sprags or teeth but later ones were increased to 18 to improve performance and reliability. In free wheel the sprags lean over to allow free rotation. When the starter is engaged, the sprags come up close to the vertical and carry the main shaft with them giving the required drive to the main shaft for starting. With use, the engine sprocket bore wears by engaging the sprags as does the gear which contacts the other end of the spragg allowing the sprags to go over centre and jamming the whole assembly, resulting in an expensive replacement sprag, sprocket and gear costing £200.00. If this happens, it’s no use replacing just the sprag, it’s necessary to replace all three items.



    2

    This happened on my bike and I was unable to turn the engine by any means. I managed to free it by dismantling the whole of the primary side and, upon examination, the I.D. of the engine sprocket and
    the O.D. of the gear, engaging the sprag were damaged with grooves where the sprags had “dug in” whilst going over centre. The sprag of course was completely wrecked. To avoid the expense of a new sprocket and gear I internally ground the sprocket diameter until the grooves had been removed, taking out 0.010” on diameter.

    The gear was not so easy as it required an increase in diameter. I overcame the problem by selecting the outer hardened sleeve of a needle roller bearing measuring 42mm O.D. and 35mm I.D. from my local bearing supplier for £5.00 and by reducing the gear diameter fixed the sleeve with LOCTITE RETAINER. This involved reducing the hardened gear diameter by rough turning the diameter to give a clearance of 0.004” on diameter below the sleeve I.D. of 35mm. Rough turning is required to give the maximum “key” and was easily achieved with a carbide tipped tool on the lathe.

    The sleeve was grooved internally with a number of spiral grooves ground freehand with a “DREMAL” hand grinder to give a similar “key”. The O.D. of the sleeve was then externally ground so that the ground diameter just entered the sprag and was free to rotate backwards but when rotated in the opposite direction, the assembly locked and drive to the main shaft would result.

    Because the clearance between the sprocket and gear dia was reduced, the sprag angle was increased making it impossible for the sprag to travel over centre thus overcoming the previous disastrous jam up.

    I have run this set up for the last 4 years and 5000 miles without a problem and although it all sounds a little complicated, it can easily be achieved with a little help from your local engineer and will save you a lot of money purchasing new.
     
  20. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    It's good to have this info and the Dobba99 info.
    However, If you don't have the machine tools and ability to do this work, I suspect it would be less costly to just purchase the new parts rather than pay machine shop current rates around $125 per hour to re &re the old worn stuff. The modified part could easily be better ( harder) than a new replacement part is though, so that is a consideration.
    Cheaper yet is to try one of the AliExpress sprags in the old somewhat worn setup as I did. It just might work as is.
    I'll mention again that this is against
    against most advice. We're supposed to change everything every time, even though the success rate of that very expensive route isn't great.

    Glen
     
    Last edited: Apr 26, 2019

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