MK III Starter Sprag?

So - I tried to start my 75 MK III today. I was using the kick starter rather than the push button. It kicked back at me and I think it jammed the starter sprag. When I try to kick it, it sounds like it is turning the entire starting system and is much stiffer to push through. I did get it started, but it was making a loud sound from the primary case that I believe is the starter gears turning with the engine. I turned it off quickly. If I push the starter button, the starter spins, but it does not engage to turn the engine over.

It did this same thing last week when I used the push button, but after it started the starter gears quickly let go and everything seemed to be fine. I will start tearing it down this week. What should I look for?

I have had this bike for several years now and have not had any issues with anything associated with the electric start.

It has been running so good of late - - frustrating.

It sounds like your sprag has flipped. I'm having good luck with this one:

http://www.vxb.com/page/bearings/PROD/O ... 7Aod5TsAZw

You won't find a better price.

If ya search sprags on this forum and google ya'll see too many reports of very competant builders only getting few dozen starts[or less] before sprag failed again so might get two of them this time and send them both to be cryo tempered in case that extends leg less starts longer.

Like anything else, there are good and bad ones. Mine is the original, 60K miles worth and I haven't used the kicker in years! If your MKIII is kicking back at you, I would get the timing set correctly to 28 degrees BTDC at 5K RPM after you fix the starter bits. I know the EI boys say 31 degrees, but don't do it on a MKIII if you use the stock starter set up. Also use oil in the primary, not ATF. Helps keep the sprag from wearing.

milfordite said:

Like anything else, there are good and bad ones. Mine is the original, 60K miles worth and I haven't used the kicker in years! If your MKIII is kicking back at you, I would get the timing set correctly to 28 degrees BTDC at 5K RPM after you fix the starter bits. I know the EI boys say 31 degrees, but don't do it on a MKIII if you use the stock starter set up. Also use oil in the primary, not ATF. Helps keep the sprag from wearing.

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Good advice. I'm at 28 degrees and using engine oil in the primary.

JimNH said:

milfordite said:

Like anything else, there are good and bad ones. Mine is the original, 60K miles worth and I haven't used the kicker in years! If your MKIII is kicking back at you, I would get the timing set correctly to 28 degrees BTDC at 5K RPM after you fix the starter bits. I know the EI boys say 31 degrees, but don't do it on a MKIII if you use the stock starter set up. Also use oil in the primary, not ATF. Helps keep the sprag from wearing.

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Good advice. I'm at 28 degrees and using engine oil in the primary.

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Thanks all for the information.

I am running a Boyer ignition, would the 28 degree advance hold true for that electronic set up?

The same thing happened to me. The sprag came apart and jammed so the starter spun with engine and self destructed. New sprag, associated gears, agm battery, CNW starter and Trispark solved the problem for now. But an expensive fix.

Do not start your engine until you have the sprag apart and see what's going on. 28 degrees timing is good advice. I do the same. I also ran at 28 degrees when I used a Boyer. It was a one kick starter with that timing. Many have advised against using an old Boyer with e start...because of potential kick back if your battery voltage drops.

Check the accuracy of the timing marks against your crankcase slot. Mine showed the timing marks to be off by 2 degrees.

Ditto the advice not to run an early Boyer with an E-start; it was my downfall. See Dyno Dave's tests at AtlanticGreen.com.

I took the primary cover off today and took a look around with some wrenches, etc. My sprag clutch is doing its best impression of a hand grenade. Apparently when what ever happened, the inner race of the sprag clutch broke into several pieces. So far, the two concerned gears inner and outer diameter tolerances are within limits. I will know more when I get it farther apart and get a new battery for my mic. I did not see any gouging or scoring on any of the surfaces. For now I am a happy guy.

I will post an update when I have one.

Ugh Sprag failures tops even anti-sump valve failure reports. The way reports say sprag fails implies to me cryo tempering may extend their use detectably.

MK III Starter Sprag? Primary Oil type

Are you saying that you can run a 20-50W engine oil in the primary with no clutch problems like slipping or sticking plates and the sprag will be better lubricated than using ATF oil ?

Re: MK III Starter Sprag? Primary Oil type

thackero said:

Are you saying that you can run a 20-50W engine oil in the primary with no clutch problems like slipping or sticking plates and the sprag will be better lubricated than using ATF oil ?

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In a word, yes. In fact, the chain tensioner is meant for engine oil not ATF although it probably doesn't matter.

What does matter is that you fill according to the volume it requires, not to the witness hole as that's too much. Dyno Dave's clutch rod seal keeps transmission oil from migrating through as well. Don't overfill the transmission either.

I'm really not sure if ATF is a good lubricant for the sprag. Considering that automatic transmissions and torque converters have them, well, maybe. Consider that the sprags in a torque converter or automatic transmission are pressure lubed, not mist lubed.

ATF is designed to lube sprag clutches, lined clutches and gears.

Motor oil is not.

The big problem is the Norton sprag clutch is very poorly lubricated. Very little splash or mist makes it to the sprag. Jim

My starter will not engage to turn the motor over when very cold. In this circumstance tickle flooding , then pull in clutch and try again.. If this fails then use the kicker in conjunction with the starter button , this does work, after all it is an electrical - assistor system. But if your sprague was taxed and destructed , try/get/fit a new one. Been thinking , if lack of lubrication to sprague and support needle roller bearing is the real issue , then perhaps someone can design a "trough" or catch basin lip arrangement to retain a bit of oil for startup stresses ? :!: I've switched oil as it is getting cold now , to 5 W 50 Synthetic with good results for cold startups. Obviously Boyer not the best option for the MK 111 . Using Tri-Spark with never a kickback so consider. :wink:

comnoz said:

ATF is designed to lube sprag clutches, lined clutches and gears.

Motor oil is not.

The big problem is the Norton sprag clutch is very poorly lubricated. Very little splash or mist makes it to the sprag. Jim

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I stumbled upon this sometime back when looking for a better replacement industrial sprag and not at the retail price. It does indeed list Dertron as suitable but also engine and hydraulic oil; grease is also listed but discouraged. Other publications I found were in general agreement.

I agree that the Norton sprag is likely under lubed. These guys recommend the sprag live in a bath of oil, one third the depth when not running although again, it allows for mist lube but suggests a direct spray.

The torque converter sprags in industrial machines generally live in hydraulic oil rather than ATF. They have common sump transmission, rear end, hydraulic systems, and perhaps wet brakes. The hydraulic oil I use also qualifies as engine oil. One issue that comes up is the oil doesn't flow like ATF in cold weather, something unacceptable in a car but not so bad in a piece of equipment that's going to be given time to warm up. I have a loader/backhoe that has 4 hydraulic pumps all drawing from the common sump. One is dedicated to steering, one for transmission clutches and torque converter, and two to run the rest of the machine. Another machine has one pump that runs steering and brakes and clutch and another that runs the rest of the machine.

60 to 120C shows SAE 30 so I figure a 20-50 is in the ball park for an air-cooled motor.

These instructions are generic one way or freewheeling clutch but I think applicable to any sprag.

I found other sprags used as anti back devices that run in grease.

Installation of Sprag Clutches

Proper lubrication with only qualified lubricants is the prerequisite for achievement of highest efficiency and long life of our high quality sprag clutches. Only with use of oil or grease lubricants specified in the tables below, GMN will warranty their Free-wheel Clutches and their trouble free function. Whenever possible, use only oil or oil mist lubrication rather than grease lubrication. Please contact our technical staff if operating temperatures are in the upper or lower temperature tolerance range, if the sprag clutch has to be mounted in vertical position or if there should be any other special conditions. Oil for oil mist lubrication please use hydraulic oil HM 10 or HM 32. The use of lubricants with additives that decrease the coefficient of friction, i.e. MoS22 or graphite is not possible.
Oil Type Operating Temperature Range
-15° C to 30°
C5° F to 86° F 15° C to 90° C59° F to 194° F 60° C to 120°
C140° F to 248° F
Hydraulic Oil Hydraulic Oil HM 10 Hydraulic Oil HM 32 D Hydraulic Oil HM 100
Motor Oil HD-Motor Oil SAE 10 WATF-DEXRON III HD-Motor Oil SAE 30

Oil lubricants described above - except hydraulic oil - are from the automotive sector. These lubricants can easily be obtained at automotive supply outlets and are excellent for the lubrication of our Freewheel Clutches. Lubricant qualification: HD-motor oil SAE 10 W or SAE 30 is equal to "API-Service SE or CC" and MIL-L-46152B".

Important: Oils shown in the table are only to be mixed with oils of the same qualification. That means ATF oil with ATF oil, HD-motor oil with HD-motor oil etc. If there is any change of oil from one qualification to the other, it is necessary to clean the Free-wheel Clutch and mating parts with cleaning or test benzine. Never use trichloroethylene or perchloroethylene.

The oil level should be in relation to the size of the Sprag Clutch. In normal installation position, not operating, one third of the clutch should be submerged in oil.

For oil mist lubrication systems we recommend ample clean oil, free of moisture, be sprayed directly onto clutches. Open or unsealed housings should be inspected frequently - at least daily - for proper lubrication level.

Having issues reading the blue but all good above it.

Blue in white

Installation of Sprag Clutches

Proper lubrication with only qualified lubricants is the prerequisite for achievement of highest efficiency and long life of our high quality sprag clutches. Only with use of oil or grease lubricants specified in the tables below, GMN will warranty their Free-wheel Clutches and their trouble free function. Whenever possible, use only oil or oil mist lubrication rather than grease lubrication. Please contact our technical staff if operating temperatures are in the upper or lower temperature tolerance range, if the sprag clutch has to be mounted in vertical position or if there should be any other special conditions. Oil for oil mist lubrication please use hydraulic oil HM 10 or HM 32. The use of lubricants with additives that decrease the coefficient of friction, i.e. MoS22 or graphite is not possible.
Oil Type Operating Temperature Range
-15° C to 30°
C5° F to 86° F 15° C to 90° C59° F to 194° F 60° C to 120°
C140° F to 248° F
Hydraulic Oil Hydraulic Oil HM 10 Hydraulic Oil HM 32 D Hydraulic Oil HM 100
Motor Oil HD-Motor Oil SAE 10 WATF-DEXRON III HD-Motor Oil SAE 30

Oil lubricants described above - except hydraulic oil - are from the automotive sector. These lubricants can easily be obtained at automotive supply outlets and are excellent for the lubrication of our Freewheel Clutches. Lubricant qualification: HD-motor oil SAE 10 W or SAE 30 is equal to "API-Service SE or CC" and MIL-L-46152B".

Important: Oils shown in the table are only to be mixed with oils of the same qualification. That means ATF oil with ATF oil, HD-motor oil with HD-motor oil etc. If there is any change of oil from one qualification to the other, it is necessary to clean the Free-wheel Clutch and mating parts with cleaning or test benzine. Never use trichloroethylene or perchloroethylene.

The oil level should be in relation to the size of the Sprag Clutch. In normal installation position, not operating, one third of the clutch should be submerged in oil.

For oil mist lubrication systems we recommend ample clean oil, free of moisture, be sprayed directly onto clutches. Open or unsealed housings should be inspected frequently - at least daily - for proper lubrication level.

I didn't understand. Blue shows up in my background OK.

JimNH said:

I didn't understand. Blue shows up in my background OK.

Click to expand...

Which board style are you using, light or dark (standard) theme, as the purple-blue text doesn't show up well on the dark background?

(Android phone users might see blue and black on white background theme as standard-unless they "Switch to full style".)

L.A.B. said:

JimNH said:

I didn't understand. Blue shows up in my background OK.

Click to expand...

Which board style are you using, light or dark (standard) theme, as the purple-blue text doesn't show up well on the dark background?

(Android phone users might see blue and black on white background theme as standard-unless they "Switch to full style".)

Click to expand...

I assume standard. Black to compose, gray on posts, black on quotes. All VIP member names show up with blue font.