I have a 1985 K100. A few days ago when I hit the starter it just whirred but wouldn't engage. After a few tries it worked and was fine for the next day. Today it happened again but wouldn't engage after about ten tries. I push started it and stopped in somewhere on my way home . It still didn't engage. Later in the day I went out and it was fine all afternoon. The first time it didn't work I rocked it slowly in gear to see if the gears weren't lined up but it did nothing.
Any ideas?
Thanks, Doug

Sprag Clutch old boy....gummed up....Drain your oil and use flushing oil...drain and fit new filter and fill with Semi Synthetic oil to the glass indicator.
Common problem and easily solved.
Don't go to the dealers or they will want to fit a new Sprag Clutch at high costs.
Good luck.
Ajays.

Pull it out and disassemble it, noting which way it comes apart. You'll probably find the carbon brushes have dusted to excess. Clean the guts of the starter (the windings and such) with contact or brake parts cleaner, measure the brushes and replace them if necessary. Otherwise, you will get a bit of extra life out of it by giving it this thorough cleaning. If the brushes are good then the sprag's the next (big) step. Ajays is correct in that using a detergent oil (like a high-quality diesel oil) can have a good effect on it. This has been my experience and a few others here as well.

I agree with Ajays and TWB. The only way to try solving the problem without a major tear down is by flushing the engine.

A sprag clutch is made of small springs and sprags. It works on the same principle as a free wheel. One of the most common application of the freewheel is the hub on a back bicycle wheel:



Here is the principle of a free wheel.
The small springs keep the rollers lightly in contact with the outer ring .
When the outer ring is rotating CCW, it will squeeze the rollers against the ramps locking the inner and outer rings together.
When turning CW, the squeeze is released and the small springs will give just enough pressure on the rollers to have them sliding against the outer ring.
The 2 majors problems on a sprag clutch are:
- the system is gummed up and nor the rollers or the springs work freely (common on K bikes).
- The ramps are marked and it prevents the rollers to ride freely on them.




The explanation of the free wheel principal should help you to understand how the sprag clutch is working.
What is a sprag?
a. A piece of wood or metal wedged beneath a wheel or between spokes to keep a vehicle from rolling.
b. A pointed stake lowered at an angle into the ground from a vehicle to prevent movement.

The sprag clutch is working on the principle of friction too. On the picture of this clutch, when the inner race is turning CCW, it will drag and tilt the sprags and subsequently lock the inner and outer races together.
The starter is driving the inner race and the outer race is the link to the crankshaft.
When the crankshaft is turning at a higher rpm than the starter, the pressure on the sprags is released. The small springs are applying just enough pressure to the sprags to have them sliding on the inner race.
If the system is dirty and the sprags or springs are not working freely, the sprags will not keep a contact on the inner race and this is when the starter will spin but not drive the crankshaft.






On the K engine, the sprag clutch is lubricated by the engine oil. The carbon deposit is what gum the clutch. You have to remove the transmission, clutch and bell housing to access the sprag clutch and clean it. This is why the flushing is the easiest way to go.
The majority of bikes are using sprag clutches for the starter, but on a lot of Japanese one it runs dry and doesn't have any contact with the motor oil. This is why they don't have the same problem.



Hope that help to understand the problem.

Bert

Thanks for the info. What is a good flushing oil and how long do you run it?
Thanks, Doug

Two Wheels Better wrote:Ajays is correct in that using a detergent oil (like a high-quality diesel oil) can have a good effect on it. This has been my experience and a few others here as well.

The answer is already there. Go to Canadian Tire and just buy one of these.



Have a new filter on hand and run the engine for about 15min with this oil.
Stop the engine every 5 min and see if it has any effect on the sprag clutch.
Drain your engine, replace the filter and refill with a good regular quality oil.
Hope that it works for you.

Bert

Cool, I'll do it today. I even have some of that Motomaster Diesel oil that I used to use on my diesel truck.
Thanks, again, Doug

Hi,
If you have the correct viscosity grade there is nothing to stop you using the high quality diesel oil till the next change. Furthermore if the oil is S rated as well as C rated (S=Spark and C = Compression) there is no reason not to use it all the time from now on. It will progressively clean your engine out and will have high pressure additives which are good in the bearings. Since diesel engines experience high stress on the oil they are high quality oils, Rotella from Shell or any of the other big brand companies will be perfect. Don't expect it to be instant it may take a few days of stop start use to thouroughly clean the sprag clutch out.
Regards,
K-BIKE

K-BIKE wrote:Hi,
If you have the correct viscosity grade there is nothing to stop you using the high quality diesel oil till the next change. Furthermore if the oil is S rated as well as C rated (S=Spark and C = Compression) there is no reason not to use it all the time from now on. It will progressively clean your engine out and will have high pressure additives which are good in the bearings. Since diesel engines experience high stress on the oil they are high quality oils, Rotella from Shell or any of the other big brand companies will be perfect. Don't expect it to be instant it may take a few days of stop start use to thouroughly clean the sprag clutch out.
Regards,
K-BIKE

That is correct. Many bike forums advocate use of good quality diesel oils for bikes with wet clutches. As our bikes do not have that complication, good quality diesel oil is fine. Our local oil company even produces a tech bulletin to list all suitable oils across their range (see link) http://www.penriteoil.com.au/tech_pdfs/126%20FOUR%20STROKE%20MOTORCYCLE%20OILS%20UPDATE.pdf

you will see a lot of diesel oils listed. International communities advocate Shell (synthetic) to be the best.

Diesel oils are considered to be of higher "quality". As I understand it this oil has no friction modifiers, but contains Zn and lots of detergents which are desirable for engines under high stress.

Good info Ned!!

And Bert, that's one of the nest descriptions of the sparg clutch I have seen ever!!

Great forum!!!

Just my "2 Bob'sworth" as we say in Oz. The sprag clutch is an extremely precisely manufactured item. They are used for many duties and are also known as "anti-runbacks & backstops" in the industrial world, which is my occupation.
They operate by allowing absolutely no runback when installed in a gearbox for example (to hold against runback by a machine which is loaded). This very clever technology relies on being kept free of any gum or sludge, and when used in an engine environment it could be argued that this is among the most arduous duties for these items (from a reliability perspective). So, by using the diesel oils of today you will be kind to the sprag clutch, but as I have stated in a previous post, the K engine doesn't need a synthetic oil to keep it happy for a very long time.
My strategy is - 15W40 mineral diesel oil and a new filter every 5,000 K's.
Oh, and to help allay any fears of using the diesel oil, I have a Nissan Skyline which has been our family car for 21 years, it has 307,000 K's on the clock and has been run always on 15W40 mineral diesel oil. It runs faultlesly, engine is absolutely clean internally and has been serviced every 5,000 K's. Speaks for itself I reckon.

Dennis, your strategy is a good one. I've been through the process of trying to extend my oil change interval, even with synthetics, but this hasn't really worked for me. The problem is that we don't really get a full synthetic unless you pay 2.5 times the price of plain ordinary good oil.

I will go back to 3months between changes. My strategy will be, 5w40 synthetic diesel or 15w40 mineral.

I have an interesting problem. K100 (dry clutch) will take anything but the Goldwing (wet clutch) will not tolerate friction modifiers, thus the Penrite tech bulletin. They make it clear that you can use anything that is in the viscosity range so long as it doesn't have friction modifiers.

Both will take diesel oils, so I will buy in bulk (20L drum) and use it for both. The only thing that I am not too sure about this is the upper viscosity range of 40. I would prefer 50 in summer, but it is rare to find 15w50 for diesel in the main stream of the popular good brands.

How about this:
http://www.penriteoil.com.au/products/motor-oil/hpr/hpr_diesel_15

Ned,
Here's a bit of tech gaff from my info library at work, it may help put you at ease regarding the viscosity thing.
SAE 40 is ISO-VG150, which means it's mean viscosity at 40 degrees C is 150 cSt (centistokes). SAE 50 is 220 cSt at 40C, but as the temperature rises, the viscosities of both oils tend to come a little closer together, till at 100 degrees C the SAE 40 will be 15 cSt and the 50 will be 19 cSt.
You will not see 100 degrees oil temp in the K engine, more likely 70 - 80 max (3.7 litres in a 1 litre engine with finned aluminium sump and extremely well designed cooling system). So, when it's all said and done, at running temp the SAE 40 will be just fine, with the added benefit of being slightly faster flowing when the engine is dead cold, and that's when the damage is done, in the first 100 turns of the crank.
So, for me, it's 15W40 Caltex Delo Multigrade, or Delo Silver, 5000 kservice with filter, warm it up well then ride it like ya stole it.

85 K100RS w 126,000 just started having this problem. Oil and filter change has fixed it twice, happened with old Belray oil the first time. Use golden spectro 20-50 mostly. Once when push starting in 2nd gear and spinning the starter, I heard a "rub" or a spinning "jam" for a second. It hasn't happened since, I figure this rub either cleaned parts of the sprag clutch or roughed parts up a bit, for the good.

Make sure you really ride it once in a while. The sprag clutch is not very well oiled and it will accumulate residue, particularly when you often drive short stretches. This residue will then prevent it from properly engaging.