Mk3 vs Mk2 battery tray, sprag issues

Hi all,
I'm ploughing through a refresh of my Mk3, aiming to have a reliable, mildly modernised bike at the end of it. I have a single Mikuni already fitted and have removed the plastic air box, and a CNW oil tank to go on. I've heard occasional mention of people retro-fitting Mk2 battery trays to Mk3's, but I'm not really clear about the advantages of the earlier arrangement. What's the deal, and is it worth doing?

Thanks, Jon

Oh, I forgot - how good do the surfaces that the sprag clutch runs against have to be? The surface on the gear is not too bad, but the ID of the primary sprocket is pretty ridged.

Retro fitting an earlier battery tray is definitely not an upgrade. There are two reasons for using the earlier battery tray. The first being that it is easier to mount the earlier ham can style air filter. However you can install captive nuts just inboard of the original air filter mounting nuts on the battery tray and get the same results. As a matter of fact if you do something like that the air filter would sit farther back at the bottom which makes the air filter just a little easier to service. The other reason for using the earlier battery tray would let you use the earlier style left hand side panel. That way you wouldn't have to figure out and fabricate a bracket for mounting the Mark III side panel. Also the earlier side panels have the added benefit of having a tool tray inside the side panel.

The earlier battery tray was designed to work with the Interpol Commando which used two 6 volt batteries. That same battery tray was then used in all of the Commandos so everyone else was stuck with a battery tray that was too big for the one battery. The battery hold down leaves something to be desired which is something a lot of guys reinvent.

The only thing I experienced when I removed the black plastic airbox from my Mark IIA was that the battery was no longer supported. It fell over when I did my first hard braking on a downhill grade. I suppose the Mark III is more likely to stay upright because of the starter wires that go to the battery might help hold them up.

One thing that could be done with your bike is to make a storage/tool box that would fit in front of the battery. At the same time it could help support the battery from falling over.

Peter Joe

Thanks Peter Joe, that sounds like good news if only for the ever-spiralling parts bill!

My bike has had 3 sprags in relatively few miles with its previous owner, probably a function of low battery voltage & a Boyer. I'm hoping to solve the problem with CNW updated battery leads, Pazon ignition and hopefully more regular use! The surfaces that the sprag runs on are a bit ropey, the one in the engine sprocket in particular is no longer smooth. I may spring for one of them as well as the new sprag, just in case it was a contributory factor in the short life of the sprag.

Norton parts suppliers can rest easy, the flow of cash from my bank account to theirs is not yet over...!

In my experience, replacing the sprag clutch without also replacing the crank gear and the drive sprocket was a waste of time. I thought I would save a few bucks, but ended up buying the gear and sprocket after all (and another sprag). Be prepared for a shock on the total cost of the three items though ......


Per oldbritts.com:
"When replacing the sprag clutch, you need to make sure the bearing race in the drive sprocket (06-4681) and the bearing race on the crank gear (06-4731) are not worn and are dimensionally correct. The drive sprocket I.D. should be 2.280" to 2.281" and the crank gear O.D. should be 1.6253" to 1.6248".
There is a backfire device designed to eliminate damage to the sprag clutch if a backfire does occur. See our article on this device at Overload backfire device assembly and adjustment.
The old sprag clutch came with 14 rollers, where the new ones come with 18 rollers and since the sprag clutch is normally a trouble spot with the starter system, it is recommended you upgrade to the new sprag if you have the old sprag. For more information on the sprag clutch and how it fits into the starter assembly see our technical article: Pictorial help with installing the E-start starter gear train and setting up the backfire assembly."

Jon
Sounds like your MK 3 could do with the sprag clearances closing up. See this thread. converting-mkiii-starter-pole-t20978.html

Even doing this to used parts stops the sprag flipping and destroying itself, AND is far cheaper than buying new drive gear/sprocket/sprag. I will be modifying a drive gear for 'trident sam' sometime this spring (after I have rebuilt my MK3) If you want your drive gear modding at the same time PM me.
regards
Peter

Hi Keith,
Yeah, I'd pretty much come to the same conclusion myself, so I ordered the bits today... before I'd spotted Peter's post!

Peter, I'm interested in your fix, and I guess I'll have a spare set of bits for modification, for next time!

So, the new gear & sprocket have arrived, I'm good to go. I read somewhere that part of the reason for the relatively short life of sprag clutches is the lack of any planned lubrication. One thought to counter this is to pack the sprag clutch with grease. Has anyone tried this? Any thoughts?

Cheers, Jon

nope,

Will slip like crazy till grease it thrown out. Might also glaze mating surface. A little primary oil will do.

Pete

Deets55 said:

nope,

Will slip like crazy till grease it thrown out. Might also glaze mating surface. A little primary oil will do.

Pete

Click to expand...

Hmmm, interesting. Is that your opinion Pete, or have you tried it? That tends to suggest that grease is slipperier than oil? I only suggested it because a guy at work who rebuilt a Honda 1000cc 4 said that the sprag in the clutch centre was to be packed with Moly grease.

I guess, to paraphrase an old saying, we all have opinions, what I'm interested in is if anyone has tried it!

Cheers, Jon.

Boxerfan said:

Deets55 said:

nope,

Will slip like crazy till grease it thrown out. Might also glaze mating surface. A little primary oil will do.

Pete

Click to expand...

Hmmm, interesting. Is that your opinion Pete, or have you tried it? That tends to suggest that grease is slipperier than oil? I only suggested it because a guy at work who rebuilt a Honda 1000cc 4 said that the sprag in the clutch centre was to be packed with Moly grease.

I guess, to paraphrase an old saying, we all have opinions, what I'm interested in is if anyone has tried it!

Cheers, Jon.

Click to expand...

Pete is right, The clutch will slip until the grease is all thrown out -the first good ride.

I always thought some kind of a baffle that would pick up oil splash and direct it to the sprag would be a good idea -but I haven't done it. Jim

Boxerfan,

Guess I should have added "ask me how I know"

Pete

BTW,

I do put a little grease on the drive and idle gears and shafts though. If you take your kickback device apart a little grease or anti-seize might be good there. This is just an opinion, Jim might be able to verify.

Pete

Ok, thanks Pete, I'll stick with oil. It looks like there are some sprags that are lubed with grease, but ours isn't one of them.

Cheers, Jon.

I've gone through at least four sprags in the last nine years. After the first sprag destroyed itself about four years ago, I changed the engine sprocket and gear drive wheel for new items at the same time as advised despite the tolerances of the original items being practically identical to the new ones, and the sprags have continued to destroy themselves albeit latterly I have altered the motor to a 9.8:1 920cc which might not have helped.
I read the article written by John Merrick about how he reduced the gap between the drive sprocket and gear wheel to stop the sprag going over centre, and thought that reducing the gap was worth trying, but I am not clever enough to do the required work.

In this thread, I noticed that Peter (dobba99) had offered to do this modification for jon (boxerfan) were he to want him to.
So this week I contacted Peter and asked him if he would be able to do this mod for me, and Peter very kindly accepted. Yesterday, I took the gearwheel to Peter in person as I only live 40 miles away, expecting to leave it with him to do at his conveinience. Peter's first action was to invite me into his house, make me a cup of tea and welcome me, and he then offered to do the job whilst I waited, so I accepted. After three hours and another cup of tea and some very nice Norton chatting, I was on my way.

So I am just writing to thank Peter. He is a top man.

Incidentally, Peter also has the made equipment to replace the exhaust port threads with (brass?) inserts and is presently renovating / improving starter motors back from being totally clapped out. He is a very knowledgeable engineer.

I will see if this mod stops or slows my Norton's appetite for sprags. Ask me in three or four years and I will have the answer.

Reggie, that is motorcycling at it's best. You Brits have some of the most capable people in the world, especially when they are well lubed with tea.
It's sometimes said that the British invented the modern world that the rest of us enjoy (computers, electric lights, telephone and so on)

Glen