The sprague clutch brings back many sad memories, I must have replaced and repaired my sprague clutch twenty times on my old MK3 back in the 80,s. At the time it did not register that I really started having trouble after I installed a Boyer EI. The Boyer retards ignition on a low battery which is the natural habitat of the bike back then. The retarded ignition causes backfires which the back fire preventer (never worked) failed the save the sprague.
The Boyer Mk3 was a real problem with the Norton Mk3 electric start. Because the voltage would drop down sometimes as low as 9 volts if the battery wasn't fully charged. The boyer would go fully advanced with any voltage below 10.5 volts and causing severe back firing, leading to sprag bearing failure. Boyer later updated to a Mk4 version, which is a little better, but if the battery is weak, it will still go fully advanced. We feel the best electronic ignition for a Mk3 Norton is a Tri-Spark as it has anti-kick back feature that cures that problem completely.
Hi again guys. I am re watching this video to help a local new commando owner with his mk3 starter problems. Appears to be a failed sprag clutch, starter just spins without engaging motor. Having trouble removing all primary cover outer bolts, someone has used locktite so needing to get an impact driver and big hammer to fully investigate. Another problem is the gear shift lever...seems to wobble in the outer cover hole...was hoping to see how to check/fit the bushing there but not shown.
There is a bushing in the outer primary cover for the cross shaft there is only a seal in the inner primary cover. The other bushing to stabilize the cross shaft is in the inner transmission cover so if its wobbling around loose the cross shaft and bushing could be worn. If somebody used locktite on the screws blue 242 is the only one that wouldn't do thread damage trying to remove the screws mild heat will loosen it. If they actually used red heat is the only way to get it apart without taking the threads out with the screws it will need 350 - 400 degrees to release red loctite. Wow that's one place loctite is never needed! It sounds like the sprag failed. We put two new ones in a close friends mk3 without any long term success his gears were worn past the tolerance so it would only spin when the button was pushed we recently installed the CNW mk3 sprag and gears upgrade we also released a RU-vid video doing that project check it out you will like that also. Good luck with the project
great video, just one a question, are you supposed to put 300cc of oil into a dry primary and then lose a little when its stored in the chain tensioner? surely if you fill the tensioner first then add 300cc to the primary case there will be extra oil in there, just a though as you are not supposed to go above the 300cc. thanks,
Well right before we put the primary cover on we primed the tensioner and I pumped both bottom and top pistons until they were tight while keeping the oil well full. Then with the bike on the center stand we poured 300 cc of oil in with the oil level plug out. It just starts to drip out at that point so if you fill till it just starts to run out you have enough oil and it'll be fine.
I don’t know what oil you use but I just switched to Castrol Classic witch is the “same” as the old 20-50 from the 70’s. It has a high level of ZDDP like the old formula, it can not be used with catalytic converters.
Yes, the Castrol Classic 20w-50 is what we're using. The only other oil we use is Mobil 1 V-twin 20w-50 if synthetic oil is wanted. It's an excellent oil but is twice as expensive as the Castrol Classic.
At 58 mins, I see nothing that accords with the Workshop Manual as follows: "Assemble the shims on the crankshaft over the engine sprocket, followed by the spacing collar with the recess outwards Fit the rotor key, the inner end of which passes into the recess in the collar."
Hey just found your videos in looking for MK 3 primary disassembly to start on seal replacements on mine. (owned since new) Found this reassembly but can't find the disassembly video. Got that somewhere? And thanks, this is great stuff!
This bike was all torn apart when we acquired it, and unfortunately we do not have a video of taking the entire primary assembly apart but it would be the exact opposite of this video.
Good one guys! That issue of centering the inner primary around the transmission shaft, does it also apply with the MKII bikes> I know the felt "seal" is able to move on the carrier plate to allow tensioning of the primary chain, but is it also important to try to center the inner case before tightening in three inner primary bolts to crankcase? My MKII case has very little gap to the header pipe near where is connects to the silencer. Was thinking the header might be from a 750 and might be slightly different than my 850 should have. But now I'm thinking maybe its the inner primary alignment that needs a little adjusting?
Well the mk2 and earlier commando's are significantly different in how the primary fits and adjusts. The inner case needs adjusted with shim washers so first you remove all washers from the center through bolt and place a new gasket for the inner chain case install the 3 fixing bolts to proper torque next measure the gap between the center bolt and inner case that dimension is how much all the shim washers must measure (several thousands thicker is fine but not less) also make sure the inner case isn't touching the swing arm as the inner case could be warped from improper shimming in the past. After the washer shims have been determined and placed on the center bolt reassemble the inner chain case at this point there is some up and down movement of the inner case and if you lift up so it's snug and tighten the 3 bolts in that position that will be as high as it can sit. So if someone last assembled your primary it could've been tightened up in the lower relaxed position causing the situation you are describing. I hope this all makes sense to you.
Our manual clearly says "All models without electric starter 7 fl oz (200 cc) Electric start model only 10.5 fl oz (300cc) I don't know what manual you have but ours covers 67 and on
Can you make this video watchable on other servers? Id like to place a link to it over on Access Norton forum but it says owner has disabled viewing directly on other platforms. Thx.
