850 Transmission failure

Hi guys - hope all is well. Here is my question. The trans on my 74 850 has a problem ( had to tow it). If you rotate the rear wheel on the center stand and work the kick-start lever, it gets tight for part of the rotation and then loose. I'm thinking maybe layshaft problem, but I have not had the time to remove the trans yet. I know it needs a re-build at this point, which I will do once I remove it. Question is, the parts are not cheap, and this is the matching number unit for the bike. I am considering buying a complete used trans on Ebay or elsewhere to use for parts. Is the trans the same for 750 and 850 cycles or are there thing I should look for? Don't want to purchase somthing I can't use. I owned an 850 back when I had brown hair and I had a similar problem, the layshaft had broken in half - but it got me home! Any info would be great. Also, what special tools ( I have Whitworth sockets, wrenches ect) besides the clutch tool might I need. Thanks in advance for your input.

Oakland850 said:

If you rotate the rear wheel on the center stand and work the kick-start lever, it gets tight for part of the rotation and then loose. I'm thinking maybe layshaft problem, but I have not had the time to remove the trans yet.

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Has the box been out before ?. If not sounds like a layshaft / bearing issue. Pull the box apart before you consider buying a gearbox off Ebay which is probably junk.

It may be as simple as a shot bearing. 850 gears are different to 750.

Good Luck

Thanks for the info - I will wait until I determine the damage before I buy some POS on Ebay. I guess better to buy whatever new parts I need. thanks again! have a great holiday!

you are correct in NOT trying to buy a used box on E Bay as you are dealing with a 40 year box of parts. the gears are the well known to have issues so unless yours is totally scrap it more than likely will be money ahead to fix yours

Oakland850 said:

Thanks for the info - I will wait until I determine the damage before I buy some POS on Ebay. I guess better to buy whatever new parts I need. thanks again! have a great holiday!

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The only gears that are different in the later 850's is the second gear pair.

Nortiboy said:

It may be as simple as a shot bearing. 850 gears are different to 750.

Good Luck

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+1, skip the used box of questionable condition, (it could be 500 miles behind where yours is now), fix yours and carry on.

You can play with the ratios / No of teeth / gear , if replaceing , worth a thought .

Shell bores wallow out, bearings break, bushes get dissolved and springs unsprung but those are all replacement wear parts so unless bent shafts or cog teeth missing its just a tedium servicing job w/o major new parts. 750 2nd gear is too low so tends to chrip rear with engine drag snicking it from 3rd and runs out of rev's before its pull get ya to decent speed. 850 taller 2nd is a delightful upgrade for traffic merging to dicing it in up canyons. Many the bushes need reaming to fit right though. Then there's the ways to seal the kicker shaft ... Btw a break in oil change after a rebuild ain't bad practice for the long run.

if no one posted it already the old britts techical articles are easy to follow and will help you immensely - the norton gearbox is pretty easy to repair - if you never done one it seems like a bit of a puzzle box but after following the old britts articles etc etc you tell yourself how simply they are when you have it back together again - i'd make sure is the bearings fit tight into the housing as many boxes now have the inference fit worn away and the bearing spins in them - if so you need a new housing or machining them .

http://www.oldbritts.com/gearbox_d.html ... 296549dc24

Oakland850 said:

Hi guys - hope all is well. Here is my question. The trans on my 74 850 has a problem ( had to tow it). If you rotate the rear wheel on the center stand and work the kick-start lever, it gets tight for part of the rotation and then loose. I'm thinking maybe layshaft problem, but I have not had the time to remove the trans yet. I know it needs a re-build at this point, which I will do once I remove it. Question is, the parts are not cheap, and this is the matching number unit for the bike. I am considering buying a complete used trans on Ebay or elsewhere to use for parts. Is the trans the same for 750 and 850 cycles or are there thing I should look for? Don't want to purchase somthing I can't use. I owned an 850 back when I had brown hair and I had a similar problem, the layshaft had broken in half - but it got me home! Any info would be great. Also, what special tools ( I have Whitworth sockets, wrenches ect) besides the clutch tool might I need. Thanks in advance for your input.

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Just keep the smaller cogs straight as to which way they go in and where they came from as I found it possible to mis-assemble about perfectly but not function. End bush of lay shaft is like that can go one either way but only one way works out. Cam plate cog and knuckle re-fit can be a bugger as must land just short of preventing cover to clear. Pawl spring arms need to be parallel to the pawl but clearance space is not hardly an issue to fuss over thankgoodness. Getting the clutch cable mechanism nipped up in right alignment is a bit trail error ttill it seats good in right position tight enough to stay put. Kicker factory oil seal groove is a bit over size in depth for factory size oil ring so can back up grove with layer of foil or get a fatter oil ring, in lieu of machining for proper oil seal. File out the kicker clamp grove and remove 3 splines on either side and run grade 8 through bolt with back up nut or expect future loose lever with skewed splines that trap it on. Add extra worn 3rd sleeve bush if the short kind to space the 2 new ones where they belong. Not bad id to oil grove spiral them and they sit above oil level and sling oil out when running so can only refill effectively when in 4th with oil sling drool back. Shell heating can take over 250'F to bump out races and not bad idea to heat nearly 400' F so new ones drop right in w/o tipped in bore hang up that froze race suddenly cools the Al to trap it tight til re-heated over 400' F. ugh. The hard ware in pawl mechanism area sits above oil level and nil oil mist reaches it so they rust up and can eventually dissolve steel stud threads so I've taken to clear or color coat paint or heavy grease smear so next time its much nicer to deal with. Always a next time if being ridden as factory intended.

Tight and then loose? How are you rotating this? Is the clutch engaged? Is it in neutral or in gear? I wholly second, or third (maybe fourth) the idea of not buying another one until you determine your problem.

Russ

Russ ( and everone else) - thanks for the response - and yes in neutral - and when I pull the clutch in ( releasing it from the primary to engine) - same problem. I guess I will know whien I pull the trans what is up.