lorenzo

Daveys - The roler bearing you have has axial location in one direction ( a shoulder on the inner race) - have I got that right ? Why not heat the inner race and fit that to the crank (shoulder to the wheel), heat the crankcase and fit the outer race ("open" side to crank). Inner and outer parts of the bearing are then located independently and you can simply slide the bearing parts together when you assemble crankcase halves. This of course ignores manufacturer's markings........( and I don't know which way they face on SKF bearing, anyway)....... having NJ series bearing also sets up requirement for the crankshaft width between bearing seats to be controlled to avoid negative axial clearance. Or maybe I'm completely off beam here.........

Model 158 original frame colour was silver.

Front wheel has had a steel/cast iron? (ferrous, anyway..) liner inserted. This is the usual means of salvaging hubs which have suffered deterioration of the chrome plating. Hard chrome originally applied direct to alloy casting. If your chrome is as intact as it looks, keep it unti it fails. Rear spokes stainless butted, or steel galvanised ?

Ian - I'm guessing here......... Front spoke part no. 86.004-003-5 appears to be one of three different spokes - with a conical hub on a Mk. V Pursang. Model 49 with parallel hub - all 36 spokes are identical.

Gentlemen, thanks very much for your response - I'm almost overwhelmed. How did we ever manage, "pre-internet" ? Vintagenut : no tabs on the air filter, and no sign they were ever there. Same thing with my mod. 92 (also '73). gooey : Alloy tank unit.........do you have a pic. ? feetupfun : Thanks again for your detailed shots - exactly what I was looking for (and was unable to find elsewhere). So it seems that the tabs were to support the front of the seat section of the fibreglass tank unit, and assuming the original "long" seat is used, support at the rear is provided by the seat resting on the frame loop ? Perhaps someone can confirm........... Additionally, could they be to maintain a clear "breathing" space above the filter intake ? This leads me to ask if anyone knows what type of seat was fitted to the UK bikes with Homerlite alloy tank unit.......my bike has a short trials type seat which may not be original, and anyway doesn't extend rearwards as far as the frame loop, meaning any weight placed on the rear of the seat would provoke bending/cracking of the alloy, assuming the tabs were still in place.

Prior to rebuilding this long-term (dismantled) project, I've begun dragging out and examining parts, with a view to doing a trial assembly before parting with serious money on chrome plating, powder coating, etc. Starting with the frame, I found two sawn/ground off welds on the seat rails either side of the air filter (arrowed in pic.) :- Anyone out there know what was there originally ? Brackets/ lugs/ a bridge across the filter ? ....and do I need to replace it ? Outer edges of the air filter body appear to stand slightly proud of the frame rails, and there are marks on the underside of the seat part of the tank/seat unit. Bike is a UK supplied and registered example from new (Aug. '73) and came to me with Homerlite fuel tank, which I assume is original -(this would have replaced the usual fibreglass item fitted for other markets, I believe). I know these are notorious for splitting the welds between tank and seat panel; I'd like to get the fit right. Ideas ?

Ian T, Hydramatic - Re the rear wheel spokes, the originals were (single) butted stainless steel , M4 X 3.5mm and used on models 27, 49, 80, 85, 91 & 92:- (from the top) r.h. inner/ outer - 18 off length 189/195mm ? ) l.h. inner - 9 off " 165/167mm ? ) depending on which parts book you are looking at l.h. outer - 9 off " 162/165mm ? ) The stumbling block for obtaining replacements is that l.h. outer - I couldn't get any for years until I found a seller in the US with NOS. (I don't think spoke suppliers are very keen on replicating the double bend in stainless, a pretty unforgiving material). The double bend is to allow sufficient offset of the rim/tyre to clear the chain line and chainguard. Ultimately, these are the first spokes to suffer damage, or breakage if the chain derails............... The alternative would be a set in single gauge galvanised, similar (but not identical, unfortunately) to Pursang fitting. Let us know how you fare.

Ian - Re removing steering head lower inner race : these can be VERY tight on the stem (unnecessarily so, in my opinion) but if your lower yoke is like the one on my M85, Bultaco very thoughtfully provided two holes for this very purpose :- I use a Hilti nail - hard as hell and at 3.85mm. dia. exactly the right size - the more affluent/better equipped would use a parallel punch. Unfortunately, you may find that once you've removed the race from its lower position you have an equal struggle getting it off past the upper race position.... If your yoke doesn't have drillings, it's probably down to grinding away and splitting the race with a chisel.

Ian - As you have already found, cylinder head nuts and carb. fixing are 8MB = m8 x 1.00, although the other end of the relevant studs are 8MA = m8 x 1.25 where they thread into the crankcase and carb. stub, respectively. (Also applies to the two cylinder head studs in the barrel) 6MA = m6 x 1.00 pitch Re the tap in the frame top tube : how does the oil/liquid get in there ?. The mind boggles.......... The frame-mounted tank is a chain oiler :- (extract from 1973 SM catalogue) Later Sherpa models incorporated a chain oiler in the swing-arm tube, from the factory.. Hope this helps.

To separate and then remove the two primary side bearings I suggest a tool similar to this :- https://www.machinemart.co.uk/p/cht226-bearing-separator/

Hi, fxst - How many plates in your clutch - plain and lined ? Are they like these :-

The problem is that a part of the outer bushing is not acting as a bushing........The effective length is shortened, just where it's most needed. It's a M85 that I'm hoping to complete first. - this should have the 15mm. bushes. (and I haven't been able to obtain replacements, either). Needle roller bearings replaced p.b. bushes on models 124/125 onward. Presumably to correct the rapid wear rate of bushes......... and the mainshaft nose in that case is yet another different diameter to the 14/15mm ones it replaces.

One for the cognoscenti, maybe........ Does anyone have any thoughts/experience regarding improving the longevity/durability of sleeve gear bronze bushes ? This applies to models 27/49 and 80 with 14mm. mainshaft nose (bushes #111.047) and later models 91/92 with 15mm. shaft (bushes #48.11-047). I've dismantled a number of engines each of which shows wear to these bushes, characterised by a step in the outer bush bore, where it overhangs the end of the mainshaft. I have to wonder if there is a particular reason for the bushes to be fitted flush to the outer end of the sleeve gear, or whether it was simply a matter of production expediency.........

You could try asking the seller.......

How does it differ from this one ? ;- https://www.inmotiontrials.com/product/sherpa-158-159-air-box/

Hi, Gas - Your first port-of-call is Dave Renham at Inmotion Trials. who should be able to date the machine from engine/frame numbers. If it's '79 (and a 5-speed) it's unlikely to be a 199B (6-speed) - these didn't appear until 1981. HTH

Bill - Frame #80***** points to a Sherpa T 250. Engine #125***** should also be Sherpa T, but 325 ("350") and approx. 3 years newer. Standard ? Well, it didn't leave the factory like this.......... Shouldn't affect the usabilty of the bike however, and as b40rt stated, probably won't bother DVLA.

Mikey - I was about to explain that the brake light and rear light bulbs seem to be sharing a common earth/ground connection...........now we know why ! I'm happy you have it sorted and glad to be of help. That's a nice looking bike, by the way. I'm presently trying to sort my own Mod. 85 (also a '74), and if it turns out half as well as yours I'd be quite satisfied. Happy trail riding, Lorenzo

Mikey - The "correct" wiring diagram I referred to was the one posted by rcgods. The schematic I posted was merely to show how the brake light works - one switch/two switch, the principle's the same. .The earth/"ground" side of the igntion coil (the green wire from the magneto) must go through the brake switch (brake off/not applied) or through the bulb and resistor (brake on), thence to earth. You appear to have bypassed this requirement by earthing the green wire at the terminal block - Brn. wire to "frame grd"., meaning the switch circuit is not working. Try removing the brown wire............ Lorenzo.

Mikey - The wiring diagram is correct for a standard mod. 85 with direct (AC) lighting. I have an original owners handbook; this uses the same diagram exactly. Your bike appears to have an original-style rear lamp; what bulbs are you using ?

Mikey - This topic cropped up a few days ago - Thumbs up! 's topic Oct. 25 - he posted a schematic/scan from Clymer manual explaining how the stop lamp works : Remember, the stop lamp is fed via the earth/"ground" side of the LT igntion coil in the magneto (the green wire). You will see that the stop lamp switch needs to have normally-closed contacts, i.e. contact is made when the rear brake is NOT applied. Is this the way your new switch operates ? I'm unclear about the fine detail of the rear lamp itself, as it was missing from my own Model 85, but the separate bulbs originally specified were a festoon type 6v. 4.5W for the rear lamp and a 12v. 18W bayonet type for the stop lamp......... Hope this helps..

Hi, Thumbs Up - I have no direct experience of model 138 and am making a few assumptions here,,,,,,my own Alpina is an earlier model. Looks to me like an OE switch, though. If it's direct (AC) lighting - no battery and no rectification - it should be wired similar to this :- Hope this helps.

Hi , Thumbs Up - If your Alpina is wired as per original direct lighting , the stop lamp circuit is via the "earth/ground " side of the ignition feed coil in the magneto. Quote from an earlier posting on the subject:- . The switch is of an unusal design and exact replacments can not be found. The original switch is held in a normaly closed condition by a tag on the brake pedal and switches to normaly open when the pedal is depressed. Ignore the previous response - you do have the correct switch.

Mag. outer cover cannot loosen the flywheel nut - the cover is marked as a result of the nut having loosened when the key sheared. (Crank rotation suggests that the nut would actually be tightened, not loosened). The reason the key sheared is the the poor condition of the shaft taper - it's this and its fit within the flywheel boss that determines the security of the flywheel - the key is there in the main to locate the flywheel/points cam in the correct place. You need to address the issue of the damaged taper(s).

It needs a k/start return spring https://www.inmotiontrials.com/product/bultaco-kick-start-spring