1975 Mk 3 Help...

Looking at a Mk3 to buy- what numbers need to match? This bike has a frame tag number that matcheds the number stamped on the case, but the number on the cylinder bakker (lower front) is different. Is that an issue?
Also, I currently own an Atlas but have never owned a Commando. What should I be looking out for?
Any help appreciated...

Frame tag, case stamping and gearbox (stamped along top mounting area).

The number on the cylinder is more than likely a casting number. Is it stamped or casted in?

Hey LAB, did I get this one right?

pvisseriii said:

Frame tag, case stamping and gearbox (stamped along top mounting area).

The number on the cylinder is more than likely a casting number. Is it stamped or casted in?

Hey LAB, did I get this one right?

Click to expand...

Yes, the 6 digit frame plate, crankcase and gearbox numbers should all match, although the number stamped directly onto the frame headstock next to the certification plate may be different.

wjrich said:

the number on the cylinder bakker (lower front) is different.

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I don't know what is meant by: "cylinder bakker (lower front)" as the barrel casting number is usually at the rear.

wjrich said:

Looking at a Mk3 to buy- what numbers need to match? This bike has a frame tag number that matcheds the number stamped on the case, but the number on the cylinder bakker (lower front) is different. Is that an issue?
Also, I currently own an Atlas but have never owned a Commando. What should I be looking out for?
Any help appreciated...

Click to expand...

Sorry- should have said cylinder "barrel". The number is cast on, and is 063850. I'm going to guess at the obvious here in that the "850" is for 850 ccs, but don't know what the other numbers would indicate.

wjrich said:

wjrich said:

Looking at a Mk3 to buy- what numbers need to match? This bike has a frame tag number that matcheds the number stamped on the case, but the number on the cylinder bakker (lower front) is different. Is that an issue?
Also, I currently own an Atlas but have never owned a Commando. What should I be looking out for?
Any help appreciated...

Click to expand...

Sorry- should have said cylinder "barrel". The number is cast on, and is 063850. I'm going to guess at the obvious here in that the "850" is for 850 ccs, but don't know what the other numbers would indicate.

Click to expand...

063850 is the usual 850 barrel casting number (note that it is not the actual barrel part number). The fact that it is 063"850" is nothing more than a coincidence-apparently.

Thanks- Ill want to make sure the tag, tranny and engine case numbers match, and won't worry about the fram neck stamped number or the barrel casting number.

Any other unique things I should be looking for on the Commando?

wjrich said:

Thanks- Ill want to make sure the tag, tranny and engine case numbers match, and won't worry about the fram neck stamped number or the barrel casting number.

Any other unique things I should be looking for on the Commando?

Click to expand...

Posting a pic will tell us most things we need to know.

Many '75 e-start bikes had issues with the starter engagement hardware - specifically, the sprague clutch.

(mine has had no such issues, but several others have)

wjrich said:

Thanks- Ill want to make sure the tag, tranny and engine case numbers match, and won't worry about the fram neck stamped number or the barrel casting number.

Click to expand...

Having matching numbers is perhaps regarded as less important so some buyers as long as the bike is in good running order (and the numbers match the documentation).

wjrich said:

Any other unique things I should be looking for on the Commando?

Click to expand...

Is it a runner, hopefully well maintained and upgraded by it's present owner-or has it just been dragged out of a shed/barn?

I expect you already know how to check the usual things like brakes, suspension, steering, and knocks, rattles, smoke from the engine etc.

Things you may be unfamiliar with are Isolastics (expect them to be shot if it's been unused for many years)

Does the electric starter motor work? Are the parts all there? If you want a working electric starter then it can prove expensive to replace the parts if they have been thrown away.

Is the (L/H) gearshift action sloppy? The cross shaft components are usually worn, however the fix is not too expensive.

Well, I went and purchased the bike this Saturday. Overall decent condition- does have some issues that will need to be addressed. End goal is to get it as close to originnal as possible- adding back correct rear tire, correct handlebars, etc. Bike was allegedly a "runner" with an upgarded Boyer ignition, sleeved front master cylinder. Starts second kick, and runs relatively strong- it was about 25 degrees F when picked it up, so my test ride didn't go too far. Motor feels strong, although there's a hint of white smoke from both pipes (could be the cold weather?). She has a bit of an erratic idle and stalled a couple of times as i would idle at a stop light. I'm guessing the carbs will require a good cleaning/rebuild.
Trans shifted well; only complaint is that you can't get neutral while the engine is running- can get neutral easily once motor is turned off. Any ideas on that one?
I did use the electric start a couple of times, and it does draw down on the battery. It did work, though.
Paint is new, and chrome on the fenders seems to be in great shape.
Seat is not hinged, must be off an earlier Commando; no passenger grab rail.
Has K&N filters instead of stock airbox, and has a sidestand but no centerstand.
Slight rust visible in the steel tank.
She's a bit dirty as I just trailered her through a couple os snow storms
It's about 25 degrees F in my garage, so it's going to be a little while before I can continue the story...
Here's the 1st pick (my Atlas is in the background)

wjrich said:

Well, I went and purchased the bike this Saturday. Overall decent condition- does have some issues that will need to be addressed. End goal is to get it as close to originnal as possible- adding back correct rear tire, correct handlebars, etc. Bike was allegedly a "runner" with an upgarded Boyer ignition, sleeved front master cylinder. Starts second kick, and runs relatively strong- it was about 25 degrees F when picked it up, so my test ride didn't go too far. Motor feels strong, although there's a hint of white smoke from both pipes (could be the cold weather?). She has a bit of an erratic idle and stalled a couple of times as i would idle at a stop light. I'm guessing the carbs will require a good cleaning/rebuild.
Trans shifted well; only complaint is that you can't get neutral while the engine is running- can get neutral easily once motor is turned off. Any ideas on that one?

Click to expand...

Might just be the thick gearbox oil dragging considering how f'n cold it is. :mrgreen: Maybe wait until it warms up to an acceptable temperature and see how it does. If that doesn't work clean the clutch plates. If that doesn't work then adjust the clutch.

wjrich said:

I did use the electric start a couple of times, and it does draw down on the battery. It did work, though.
Paint is new, and chrome on the fenders seems to be in great shape.
Seat is not hinged, must be off an earlier Commando; no passenger grab rail.
Has K&N filters instead of stock airbox, and has a sidestand but no centerstand.
Slight rust visible in the steel tank.
She's a bit dirty as I just trailered her through a couple os snow storms
It's about 25 degrees F in my garage, so it's going to be a little while before I can continue the story...
Here's the 1st pick (my Atlas is in the background)

Click to expand...

I would think they first pick would be the snowblower. :mrgreen:

Watch out for the layshaft bearing in the trans. If it has not been upgraded then it needs to be changed.

Yes ,change out that bearing. Also some MK 111's had soft camshaft lobes so if the barrels ever are off take a critical look at them. Looks like the P.O. went for a smaller dia. rear rim with fatter more modern rubber.

Unless youre over six foot , Id leave the bars for a while .
Ditto the fitted air cleaners are probly a improvement .
At least for improved acces ( & weight reduction ) .

Blanket Iso's shimmed at 2 1/2 to 4 1/2 thou (adjusted)
Tecnically the min. clearance giveing NO binding / Vibe transferance . for optimum steering .

Might pay to add some ' top end lube ' to promote ring seating , if its not covered 2.000 miles since build .

Redex or STP or better . Wouldnt harm anyway .

Stalling ? :shock: They ALL Do That . with stock Ign. Carbs . If youre a points perfectionist , the BSA A65
advance unit give better idle / low speed range . If you set them up meticulously . If you ' havnt got the time ',
Elec. Ign. is mandatory . As a Mag. wont fit . :lol:

Some swing arm spindles are a light hand press fit . Well worthwhile fitting clamps over the houseing to secure.

If its a 18 in. rear . Id LEAVE IT . Light mods / updates improve the utilability of the device .

Matt Spencer said:

Blanket Iso's shimmed at 2 1/2 to 4 1/2 thou (adjusted)
Tecnically the min. clearance giveing NO binding / Vibe transferance . for optimum steering .

Click to expand...

850 Mk.3 has vernier Iso. adjustment, no "shimming" required.

Matt Spencer said:

Some swing arm spindles are a light hand press fit . Well worthwhile fitting clamps over the houseing to secure.

Click to expand...

Again, as it is a Mk.3 it already has the double cotter located spindle so there's no need for "clamps" (no space for them on the Mk.3 cradle tube).

Torontonian said:

Yes ,change out that bearing. Also some MK 111's had soft camshaft lobes so if the barrels ever are off take a critical look at them. Looks like the P.O. went for a smaller dia. rear rim with fatter more modern rubber.

Click to expand...

Any idea what engine numbers might have had the soft lobes?
The po did go with smaller fatter rear tire. Part of me wants to return to original spec, part wants to leave the fatty in place.

When Noah built the Arc , a 3.50 19 & a 4.00 18 were both 26 inches tall , so both had the same rolling radius .

Was usual for American triumphs ( .40 inches ) to run 4.00 18 rear .

Two up with a bit of baggage , cranked over at a fair crack of the whip , most would appreciate the added adhesion .

Looks pretty darn good in the pic.
The mudguards are stainless, won't rust as chromed steel would.
Missing the RH stantion gaiter in the pic.
The clutch likely just needs cleaned if N is hard to achieve while the engine is running.
Switch gear colors are really too bright to be OE.
How about some more pics?
All the best.

That's the limit of my leads on the soft lobes as I recall 2 other owners telling me there was a bad batch/run on the 75's as per the hardening process to the lobes. When I opened up my motor all 4 lobes were rough at the tips. Perhaps other forum-folk know more on this to warn owners in a certain numbers slot ?