Norton 850 motor.

When I built my Seeley 850, I never believed in the Commando motor. However it is the best motorcycle I have ever ridden. I only built it because it remotely resembles a Gus Kuhn Commando, which has a place in history. But that 850 motor is excellent. It just took some tine to find out how to use it. With the heavy crank, if you lose revs, it takes ages to get them back because you rely on throttle response. But with close ratio gears you do not lose enough revs on up-changes for that to be a problem. The heavy crank becomes an advantage. You cannot expect to win a drag race down a long straight, so your frame and machine weight and power characteristic need to be suitable for faster cornering.
You figure it out. Most race circuits are about 40 % corners. If you are 5 % slower down the straights and 10 % faster in the corners - who wins ?
There is a general rule - 'the system runs on bullshit, and if you have a victim's mindset you will be a victim'. When you watch MotoGP, on fast bends most bikes follow each other at full lean on the limit of tyre adhesion. When they pass, they usually slip under each other in corners.

74ok said:

vets have been about here prob 20-30 yrs+ lots more, often ends up with a rep & stuff unknown to noobs

tonnnnnnnnnnnnnnnnnn of history here tho & know what u mean by fascinating, but often same ol sh.. for vets/geezers lol

the utube channel is prob news to most

Click to expand...

I've only been here a year and that is definitely long enough to identify posters that I won't read. There is one that has three points to make, whatever the question, we get one, two or sometimes all three of those points. I'm sure if you asked how to spell repetitive you'd get an answer about heavy crankshafts

maan ..the crank stuff here ..mind blowing ..best ones of course are oil lol




best stuff is new guy shows up & asks what oil should i use lmao

worntorn said:

I wouldnt build that type of engine for racing as it becomes a time bomb for that application.
I recall that Doug McRae's horrific crash was caused by a stock crank letting go in a hotrodded engine that was being raced.

Click to expand...

Markets wax and wane, but through about 10 years within the 14 years I was refurbishing, restoring, overhauling and custom building old bikes, I sold 9 complete Commando engines for $1,000 each (plus shipping), needing overhaul, but nothing destroyed and the major triad components included (power unit, primary drive, and transmission; not always with cradle included). These days they don't sell for that much, although that fact is somewhat puzzling to me.

Anyway, I plan to do a financial analysis of all the Commando engines I've rebuilt over the years (around a dozen) and come up with an average or a range of costs incurred.

Basically (from memory, when the main bits were there and nothing destroyed):
Full gasket set - all three components
Full bearing/bushing set (all 3) including Superblends & approved layshaft bearing every time
Full seal set (all 3)
TYPICALLY new valves and guides (not always, depending on wear status and client budget)
Full head remediation almost always, DEFINITELY valves & seats ground or lapped for best results
Cylinders bored & honed
Pistons replaced 95% of the time, rings replaced 100%
Cam inspected and polished, only replaced with Megacycle at client's direction, only 1 destroyed cam found
Cam followers polished (VERY infrequently required replacements, maybe twice)
Rockers polished
TYPICALLY didn't require new valve springs (maybe 30% of the time)
Head & cylinder decks checked and resurfaced as minimally as required (maybe 10% of the time needing resurface)
Crankcase mating faces & deck checked and resurfaced as required (less than 10%)
New cam & primary chains
New camchain adjuster foot w/ nylon block
Oil pump disassembled, checked and polished or resurfaced (50/50)
Crank disassembled, throughly cleaned including galleries, (all new hardware 50/50)
Crank journals polished, (ground about 20% of the time)
Rods checked, only 1 set needing oversizing out of ALL (hardware replaced 50/50)
Check and resurface clutch plates (replace friction plates about 50/50)
Mainshaft oil seal & lock washer for clutch hub. Clutch bearing replaced 10% of the time
All new tab washers
Primary mainshaft felt seal replaced (bugger) 50/50
Replaced final drive sprocket as required or directed 50/50
RARELY ever needed to replace any gears, shafts or forks
Only replaced ONE crank, and ONE pair of rods due to buggering by others
Replaced 2 sets cylinders due to max limit
Never replaced a crankcase, primary case, or transmission box
Replaced ONE head because cost to replace with a nice e-bay head was cheaper than a total rebuild which was still possible

I'm sure I'm overlooking a few items, but if you go to the Andover site and price out all of the above, you'll get a fair idea as to the cost of an overhaul.

I only ever race on small circuits which do not have very long straights. I have raced at Phillip Island, it is too big for a Commando. With a rebalanced crank, the motor is unlikely to explode, but I never ride faster than the speeds at which I am prepared to crash. And I do not stick my neck out at places where I am facing a wall. Big circuit or small the gearing determines the revs, but a get-off at over 100 MPH is too fast.
If I was still racing and serious about it, I would make a billet crank.
When I first started building the bike, the crank looked horrendous to me, so the bike sat unraced for about 20 years until I retired and had the time to try it. It has copped 7000 RPM reliably at about 5 race meetings with about 5 rides at each.
I suggest racing at Daytona is silly stuff. When Doug MacRae crashed, I don't think he was towards the end of the banking. It looks to me as though the bike was just beginning to get wound-up. When Barry Sheene crashed there, I think he broke both legs. It is not a normal race circuit.
I actually think my Seeley 850 is a joke. It is so bad that it is good. I would never have believed it could do what it does.
I think the rod length to stroke ratio and crank weight in the 850 motor must be technically correct, but it needs the close ratio gear-box behind it. With wide ratios, the crank is subjected to more load. Spinning high with less load is safer.

Unless you need an engine for a specific reason, forget it. Most engine builders will quote a starting price for just rebuild of £3000 plus parts. Not sure what it's like around the globe but with Commando's selling for peanuts in the UK then I don't see the point in new engines. With Matching numbers bikes not even achieving £5K and selling at auction and some unsold at £4200, some will now think that large expenditure on a bike that dropped in value is not worth it.

acotrel said:

I only ever race on small circuits which do not have very long straights. I have raced at Phillip Island, it is too big for a Commando. With a rebalanced crank, the motor is unlikely to explode, but I never ride faster than the speeds at which I am prepared to crash. And I do not stick my neck out at places where I am facing a wall. Big circuit or small the gearing determines the revs, but a get-off at over 100 MPH is too fast.
If I was still racing and serious about it, I would make a billet crank.
When I first started building the bike, the crank looked horrendous to me, so the bike sat unraced for about 20 years until I retired and had the time to try it. It has copped 7000 RPM reliably at about 5 race meetings with about 5 rides at each.
I suggest racing at Daytona is silly stuff. When Doug MacRae crashed, I don't think he was towards the end of the banking. It looks to me as though the bike was just beginning to get wound-up. When Barry Sheene crashed there, I think he broke both legs. It is not a normal race circuit.
I actually think my Seeley 850 is a joke. It is so bad that it is good. I would never have believed it could do what it does.
I think the rod length to stroke ratio and crank weight in the 850 motor must be technically correct, but it needs the close ratio gear-box behind it. With wide ratios, the crank is subjected to more load. Spinning high with less load is safer.

Click to expand...

Please explain how any of that pertains to a newly constructed 850 engine - I don't get it?

robs ss said:

I don't get it?

Click to expand...

You are not alone !!!

robs ss said:

Please explain how any of that pertains to a newly constructed 850 engine - I don't get it?

Click to expand...

I was commenting on the likelihood of an engine spreading itself. It does not happen often, but it can. When you race, you should not stick your neck out too far. I looked at the 850 crank and wass horrified, but it actually seems to work well. Unmodified, the balance factor is not suited to high revs. I have a steel plug filling the hole in mine. If it ever comes out, I would be stuffed. The balance factor is about 72%, and at 7000 RPM, the motor wants to spin faster.

What I am suggesting is - if the 961 barrels and cylinder head become available as spares, or from an Asian supplier, it might be worth modifying early Commando crankcases to accept them - or even casting new crankcases to fit the old Commando frame, and accomodate the newer top end. It all depends on costs and economies of scale. A new Full Auto cylinder head is not cheap and neither are aluminium barrels. The crankshaft will always be a problem, but not insurmountable.

Al, you are rightly saying that your concern is the engine failing under racing conditions due to weak bottom end.

Heres a few obstacles for you to ponder:

I don’t see how grafting on a modern top end helps that?

The 961 top end DOES NOT FIT.

The 961 boys struggle to get parts for their bikes as it is. So I don’t see cheap parts being available any time soon.

In what class would something like this be eligible to race?

Fast strong Norton race engines have been available for a LONG time via Steve Maney, and now by Andy Molnar. The ‘problem’ you’re trying to solving was therefore solved many YEARS ago.

If you want a fast and strong Norton race engine you shudda bought one from Steve Maney, or you can now buy the parts to build one from Andy Molnar. AND this motor will be eligible to race.

Problem solved.

End of.

Move on.