adjustable Norton balance factor

Anyone have details about this crank machining to allow changing the balance factor in the field?
Crank: Crank is a Steve Maney lightweight crank with standard 89mm stroke and a balance factor of 72% WET, balanced at Lindskog Balancing in Massachusetts. Kenny has tried balance factors from 84% down to 60%, and settled on a low to mid 70s range for a Seeley MK2 application. According to Kenny, the bike feels better than any rigid mounted Seeley that he has ridden yet. Crank has a 3/4″ threaded hole at exactly BDC allowing a mallory slug to be threaded in through the sump plug, thus being able to change the balance factor while testing without having to tear down, or even remove the motor.

Here is the Seeley website
http://seeleynorton.com/technical/motor-and-transmission

I would like to see some photos of machined holes in crank and weights to suit, if possible.
Thanks

Here is a picture of left half crank case.

"

p400, the crankcase picture you posted is from a MK3 crankcase I use in a short stroke 750 race engine. I'm not sure how it relates to the removable crankshaft plugs. I did a crankshaft mod for hobot that includes removable plugs, and posted pictures here, but didn't have anything to do with that crankcase. I'll see if I can find the links and post them. As I recall, you can't change the plugs through the crankcase oil screen plug hole, but have to pull the top end to do it through the crankcase mouth.

Ken

This is a link to the thread with the crankcase picture.

short-stroke-750-build-t5490.html

Haven't found the one to the crankshaft yet.

Ken

And the removable plugs in hobot's crankshaft.

peel-boring-tough-crank-crying-t8268-45.html?hilit=hobot%20crankshaft

Ken

How do you lock those screw-in plugs there. ?

If they came loose and came out, the word grenade may not even be enough....
There is a good reason most slugs are fitted from the side = they can't just sling out, ever.

P.S. Was looking at a stray dommie engine here, and the big sump screen hole.
You could potentially get a small weight in through there and into the crank, if it was prepared for it.
Or even a few of them.

But you'd have to be able to lock them there. (?).
And they wouldn't quite be on the centreline of the crank, but offset to one side.
Which could be a problem ?

They are held in by the proper torque, just like other threaded fastener, although I also recommend a few dabs of Loctite. Nourish have been making their cranks with radially screwed in balance plugs for decades, with no issues. The heavy metal slugs you are probably referring to as fitted from the side are pressed in, sometimes with a bit of weld, or even a welded cover plate, but all the plugs I've seen that are fitted radially have been threaded.

The offset from the centerline on the sump plug in Commandos is the issue with trying to change plugs through it. If I recall correctly, you can't do that with the plugs in hobot's crankshaft. If we'd used smaller plugs, as you mentioned, it might have been possible, but we needed pretty large diameter plugs to get the range of adjustment that Steve wanted.

Ken

Thanks Ken and Hobot, Great info and great links to threads I needed to review.
Actually this request applies to a ridged Norton engine in a ridged chassis, so I will check dimensions of this earlier (67 750 Norton) crank and cases to see how easily (or close) the dimensions are to centerline.
Did the plugs get machined from Mallory metal?
Or inserts (in the plug) of Mallory metal?
Or plugs of steel?

Mallory metal list for reference -

Here is a list of Mallory inserts and weights for reference -

p400 said:

Thanks Ken and Hobot, Great info and great links to threads I needed to review.
Actually this request applies to a ridged Norton engine in a ridged chassis, so I will check dimensions of this earlier (67 750 Norton) crank and cases to see how easily (or close) the dimensions are to centerline.
Did the plugs get machined from Mallory metal?
Or inserts (in the plug) of Mallory metal?
Or plugs of steel?

Click to expand...

The plugs for hobots crankshaft are high strength steel. I have in the past used Mallory metal plugs in the crankshaft cheeks, as well as in steel flywheels, and have also added Mallory metal slugs to the threaded plugs in Nourish crankshafts (like the one in the picture you attached). But with the two different lengths of steel plugs I gave to Steve, he can try balance factors of 62% with no plugs, 74% with 7/8" plugs, and 80% with 1" plugs. If he needs a higher balance factor (really unlikely) I could drill the 1" plugs and fill with Mallory metal. If he needs something in between, he can drill out, or shorten the plugs he has. Plenty of room to experiment, which is what Steve wanted.

For my own use, I have always balanced my own Commando engines at 62%, because experience tells me that works really well with isolastics. In my wideline featherbed race bike, with the engine tilted forward as in a Commando, 62% also works quite well. For anything else, like your rigid mount '67, I don't have enough experience to have a good recommendation. The recommendations I've seen for 750 engines in solid mount frames run from 62% to 85%. It also depends on what rpm range you spend most of your time in. All my experience with balance factors in solid mount frames is with race bikes, and you might want a different BF for a street bike. If it would be of any use to you, pm me with your email, and I'll send you a spreadsheet I've built up over the years with balancing information and recommendations for Nortons from a variety of experts.

Ken

The ugly crank plug photo's are not hobot's nor Ken's work just example i found as couldn't find Ken's shots of it yet after 'puter crash burn. Ken had to use masonry carbide bits to break through Peel's silver-grey nitride layer. Isolastics can isolate a range of BF and Seeley's are not Commandos so vibes isolastion is not my reason for experimentation. Highest BF I came across in world wide survey was 94% racer.

hobot said:

The ugly crank plug photo's are not hobot's nor Ken's work just example i found as couldn't find Ken's shots of it yet after 'puter crash burn. Ken had to use masonry carbide bits to break through Peel's silver-grey nitride layer. Isolastics can isolate a range of BF and Seeley's are not Commandos so vibes isolastion is not my reason for experimentation. Highest BF I came across in world wide survey was 94% racer.

Click to expand...

Sorry to contradict you, Steve, but those pictures are your crankshaft. You can find them in this thread:

peel-boring-tough-crank-crying-t8268-45.html?hilit=hobot%20crankshaft

Ken

OHHhh what a shock its so scared up ugly! Prior views are much brighter. I am still totally flabbergasted by the level of past Peel's isolastion and can only be better with oil mass in frame, beefier engine with JMS kit and beveled cushions, links + air chin lifter so its the loose hill climb out of Kings river valley on off sloped banked Gravel sweeper I'm so curious about. There are four inherent suspension systems in isolastic Commando to harmonize if they can be spearated out-felt to reveal their magic. Fifth is exterior so unrelated to BF. For my sense of awe an old movie tilte Run Silent Run Deep flashes in my screen as only bubbles and sonar pings off railing sensed with interuptions of whale call tire chrips. Here's just mid range 4000 rpm tone.
https://www.youtube.com/watch?v=oj7_9Fkkp7g

When I balanced my 850 crank, I threaded the hole, screwed the plug in by holding the extension, and glued it with loctiite. I then trimmed and ground the excess off flush with the counter weight surface. With only two small 6mm holes on the top side of the flywheel, I achieved 72 % balance factor with the standard rods and pistons. I punched the end of the thread of the plug and stopped right there. I'm still paranoid about that plug coming out or the flywheel fracturing where I have drilled it. With the 850 engine, rigidly mounted in the Mk3 Seeley frame, the bike rocks to and fro when idling, however at 7,000 RPM it is extremely smooth

hobot said:

OHHhh what a shock its so scared up ugly! Prior views are much brighter.

Click to expand...

Like this? This is the crankshaft, as welded by Geoff Collins, before I added the balance plugs. It isn't really that much different in "brightness." That's mostly the difference in lighting while photographing.





Ken