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E: Engine Balance factor


BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Hello Eddy, Is there an easy way to work out the Balance Factor, I have read the Higgins bit and checked a few Web sites, But I am lost on the Maths side of it.
I want to do a Comet soon. Cheers Bill.
Dear Bill,
I don't think you can go far wrong if you read what Phil Irving wrote about engine balance.
In Motorcycle Engineering, Chapter 16, he got quite technical writing about balance. He says that the balance factor on the post-war Comet was 66%.
I suggest that for what you want, his explanation of how to balance in Tuning for Speed is much simpler to follow. In my 3rd edition copy, Truing and Balancing Flywheels is chapter 7. He explains what to do in 4 pages. In those pages, he gives some simple maths to work out the balance factor for the weights you find. If you don't have a copy of his Tuning for Speed I can probably sort out some simple writing to explain the process.
You will need some scales to weigh your piston and the small end. (He explains how to do this.)
If maths is an absolute no-no for you then I, or someone else could work out the balance factor for you if you supply the numbers for the weights.
If your new computer has Microsoft Excel I can send you a very simple spreadsheet where you just have to type in your weights and the spreadsheet does the maths to calculate the balance factor. ( I appreciate that you are not actually a computer buff so this might not be a good option for you.)
 
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Jez Nemeth

Well Known and Active Website User
VOC Member
Removed download link...just didn't feel right in the end...
 
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bmetcalf

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VOC Member
I remember PEI being unhappy that Clymer had pirated the book with no royalties paid. Wonder what he would think of it being scanned and posted?
 

Jez Nemeth

Well Known and Active Website User
VOC Member
You're right -been thinking about that all evening -best remove. Enthusiasm of finding a PDF of it on the web overtook reason there...
 
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TouringComet

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VOC Member
VOC Forum Administrator
Back in the ‘80s when Phil Irving was in LA, a new-ish section member offered up his Clymer print of one of his books, for a signature. Phil was gracious, but definitely let him know how he felt.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Bill,I like those headlamp brackets,I had an identical set on my Rapide when I bought it in 1970.They must have been a fashion trend that didn't catch on!
Can't think why not Garth, There is no way I would have those rubbish bits of small tube on any of my bikes.
Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Back in the ‘80s when Phil Irving was in LA, a new-ish section member offered up his Clymer print of one of his books, for a signature. Phil was gracious, but definitely let him know how he felt.
Yes he didn't hold anything back, I came up behind him once, When he was looking at my Special,
He was telling his friends, There was no way us blokes who did Mod's, Would ever improve on what he did !.
Cheers Bill.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Must have been a weird feeling Bill, slightly honored and insulted at the same time! Funny.

Did buy an old copy of 'Tuning for speed' -didn't realise he'd been out of the royalties though, quite a sad story as reward for the effort and innovation it contains, really spot on stuff -inside of my crankcases gleam like a polished mirror, and it makes sense...all those little things mount up.
 
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Bill Thomas

Well Known and Active Website User
VOC Member
Next is your Flywheels ?, George Brown had mine Polished !, Top Man, He told me not to touch the wheels with bare hands, The sweat would turn them to Rust !, It was the best Crank I had ever had done.
Good Luck with yours, Bill.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Steve at Conways balanced and polished them, can't take credit for that.

Can take credit for handling them with greasy mitts though!
Wd 40 all over them so should stave off print rust hopefully.
-drove up to Kent rather than having 'em posted, for fear of knocking them before being installed.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Yes I feel the same about postage, But Alpha's did send us a checked over set of wheels, For a project we were doing, Not ours.
I now see I should have got Conways to build me a 560 cc Crank, The money I have spent and the time lost,
Huge mistake, I may now do it as a 500. Cheers Bill.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
What would be the difference in the crank if upping the CC, or opening the head Bill? Flywheels off a twin fit on a comet crank -is that a done thing?
 

Bill Thomas

Well Known and Active Website User
VOC Member
Not sure what you mean Jez, Comet wheels are same thickness with a big hole the other end of the bigend hole, Twin wheels have a big bit milled away near the bigend.
I have been told someone fitted Twin wheels to a Comet, But I think it would have Shook !!.
I am about to weld a bit of the bigend hole and bore it a 1/4" nearer the edge of the wheels, To change the stroke from 90 mm to 102mm ish ?, I keep thinking of nicking another mm or so !!.
But I think it will be a disaster, I work + or - an inch !.
Just bought a spinning centre for my lathe, And am sure it don't run true, So what chance of trueing up my wheels !, I have a set of V blocks, So could use them.
Don't want to go bigger piston, It would mess up the C/cases for anybody, After I have gone, + the cost and
I don't like squish and T/P parts.
We will see, Can you P.M. me the price of your Conways Crank, I could maybe pop it in later ??, First thing is to get it on the road, If I can get a number plate for it from Simon.
Cheers Bill.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
I see. Balancing tables, all makes sense now -and got how you're approaching achieving the longer stroke - I'll find the ticket and pm over the details Bill
 

Bill Thomas

Well Known and Active Website User
VOC Member
Thanks Jez, Forgot to say , I have a conrod from USA, Made 1/4" shorter than standard, So don't have to pack out the barrel and use longer pushrods, From the outside , It will look Standard. Cheers Bill.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Had wondered about connecting rod length -found ticket, but its for bearings and balance + 20% dreaded. Be less I'm sure depending what you're bringing to the party - pm now
 

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