Crank balance

Ian,

Sometime back I looked at putting a Matchless piston in my 19S as well, I recall that the deck height of the matchless piston was a good deal higher than the Norton item and incompatible with the Norton engine, I wound up boring the cylinder 2mm oversize and fitting a 7.3:1 Vincent comet piston, the wrist or gudgeon pin is the same diameter as the Norton item, the deck height of the Vincent piston is lower than the Norton piston and the compression receives a modest increase, the 84mm piston is somewhat lighter as well, I did not experience any undue increase in the shaking department and the sheer grunt power of the model 19 engine was enhanced by the bump to 626cc.

RGM motors do offer a spun cast cylinder liner for the 19S, sadly no pistons or rings, the item appears on page 35

I also made up and fitted a head steady to my 19S, yes, I know that they weren't fitted to begin with, but, that doesn't mean one wasn't necessary, my BSA Gold Star without one really rattled my brain pan, fitting one to my 19S really calmed it down, I'm a believer now. Mine runs from the back of the rocker box on either side of the big upper frame tube back towards the lugs near the fuel tank support lugs, I twisted the stays at a right angle to line them up with the vertically oriented lugs.

Hope this helps,

Albert.

Hello again Ian,

According to the site at www.vintagemotorcyclepistons.co.uk they carry model 19S and 19R pistons, standard bore up to +.060" in 6.4:1 compression, they aren't cheap at 135 GBP and change.

The site claims to be faithful to the old Hepolite piston range, I don't know anything more than that about the company, I suppose someone else can fill you in on any issues with the pistons offered by this firm.

Cheers!

Albert.

Regarding Ian McD's reference to the AJ / Matchless crank balance notes........................

I followed this method and balanced the crank in my Model 18. I followed Phil Irving's notes in his book "Tuning for Speed". The method I used being the same as in the AJ notes. Phil goes into how to layout the hole pattern relative to the big end pin and crank pin, he also outlines how to estimate the volume of metal to be removed.

This "volume" is only a starting guide and in the end you will see where you are with it all as you roll the crank along your knife edges. I used similar knife edges to those in the photo in the AJ notes. My knife edges were more flate than knife. I filed them smooth so there would be as little rolling resistance as possible. It all worked quite well and was not hard to do. My wife has a very good set of kitchen balance type scales which are quite accurate.

After calculating the weight I needed to hang from the small end to either find the existing balance factor, or set my new balance factor, I used a tin can and filled it with water. This way, you can get a very accurate weight very easily. You can also adust the weight very easily by adding or subtracting water.

I set my new balance factor to around 62%. This is easily achievable and was far from the balance factor the crank had before I started.

If anyone wants to "play" with this method. Simply set up a couple of pieces of angle as in the picture. I used long lengths and "G" clamped the ends to the bench. I supported the outer ends on an hydraulic car jack and fiddled with the setup until the rails or knife edges were as level as I could get them with a small spirit level so there would be no up hill or down hill running. Weigh your piston assembly plus the small end of the conrod (you don't need to remove the conrod from the crank to do this, just make sure it freely rotates and doesn't get hung up when weighing therefore giving a false reading. Add these weights together.

Mount the crank on your knife edges, make a little wire hook to hang in the little end eye and use a common kitchen "jam tin" (Australian term) with a wire handle on it (commonly called a "billy") Hang the billy on the wire hook. Now roll the crank back and forth, filling the billy with water until the crank is balanced and will stop anywhere in it's rotation.

Weigh the Billy of water plus the hook. Calculate what percentage the weight of the billy of water is to the weight of the piston assembly + little end and you'll have the balance factor of your crank.

If this percentage is not what you want as a balance factor you now need to calculate how much material you will need to remove from the crank by drilling holes in the appropriate places.

NOTE: This method really only works for cranks with rolling element big end bearings as these bearings will allow the conrod to rotate freely therefore allowing the crank to roll along the knife edges freely. There is too much friction in plain or slipper bearings for this method to work. I guess you could do the same for cranks with more than one conrod, but it would be a much bigger headache.

There are sceptics and non believers out there who said to me......nar, that won't work. If you play with the set up and add & subtract water and do your sums you will see how far from the ideal your balance factor is. You will easily get your balance factor close to the ideal of 62% and you will be a lot closer than the 52% or 57% the crank was before you started. My model 18 engine runs quite smoothly and I am happy to give it the berries.

My Big 4 will need a piston soon and when it gets it's new piston, I'll balance the crank as well. For an engine with a big lump of a crank and a top speed around 65mph balancing the crank will give a reliable running top speed of another 5 mph. It means the engine will be doing it easier.

Give it a go.........check the balance factor of that single in bits under the bench......you've got nothing better to do and you'll learn something.......

Bob

Sorry to hijack the thread but i have a WD16H bottom end apart at the moment, the current balance factor has been measured at 48% and i have been dithering over whether to have this adjusted while all is apart.

The girders were so worn that i couldn't get over 45mph(ish) without the front end going mad when all was together so i don't know how smooth things are at speed (if i can use that word with a 16H) on the current set up.

Bob, any comment on the applicability of your 62% factor to a 16H would be appreciated. I am likely to spend more time on the open road than around town.

I just looked up my notes and re read the "Single Cylinder Balancing Theory" paragraph in Phil's book...................

Phil says "failing any reliable information 66% is a good starting off point."

My notes indicate I was going for 66% in my calculations.

I'd be going for that factor on any of my singles, 16H included. As you can see, 48% is a long way off 66%. My engine definately ran better.

As Phil says, it's a starting point and may not be perfect. To get perfection for your bike and the way you ride it may take a few goes at it. I realised this after reading Phils notes the first time, I decided to have a go at it regardless, however my bike ran much better after my attempt at getting it to be 66% and I went no further.

If your forks are out of control as you ride it now, I'm sure you can't do much worse. You could try and calculate the present balance factor for yourself and see if you get 48%.

While I encourage you to check it and have a go yourself, it's up to you to make these decisions for yourself. Your the one who knows your ability.

All the best

Bob

Thank you Bob, will let you know how i get on.

cheers

Iain

Previously wrote:

I just looked up my notes and re read the "Single Cylinder Balancing Theory" paragraph in Phil's book...................

Phil says "failing any reliable information 66% is a good starting off point."

My notes indicate I was going for 66% in my calculations.

I'd be going for that factor on any of my singles, 16H included. As you can see, 48% is a long way off 66%. My engine definately ran better.

As Phil says, it's a starting point and may not be perfect. To get perfection for your bike and the way you ride it may take a few goes at it. I realised this after reading Phils notes the first time, I decided to have a go at it regardless, however my bike ran much better after my attempt at getting it to be 66% and I went no further.

If your forks are out of control as you ride it now, I'm sure you can't do much worse. You could try and calculate the present balance factor for yourself and see if you get 48%.

While I encourage you to check it and have a go yourself, it's up to you to make these decisions for yourself. Your the one who knows your ability.

All the best

Bob

Hello again Ian,

I've attempted to post photos of my head steady modification as done to my 19S, alas, I am not smarter than a fifth grader when it comes to computrons, I'm not sure if this forum allows the posting of private Email addresses, if I had yours I could send you the photos directly, til then cheers!

Albert.