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Replace Flywheel bolts? #758310
12/06/18 2:33 am
12/06/18 2:33 am
Joined: Feb 2018
Posts: 100
Oklahoma
T
Tracey Spear Offline OP
BritBike Forum member
Tracey Spear  Offline OP
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T

Joined: Feb 2018
Posts: 100
Oklahoma
For my first A65 rebuild I've almost got the crank assembly ready for balancing. The new pistons, pins, clips, rings, and rods weigh +30 and +35 grams over the original. And that's without the big end shells. One of the original pistons is +5 grams heaver than it's mate. I haven't weighed the old shells but I'm guessing that's easily 10 grams maybe more. So that's an extra 75-80 grams over original.
Is that even worth bothering over? Am I overthinking it?

I was surprised by how little gunk was in the sludge trap, maybe 1/8 inch. I soaked in mineral spirits and kept cleaning until the solvent came out clear. The original flywheel bolts appear in good shape. Is it advised to reuse the flywheel bolts, or should they be replaced just because?

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Re: Replace Flywheel bolts? [Re: Tracey Spear] #758330
12/06/18 7:57 am
12/06/18 7:57 am
Joined: Jan 2014
Posts: 4,171
Aus
N
NickL Offline
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NickL  Offline
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N

Joined: Jan 2014
Posts: 4,171
Aus
Did you actually pull the sludge tube out?
I know it sounds like a silly question but some blokes don't and the cavity can still be dirty.
A small baby bottle cleaning brush is a good implement for the job.
The piston weights should be as close as possible, 2 grams is ok. 1 gram is better etc.
Small amounts of material can normally be removed just below the pin bosses.
The shells shouldn't be significantly different from the old ones, don't worry about those.
The original beezer weights are around 650 grams each to give 70% balance factor.
I wouldn't change the flywheel bolts but that's up to you. Put them in with a drop of blue loctite though.

If you are taking it to be dynamically balanced, the bloke doing the job will weigh everything and do
the reciprocating values etc. As i said the standard value is 70%. Beezer didn't change the weights
for increased size pistons up to +0.040 so the value would decrease as heavier pistons were fitted.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: Replace Flywheel bolts? [Re: Tracey Spear] #758358
12/06/18 3:15 pm
12/06/18 3:15 pm
Joined: Feb 2018
Posts: 100
Oklahoma
T
Tracey Spear Offline OP
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Tracey Spear  Offline OP
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T

Joined: Feb 2018
Posts: 100
Oklahoma
Yes. I removed the tube, soaked and cleaned. Cavity and oil passages were soaked and cleaned till I could run clear mineral spirits through it and the solvent stays clear. Going back the rods weigh 410 gm each - shells, and the piston assemblies weigh 425 gm each. A total of 835 gm on each side.

Re: Replace Flywheel bolts? [Re: Tracey Spear] #758360
12/06/18 3:34 pm
12/06/18 3:34 pm
Joined: May 2013
Posts: 5,135
Rotherham - S. Yorkshire
Allan Gill Offline

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Allan Gill  Offline

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Joined: May 2013
Posts: 5,135
Rotherham - S. Yorkshire
I replace flywheel bolts because you don't know the stresses they have been under but many don't. Ive had motors done with original bolts (before I knew any better) I've checked them after a period of running and found them no longer tight... so each to their own, I like to think of it as cheap insurance.

As for rods and pistons etc, try as much as you can to get the weights of the 2 sides equal, it'll help a lot before you start doing any dynamic balancing.


beerchug
Re: Replace Flywheel bolts? [Re: Tracey Spear] #758379
12/06/18 10:19 pm
12/06/18 10:19 pm
Joined: Jan 2014
Posts: 4,171
Aus
N
NickL Offline
BritBike Forum member
NickL  Offline
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N

Joined: Jan 2014
Posts: 4,171
Aus
Originally Posted by Tracey Spear
Yes. I removed the tube, soaked and cleaned. Cavity and oil passages were soaked and cleaned till I could run clear mineral spirits through it and the solvent stays clear. Going back the rods weigh 410 gm each - shells, and the piston assemblies weigh 425 gm each. A total of 835 gm on each side.



You balance the engine statically by using a percentage of the reciprocating weight, so you need to weigh the small-end
of the rod separate to the big-end . That's why i gave you the actual weights of the bsa factory devices, it saves you
doing all the fiddling about. The accurate weights of the factory devices are 22oz 14drams which is 648 point something grams each.
If you make a couple up they need to fix and centre on the big-ends, then you need a set of knife edges etc.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'

Moderated by  Allan Gill, Jon W. Whitley 


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