Author Topic: My engine rebuild / crank balancing considerations  (Read 7203 times)

Offline MG

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Re: My engine rebuild / crank balancing considerations
« Reply #15 on: 13.09. 2010 14:09 »
Stu,
thanks for the nice comment.

Trev,
it was balanced dynamically. Usually this is nothing to pay out of petty cash, but my engine reconditioner allowed me to use his machinery during an afternoon when he didn't need it, so all it did actually cost was some hours of work and a crate o' beer for the staff.  *smile* *beer*

muskrat,
I didn't have any oil in the galleries and the sludge trap, but I calculated the weight of the oil in there (volume of the sludge trap hole and galleries less the sludge trap tube and plugs, multiplied by the specific gravity of the engine oil at 80°C) and added it to the rotary weight of the bob weights (more calculating, less oily mess *smile*)
This makes quite a difference, I seem to remember it was about 25 to 30grams.

See, you won't catch me on that one!  *lol*

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Online muskrat

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Re: My engine rebuild / crank balancing considerations
« Reply #16 on: 13.09. 2010 14:13 »
Smartypants  *smile*
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Offline Hubie

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Re: My engine rebuild / crank balancing considerations
« Reply #17 on: 14.09. 2010 02:17 »
I'm now very curious to see how mine will turn out.  My crank is going in for balancing tomorrow so I am very keen to get it back in and see how it goes.  Balance factor is going to be 60-62%.

Great job mate, you'ev only got me more eager to complete my rebuild!

Cheers,

Hubie.
1959 BSA Golden Flash
1956 Royal Enfield Super Meteor
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2007 Harley Davidson Sportster 1200 Custom

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Offline MG

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Re: My engine rebuild / crank balancing considerations
« Reply #18 on: 14.09. 2010 11:09 »
Hubie,

I'm sure it'll turn out good with 60-62%.
But don't forget fitting the sludge trap tube, plugs and flywheel bolts prior to having it balanced.
Plus, like muskrat mentioned, the sludge trap should be filled with oil (the oil holes covered with adhesive film to keep it in there). Otherwise you won't have the rotating masses right and the final balance factor will be lower than the 60% you were aiming for. The other way is adding the weight of the oil to the bob weights, like I did.

Let us know how the engine runs once you got it all back together!

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline A10Boy

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Re: My engine rebuild / crank balancing considerations
« Reply #19 on: 26.10. 2010 18:31 »
Blimey Markus she looks great, well done. Now for the CSR...........  ;)
Regards

Andy

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Offline a10gf

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Re: My engine rebuild / crank balancing considerations
« Reply #20 on: 10.02. 2015 21:20 »
Just a comment about why it's preferable to upload pictures to the forum as attachments > see 1st page of this topic (another example here).

When using some image host and then doing some changes there, forgetting about all the links getting killed in the process, informative content is lost \ made meaningless due to the the lack of the pictures which were the basis for the post.

MG, if you read this, can it be fixed ? :O)

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Offline MG

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Re: My engine rebuild / crank balancing considerations
« Reply #21 on: 11.02. 2015 20:09 »
Fixed  ;)
Well, almost, can't find the spreadsheet pics I used back then, but the photos are all still there.

Been checking the forum regularly (more or less), but had very little to no time for writing, sorry chaps! But I am happy to see this place growing and blooming while maintaining the excellent level of quality, helpfulness and friendliness I was used to! Great job, and credit to E and Musky for their admin and mod work!

I am also glad to report that the Beezas are running well and being ridden regularly while giving suspiciously little trouble...  *smile*

Keep them on the road!
Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline Topdad

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Re: My engine rebuild / crank balancing considerations
« Reply #22 on: 11.02. 2015 21:15 »
Good to hear from you MG,been wondering where you'd got to, take care BobH
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Offline a10gf

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Re: My engine rebuild / crank balancing considerations
« Reply #23 on: 12.02. 2015 18:30 »
Thanks for the news & picture fix  *smile*

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Online Rocket Racer

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Re: My engine rebuild / crank balancing considerations
« Reply #24 on: 20.03. 2015 07:13 »
What should I say, the weather was perfect and the engine is sweeter than ever. In 4th there's almost zero vibration up to 60-65mph, then at 70 it starts to get noticeable in the footrests, it only gets a little bit worse up to 80. I haven't ridden any faster today, as I tried to keep the revs in reasonable limits while running the engine in.
For highway speeds you might want to go a tad higher with the balance factor probably, about 60-65% I'd say, but for the alpine roads here it is ideal, almost vibration-free between 50 and 70 in 4th gear and 35-55 in 3rd, where it is used most.
When I had my road rocket (rigid framed and three wheels) my balancer mentioned the figures of the day were based around pre motorway speeds and B roads. For modern roads with higher speeds typically higher balance factors help. I recall we went for 70% and the motor is sweet through to the red line. It does however rarely get used below 3/4000 so I cannot comment on town manners because it doesn't need them. As it had been originally at around 50% it was great for a stationary motor and was breaking engine flanges, head steadies and loosing bolts galore!

Its done four meetings now without needing a spanner laying on it (excepting fuel and fluid dumps)
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Online edboy

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Re: My engine rebuild / crank balancing considerations
« Reply #25 on: 20.03. 2015 10:59 »
almost 30 years ago my pride and joy was a a65 mk3 spitfire slightly customised and at the time i put the plentiful 11/1 pistons in and it went like a rocket up to 65mph - 70mph and then it felt like a pnematic drill through the handlebars. eventualy bits would snap and pre locktite things would come loose. however on the motorway with the missus on pillion to some rally i chanced the std bottom end up to 80mph-90mph and from the comfort of the middle lane i was in smooth heaven. no vibs for me any longer.unfortunately all the vibration went south and missus went mad punching me in the back and swearing as if it was all my fault. also the fear of a rod banging and through the cases kept my speed down to white finger 65 and 70mph and the missus was content.some time later the frame snapped which i had repaired then sold it.
my conclusion regarding vibration was that piston weight and compression has lot to do with vibration bands and you really have to ride your machine up to top speed before any radical change of balance factor as you may find its smooth enougth to live with at a particular speed.

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Re: My engine rebuild / crank balancing considerations
« Reply #26 on: 21.03. 2015 20:34 »
my conclusion regarding vibration was that piston weight and compression has lot to do with vibration bands and you really have to ride your machine up to top speed before any radical change of balance factor as you may find its smooth enougth to live with at a particular speed.
I agree, higher compression motors are typically "harsher" and reciprocating small end of the rod and piston weights accelerating and stopping each cycle doesnt help. The bigger oversize pistons are typically heavier which also doesnt help
I recently lend my outfit to a relative novice for a couple of meetings as his (a65) rig was in bits and he couldnt believe how smooth my a10 is.
It currently runs genuine BSA 8.25 pistons which are also flycut (to clear the short rods) .
Having said that once I finally can get back to working on my twins (currently distracted by a '72 a75), am planning to try some genuine BSA 14:1's that I have on the shelf  *grins* , but I digress.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Online edboy

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Re: My engine rebuild / crank balancing considerations
« Reply #27 on: 26.04. 2015 18:39 »
ah yes_ the legendary 14-1 bsa a10 go-kart pistons. at one time they were the only pistons you could buy for the a10 as 5 star was dropped by the oil companies. they look nice on the mantlepiece though rocket racer, but not so nice hanging from a bent rod if your unlucky. 9-1 pistons aways felt so right to me with an ally head on an a10 but i m sure you know what your doing though.

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Re: My engine rebuild / crank balancing considerations
« Reply #28 on: 26.04. 2015 22:42 »
ah yes_ the legendary 14-1 bsa a10 go-kart pistons. at one time they were the only pistons you could buy for the a10 as 5 star was dropped by the oil companies. they look nice on the mantlepiece though rocket racer, but not so nice hanging from a bent rod if your unlucky. 9-1 pistons aways felt so right to me with an ally head on an a10 but i m sure you know what your doing though.

I'd certainly never claim I know what I'm doing... I was chatting to a club member who is putting 7.25 flat tops in his super rocket for smoothness, not a bad idea for the road and my track bike has been amazingly reliable given the stick it gets. I'm expecting that my next race pistons will be decided by what fits that barrel best. At least  methanol removes the harshness of high comp, but it certainly adds to the odds of having catastrophic failure :(
Was helping a mate with his golden Flash rebuilt where he's gone from +60's back to Std's and the weight reduction in the pistons (both modern 7.25 hepolites) was noticable just picking them up.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand