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E: Engine Crankshaft Balance Method

LoneStar

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VOC Member
Hello all,

I'm rebuilding my Series C Black Shadow with new pistons and rods, due to a catastrophic failure last summer. I now have the crank assembled with the rods, and need to check the balance. Based on a consensus of informed opinion, I’m targeting a 50% balance factor.

After doing a lot of reading, I think I understand what needs to be done to reach this figure. But, I’ve made stupid mistakes before and it would be inconvenient to tear down the engine again to correct one. So I’d like to outline my logic, and ask if anyone sees errors or faulty assumptions.

Here are the basic figures:

pistons: 417g each, with rings and pin

rod reciprocating weight: 187g

This gives total reciprocating weight on the crank of 1208g

The idea is to balance 50% of this reciprocating weight, or 604g. This means with 604g reciprocating weight, the crank should be balanced, and stop at any location when rotated on bearings.

To test this, I subtracted the 374g reciprocating weight of the rod small ends, as they’re already in place, and attached 230g to the small ends to reach the 604g figure.

Unfortunately, but not surprisingly, the crank wasn’t in balance at this point: the crankpin side was heavier. This means I need to add weight to the flywheels opposite the crankpin, so I attached weights there until the crank was in balance. This took 113g.

The next question is how to implement this on a permanent basis. The accepted method appears to be inserting plugs of heavy metal, such as tungsten, into holes drilled near the flywheel rim. So, how much tungsten is required?

The weight required will differ with the distance from the center of rotation. My test weight was on the outside of the rim, at a radius of 4.2”. The holes to be drilled for plugs will be c. 3.5” out, so I increased the weight requirement by the ratio – multiply by 1.2. This gives a weight requirement of 135g.

Now in order to insert the plugs, holes must be drilled. This has the unfortunate effect of removing steel, so requiring more tungsten to compensate. The density of tungsten is 19.6g/cc, while steel is 7.85. Based on this, the effective density of tungsten when replacing steel is 11.75g/cc. Therefore the weight of the tungsten plugs will be the required net weight increase x (19.6/11.75), or 225g.

Is this all correct?

The rods and pistons are both Carrillo, and I’m told by the supplier that it’s normal to need to add weight to the flywheels when balancing them.

Thanks!

Dave
 

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Albervin

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MartynG

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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LoneStar

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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LoneStar

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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LoneStar

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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MartynG

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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MartynG

Well Known and Active Website User
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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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Chris Launders

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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vibrac

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

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Bill Thomas

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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greg brillus

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Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

You can join the Vincent H.R.D. Owners Club, remove this annoying message, and gain full access to all website facilities by CLICKING HERE.

 

Bill Thomas

Well Known and Active Website User
VOC Member
Running the Vincent H.R.D. Owners Club online forum costs money, and like other organisations, we have annual software and hosting costs which are significant. These costs are paid for entirely by the Members of our Club. Sadly, we don't have a magic money tree!

If you're viewing this annoying messsage, you have been identified as a regular non-Member user of our online forum for some time, and we’d really appreciate it if you could give some thought to joining the Club to offset some of the costs mentioned previously.

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