Harmonic Balancer Question(s)
- Thread starter Bock350Dog
- Start date
err, we-ell, errrr:shrug: nope:!blank::embarassed::laugh:
Daves going to hate me for this
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I often think when I see crank assy's on a balance machine with the bob weight on each throw where the weight is added on long studs out each side that a larger portion of that weight is outside the effective throw radius as per the attached drawing ( Red Weights ) and would be more correct if the studs & weights were configured as per the ( Blue Weights ) on the drawing.
Other pic is an example of the bob-weights .
...I often think when I see crank assy's on a balance machine with the bob weight on each throw where the weight is added on long studs out each side that a larger portion of that weight is outside the effective throw radius as per the attached drawing ( Red Weights ) and would be more correct if the studs & weights were configured as per the ( Blue Weights ) on the drawing.
Other pic is an example of the bob-weights .
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Not at all, thats right jacmac, you are just as pedantic as me!:laugh:
The important parameter is the moment (integral of weight times radius), so you have to make sure that you have the right moment. So if you have some of the weight at a higher radius, you don't need quite so much weight to get the same moment.
When designing correction weights, or cutouts, I use Solidworks to get an accurate moment, so that with large corrections (as much as 70kg for big stuff) we only have to transport a 10 tonne impeller from the balancing machine to the CNC workstation once. I am unpopular if a further correction is required as it will take up to a shift to go through the process a second time:cry:.
The important parameter is the moment (integral of weight times radius), so you have to make sure that you have the right moment. So if you have some of the weight at a higher radius, you don't need quite so much weight to get the same moment.
When designing correction weights, or cutouts, I use Solidworks to get an accurate moment, so that with large corrections (as much as 70kg for big stuff) we only have to transport a 10 tonne impeller from the balancing machine to the CNC workstation once. I am unpopular if a further correction is required as it will take up to a shift to go through the process a second time:cry:.
Apologies for the thread resurrection, but rather than ask a new question with the same type of subject that has gone before I thought that I'd ask on this thread.
I think I get this thread (maybe!), so as a test of this, does it matter how heavy the flywheel is? I guess it doesn't so long as the counterweight is 10oz at 5in (for a '50oz' engine), right?
I think I get this thread (maybe!), so as a test of this, does it matter how heavy the flywheel is? I guess it doesn't so long as the counterweight is 10oz at 5in (for a '50oz' engine), right?
I have a question for you guys. I have been told that if you have an internal balanced crank and taking it everything eles is done you don't need to run a Harmonic Balancer, now to back this up and the reason I ask is, Most Sprint cars and some drag cars run those crank driven water pumps, if so you can't fit a Balancer. I want to run said water pump hence the question. Cheers Leon.
I am sure there are others more knowledgeable, but from the forgoing thread I understand that the harmonic balancer on a SBF does 2 things.
It is part of the engine (external) balance, and also balances the inherent harmonics of the engine. (I have had diabolical evidence of ignoring the 6300RPM harmonic of a 6 cylinder motor).
External balance strikes me as agricultural, but hey, they've been building these motors for donkey's years, so maybe its not as bad as it seems.
Clive
It is part of the engine (external) balance, and also balances the inherent harmonics of the engine. (I have had diabolical evidence of ignoring the 6300RPM harmonic of a 6 cylinder motor).
External balance strikes me as agricultural, but hey, they've been building these motors for donkey's years, so maybe its not as bad as it seems.
Clive
There are reasons why the drag & sprint guys can get away without the conventional damper ( provided they are internally balanced )
The motors never run at constant RPM for long periods, hence the chance of a 'harmonic' vibration building up to the point where they destroy themselves is remote.
Using a water pump direct driven off the nose of the crank actually acts to some degree as a vibration damper ( Fluid Damper
)Some race hydros Ive been involved with drove the prop this way without a damper [ broke a lot of other unrelated stuff, but never a crank ]
Your car 'might ' be able to run with a system such as this for what you intend doing, but just to be safe I would build enough room to allow a conventional pump or perhaps an electric setup... but FWIW I have not seen an original with other than the Std Chev pump yet, & we had plenty out here at SFOS a few years ago..
As Dave has pointed out earlier, there is no real practical way a V8 can be perfectly balanced for every RPM & condition, we can only hope to optimise it for whatever end use we intend, the original OE stuff does very well in this form with engines going well into the 100/200K miles arena before requiring attention, as long as us Humans dont tinker with them...
Hi Jac, The reason I,m Looking at this setup is I want to run my dry sump pump and fuel pump off the Cam, I don't want to run an alternator as I will be running a mag so electric pump is probably out as well, and I just like the idea of no belts on the front of the engine. Whats your thoughts?? Cheers Leon
While I can understand your train of thought, personally I feel its somewhat flawed.
If you direct drive the Dry Sump pump off the cam your locked into that 2 to 1 drive ratio which might give you problems down the track in balancing oil flow etc, same applies to water pump flow & even fuel pump with a Hillborn setup. With belts,esp toothed belt drives you can keep all this stuff very compact at front with the advantage of change if reqd.
Theoretically, yes, it does matter. The more mass the flywheel has, the harder it is to get it turning, and the harder it is to slow it down once it is turning. This is where the twisting of the crankshaft comes into play (tortional vibrations, hence the tortional vibration damper, or harmonic balancer, if you will). Sometimes it is hard to think of crankshaft being able to twist about its long axis, but it does.
Eric
Yeh I hear you Jack, My main reason was that there are some nice set ups from Barns and others that really keep the enigne clean, no belts to break or fly off, the other thing I was looking at was the barns "In Sump" system, Only 2 Lines from the pump to the tank and back to the pump and nothing hanging off the engine.
I'm NO engine expert but can you not control oil flow with Pressure valves and the like and the fuel by your "Pills"and Bypasses etc. As I say I'm NOT an engine expert just what I read and learn from. I respect any help you have to offer.
Cheers Leon.
I'm NO engine expert but can you not control oil flow with Pressure valves and the like and the fuel by your "Pills"and Bypasses etc. As I say I'm NOT an engine expert just what I read and learn from. I respect any help you have to offer.
Cheers Leon.
The closer you can tailor the pump flow & pressure to the actual engine requirements without the need to have extra bypass or large relief pressure reliefs, the better, anything more is just power out the back door.
Is the barnes in sump setup driven off the crank nose or off the distributor gear as per std, I would not be keen on a two or three stage setup driven off the distributor gear in light of all the marginal gear failures we have these days with politically correct oil blends. Also if its the latter then the pump depth with two stages might be an issue with regard to ground clearance.
I/We must be just lucky with our belt drive pump on the TVR, havent lost one yet & anyone who's seen it race knows it spends far to much time off road in the 'Kitty Litter'- gravel traps...
Eggs Benedict... With a road car a heavier flywheel makes the car more pleasant to drive, without one every small hill would require a downshift or large throttle increase, think back to those times where you might have driven a small capacity car with a lightened flywheel & have had to use the gearlever more often. Its a personal choice thing I suppose, not really an issue on a car you only use for a bit of fun at the weekends, but if you also have to drive it to work every day, perhaps not so much fun...
Is the barnes in sump setup driven off the crank nose or off the distributor gear as per std, I would not be keen on a two or three stage setup driven off the distributor gear in light of all the marginal gear failures we have these days with politically correct oil blends. Also if its the latter then the pump depth with two stages might be an issue with regard to ground clearance.
I/We must be just lucky with our belt drive pump on the TVR, havent lost one yet & anyone who's seen it race knows it spends far to much time off road in the 'Kitty Litter'- gravel traps...
Eggs Benedict... With a road car a heavier flywheel makes the car more pleasant to drive, without one every small hill would require a downshift or large throttle increase, think back to those times where you might have driven a small capacity car with a lightened flywheel & have had to use the gearlever more often. Its a personal choice thing I suppose, not really an issue on a car you only use for a bit of fun at the weekends, but if you also have to drive it to work every day, perhaps not so much fun...
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I have seen that TVR run and mate does it go or what!!! I was at SFOS Timaru last year. The "In sump" is driven off the dizzy drive as per std, Steve Hildred from NP was running one in his Monaro a while back and although he has gone to an external pump now, he said to me he had no issues with the insump but wanted more scavenge. From what I have seen the insump basicaly has the same scavenge as a std type pickup (More efficient as it were) and then pumps the oil to the tank, sucks it back and feeds it into the std engine system so you still can run your oil filter in the std position if you wanted to. I'm under no illusion that this wouldn't be even close to the performance of a multi stage external pump but it would still be streets ahead of a std wet sump and stop the all important oil surge issue. I have built my engine mounts to allow for a 6.5" sump depth anyway so ground clearence is not an issue for me. I know the original engines sat about 2" lower but I'm building a car for track days and occasional races, I'm not trying to win the Can-Am, I have even thought about leaving it wet sump as there is some pretty good systems out there but I know thats a NO NO for real racing. @ the end of the day alot will be governed by budget when I do come to build the motor and I do Listen to what you say and appreciate you help. Cheers Leon
I really meant 'does it matter from a balance perspective'. So essentially, if the flywheel has the requisite 50oz/in, it doesn't matter how light it is overall? My last 'toy' car had a lightened flywheel - it added a good deal more zip to its responsiveness, and I'd like to have the same responsiveness with my 302.
IMHO, mass is what makes the torque value of the motor. But the flywheell can be lightened at the outer edge only, and a heavier pulley put on the front of the crank, to make the total package weigh the same. It improved the acceleration rate. In all of the engines I've worked on, and I can't count how many that is, We always got the pistons to weigh the same, the rods to weigh the same and also end to end weigh the same. That weight was then totaled and the weights added to the crank journals. Then the crankshaft was spun up to 10,000 rpm, when balanced and checked again. Then the pulley, and the flywheel with the pressure plate on was checked to make sure that harmonics were directed to the main bearings. Take the whole thing to a professional balancer and explain what you plan to do with the engine, they will usually be only too glad to help. An old rule was that a gram of weight out of balance at 10,000 rpm was equal to a 187 lb side load on the bearings. Of course, all of this is just IMHO. I hope it helps, I really do.
I will find out the name of the machine, I used a professional racing balancing company. The statement quoted came from a man who first did my balancing up until he died. But that said, some of the engines that I felt I was lucky enough to be a part of, left the starting line of the track at 9500 RPM, and the harmonics were not a problem. I stress more than anything that the number of force given is just a physics number, and I always used that to stress the importance of getting the balance right.
You guys build really impressive cars and the workmanship and attention to detail is just nothing short of perfect. I offer the information that I did with nothing but respect.
You guys build really impressive cars and the workmanship and attention to detail is just nothing short of perfect. I offer the information that I did with nothing but respect.