Engine balancing
Discussion
Spoke to the guys at Vibrationfree today just after they'd finished balancing my 4.5 bits - crank, flywheel, clutch and pistons / rods etc. I was unsure as to whether it would be worth the hassle but having heard the pre-balance results it sounds like it was well worth the time and investment.
Apparently the crank was out by 14 grams, which (I am told) is horribly out of balance. Pistons were out by just over 2g and the rods by about 4g. After their work everything is now within 0.1g.
Hopefully this will help ensure that it runs as well, powerfully and smoothly as it can for as long as possible. I'm picking it all up on Friday so can start the re-assembly at the weekend
Apparently the crank was out by 14 grams, which (I am told) is horribly out of balance. Pistons were out by just over 2g and the rods by about 4g. After their work everything is now within 0.1g.
Hopefully this will help ensure that it runs as well, powerfully and smoothly as it can for as long as possible. I'm picking it all up on Friday so can start the re-assembly at the weekend
Well worth doing. Mine was out by miles as well. You'll find more power after doing all that.
It'll be realy smooth aswell. If anyone is rebuilding an engine this has got to be one of the
best things you can do. I remember speaking to David at Austec, he considered my crank to be
highly out of balance. Those fourteen gramm's will be such a massive weight when the crank is
revolving at high revs.
It'll be realy smooth aswell. If anyone is rebuilding an engine this has got to be one of the
best things you can do. I remember speaking to David at Austec, he considered my crank to be
highly out of balance. Those fourteen gramm's will be such a massive weight when the crank is
revolving at high revs.
£345 + VAT. Due to the AJP being a flat plane crank it's a little cheaper than a RV8 as they don't have to do the counter weights. Not cheap, but I only want to rebuild my engine once 
Actually, I was delighted when I heard it was so bad!
Apparently they use a formula of grammes of imbalance X diameter of crank to understand the impact of the imbalance when the crank is spinning. Before the work it was 1126 and after balancing they got it down to 14. I'm not an engineer, but that can only help an engine make more reliable power for longer!
They balanced the Bentley Le Mans engines etc, so seem to know what they're up to.
Actually, I was delighted when I heard it was so bad!Apparently they use a formula of grammes of imbalance X diameter of crank to understand the impact of the imbalance when the crank is spinning. Before the work it was 1126 and after balancing they got it down to 14. I'm not an engineer, but that can only help an engine make more reliable power for longer!
They balanced the Bentley Le Mans engines etc, so seem to know what they're up to.
Now I'm going to sound like an idiot. 
I never have managed to trust what I can't see. Its a failing of mine. I have great trouble believing anyone who says they have done something but I can't measure the results. It will/would forever nag at me that I couldn't tell if it was out of balance, or if they had done anything at all for their money. Obviously I'm not the trusting sort.
Problem is I can't dupicate their machine, which I'm sure is a super dooper mechanical marvel which just prints out where it wants them to take a bit off, like a wheel balancing machine.
I can weigh my own pistons, but I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
What I need here is a verbal slapping from the Cerb forum.
I never have managed to trust what I can't see. Its a failing of mine. I have great trouble believing anyone who says they have done something but I can't measure the results. It will/would forever nag at me that I couldn't tell if it was out of balance, or if they had done anything at all for their money. Obviously I'm not the trusting sort.
Problem is I can't dupicate their machine, which I'm sure is a super dooper mechanical marvel which just prints out where it wants them to take a bit off, like a wheel balancing machine.
I can weigh my own pistons, but I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
What I need here is a verbal slapping from the Cerb forum.
julian64 said:
I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
julian64 said:
What I need here is a verbal slapping from the Cerb forum.
I can give you a physical slapping if you want 
julian64 said:
Now I'm going to sound like an idiot.
I never have managed to trust what I can't see. Its a failing of mine. I have great trouble believing anyone who says they have done something but I can't measure the results. It will/would forever nag at me that I couldn't tell if it was out of balance, or if they had done anything at all for their money. Obviously I'm not the trusting sort.
Problem is I can't dupicate their machine, which I'm sure is a super dooper mechanical marvel which just prints out where it wants them to take a bit off, like a wheel balancing machine.
I can weigh my own pistons, but I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
What I need here is a verbal slapping from the Cerb forum.
Surely being flat plane, you can support the crank on the main journals and rotate it then measure any change in stress in a horizontal plane on the support as it rotates. If it is perfectly balanced then there should be no 'wobble' with rotation. If it is not then as the heavy point of the crank passes your reference point on the support you will see a displacemnet in one direction and 180 degrees away you will see an identical displacement in the opposite direction. I would have thought you wouldn't have to rotate the crank particularly fast, and a small stress gauge should be able to do the measurement without problem. stick a degree wheel on one end of the crank and use a strobe light synchronised with the rotation to tie the peak displacement to crank position?I never have managed to trust what I can't see. Its a failing of mine. I have great trouble believing anyone who says they have done something but I can't measure the results. It will/would forever nag at me that I couldn't tell if it was out of balance, or if they had done anything at all for their money. Obviously I'm not the trusting sort.
Problem is I can't dupicate their machine, which I'm sure is a super dooper mechanical marvel which just prints out where it wants them to take a bit off, like a wheel balancing machine.
I can weigh my own pistons, but I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
What I need here is a verbal slapping from the Cerb forum.
Hmmm perhaps I need a verbal slap too....
Try and find an engineering place that will allow you to go down on the day they are working on your engine so you can watch the process. I know of one engine builder that actively encourages people to get involved in the build process of their engines, and they do engine balancing, but unfortunately he's not a TVR indie. To be honest I don't think this would be a problem, for this sort of thing and engine is an engine, the process is the same. He's a genius in the classic Mini scene though, used to work for the Works team. I'll give you his contact details if your interested?
Tanguero said:
julian64 said:
Now I'm going to sound like an idiot.
I never have managed to trust what I can't see. Its a failing of mine. I have great trouble believing anyone who says they have done something but I can't measure the results. It will/would forever nag at me that I couldn't tell if it was out of balance, or if they had done anything at all for their money. Obviously I'm not the trusting sort.
Problem is I can't dupicate their machine, which I'm sure is a super dooper mechanical marvel which just prints out where it wants them to take a bit off, like a wheel balancing machine.
I can weigh my own pistons, but I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
What I need here is a verbal slapping from the Cerb forum.
Surely being flat plane, you can support the crank on the main journals and rotate it then measure any change in stress in a horizontal plane on the support as it rotates. If it is perfectly balanced then there should be no 'wobble' with rotation. If it is not then as the heavy point of the crank passes your reference point on the support you will see a displacemnet in one direction and 180 degrees away you will see an identical displacement in the opposite direction. I would have thought you wouldn't have to rotate the crank particularly fast, and a small stress gauge should be able to do the measurement without problem. stick a degree wheel on one end of the crank and use a strobe light synchronised with the rotation to tie the peak displacement to crank position?I never have managed to trust what I can't see. Its a failing of mine. I have great trouble believing anyone who says they have done something but I can't measure the results. It will/would forever nag at me that I couldn't tell if it was out of balance, or if they had done anything at all for their money. Obviously I'm not the trusting sort.
Problem is I can't dupicate their machine, which I'm sure is a super dooper mechanical marvel which just prints out where it wants them to take a bit off, like a wheel balancing machine.
I can weigh my own pistons, but I can't stop thinking how I would balance my own crank.
The closest I have come is to mount two temporary magnets linked to a big battery which suspends the crankshaft at either end. I haven't managed to wind enough wire to get the heavy old crank suspended but am convinced when I do it will be so frictionless that the heaviest part of it will always rotate down.
What I need here is a verbal slapping from the Cerb forum.
Hmmm perhaps I need a verbal slap too....
jammy_basturd said:
Try and find an engineering place that will allow you to go down on the day they are working on your engine so you can watch the process. I know of one engine builder that actively encourages people to get involved in the build process of their engines, and they do engine balancing, but unfortunately he's not a TVR indie. To be honest I don't think this would be a problem, for this sort of thing and engine is an engine, the process is the same. He's a genius in the classic Mini scene though, used to work for the Works team. I'll give you his contact details if your interested?
I wouldn't mind that as Ibeleive you are not that far away from me. Out of interest have you finished with the deadstop and cam rest yet?Certainly, the guy is Bill Richards, of www.billrichardsracing.com.
And, yes, for the time being. In the end I haven't yet used them because of getting that spacer out the engine (which I've still not done, still not got the engine out either), but I'll certainly drop them off as soon as poss! I'll give you an email over the weekend or next week to arrange a time. Thanks for that again!
And, yes, for the time being. In the end I haven't yet used them because of getting that spacer out the engine (which I've still not done, still not got the engine out either), but I'll certainly drop them off as soon as poss! I'll give you an email over the weekend or next week to arrange a time. Thanks for that again!
I do understand what you getting at with the "if I can't see it it doesn't exist" sentiment, however, that didn't stop me getting the relevant bits crack tested, because I can't see what they can! 
Regarding the balancing, if you look on the Vibrationfree website there are a number of technical articles which explain the importance and science behind balancing. Whilst I am sure that you could jury rig something to have a stab at improving the balancing (probably not hard given how far out it was) I can't see how you are going to get within 0.1 of a gramme and deal with variance along the length of the crank. I checked with the results sheet that they sent me and it is balanced a different points along it's length.
Granted, with the right scales you could do the pistons, but as already mentioned you've got to know how and where to safely remove weight.
Ultimately, you can take DIY to varying degrees. Lots of people just take their car to TVR Power and spent £9kish on an engine rebuild whilst others will want to go as far as devising their own balancing machines! I have tried to take the middle ground, all the machining and specialist work (eg balancing) has been done by the necessary experts whilst I deal with engine removal, strip, reassembly and refitting which both saves me money and also ensures that I know the standard of work! - The previous rebuild was done by a "specialist" (now defunct) and I have uncovered a few horrors that mean that I would rather trust my own skills where possible.
Regarding the balancing, if you look on the Vibrationfree website there are a number of technical articles which explain the importance and science behind balancing. Whilst I am sure that you could jury rig something to have a stab at improving the balancing (probably not hard given how far out it was) I can't see how you are going to get within 0.1 of a gramme and deal with variance along the length of the crank. I checked with the results sheet that they sent me and it is balanced a different points along it's length.
Granted, with the right scales you could do the pistons, but as already mentioned you've got to know how and where to safely remove weight.
Ultimately, you can take DIY to varying degrees. Lots of people just take their car to TVR Power and spent £9kish on an engine rebuild whilst others will want to go as far as devising their own balancing machines! I have tried to take the middle ground, all the machining and specialist work (eg balancing) has been done by the necessary experts whilst I deal with engine removal, strip, reassembly and refitting which both saves me money and also ensures that I know the standard of work! - The previous rebuild was done by a "specialist" (now defunct) and I have uncovered a few horrors that mean that I would rather trust my own skills where possible.
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