Torque tube bearings?
11-26-2014, 10:07 PM
#16
Rennlist Junkie Forever
The problem is that this current motor was sort of thrown together in a manner of speaking. The knife crank was done by whoever does LR's. The rods were bought from another vendor and the motor was assembled with another set of pistons. I don't know if the components were ever actually balanced as this was motor was kind of initially designed as more a street rod thing. I had another 16v project with the builder going on simultaneously. The motor was shipped down here and we didn't pull it down to do our own balancing plus added a custom puk clutch. Plus hanging the extra dry sump pulley off the nose would have just made things worse I suspect. Retaining the balance shafts may have made things worse or not. The system wouldn't have been very integrated, more like a 'suck it and see' outcome. Running all these unmatched and unbalanced parts was probably a recipe for disaster.
The balance shafts have zero to do with it. They just counter the vibrations that appear externally. The vibration doesn't go away because you have balance shafts... they [the balance shafts] just counter it so the net vibration to everything bolted to the block is as close to zero as possible.
TonyG
11-26-2014, 10:39 PM
#17
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How tight was your crank bolt when removing the pulleys?
Mine did something similar but smaller damage. the keyway was chewed up 20mm away, not all thhe way around like yours.
The crank bolt came loose causing the balance shaft pulley to move around and cause the car to vibrate badly.
How it came loose? no idea. it was torqued down to spec.
Mine did something similar but smaller damage. the keyway was chewed up 20mm away, not all thhe way around like yours.
The crank bolt came loose causing the balance shaft pulley to move around and cause the car to vibrate badly.
How it came loose? no idea. it was torqued down to spec.
11-26-2014, 11:01 PM
#18
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Thread Starter
I don't know if it was balanced or not. Wasn't there. Even if it was, we still put on a non stock clutch assembly and also the dry sump system that would change drag on the motor. The unmatched components whether balanced or not were quite likely a mismatch. The balance shafts which were stock would have been designed around the harmonics of the stock motor. By changing virtually every part of the recirc and recip masses, the balance shafts may have had little effect. Not to mention that if you skip a tooth which is not uncommon. Albert Broadfoot modifies the balance shafts (lightens I think) on his motors. Surely the stock b/shafts aren't perfect for modified race motors.
11-26-2014, 11:20 PM
#19
Rennlist Junkie Forever
I don't know if it was balanced or not. Wasn't there. Even if it was, we still put on a non stock clutch assembly and also the dry sump system that would change drag on the motor. The unmatched components whether balanced or not were quite likely a mismatch. The balance shafts which were stock would have been designed around the harmonics of the stock motor. By changing virtually every part of the recirc and recip masses, the balance shafts may have had little effect. Not to mention that if you skip a tooth which is not uncommon. Albert Broadfoot modifies the balance shafts (lightens I think) on his motors. Surely the stock b/shafts aren't perfect for modified race motors.
Just because it's a race engine changes not much with respect to 1st and 2nd order vibrations. The vibration is inherent to any inline 4 engine, race or bone stock. The only difference being that the amplitude if the these vibrations might be less in the race engine, due to lower bobweights... but the difference would probably be minimal.
And yes... the stock balance shafts aren't perfect for a modified engine... but they will still make a big difference.
You can always just take off the belt and try it out. I just know that when I ran without them I always had things cracking (strange things) or loosening up. I really had to watch everything.
TonyG
11-27-2014, 01:22 AM
#20
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Thread Starter
Yes but the drag could change things and maybe even offset some of the vibrations effects. The clutch system might be balanced by itself but as it's part of the recirculating mass, you would think that it needs to be balanced along with some of the other components.
If you design a motor and run it on an engine dyno then add all the rest of the drivetrain, all the other parts of the drivetrain must also have an effect on the harmonics going through the motor in addition to the natural i4 harmonics. With different weight to stock CVs and axles, non rubber suspension bushings/bearings, a different transmission, who knows what condition my TTube bearings are in, different clutch, crank, rods, pistons, pulleys etc than a stock motor PLUS the fact that we had a bent torsion tube carrier and CV failure...something had to change and have an effect on the harmonics.
I was thinking about doing exactly what you said. Try removing balance shaft belts and see what happens. I'm not chasing those 3-5 horses that we might lose through parasitic loss due to running the belts but I am wanting to rebuild this motor more efficiently. Perhaps that will involve retaining the stock b/shafts. If we wind up finishing the other 16v motor that will likely come down in capacity to about 2.6lt and be built to run without shafts for sure. Maybe this 3.1lt tractor motor needs to retain them?
If you design a motor and run it on an engine dyno then add all the rest of the drivetrain, all the other parts of the drivetrain must also have an effect on the harmonics going through the motor in addition to the natural i4 harmonics. With different weight to stock CVs and axles, non rubber suspension bushings/bearings, a different transmission, who knows what condition my TTube bearings are in, different clutch, crank, rods, pistons, pulleys etc than a stock motor PLUS the fact that we had a bent torsion tube carrier and CV failure...something had to change and have an effect on the harmonics.
I was thinking about doing exactly what you said. Try removing balance shaft belts and see what happens. I'm not chasing those 3-5 horses that we might lose through parasitic loss due to running the belts but I am wanting to rebuild this motor more efficiently. Perhaps that will involve retaining the stock b/shafts. If we wind up finishing the other 16v motor that will likely come down in capacity to about 2.6lt and be built to run without shafts for sure. Maybe this 3.1lt tractor motor needs to retain them?
11-27-2014, 02:14 AM
#21
If the failures of the various pulleys were caused by an excess of vibrations, you have to admit Patrick that it's not the removal of balance shafts here, adding beefier TT bearings there, balancing axles or whatever and then shaking the cocktail all together whistling on voodoo tunes that is going to scientifically address the fundamental physical problem (or should we say feature) as correctly described in earlier posts... 
The combination of minor vibrations in the complete driveline may have caused your problem, but adding solid mounts everywhere between the driveline and the shell may cause some mirror effect in between the two, and this would get uglier the larger the I4 engine used.
Your dry sump parts turned out to be a poor design, some correct ones with a stock-ish crank should already help. But please keep the balance shafts, otherwise you may be in for another expensive tail-chasing tale.
The combination of minor vibrations in the complete driveline may have caused your problem, but adding solid mounts everywhere between the driveline and the shell may cause some mirror effect in between the two, and this would get uglier the larger the I4 engine used.
Your dry sump parts turned out to be a poor design, some correct ones with a stock-ish crank should already help. But please keep the balance shafts, otherwise you may be in for another expensive tail-chasing tale.
Last edited by Thom; 11-27-2014 at 03:26 AM.
11-27-2014, 05:56 AM
#22
Rennlist Member
Thread Starter
How tight was your crank bolt when removing the pulleys?
Mine did something similar but smaller damage. the keyway was chewed up 20mm away, not all thhe way around like yours.
The crank bolt came loose causing the balance shaft pulley to move around and cause the car to vibrate badly.
How it came loose? no idea. it was torqued down to spec.
Mine did something similar but smaller damage. the keyway was chewed up 20mm away, not all thhe way around like yours.
The crank bolt came loose causing the balance shaft pulley to move around and cause the car to vibrate badly.
How it came loose? no idea. it was torqued down to spec.
If the failures of the various pulleys were caused by an excess of vibrations, you have to admit Patrick that it's not the removal of balance shafts here, adding beefier TT bearings there, balancing axles or whatever and then shaking the cocktail all together whistling on voodoo tunes that is going to scientifically address the fundamental physical problem (or should we say feature) as correctly described in earlier posts.
The combination of minor vibrations in the complete driveline may have caused your problem, but adding solid mounts everywhere between the driveline and the shell may cause some mirror effect in between the two, and this would get uglier the larger the I4 engine used.
Your dry sump parts turned out to be a poor design, some correct ones with a stock-ish crank should already help. But please keep the balance shafts, otherwise you may be in for another expensive tail-chasing tale.
The combination of minor vibrations in the complete driveline may have caused your problem, but adding solid mounts everywhere between the driveline and the shell may cause some mirror effect in between the two, and this would get uglier the larger the I4 engine used.
Your dry sump parts turned out to be a poor design, some correct ones with a stock-ish crank should already help. But please keep the balance shafts, otherwise you may be in for another expensive tail-chasing tale.
11-27-2014, 05:59 AM
#23
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4cylinder engine inherently vibrate because it doesn't have the ability to cancel its own vibration with opposing cylinder vibration. That is called secondary or second order vibration and it gets stronger with higher rpm. Small 4 cly engines can live with it, large engines (I think everything over 2.0L) needs a device to counter secondary vibrations.
http://en.wikipedia.org/wiki/Engine_balance
http://www.eng-tips.com/viewthread.cfm?qid=366049
http://en.wikipedia.org/wiki/Engine_balance
http://www.eng-tips.com/viewthread.cfm?qid=366049
1/2 order -cylinder to cylinder variation in firing pressures or timing
1 order - balance of the crank
2 order- most troublesome frequency component from non sinusoidal motion of piston and conrod, worse on an inline 4 due to the crank layout
3 order - firing frequency on a 6 cylinder
1 and 2 order in particular can be very large forces, very hard to isolate in your engine mounts.
2nd order vibration: this one is a bit tougher. Picture a conventional inline four. The two outer pistons are 180 degree opposed to the inners. When the outers are at the top, the inners are at the bottom. Balanced, right? Not quite. Look at the angle of the connecting rods. When the pistons are at TDC/BDC, the rods are straight up and down. When the crankshaft position is mid-travel, the pistons are NOT mid-travel. The connecting rods are at an angle to the side, which means the pistons are a little below the mid-position. This happens twice per revolution, so the resulting vertical vibration is at double crank rotation frequency.
1 order - balance of the crank
2 order- most troublesome frequency component from non sinusoidal motion of piston and conrod, worse on an inline 4 due to the crank layout
3 order - firing frequency on a 6 cylinder
1 and 2 order in particular can be very large forces, very hard to isolate in your engine mounts.
2nd order vibration: this one is a bit tougher. Picture a conventional inline four. The two outer pistons are 180 degree opposed to the inners. When the outers are at the top, the inners are at the bottom. Balanced, right? Not quite. Look at the angle of the connecting rods. When the pistons are at TDC/BDC, the rods are straight up and down. When the crankshaft position is mid-travel, the pistons are NOT mid-travel. The connecting rods are at an angle to the side, which means the pistons are a little below the mid-position. This happens twice per revolution, so the resulting vertical vibration is at double crank rotation frequency.
11-27-2014, 06:10 AM
#24
Rennlist Member
Thread Starter
Yes, hence why we are looking at a dampener on the front of the motor. I've known of i4 motors that threw things off the front or at least cracked and once a dampener was put on, all problems ceased to exist. Admittedly smaller capacity with less power but I am pretty sure a dampener is going to be a big help for us.
11-27-2014, 06:14 AM
#25
Three Wheelin'
Good info here from Tony and others. Gotta be careful when talking about vibration as if it's all the same, though.
Maybe the easiest way to summarise is to say that the balance shafts counter the vertical vibration whereas the crank damper counters the torsional vibration. Different horses for different courses...
Cheers,
Mike
Maybe the easiest way to summarise is to say that the balance shafts counter the vertical vibration whereas the crank damper counters the torsional vibration. Different horses for different courses...
Cheers,
Mike
11-27-2014, 06:19 AM
#26
Rennlist Member
Thread Starter
Yeah, I realise I'm sweeping with a broad brush on the vibration thing. I think the torsional issue is potentially worse than the vertical one though. Potentially.
Wonder what happens on i5 motors as an aside?
Wonder what happens on i5 motors as an aside?
11-27-2014, 06:19 AM
#27
Three Wheelin'
Yes, hence why we are looking at a dampener on the front of the motor. I've known of i4 motors that threw things off the front or at least cracked and once a dampener was put on, all problems ceased to exist. Admittedly smaller capacity with less power but I am pretty sure a dampener is going to be a big help for us.
Cheers,
Mike
11-27-2014, 06:22 AM
#28
Rennlist Member
Thread Starter
Seems all contrary to what I thought previously. The whole lighter = better might be ok in theory..but when bits of metal start separating that takes precedence. Learning curve, steep...check!
11-27-2014, 06:42 AM
#29
Three Wheelin'
Yep tough subject, but interesting.
So, ponder this: A crank damper consists of a mass that is torsionally coupled to the crank via an elastic element.
A balance shaft... consists of a mass that is torsionally coupled to the crank via an elastic element!
So maybe the balance shafts do more than the obvious?
Cheers,
Mike
So, ponder this: A crank damper consists of a mass that is torsionally coupled to the crank via an elastic element.
A balance shaft... consists of a mass that is torsionally coupled to the crank via an elastic element!
So maybe the balance shafts do more than the obvious?
Cheers,
Mike
11-27-2014, 10:17 AM
#30
I don't know if it was balanced or not. Wasn't there. Even if it was, we still put on a non stock clutch assembly and also the dry sump system that would change drag on the motor. The unmatched components whether balanced or not were quite likely a mismatch. The balance shafts which were stock would have been designed around the harmonics of the stock motor. By changing virtually every part of the recirc and recip masses, the balance shafts may have had little effect. Not to mention that if you skip a tooth which is not uncommon. Albert Broadfoot modifies the balance shafts (lightens I think) on his motors. Surely the stock b/shafts aren't perfect for modified race motors.
I always find this topic interesting as it is a very complex problem to solve. There is another thread that attempts to provide a formula so you can calculate how much weight to remove from the shafts based on your engine internals but not sure anyone has done it yet. If I ever remove my engine I would try it.
+1 on things coming loose or breaking due to vibrations. My fuel rail cracked. Had exhaust leaks, power steering bolts backed out to name a few but that was with the "lightened shafts" still functioning. I experimented with aligning the shafts +- 1 or two teeth in either direction, but in the end the best option for my motor was without the bs.