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It's making sense now. The BS reduces up/down vibrations from power strokes while the dampener helps to reduce the twisting in rhe crankshaft.
Removing either just lets all the movements go unchecked.
Without BS, engine pushes down and pivots at flywheel. Without dampener, there's more and more twisting inside crankshaft as power moves to flywheel. So I can imagine that without a good dampener, we can see cracks from internal twisting. And without BS, we can see cracks from pivoting motions.
I'm putting away my crayons now. I have a brain cramp.
Well said Don. Most of the guys are true believers in the BS delete & they like to push back on the engineering value of the BS
I take the simple approach to running them. They were specifically designed to dampen vibrations / harmonics.
Mitsu spent a lot of money in the design & implementation of the BS
We certainly have enough reported occurrences of failed cranks & other associated failures to justify running them
There's no good reason not to run the shafts, as originally intended!!!!
Brain is a bit refreshed. Looking at this crank, my best guess us that the crank is strong. The oiling hole made that rod connection weak. The flywheel provides the resistance and all the power of cylinder 4 is transferred there. With a cracked surface contact area, extra wear is occurring and it's probably getting hot enough to cook the oil. Eventually, the crank would have worn out the bearing enough where it comes loose and would start knocking or rattling. By catching this early, you saved your rod and potentially your block.
Is the flywheel to the right of picture? I think the oil hole is too big and integrity was compromised. And is this the same types of failures on all the cranks?
Last edited by 2006EvoIXer; May 3, 2018 at 03:08 PM.
Go with an Eagle or K1. I would also consider going to a 94mm stroke. The crank flexes a lot less, and is therefore less prone to cracking.
Looks like the Manley billets crack just like their forged pieces though.
billet and forged versions look like they have the same oil port in cylinder 4 rod connection. Do you have a photo of Eagle's #4 oil port for us to see how different they are?
I just remembered that cylinder 4 gets more air than others because it's intake runner is closest to throttle body. This make things worse at crank since it will usually make more power from running leaner than others.
Manley crank and K1 are made in China, but so are many other parts, such as compressor wheels used by well known turbo companies, and even oem parts used by car manufacturers. The fact that something is made in Chine does not mean that it is necessarily of low quality, it can be yes, but it is often not the case. It's all down to what you buy from which Chinese company.
For the record, K1 cranks are better than manley, higher quality casting and forging processes, more precise tooling, higher grade alloy. I have yet to see a K1 crank crack. Oem 4g64 crank is of very high quality in all aspects, it can certainly take 700+whp. The 4g63 one has even higher fatigue and torsional stress resistance which makes it able to handle an excess of 1000whp.
Are you BS delete? Just curious. The topic has been of interest to me after reading the "White Paper" from Jacks Trans
Heres an excerpt / Pasted here:
Imagine the forces the crank has to endure at high RPM. Lets say you are zinging your engine up to 8000RPM. At that speed your crank is twisting forward and back 133 times a second!! This whip is not gentle either, it's like a large hammer beating on your drive-train 133 times a second. When we think of what a crank is going through at high RPM, we think if just how fast it is rotating and how amazing it is that it can hold the power which we are forcing through it, but that's not all. It is also flexing and twisting while it is rotating and 133 times a second at your 8000RPM rev limit. It's something our minds just can't comprehend. This whip creates a series of problems for us.Torsional whip is very destructive. Bolts will work their way loose in various places, you get a buzz from the engine, clutches drag and break, crankshafts break
The cause for cracking is completely unrelated to balance shafts being removed. If lack of balance shafts caused cranks to crank then you would see miatas breaking cranks left and right, but they don't. Mitsubishi also wouldn't sell balance shaft delete parts if it would cause harm to the engine.
Manley themselves have said the issue with their cranks cracking is because how they have the oiling hole drilled for the #4 rod.
The cause for cracking is completely unrelated to balance shafts being removed. If lack of balance shafts caused cranks to crank then you would see miatas breaking cranks left and right, but they don't. Mitsubishi also wouldn't sell balance shaft delete parts if it would cause harm to the engine.
Manley themselves have said the issue with their cranks cracking is because how they have the oiling hole drilled for the #4 rod.
this crack is from twisting. It is a diagonal fracture. And the damper is on the other end of crank, so that wouldn't help much. What will help is a softer sprung clutch (which is similar to a damper itself). If you have unsprung or puck clutch with a heavy rotational mass, you're asking for this oil port to crack. I'm not discounting that damper on other end wouldn't help since it can reduce some of the harmonics when the biggest stress hits that oil port area.
BS will help with the vertical vibrations getting to the flywheel. The frequency will be double the RPM, so what ever your normal driving RPM is, your exposing 2x the RPM in vertical vibrations.
I just remembered that cylinder 4 gets more air than others because it's intake runner is closest to throttle body. This make things worse at crank since it will usually make more power from running leaner than others.
