weightless crankshaft

[AWD-TSI]

So like the title says, Has anyone had any experience with or has used them? Im gonna build a 2.1 destroker and was wondering if anone has anything good or bad/ pros and cons to say about these. The ones i have seen are from jacks transmission.

www.jackstransmissions.com



Thanks again

 

[jdombrow]

I was thinking of running this on my car along with dsmlinks nlts to keep the revs in the right place. whats everyone think?

 

[TastyTalon]

I have read awesome things about these cranks, I think you should run it and then post up and tell us what's up firsthand. gl.

 

[AWD-TSI]

so i have the funds to continue with my build. But am at a crossroads. Do i purchase the crank and run the risk of destroying my motor or not. Or just get it dead nuts on the balance?
oh BTW im gonna run a 2.1 destroker

 

[Rob10_99]

Might as well giver a shot!

 

[spoonman]

I would really like to see a dyno/quarter mile comparison between a weightless crankshaft engine VS a properly balance crankshaft. I really do not think that the removal of the counterweights will net that much power if any, I have seen a car on the dyno running an aluminum crankshaft pulley and then switched to an aftermarket ATI harmonic damper and the extra 25-30 pound harmonic damper actually made more power in the higher RPMS and the Torque curve rose and peaked later in the RPM's. The justification for why the ATI damper made more power was not because of the added weight but because there were was considerably less degrees of crankshaft distortion due to torsional vibration.



As long as you have idle control of any kind the engine will stay idling, I am sure it will be a little weak at idle due to the low RPM's and the crankshaft not having as much inertia.

 

[tkelly27]

As far as torsional systems go, a mass can't act as a damper. It can only resist motion. It's also the job of the flywheel to store mechanical energy, and it would be a lot easier to make a heavier flywheel than to add complexity to the crankshaft.

Where does the main bearing loading come from that wouldn't otherwise exist? All I can really see is that the couple moment goes away during angular acceleration, but there is a really unbalanced moment during every power stroke that the mains must take up no matter what.

I feel like I'm missing something, they wouldn't just put them on there if there wasn't a point. I normally agree with pboglio, but I've never seen a non V style formula engine, and the V layout requires balancing.

 

[1gDSM4g63]

This is from Butcher crank. Safe or not?.

My cousin has it in his car, I built the engine and tuned it, honestly I didn't notice anything negative or positive. I'm sure less reciprocating weight is good, but I didn't notice any quicker revs or stalling because of the weight loss.

 

[420a_turbo]

So the site has finally made me feel like a noob.

I don't understand. I have built several motors, all with stock cranks, eagle rods and JE pistons. I have always bought balanced rods, or they claim to be within .01 g of the same weight. Anywho, I have never taken my lower end to be balanced, and have run 30-40k miles without any issues depending on which motor. Only one ever broke, and it happened in less then 3k but that was due to waterI sucked into the cylinder not anything else. I pulled the pan and checked my bearings when I crossed the 40k mark in the oldest build I have and everything still looks brand new. I suppose I only checked the bottom half of the crank, but both on the rods and all was well. I will be doing this on another motor in about 8k miles, but on that motor there is no obvious issues either.

So anyways, is this some unspoken rule of thumb sort of thing to have done on every build or a preference thing? Or is getting everything balanced for people making huge power? Or have I dodged a bullet by using good parts and a stock crank? I guess I dont understand. I mean I get what everyone is saying, I understand the science to it, but is there any obvious reason I have never had an issue with balance in the motors I have built?

Thanks for the help
-Justin

 

[4g64fiero]

Its a way of double checking the factory balancing on aftermarket parts.

I dont have a way to do it so I dont either. Never had a problem as well. Then again, I never rev past 8k.

 

[MOTOR-RX]

I will be starting a build here very soon for my GVR4.

i am going to try a weightless crank.

I am going to be a 2.3 l

We will see what happens.

 

[420a_turbo]

Its a way of double checking the factory balancing on aftermarket parts.

I dont have a way to do it so I dont either. Never had a problem as well. Then again, I never rev past 8k.

Hmmmmmm

Me either, usually dont push past 6500 ish when really stomping it, and she keeps around 3000-4000 for normal driving... Maybe thats the key... Who knows, atleast Im not the only one

 

[donniekak]

I am curious to see if a weightless crank, with a lightweight flywheel, will cause valvetrain problems.

 

[brownfinger]

I just got a huge kick out of this thread. Admitedly, 50% of it was the video clip of the F1 car. At first I thought I could resist it. Then I thought I could stop it before watching the whole thing. Then those headers started glowing! Soon I was wearing an ear to ear poop-eating grin! Anyway, there is always controversy on this topic, CW vs. non-CW. It's all-over in the air-cooled VW scene. Stock had no CW. Almost every modern build uses a CW crank. Drag engines use knife-edged and non CW cranks.
The stock crank is part of an engine that is designed so your mom can drive to get groceries for 200,000 miles without a rebuild. I don't think anyone's drag engine needs to meet those criteria.
I think it's paranoid to suggest that the crank will fail or the bearings will be ruined. It's just that much less rotating mass resisting acceleration. Sure would be a waste of time and money on a DD, though.

 

[tkelly27]

http://www.gurneyflap.com/Resources/BMW engine2.jpg

So that's an inline 4 for a F1 car and it has counterweights. Butcher style, but they exist. I've been meaning to do a free body diagram of the forces on the main journal, and also figure out how much energy it takes to get a weight like that up to speed to see if it is even significant in comparison to the energy required to move a car, but I haven't had any time.

 

[Defiant]

I am curious to see if a weightless crank, with a lightweight flywheel, will cause valvetrain problems.

How do you imagine they could possibly be related? Seriously.

 

[donniekak]

How do you imagine they could possibly be related? Seriously.

It is well known in the engine building community that a heavier flywheel and damper reduces the likelyhood of valve float. A crank shaft spinning at 6,000 rpm's is actually rotating much faster than that when the charge fires. 6,000 rpm's is just the average speed. A heavy flywheel and damper dampens the pulses to produce a more uniform rotational speed. The smoother the rotation of the crank the smoother the rotation of the camshaft, and lowered is the likelyhood of the valve/rocker assembly losing contact with the cam.


Have you ever seen camshafts operate under a strobe? The pulsed force transfered to the cams from the crank adds to the torsional distortion of the camshaft. The end away from the gears will lag several degrees behind the driven end of the cam, and then whip back, very interesting video's.

 

[Defiant]

Sounds like cam-in-block V engine characteristics. I can't envision a foot of timing belt transferring that kind of shock, nor can I see it being more force than the followers exert at their contacting lobe. However, this cam windup is the reason the timing belt is more prone to fail during engine startup or at idle, when the most follower force is present on the lobes.

 

[Lofty]

I can't imagine valve train harm with a setup like this.

They make timing belts because they are elastic (To a point) and depending on how you look at it, they are stronger than a timing chain because with belts they don't have chain shock or anything of that matter.
But this is all hypothetical, I could be completely wrong.

 

[e85_4g63]

What ever happened with these cranks? There is no listing on there new website for them? Special order maybe?

 

[Rob10_99]

Lack of sales?

 

[tkelly27]

After looking at this, I think I see a point to counterweights, but I'm not convinced it's that big of a deal, although it probably could be. It's also not a balance, or a torsional vibration issue as long as the counterweights are all the same size.

A four cylinder is always in primary balance, as there is always an equal and opposite mass at the same point in rotation regardless of counterweight, rod, piston, etc. size. As long as they are all equal from one cylinder to another, it is in balance.

To damp a vibration requires a DAMPER. Adding material to the crankshaft adds to damping about as much as adding material to the flywheel or rods. The steel in the crank acts as a spring, and as such has a minute amount of damping, but requires a true damping system.

Because the crank is always rotating there is an inherent force on the pieces spinning from it caused by centripetal acceleration. Without counterweights there is only one going one direction per throw, so if you are facing the crank snout on it will be a radial load, with 1&4 going one way, and 2&3 going the other way. When viewed from the side it would make the crank look like it was smiling. If it was dramatically bent, the crank snout would go up and down, but this load is static (aside from the fact that it increases with RPM) as far as the crank is concerned and would not cause damaging harmonics.

The other thing is that the crank is designed with this type of loading in mind, because it's the same kind of bending that occurs during the power stroke. The bearings are also designed to handle this kind of load, and I think it pales in comparison to the power stroke, and the piston/rod at peak accel/decel. With the stiffness of the crank and 5 main bearings, it doesn't seem like it should ever be an issue.

As for me, I'll be keeping my counterweights, only because I can't afford to loose them, and I'd like some other rich sucker to prove me right or wrong by breaking their own : D

 

[e85_4g63]

Has anyone emailed Jack to find out why these are no longer on the website? I'm just curious.

 

[juvi1624]

I talked to him earlier this summer about them and he was still doing them then. He seems to like them, but I talked to a shop in Florida that builds nissan motors(I know, apples to oranges) and they said they have tried weightless crankshafts(and Nissan's counterweights are waaaaay bigger than ours) but saw no noticeable gains. That said, it appears to be an unnecessary risk and I decided it wasn't for me.

 

[pboglio]

I wouldn't do it on my car. The opposing cylinders may help counteract the inertial loading, but they are not in direct line with those cylinders needing counterbalancing. I'd rather have a counterweight nearly directly inline with the piston/rod assembly than count on a piston/rod assembly a couple inches to the side doing it. This is what increases bearing wear IMHO. I don't think its an all or nothing affair, as it is discussed quite a bit as a design tradeoff. Anything that sees high mileage/high rpms I'd avoid this thing like the plague.

 

[dsm-onster]

Amen!

The primary vibration is canceled because the total mass counters every revolution. But the way the vibration is countered is what the issue is. The center two pistons go down when the outer two go up. Jumproping is something left at the playground when you were 15 years younger. Not now when you're trying to build a motor that moves at 8500rpms where less reciprocating mass begins to show decent gains.

I'd like to see live a stroker setup with this done after some abuse