Crankshaft lightening, photos...

[Lazy JW]

I read several years ago in the Farm Show Magazine of a couple who drove a later model two-cylinder John Deere tractor from the midwest to Alaska. They pulled a small camp trailer. This wasn't too many years ago, they were doing it more as a stunt than from necessity. Of course their rig had electric starter, lights, etc.

My wife's grandparents starved out of South Dakota and left in 1939 driving a Ford Model "A" and pulling a home built cargo trailer. Three small children, the oldest being my Father-in-law, he was about six. They worked their way westward, ended up in the Boise valley a year later. They often told of that journey, it really took a lot of courage. Grandpa couldn't have cared less how much the flywheel weighed on that Model A, he was just happy when it started.
Joe

 

[rmt]

I don't think that trip was as pleasant as it would first seem.... I'm sure it got nervous from time to time, as that was still rough country back then; Wyatt Earp had died only 7 years before. And the fact that the tractor wasn't trucked up to where he was tells me he wasn't made of money. Since it was the depression, all the way back he was probably wondering just how the hell he was going to pay for it...

Actually picturing that trip I was thinking of nice or hot California weather up to about Redding/Eureka, overcast and rain just about the rest of the way to Puget Sound like it is so often now. At that "speed" you could probably stay fairly comfortable most of the time. Most cars on the road in the tulies out West in 1936 were probably still Model T's and the like, wouldn't you think? The John Deere probably wouldn't have seemed nearly as different then as it does today. A little odd but not unreasonable. Just about everyone was a farmer, or had been.

When he got home his answer to every question was probably "What?" That bugger was loud.

The Burlington Northern came cross country right through the Snohomish River valley (where he lived) to Puget Sound. I don't why he had to go to LA to get it. Being the Depression, I always figured the guy had money just to get the tractor at all, then go down LA, bring it back (I imagine fuel was a little pricey in places along the way) and everything else that went with such an endeavour. He must have been known as the rich guy in the area.

I wish I had heard more of the story. It was one of those things we hear of now and just find incredible.

And to think he did it with out lightening his crankshaft.

 

[Anonymous]

Maybe we really need an enlightened crankshaft....

 

[StrangeRanger]

Isn't an enlightened crank a bit of an oxymoron?

 

[Anonymous]

....intended !

 

[STEVEN.]

Back to the 'ole grind,then... . ~OO6.

 

[StrangeRanger]

Miss Quote, nice to see you here at last.

 

[Anonymous]

I spoke to the guy who does the balancing at my local machine shop today about the lightening method from the first post (trimming the edge off the counterweights) and he flat out said dont do it because as he put it, the counterweights are there for a reason and if you take to much off you need to add plugs to bring the weight back up. He was busy so I didnt have a chance to pick his brain, but it has always been my understanding that with the inline 6 engines (unlike most other layouts) that the counterweights are not there so much for balancing, more to reduce flex and add some flywheel effect.

Is he right - if you only remove metal from the counterweights are you going to turn a crank into a heavy paperweight?

 

[Anonymous]

Anybody?

I have a 12 counterweight 4.0 crank here that I am 1/2 way through and dont want to spend any more time machining if its not going to work anyway.

 

[Lazy JW]

... dont do it because as he put it, the counterweights are there for a reason...

The reason the counterweights are put there is for smoothness and longevity. If you are going to run circle tracks then it may be worthwhile to remove them to increase acceleration out of the corners. Every engineering endeavor is a compromise. I wouldn't even consider this for a daily driver, possibly for a street rod though.
Joe

 

[Stubby]

If everybody is scared of it, I'll take it. I can't pay much, because I can do it myself.

In the pic, it doesn't look like you have taken too much. How much have you taken off of the counterweights? If you drill the journals and profile the throws, you might be able to have a lighter crank that is still ballanced fairly well.

 

[Anonymous]

I have taken 9mm from the outside of the counterweights (I estimate nearly 2.5kg worth). The plan was to now deburr and reshape the rest of the counterweights and the throws. You can see here roughly how much was taken off

I have never touched the cranks in the engines I have previously built because they say 95% street use. This engine will be 95% track, so lightening the crank makes sense. These 94DA fully counterweighted cranks are particularly heavy, around 3kg more meat on them than the earlier and later models. It would have been easier just to throw in an EA crank but I had this one lying around and it has been an interesting exercise so far.

In this crank here I see lots of metal removed by undercutting the counterweights (not sure how effective this would be in reducing the moment of inertia so close to the centerline), and also some off the throws and drilling the journals. I was not planning to machine my crank to this extent but it has made me think.

I guess the questions I have that I am still unsure of are -
Do you aim to try to match the weight taken off the counterweight to the weight taken off the throw, or can you just take the easy way and cut the counterweights?
how much metal should a person aim to take off? It seems to me that around 3-4kg for a street/track to 6kg+ for a race engine is what most people talk about.

Stubby I am in the same boat as you. I wouldn't be paying somebody to do it bust since it only costs me time Ill experiment a little. Its just working out exactly what to do that is the problem - so many different opinions (of contradictory).

 

[Stubby]

I didn't have time to reply this morning.

What kind of track? Dirt, pavement, short track, long straights, momentum track where you get up to speed and hold it there?

Working range, from xxxx rpms to xxxx rpms.

Trans? Five speed where it will be constantly running up and down thru the rpms?

I have always been fairly conservative when it comes to cutting counterweights. From the pics, I don't think you have hurt it. As far as the dynamic thing goes, if you will be running lighter than stock pistons and rods, then you have possibly helped it.
On dirt motors, I have seen some wild jobs. Some of the Pinto guys used to cut all of the counterweights off. I, like your ballancer guy, always said don't do it. However, I have not seen any real reliability issues.

I have seen some other issues that can possibly be linked to extremely light cranks. One is the timing chain. I have had engines brought in for a freshen up and the double row Cloyes True Roller chain had the center link broken. I have also seen this on other dirt motors but mostly on lightened cranks. This can also be related to improper damper for the application (read Fluid Damper) Which is closely related to dampening effects of the counterweights. This could be the timing chains, but I suspect the cranks are agravating the issue. I wouldn't call it unreliable, these engines had a full season on them of a minimum of 500 to a maximum of 1500 race laps on a 3/8 to 1/2 mile dirt track. The 3/8 is a momentum track, you get up to speed and with the wide sweeping turns the rpms stay up high. These cars spend a lot of time in a certain range. The 1/2 mile track has long straights and adds some revs but is similar. I haven't seen this on the 1/4 mile tracks. These guys are pulling less gear and the revs go thru the range very quickly.

I had a Ford customer who backed his car into the wall with a lightened crank. He wasn't used to the extra engine braking and while trying to dial in the front to rear brake bias, he locked the rear tires and the car was sideways before he could get off the throttle, causing the engine to die and he was just there for the ride. If you choose to use this crank, remember all of the little things it affects. On a road race car, it will help save the brakes.

I would probably drill a 3/4 in (19 mm) hole in the rod journal. If the placement of the oil passage allows it. Then I would profile the rod throws. Follow this with a full grind and polish of all the rough casting and shot peen.

I suppose a guy could get down the nitty gritty if he knew the original ballance parameters. Break it down to a one cylinder. Maybe take a bad crank and cut it off at the back of the second main journal, then face it off smooth. Take it to your ballancer guy and have him find the proper bobweight for it. This would be a time consuming project. It would be made easier with a digital ballancer. Spin it real slow and measure the imballance. Build a bobweighht and install it, spin it a little faster, and fine tune the bobweight till it spins in ballance. Then you could compare the bobweight to the weight of the OEM parts and arive at the original percentage.

Now this is where it gets funky. A one cylinder engine is balanced to different percentages for different applications. If your ballancer guy does carts, Jr Dragsters or lawnmowers he can shed some light on the differences. Then you could decide on the proper bobweight for your application based on the weight of the new parts (ground, polished and shotpeened rods, and new light weight forged pistons). As for the dynamic ballancing? This crank was designed to offer a smooth cruise in a passenger car not for acceleration. Granted, the factory system will give the most longevity, it is not the best for acceleration. As with other performance gains, you have to decide how much you want to give up and how much you want to get in return.

Now take the one cylinder crank to your handy mill and drill the rod journal (remember, the hole you drill will have to be angled like it would be on the middle journals of the six cylinder crank) then mill the profile on the rod throw. Follow this with a full grind and polish of all rough casting. This will have reduced the need for counterweights to get the same ballance. Install the new bobweight and spin it slowly on the ballancer, take it out and mill the counterweights down a little, repeat this process till it is ballanced to your liking. Now you have a pattern for modifying your cranks.

I have also seen V8 engines overballanced for getting off the turns better, but that is a story for another day. Think about that word, overballanced, that doesn't meen heavier crank but it does meen a heavier counterweight than needed for a smooth engine. I think some of the fuelers run overballanced cranks. Not a problem with their budget.

When I unpacked a brand new Hines Digital Ballancer, I thought it would be a simple thing ballancing cranks. I opened the book and it explained the THEORY of ballancing engines. We spent thousands of dollars for a machine that will measure a tenth of a gram on the counterweight and the book talks about the theory. I miss that machine.

Print this out and have your ballancer guy read it. If he is anything like me, he will probably work with you and explore this project for the education.

 

[Stubby]

I would cut the profile along the lines. Just level it out from the bottom of the counterweight to the top edge of the shoulder on the rod journal and mill it. This will result in the throw being tapered from the main to the rod.

You might want to drill the journals first. If you want to persue this further, let me know and I will draw up a diagram of my setup for drilling the crank.

 

[Anonymous]

Top stuff stubby, given me more to think about. I think I will follow your advice, drill the journals, shape the throws, and finish up with polishing before sending the crank off for the rest of the work.

Swamped at work at the moment so I probably wont get the crank back on the mill until this weekend. If you could sketch up how you go about drilling the journals that would be very helpful.

Will post more progress pics when the work continues.

 

[Stubby]

These are just a couple of quick ideas. The top of the page would be a V block. The E shaped thing is what I was considering building for a drill press.

When I drilled cranks, I would bolt a plate of aluminum on the table and let it hang off the back of the table. I would the hang the crank on the plate and clamp it down. This was easy on V8 cranks because the counterweights are fully machined allowing me to slide the first counterweight onto the plate and let the crank hang from there. Then I would swing the head around on the Brigeport mill, align it, and drill it.

On some cranks, I had difficultiy aligning up for drilling and often thought about making a V block so I could setup on the journal and simplify the process. This would also make it possible to repeat the setup with accurate results.

The other images are an idea I had to do this on the drill press.
It is basicly, three V blocks welded to a support. It should bolt down fairly rigid and allow you to turn the crank for drilling the top three journals then flip the crank and drill the other three journals. One or two of the V blocks would need to be located for the thrust journal (depending on thrust location). This would help on repeating the setup. The jig would also have to be moved between top and bottom holes, because the offsets for the oil holes are reversed when you turn the crank over.
I was also thinking about building a support with a drill bushing that would clamp to the post on the drill press. This would possibly allow drilling the angled surface without having to pregrind the angle.
This was a thought to move this operation off the mill and increase production or profit.


The tricky part is the location of the hole in the rod journals. I think I used to use .200" or 5mm as a minimum thickness. I have seen SBC Chevy 400 cranks with .156" thickness. You also have to consider the location of the oil holes. On most cranks this meens the hole will need to be offset. The next image is what I used for the offset.



I would make these out of business cards. The offset is cut into the card and you can hold it to the crank and locate the bit. I would feed the crank into the bit while holding the card and when the bit started hitting the card, I would back of a little.
Then you will install a rod thru the oil hole and visualy locate for oil hole clearence. With a little patients and care you will sucede. I usualy drilled the journals first incase I drilled into an oil hole. I never did, and if you have been doing machine work long, you won't either.

The next challenge is the surface you will be drilling will almost always be angled. This will make the bit walk towards the outside of the journal. You can mill the area where you will be drilling while you have it in the mill, grind it by hand or any other method you feel comfortable with. Of all the cranks I have done, only one had the bit walk off to the point where I felt it was too thin. Keep an eye on this area. You cannot undrill it.

I used several different types of bits. The best were two jober length bits, a 1/2" split point and a 3/4" or 7/8 " homemade coredrill. I used my crank grinder to grind a pilot and recut the edges myself. A storebought coredrill would be even better. For the second hole down, I had to make an extension for the bits. I made more bits and inserted/tack welded them into a piece of drilled and reamed 3/4" cold rolled steel that had the end turned down to fit the drill chuck. If I make more, I will just use collets.

Now, if I have led you into confusion, don't feel bad. I am not a writer. This should give you something to think about. If I can clear anything up, just ask.

Your profile is vague. Where are you? What are we building?
And, welcome to the forum.

 

[Anonymous]

Thanks again, I am sure the info will come in handy.

I am in Adelaide South Australia. The engine this crank is going into is a 4.0 SOHC from a 1994 falcon. The block is bored ready for 20 thou over ACL race series pistons on prepped 5.88" factory rods (although this is likely to change to 6" before it gets bolted together). Other parts in the shed waiting include a 94da head that has had a good going over (flowed 244cfm by 450 thou lift) and a new cam (around .560" and 230@50). I will leave fuel and spark control to a Megasquirt 2 since I have played around with them for some time now.

The engine will be fitted to a '86 XF falcon for now (dime a dozen over here). The car was a EFI 250 Xflow, borgy 3 speed, 2.77 rear end. I have rebuilt the diff with 3.9 gears and have a T5 here ready to go in behind the 4.0.

The car is being put together basically from parts I have lying around. I have no specific class of racing in mind, more to satisfy my own curiosities and give me a good platform for further r&d on these engines. I have the Adelaide International Raceway and Mallala Motorsport park nearby so plenty of opportunities to try my hand at different tracks and styles of driving.

 

[Anonymous]

Looking at the rigs you posted I thought about drilling flat to the angle of the outside of the throws meeting in the center to look like this

instead of the usual way I see it done

By chance this morning I tripped over an old 250 crank and noticed that its throws were drilled, angled downwards perpendicular to the face as well (never taken any notice before). The holes are deep but dont go all the way though.

Drilling the 4.0 crank like the 250's is trivial. Any reason not to go this way? Would drilling from both sides be worth it (like the V in the first pic) or is this likely to compromise strength?

 

[Stubby]

The weakest part is usualy where the white line is. I don't think you will hurt it either way. Remember, the farther from the centerline you drill, the more effect it will have. Also, the farther you drill from centerline, the less counterweight you need. 8)

This would require long bits to drill straight holes. The factory probably drilled angled holes for speed and reduced tooling cost. The angled holes would remove a little more weight but it would be closer to centerline. Descisions, descisions,

If you compare te overlap of the rod journals and the main journals you will notice the shorter strokes give more strength due to increased overlap.

Remember to keep an eye on those oil holes. When you flip that crank over the holes will be offset the other way.