B18-B20 Racing Crankshaft Balance

This B18 crankshaft which is going to be used for vintage road racing on a variety of different tracks and hill climbs after it is ground and re-balanced.

The standard rod journal dia. is 2.135 but it is going to be ground approximately .246" to 1.889" and Carrello connecting rods with a Honda Clevite CB1663 (or possibly a 1.850 Clevite CB1798) rod bearing are going to be used. The grind will remove some weight plus the rod bottom end will be smaller, narrower and lighter and will have only about 380 grams of rotating weight.

Photos found of other Volvo racing cranks show counterweights that have been lightened considerably. I would like to cut down the counter weights here on our heavy-duty lathe (balancing shop does not what to do it because of only having a light weight tool room lathe.) to above the final finished target weight before it goes out to be ground and balanced. This will end up leaving a lot less time spent at the balancing shop and in overall time it can be finished faster this way (spring is on the way). Also will round off or knife edge the weights in the milling machine.

Can anyone give some guidance on how to approach this project and would it be better to narrow the counterweights, which has been done in the past, or take it off of the OD of the weights assuming it can be balanced if it is done that way. Looking to have it run as smooth as possible in the 2500 to 7500 rpm range.

vintagewrench said:

(balancing shop does what to do it)

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I'm a little confused, did you leave something out? They want too much money? Or they do NOT want to lighten it?

I have opinions on this, based on first-hand failures at this ordeal.
Either find someone who has lots of experience, or skip it and just balance it.
Short story, I broke a 4A-GE crank doing what you want to do, and the machine shop that was letting me use their huge lathe told me they don't see any advantage anyway (they build and race a lot of stuff, big and small). They prefer to lose the weight out at the perimeter of the flywheel, where it matters. After that I switched from the double-weight crank to a single-weight crank from a 4A-C, and felt no difference. Later I removed about a pound from the perimeter of the flywheel. I felt and measured a difference.

Always send all your stuff together for balance. Rods, pistons, flywheel, clutch cover and bolts, front balancer/pulley.

Alway heard knife edge would create less windage. Then balance the crank with rods, piston, rings and it will be fine. I can’t afford to race but always balance engine that I build.

mikep said:

I'm a little confused, did you leave something out? They want too much money? Or they do NOT want to lighten it?

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Sorry, I meant say: balancing shop does not what to do it because of only having a light weight tool room lathe.

The 22lb lump of a flywheel is being replaced with a 8lb Fidanza piece.

mikep said:

I have opinions on this, based on first-hand failures at this ordeal.
Either find someone who has lots of experience, or skip it and just balance it.
Short story, I broke a 4A-GE crank doing what you want to do, and the machine shop that was letting me use their huge lathe told me they don't see any advantage anyway (they build and race a lot of stuff, big and small). They prefer to lose the weight out at the perimeter of the flywheel, where it matters. After that I switched from the double-weight crank to a single-weight crank from a 4A-C, and felt no difference....

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^Yup. I looked into turning a b230 crank down, and all the engine builders I talked with said it?s a bad idea on a 4cyl that sees high RPMs. Secondary harmonics and crank twist are increased when weight is removed. The crank in the picture above is missing about half the counterweights a b21/23/230 crank has... I wouldn?t lighten it anymore than needed for balance.

Rotational moment of inertia formula has a r^2 term right next to the mass variable. Removing weight from a crank sees very little return, unless it?s grossly overweight.

culberro said:

^Yup. I looked into turning a b230 crank down, and all the engine builders I talked with said it’s a bad idea on a 4cyl that sees high RPMs. Secondary harmonics and crank twist are increased when weight is removed. The crank in the picture above is missing about half the counterweights a b21/23/230 crank has... I wouldn’t lighten it anymore than needed for balance.

Rotational moment of inertia formula has a r^2 term right next to the mass variable. Removing weight from a crank sees very little return, unless it’s grossly overweight.

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culberro thanks for your reply. Even though some b18-B20 racers are doing it I have also been advised not to do it on the Speed Talk forum.

Yeah, keep the crank as it is weight wise. You already have a super light flywheel. Why not check the driveline side of things weight wise ? Light shaft and all.

I assume you have lightweight pistons as well ?

Victorrr said:

Yeah, keep the crank as it is weight wise. You already have a super light flywheel. Why not check the driveline side of things weight wise ? Light shaft and all.

I assume you have lightweight pistons as well ?

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I have finally found the correct way to do it but its quite a bit of work. If the crank pins are drilled weight can be removed, although thin plugs much like a core plugs used on the side of the block have to be inserted in the hole to keep the oil from leaking out to the sides.

Then the counterweights can to be lightened to put it back in balance. The end result should remove a consideable amount of weight rotating weight near the outside of the crank where it is the most important. Thats going to have to wait until until the engine comes back apart after the season is over if it is needed.

In the driveline lightening the wheels, flywheel and clutch, the larger diameter pieces, pays the biggest dividend.

The pistons are going to weigh about a third or more lighter than the originals.

The photo above shows the crank as it is now after removing all of the stress risers and semi-polishing it while checking flywheel runout (8lbs the original is 22 lbs), and the runout of the center main bearing (only .0005) before it gets cryogenically treated and the journals get reground.

The rods (below) are also lighter than the originals, and the steel cam gear (only runs at half speed) has also be lightened (one pound) and balanced.

Wow, that's what I call pushing the limits !

I assume vintage road racing means you can't use anything but stock-ish/period correct parts nah ?

If it was me I would've turbo-ed the thing already ^^

That's some quality equipment btw

Victorrr said:

Wow, that's what I call pushing the limits !

I assume vintage road racing means you can't use anything but stock-ish/period correct parts nah ?

If it was me I would've turbo-ed the thing already ^^

That's some quality equipment btw

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Thanks, rod or rod bolt failure is probably the one only things that would cause one of these engines to blow other than a broken lifter or cam so we went with what many engine builders consider to be the best on the market. In doing so the result was ending up with a rod that is stronger and lighter than any of the knock offs on the market.

No rod failures means no ruined engines that are expensive to replace and time consuming. Spending the $$ up front means saving down the road...errr track.

Yes, due to the rules the engine size is limited to one .030" B18 over bore.

You can follow the project here.

vintagewrench said:

Thanks, rod or rod bolt failure is probably the one only things that would cause one of these engines to blow other than a broken lifter or cam so we went with what many engine builders consider to be the best on the market. In doing so the result was ending up with a rod that is stronger and lighter than any of the knock offs on the market.

No rod failures means no ruined engines that are expensive to replace and time consuming. Spending the $$ up front means saving down the road...errr track.

Yes, due to the rules the engine size is limited to one .030" B18 over bore.

You can follow the project here.

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"saving money" more like spending less ^^

That's a nice engine, I can already hear the thing screaming, It's going to rev easily. What do you plan for it fueling wise ? Dual Webers ?
Nvm, saw the thread - nice little car

It was common to narrow camshaft gear at 80's

OttoB said:

It was common to narrow camshaft gear at 80's

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Not a bad idea, as you know the gears are hardened and don't wear very much. Maybe I should fire up the lathe again and take some more weight off.

vintagewrench said:

I have finally found the correct way to do it but its quite a bit of work. If the crank pins are drilled weight can be removed, although thin plugs much like a core plugs used on the side of the block have to be inserted in the hole to keep the oil from leaking out to the sides.

Then the counterweights can to be lightened to put it back in balance. The end result should remove a consideable amount of weight rotating weight near the outside of the crank where it is the most important. Thats going to have to wait until until the engine comes back apart after the season is over if it is needed.

In the driveline lightening the wheels, flywheel and clutch, the larger diameter pieces, pays the biggest dividend.

The pistons are going to weigh about a third or more lighter than the originals.

The photo above shows the crank as it is now after removing all of the stress risers and semi-polishing it while checking flywheel runout (8lbs the original is 22 lbs), and the runout of the center main bearing (only .0005) before it gets cryogenically treated and the journals get reground.

The rods (below) are also lighter than the originals, and the steel cam gear (only runs at half speed) has also be lightened (one pound) and balanced.

Click to expand...

Just one question before I ask a whole lotta other questions:

Have you already bought those rods? What are the dimesnions?