Flathead Engine Balancing-"101"

[flatrod]

Gary, I don't see where you have a space for oil on your balance card. As John said Merc cranks can hold as much as 8 grams of oil in the journal. We normally use 6 grams of oil on our balance cards for most all cranks.

[Brian]

Jack E/NJ, Like our most learned scribe 'Bored and Stroked' explains here; http://www.jalopyjournal.com/forum/t....862832/page-6

[russcc]

Very informative. How is the pressure plate balanced, with or without the flywheel. have one in an engine shop right now to be balanced so I would like to get up to speed. Seems to me they wanted North of $150 to balance the flywheel and pressure plate. Plus $60. to resurface the flywheel. Thank you Fordbarners.

[revkev6]

one question i had was in relation to a comment that B&S made during his build of the 99 block he has. what are engine builders doing for the floater bearing rods?? do Any of you specifically ask about how they are finishing the ID of the big end of the rod as a bearing surface??

[flatheadmurre]

Bearing surfaces and honing is a big can of worm to open up...
You should really specify a desired surface finish in Ra....but Ra is an average meaning you can have 9 shallow and 1 to high spot...leading to that you should specify Rk and Rz to.
Wow that was a boring hord of symbols..lol
Sum is most non flathead shops don´t realise it´s a bearing surface...and how many shops actually has the ability to test the surface...
For compairsion a inserted rod needs a Ra of 50-80 but the crankpin bearing needs something in the Ra 10 range.
Rz of about 50 for a normal car value goes to half for a performance crank.
Im not the best tutor so sorry if your falling asleep.

[Tim Ayers]

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This is a great discussion and once again proves that are many ways to skin a cat. I never thought of factoring in oil weight into balancing a crank for 8 grams of oil seems like it could throw off the dry measurements somewhat.

I guess there are two schools of thought...

One, like my father, who believes these engines are just a step above 8 Briggs & Stratton engines cast together.

Or, others like B&S & Ronnie the Roadster, who go all out to squeeze every possible ounce of performance out of these beloved engines.

That said, my father's stock build flathead has been running well for over 40 years in his '32. As much as he raises an eye brow when I talk about all the things I'd like to do, I'm leaning towards the performance camp in that I want to get all I can out of my motor while having it stay together for a long time.

[GOSFAST]

Originally Posted by Ol' Ron

I was told once by a NASCAR engine builder, that piston weight was not as critical as rotating weight, and several formulas have different percentages for BoB weights. I still think your putting to much emphfis on the balancing. I think you can't make a silk purse from a sows ear.

You all need to listen to Ron here, this statement is 1000% correct. If you were to contact my friends down at Federal-Mogul they will verify the fact you can change a set of pistons with as much as a 30 gram spread from the original's and all will be fine, no re-balance needed. Way back when I was with Chrysler we would open many 100% original units (both SB's and BB's) and find as much as a 40 gram spread between the 8 rods in the same set. And this spread was found on the big-end's (rotating), not the pin-ends (reciprocating)?

Originally Posted by Brian

Gary, In that 1st photo, showing the rod, it appears the big end of the rod has been lightened by machining the ribs at the bottom of the cap off straight across. It is my understanding that that is the incorrect method by which to remove stock from the cap. Please explain, thank you, Brian

Originally Posted by Jack E/NJ

>>>It is my understanding that that is the incorrect method >>>
What's your understanding of the correct method? Jack E/NJ

(Ans) Both above, we still get many of these rods in the door already done, the one in that photo was one, actually many years ago we felt comfortable "trimming" some off those stiffeners but eventually stopped it, was really unnecessary.

Originally Posted by flatrod

Gary, I don't see where you have a space for oil on your balance card. As John said Merc cranks can hold as much as 8 grams of oil in the journal. We normally use 6 grams of oil on our balance cards for most all cranks.

(Ans) I've never factored in oil weight, it's not necessary in my opinion. Read the "P.S." below, it WILL explain why! The Flathead may be the only unit on Earth capable of "holding" 8 grams of oil in the rod journals and again, based on the weights of the Chrysler rods above here, we consider even 8 grams a "non-isuue", With respect to all "aftermarket" cranks, these fall into a separate category and MUST be run up and usually need some amount of correction. (During running the shaft up 8 grams here would get corrected, but would also in no way would be detrimental to the build if left uncorrected)

Originally Posted by russcc

Very informative. How is the pressure plate balanced, with or without the flywheel. have one in an engine shop right now to be balanced so I would like to get up to speed. Seems to me they wanted North of $150 to balance the flywheel and pressure plate. Plus $60. to resurface the flywheel. Thank you Fordbarners.

(Ans) Hi Russ, above I mentioned we balance the flywheel/pressure-plate as a single unit. First, balancing a flywheel (whether or not the plate is mounted to it) is considered "single-plane" balancing, making it acceptable to do both pieces as an ass'y. They MUST be indexed however so they are installed in the same position as they were together on the balancer. I mentioned above my reasoning for this is it avoids any unnecessary drilling (nearly impossible on plates) or welding. We choose this method on all our independently balanced units. It is OK to do it either way, I have no issue with either. I will add this, it is less labor-intensive as a single unit which technically should be reflected in the cost to balance. A very fair price to balance both pieces as a single unit should be in the neighborhood of $100.00/$125.00 (we average the lower). Refacing the wheel would be add'l, probably be in the $50.00/$60.00 range We are at $50.00 for refacing most wheels here.

I do my best to keep ALL this info as accurate as possible, at least with respect to how it's all done here! We CANNOT send a single unit down the road (many out-of-state) and have even as little as a 1% risk of ANY failure/issue. This is the exact reason if I can't dyno any unit I build/assemble here I will not get involved. Just had this scenario up here with another member recently, an earlier "babbitted" unit!

(Add) One belief I have here is: "if it ain't broke don't fix it".

Thanks, Gary in N.Y.

P.S. I know many here won't really believe this but "technically" speaking you CANNOT balance any V-8's, all you can accomplish is making them reasonably "comfortable". Here's where the oil factor comes in, in the larger picture it makes no difference in the longevity OR vibration issue's. This goes directly back to Ron's statement above about changing a set of replacement pistons with different weights than the originals, but using the OEM rods/crank over. For us with 2 balancers we would correct this here, but if not re-balanced it would end up being just fine. You CAN "truly" balance any "opposed" units (Porsche, VW, Corvair, etc.), I believe (not certain) you can also "truly" balance "radial" units?. On most inline 4's and 6's there's no bob-weights required, we do run up these shafts ONLY to make sure they're OK, most are!

[rotorwrench]

It looks like those modern CWT machines take a lot of the guesswork out of the situation. I've never balanced a crankshaft but I used to work on the turbine engines which require balance checks any time the wheels are separated. The old Balreco machine I used back then was all analog with just an IPS meter and a strobe to get the clock angle. Wax was used to get the balance on both ends first then you weigh the wax and remove material from the 180 degree position. It took a while to get good with that machine. A guy had to be careful or you would whittle away too much and have to go back to the other side. Those modern CWT machines look impressive in their adds. They even have the drilling rig right there.

PS: we never got any of them to "0 IPS" (zero imbalance) but we got the close enough and I think better than they were when they came out of the factory in many cases.

[GOSFAST]

Originally Posted by rotorwrench

It looks like those modern CWT machines take a lot of the guesswork out of the situation. I've never balanced a crankshaft but I used to work on the turbine engines which require balance checks any time the wheels are separated. The old Balreco machine I used back then was all analog with just an IPS meter and a strobe to get the clock angle. Wax was used to get the balance on both ends first then you weigh the wax and remove material from the 180 degree position. It took a while to get good with that machine. A guy had to be careful or you would whittle away too much and have to go back to the other side. Those modern CWT machines look impressive in their adds. They even have the drilling rig right there.

PS: we never got any of them to "0 IPS" (zero imbalance) but we got the close enough and I think better than they were when they came out of the factory in many cases.

Hi "Rotor", exactly correct, the CWT will give you ALL the numbers, how far "out-of-balance" the shaft is, exactly where the correction will be needed, and the amount of correction, drill or fill. All in a matter of a minute or two.

The Stewart-Warner works like you describe above, but we use "clay" on the counter-weights to get it sort of "dialed-in". It does have the meter but this basically tells you where the correction is needed, uses a "strobe" light! This is why I say the CWT really cuts the checking-time way down. We really can't do any strokers on the Stewart-Warner machine (strictly due to the time involved), we did at one time but that went away with the CWT!

(Add) On a side note, I put a shot below here of a "real" heavy-metal job on a BBC shaft we converted from a "dependent" to "independent" balance. It takes that many Tungsten plugs to go from a "dependent" OEM 454" damper to the "independent" 427" one! There's a total of 9 plugs (4 in the front/5 in the rear/photo below) in those counter-weights, all measure 1.000" diameter x 1.000" long. Each piece weighs 227 grams and our cost on the plugs alone is over $360.00 without shipping. With that price, the labor to install them, and completing the balance operation, puts a $1000.00+ price tag just for the crank balancing?? Also when installing ANY of these type plugs, they should be put in "horizontally", as seen in the counter-weights, NEVER "vertically"! The "attached" drill press on the CWT is of no value on this type job. This job would be all but impossible to do on the S-W balancer.

Thanks, Gary in N.Y.

P.S. Also, having that drill press attached directly over the shaft is "a blessing & a curse" at the same time. It can turn into a real headache if you aren't VERY careful. It's very easy to get a "chip" (when drilling) caught between the main saddle and the "shoes". You won't know it even happened until you see the large "scratch" show up on the main journal. I make sure when drilling, BOTH ends of the shaft are covered over, the #1 and #5 mains! Those drilling chips fly around pretty good! It's makes a real "mess" drilling some 1.000" diameter by 1.000"+ deep holes in "4340" steel!

[jake197000]

jwl,where are you adding the 8 grams for oil? in the big end weight ?

[Ol' Ron]

It's a BLACK art!!!

[JWL]

Jake, yes.

Perhaps I am more discriminating, than necessary, in my approach to setting things "right" within a engine. But, I don't think so. Even when we get all the characteristics as close as we can it is never "perfect".