Engine and Transmission Tech

I had a very interesting conversation with my engine machine shop owner. His shop has been around for a very long time, third generation. He builds many race engines as well as custom work. I asked him his opion on balancing. He said if you are building a race engine for very high rpm applications then yes it is criticle. However if you are building an engine for street use nothing too hot which would not see alot of milage sometimes balancing may not be required. He showed me an engine he was working on, a Ford 302 that had been bored .20 over. The new piston and ring set with the rod installed was less than 2 grams heavier than the original. He told me factory tolerences are balanced to less that 2 grams. This new piston would have fallen within factory specs. He said in this case if money was tight it would have been better spent on rebuilding the rods. When the engine was done I was there for the dyno run it was very smooth all the way to 6000 rpm. Now he did hedge his bet that each engine is unique but if careful measurements (weights) are taken sometimes money can be better spent.
Has anyone else run across this before? I know the hard core racers wont agree but I would be interested in the groups opinion.
Thanks,
JB

He's got a good point about not really stressing an engine that isn't going to rotate much faster than 5K.

I always balance any engine I rebuild because it can't hurt to get the best case scenario right off the bat. Your hopefully only going to have to be in there once. Might as well have it done. Then again it isn't necessarily cheap.

That said definitely get the engine blueprinted. Perfect tolerances will make a difference on any engine. SO you could save your money for that.

For me I would balance anything I built.. Balancing and tolerances go a long way toward longevity of an engine as well as performance..
It always amazes me the amount of money a guy would spend on parts only to skimp on something as relatively inexpensive as balancing.

Well, you know, it really depends on your budget. There were plenty of times when I was younger and needed almost all the money I could get my hands on for critical expenses like bar nights and albums and a cheap rebuild was the only rebuild I could afford. Things like magnafluxing, align boring and balancing were just luxuries I couldn't manage, and I figured (with some degree of justification) that if the engine ran OK before being rebuilt and had no obvious signs of distress other than burning oil or evenly worn bearings it would run OK afterwards. I can honestly say that I never had any sort of a severe (or even moderate) vibration problem with those engines, as a rule I ran them as hard as they would go, and when they failed it was always from some other cause, such as expecting stock type cast pistons to sustain a 7 grand redline. The lesson, you can break just about anything if you try hard enough, and it's damn near impossible to build an engine that can't be broken by a driver without any restraints. Below that extreme there is a reasonable limit for any engine ever built below which it will have a long and useful life and above which all bets are off. Balancing only helps to move that limit upwards, but if your valve springs or your pistons won't support it you have gained nothing and spent money to do it.

For that reason alone I agree with your machinist friend. With a stock or near-stock redline your money can be better spent elsewhere. The cost of that balancing job can keep you shooting pool for a couple years if you're any good at it.

Of course, a smooth running engine is a sweet thing. If your budget will support it, certainly it makes sense. Bearing in mind of course that this new smoother engine will feel much happier winding up and will therefore need other improvements as well.... and there we go, next thing you know you're springing for that high dollar billet crankshaft and aftermarket block.

Jim



Edited 1 time(s). Last edit at 10/08/2008 08:58AM by BlownMGB-V8.

John
I have balanced mgb, mgc, and sb chevy engines and was always amazed at the smoothness at idle and how low I could set it.
It just feels smoother as you rev the engine. I'm thinking improved gas milage would justify the balance alone. If you can get your hands on a triple beam scale and get someone to tell you where and where not to remove metal from pistons and rods you can diy balance these item to .1 gram each. The machine shop still has to spin it up for the crank, and flywheel, etc., balance. Well worth the investment me thinks.

dave bash

BlownMGB-V8 Wrote:
-------------------------------------------------------
> …and will therefore need other
> improvements as well.... and there we go, next
> thing you know you're springing for that high
> dollar billet crankshaft and aftermarket block.
>
> Jim


LOL! Too true, Jim. I've got $5400ish in my engine now.



Edited 1 time(s). Last edit at 10/09/2008 11:49AM by NixVegaGT.

I've been told that dynamic balancing is more important on V type engines and all that is usually required on inlines is to make sure that all the rod/piston assemblies are the same weight as they counterbalance each other. The racers do work on the crankshaft counterweights to make sure they are the same on both sides as well. For a street motor, if you're really tight on money and you keep the rpm lower then I'd think you'd be ok to pass on the balancing.

Nick wrote: LOL! Too true, Jim. I've got $5400ish in my engine now.

Wow Nick, I don't think I have $5400 in my whole car. LOL That old V6 is balanced exactly the way GM did it, the only thing I've done is change the valve covers and plugs and the odometer in the donor Camaro showed 150K when I pulled it out.

LOL! Yeah. I kept records on everything from buying a core to the waffling I did on various parts.



Edited 1 time(s). Last edit at 10/09/2008 05:21PM by NixVegaGT.

I don't keep track of costs. 'Fraid of it. Don't want to know what the 340 costs me, that'd be most alarming. It'll be balanced btw.

On those 4's the racers like to use a flat crank for maximum power or so I hear. Seems it makes the engine sound a little funny but makes for more power output. I don't think a flat crank is going to work very well in a V8 though.

Jim

I've heard a couple Ford 302s with a flat plane crank. They sound really weird.

My two cents...

Years ago, it was a real special deal to balance a motor-- $250 (when that was more than a set of pistons!)

We balance EVERYTHING in the shop nowadays, because our machine shop can and is relatively cheap ($150.) I'll admit, though, that the amount of balancing performed seems directly related to the quality of the parts! AE hepolite pistons, for instance, are often within 2 grams of each other! (County pistons, ahem... are NOT.) Most clutches are reasonably balanced. So are most factory cranks. Usually the rods need some attention, and also the flywheels.

I don't disagree that a balanced motor is a wonderful thing. But I agree with Jim-- some motors (and some DRIVERS!) just don't need it.

If on a budget, i would actually save the $150 for the Line Bore. That being dead nuts right will give longer bearing life and smoother idle, in my opinion... And, besides the deck, it's the one area of the motor most likely to get distorted due to "seasoning". :-) And checking your old bearings tells you whether you need a line bore or not. (Any mis-matched wear pattern between saddles, basically.) You tell your machine shop your suspicion, he'll check the line bore and then true it if he finds it's out of spec. (If you 'suspect", 9 times out of 10 he'll have to do it!)


Where I think people waste too much money (in machine work) is with cleaning and magnafluxing. The pro machine shops do a beautiful job of having stuff cleaned and ready for assembly, but was it all worth $225? Likewise, only magnaflux things that are KNOWN to have problems! (Heads, obviously). Some motors crack blocks and cranks, and these should be checked. But if you are just rebuilding your high-mileage beater motor, why do you now suspect the block or the crank are cracked? I only pay to have "suspicious" parts mag'ed. I don't just pencil whip the whole job... (For those that wonder, I was burned ONCE for this assumption... Still, I view the money saved by NOT magnafluxing everything all the time easily covered that one time several times over!)

Max
Flying Circus English Cars

Funny how much prices differ around the country. In the Northeast in my area most of the machine shops have closed up. In my case the cleaning which included mag testing and new freeze plugs was $90.00. The cheepest balancing I could find was $450.00. Boring and honing was $8.00 per cylinder. I supplied the cam bearings and they installed them and lined honed them for $35.00. I had the deck machined to clean for $65.00. I balanced the rods and pistons myself then compared them to the pistons and rods that came out. All the sets were less than one gram difference between them all. Then I matched them to the originals as close as I could. Each set went in the cylinder that the original came from that matched. Then I had my Machinist take the piston set weights and check the crank balance. It came in so close he said he wouldnt add any weight to the crank.
(less than 1.2 grams out.) He charged me $100.00 for the crank check. SO total machine work was about $350.00. I saved that much by not having a full balance done but only because of the quality of the parts used.

Jim B. mentioned cam bearings being align bored at the factory, so I did a search to try to find more about this. I am also working with a Ford Cleveland 351 and Ford also align bored their cam bearings at the factory.

The previous poster of this thread from a year ago said that his machinist align bored the cam bearings for $35. I would love to find someone within a 500 mile radius of where I live (Boise, Idaho) who I could trust to align bore cam bearings. I would travel to Salt Lake City, Seattle, or Portland, Oregon to get it done.

Do any of you guys get cam bearings align bored?



Edited 1 time(s). Last edit at 03/19/2010 03:58PM by pcmenten.

Clan, may want to check my post,"3.5 lubrication". FWIW . Not a panacea, just something that worked for me. 3 beam scale, absolutely ! What makes an engine smoother, in balance, is matching your recip. weights. YOU can do this, and save money. Were I building a high rpm. motor, I would consider, "overbalancing", and carefully consider the %, based on redline. This is nothing more than, more counter weight ,than recip. weight. Why?, at some point in the stratosphere of rpm, extensive loads will exceed compressive. Overbalancing correctly, will help keep it together,(racing). Expect roughness at lower rpm. Drag racing, as we know it today, would not be possible-with out. At least (1) funny car motor, ran 1800 lbs, dynamic, at redline. Not saying YOU should. Let's stay balanced ? roverman.



Edited 1 time(s). Last edit at 03/19/2010 02:59PM by roverman.