Engine balancing

[MIGHTY 8]

Hello,

Am awaiting to install a new lightened flywheel, and several other lightened ancillary engine parts....water pulley, crank pulley,'etc.

I have been advised that these parts are pre-balanced and are ready for installation as is.

However, I wanted to learn more about engine balancing (process, cost, etc. ) in general terms.

Any takers on the subject, or maybe those that have had similar parts installed on their car's.?

Thank you in advance.

[djape1977]

well if you plan on revving it at around 9k rpm than balancing would be a smart thing to do. otherwise, fiat parts are quite well balanced coming from the factory.
lightened flywheel does need rebalancing because when you take material off it, you disturb factory balance.
pressure plate might be worth checking too since i've seen some really bad ones in past several years, probably chinese s**** quality parts. if it's from some decent manufacturer (lucas, valeo, sachs etc) it's fine as is.

[westy64]

well if you plan on revving it at around 9k rpm than balancing would be a smart thing to do. otherwise, fiat parts are quite well balanced coming from the factory.
lightened flywheel does need rebalancing because when you take material off it, you disturb factory balance.
pressure plate might be worth checking too since i've seen some really bad ones in past several years, probably chinese s**** quality parts. if it's from some decent manufacturer (lucas, valeo, sachs etc) it's fine as is.

I certainly do not rev at 9krpm, not even at 6k, but at idle, my engine is a pretty good dancer.
If we assume that everything is well balanced inside, what is causing this shaking that makes everything move ?
for example, waiting at the red traffic light, I cannot smile to the girl behind through the widshield mirror as it moves too much.
I do nor see anything trough the mirror at idle.
any idea ?
silent blocks?

[djape1977]

wrong timing for one. a tooth off on one of the cams.
or bad sparkplugs
or cables
or play in the distributor shaft
busted engine mounts

anyways nothing to do with balancing of rotating assemblys

take it to someone who knows his way around old fiats for a precise diagnose

you wouldn't believe the diference that just a spark plugs change can make. and before you say you changed 'em, have you tested them? i've seen bad plugs more than once, brand new, straight from the box.

[MIGHTY 8]

Thank you everyone for all your responses. But sorry, Westy64, that was a bit of a thread drift to use Internet parlance!

I'm talking about balancing rotating assemblies/ components, not rough idling engines.

Don't get me wrong.... I always appreciate a good story with a pretty girl in it!

[paladin124]

I have my block and rotating assembly at the machine shop right now, nothing high performance I just want a good reliable motor that i wont have to rebuild again. With that said, I race an ITA honda which lasts 3 seasons before needing to be pulled out and rebuild or freshened up, not something I want to be doing to my fiat. Balancing will help the longevity of you're motor, sort of like having a wheel perfectly in balance, it will wear better and last longer. If you already have it at he machine shop for honing or boring work, the couple of hundred dollars to get it balanced is cheap. A good Machine shop will want your clutch and flywheel with the rest of your short block.

[djape1977]

still, shaking everything, the whole car in fact, so much that you can't see what's in your rear view mirror, means that engine has a very rough idle. having a dozen fiats from 60's, 70's and 80's, i haven't expirienced anything like that so far. i've seen it in a VW golf and in a ford fiesta and it was a result of aftermarket engine mounts that were made of rock hard rubber instead of soft one.
provided that you're using stock fiat engine mounts, you should be fine since they're made of excellent material that lasts for decades. if mounts are ok, meaning that engine or exaust is not sitting somewhere on the body of the car, i'd look for problems elsewhere.
now, fiat twincam is not the smootest engine in the world when it comes to idling and post 1990 models have balancing shafts to rectify that, but still it's far from being that bad

[westy64]

Thank you for sharing your experience and sorry if I steal this post...
I thought this shaking was due to the structure (ie the mirror is at the top of the windshield structure, which could amplify the vibration.
I could not place the car on a lift yet (is that the word ?) to have a look under it, but I will do it soon to have a deep look in all mountings.
At idle, the rear corners of the hood are also shaking a lot, and this disappear at higher rpm.
Are hard engine mounts recommended for a rally use ?
I ask this because I bought the car from a rallyman (soft rallyes, but rallyes anaways).
regards

[djape1977]

could be.
i've seen engine mounts made of polyurethane on race cars. drivers claim that soft mounts steal a fair bit of trottle response because all of engine and gearbox first lean to one side and than they start producing movement. in my humble oppinion it's a load off bull since it would only be for a tiny fraction of a second.
also, race prepaired engines have very rough idle, so much so that they can hardly run under 2 or 3k rpm. maybe you have a beast under the bonnet that you know nothing about?

[djape1977]

thinking about it, once, about 7-8 years ago, i decided to see "what if" and i installed 9mm dome pistons into 2 liter block and bolted on a 1756cc head. compression ratio was so high that starter motor could hardly turn it over but once started it did have a pretty rough idle. not that it was shaking the car, engine mounts were stock fiat ones, but there was still noticeably more vibration than with "normal" engine.
boy did that thing go!
revved like mad and had A LOT of power. naturally, it blew a head gasket about 1000kms later
swapped it for a volumex gasket and it was fine until about 15k kms later when it blew out the piston rings

moral of the story? dunno but it's a good one.

and a short vid of that particular engine in action
http://www.youtube.com/watch?v=488sWbbhmkg

[maytag]

y'all are funny.

to the OP:
the Fiat TC is an inherently balanced motor, because it has a 180d crank. that is to say: each rod/piston assembly (and resultant cylinder pressure) is offset by another, exactly 180d from it. This is the same technology used on most Ferraris, and many hi-revving sportbikes. No outside mechanism is required to balance this motor, the way many other motors require.

Having said that; not all are balanced equally. Any time you spend further balancing the reciprocating assembly & the rotating assembly will pay off in the end, especially in a performance application. When I built my current motor, I used what is common practice on hi-revving superbikes, as well as the big-inch drag motors I used to build. I first lightened the pistons, and then balanced them to each other. Then I did the same with the rods. I had my machinist re-balance the entire assembly with aluminum pulley, lightened flywheel & clutch. (turns-out Jason Miller is pretty good though, as the pulley and flywheel were already dead-nuts-on.)

For a mildly-driven street motor, this would be absolute overkill.


To the thread-hijackers:
what you are describing does not occur from hi-compression pistons. Big cams, yes. Lots of duration, yes. Being off a tooth on your belt, yes. having a compression leak in a cylinder, yes.
Your mirror rattling is more likely about bad motor mounts, pr busted stuff.

And yes: poly motor mounts DO make a difference on a race car. As do SOLID ones, the way we used to use on the drag cars, and the circle-burners. ANY flex that occurs prior to the power transferring to the wheels is simply wasted energy. And it all adds-up. Ideally, you eliminate the flex you can't control (like motormounts, body mounts, etc) and then you use flex you CAN control (like spring rates, slapper bars, etc) to tune the power delivery.

[MIGHTY 8]

y'all are funny.

to the OP:
the Fiat TC is an inherently balanced motor, because it has a 180d crank. that is to say: each rod/piston assembly (and resultant cylinder pressure) is offset by another, exactly 180d from it. This is the same technology used on most Ferraris, and many hi-revving sportbikes. No outside mechanism is required to balance this motor, the way many other motors require.

Having said that; not all are balanced equally. Any time you spend further balancing the reciprocating assembly & the rotating assembly will pay off in the end, especially in a performance application. When I built my current motor, I used what is common practice on hi-revving superbikes, as well as the big-inch drag motors I used to build. I first lightened the pistons, and then balanced them to each other. Then I did the same with the rods. I had my machinist re-balance the entire assembly with aluminum pulley, lightened flywheel & clutch. (turns-out Jason Miller is pretty good though, as the pulley and flywheel were already dead-nuts-on.)

For a mildly-driven street motor, this would be absolute overkill.


To the thread-hijackers:
what you are describing does not occur from hi-compression pistons. Big cams, yes. Lots of duration, yes. Being off a tooth on your belt, yes. having a compression leak in a cylinder, yes.
Your mirror rattling is more likely about bad motor mounts, pr busted stuff.

And yes: poly motor mounts DO make a difference on a race car. As do SOLID ones, the way we used to use on the drag cars, and the circle-burners. ANY flex that occurs prior to the power transferring to the wheels is simply wasted energy. And it all adds-up. Ideally, you eliminate the flex you can't control (like motormounts, body mounts, etc) and then you use flex you CAN control (like spring rates, slapper bars, etc) to tune the power delivery.

Thanks for the informative response!

I don't know if there is such a thing as "over-anticipating" something, or I'm just being paranoid....but since I don't do the work myself, I'm just researching here and there on what to expect after I show up and DUMP all these aftermarket parts on my trusty mechanic and basically say..."have at it, ragazzo!"

I just want to learn more about these things and I find the Internet, and more specifically this web forum so valuable and up to the task.
Thank you again and I think you generally did answer my question.

[djape1977]

well, there you go, i haven't sucked up all the knowlege in the world tru my mom's tit.
guess it does all add up in the end.
mentioning the cams, ones from 132 special that were in that 1756cc head do have considerably less pointy lobes than most fiat twincam camshafts so i guess that translates into longer duration. haven't bothered to measure exact duration though.

still, if i were you i'd jack up that 124 and get under it with a crowbar. if there's nothing obviously wrong with the mounts, try lifting the engine or gearbox from the mounts. also, engine and gearbox mouns should be made of soft rubber, considerably softer than your tyres for easy comparison.