Story so far.. VG30DETT in black 1993 ZX300.. blowing smoke and breathing really bad so jerked it out and stripped it down to find shattered ring lands on no.6. So bought lots of expensive goodies and started the rebuild only to find no.3 rod in shape of a banana. Question, if I replace all rods does bottom end need balancing because of change in weight and should I rebalance with new forged pistons. This is not a big H/P project, just a pain in butt for father of ungratefull driver.
Thanks Chrispy, Must have been misled in the past as I was under the impression with reciprocating internals that each rod had to be matched in weight and each piston etc.
Are you just replacing with stock components which are the same?? Or are you putting aftermarket forged gear in it? I put eagle rods and wiseco pistons in mine and got it balanced cause they are substantially lighter than stock components.
I have already bought forged pistons but I am now tossing up which way to go with rods.. Like I said earlier, It is not a big H/P machine, just a toy...
Well for all but full house race engines, then stock items would have been much more than adequate. IMO, forged pistons and aftermarket funky rods are not necessary in any but the most insanely high revving race motors. Even big HP engines do NOT require such forged clobber unless they are turning insane revs. Its RPM that kills engine parts. Not horsepower. A bad tune kills a high horsepower engine. Balancing the entire show is not really essential but its certainly desireable. Fit your forged clobber for bragging rights only or if you just want to. L8r E
I'd have to disagree with you on this. Its not always about rev limits that determine the need for forged internals. You have to look at pressures being exerted and so forth. TQ is the end all be all of the equation. Thats what ultimately puts the strain on parts. As the rev limit increases the tq variance in how much stress it puts on the parts increases as well. That is the need we have for using forged products. In any even what do you consider "insane revs"? I do agree that a bad tune will kill an engine but that goes for any engine be it that of a 400HP or a 1000HP built engine. In regards to balancing, that is one of the single most important things you MUST do when building any engine. You have enough issues with harmonics and overcoming rotating/reciprocating weight as it is and not having the assembly balanced just makes it even worse.
No, its not that cut and dries at the very high end of the performance scale but at the street end of the scale its pretty close and you know it. The factories dont care too much for careful balancing of street engines, Id expect largely due to cost constraints. If all these funky weights and harmonics you speak of are sufficiently demonic to the continued reliable operation of the vast majority of the worlds engines then the factory/ies would, as a matter of course carefully balance the complete assembly. There are countless numbers of VG engines the world around, happily revving their tits off regularly to their rev limiters which seem to last a surprisingly long time without flying to pieces or suffering undue wear. So no, balancing is NOT essential at all. I said it was certainly desireable tho, but nowhere near as essential as you allude to. Yes, im well aware of the pressures and loads exerted on those components,...which seem to stand up mightily well under surprisingly high rpm's, boost pressures and high specific outputs.... far inexcess of the everyday running limitations originally determined by the manufacturer. They too seem to cope with this activity with remarkable reliability for a very long time..... Id agree the goalpost move somewhat in a race engine but Im specifically excluding race engines here as the topic clearly stated the engine was a stock toy. Presumably limited to stock rpm limits and conservatively boosted......nope sorry, all that high end stuff is very very desireable but not necessary in the slightest. In my view, good bench racing/tyre kicking conversation. Out E
Many years ago when i was a young bloke i worked for a few months on the conrod line in the engine plant of one of the major car manufactures. At the end of the conrod line they were checked for the alignement of the bearing ends ( big and small ). THEY WERE NEVER CHECKED FOR BALANCE - EVER. 99% of the the conrods where twisted so as the bearings did not aligned correctly. THIS WAS ADJUST ( very roughly ) by BELTING VERY HARD WITH A LARGE HAMMER on the opposite side to the twist , then put back onto the air guage to check the alignment SOMETIMES but mostly not. These motors then where fitted to to the cars. While i worked there if our line broke down ( often did ) we where sent to other lines. On the cam line i had many cams just fall apart lifting the out of the crate from the casting plant ( i wonder how many made it thru into motor to then let go ). We once got a roza about the quality of the end product and where told if it's not up to scratch take it of the line. 2 days latter we where told that there was to many rejects and it was costing to much. THE FIX - PUT IT BACK ON THE LINE. I don't know if it's improved any since but it just goes to show what the manufacturers quality is like . Dave.
Its not until you get a high end car are the engines balanced at all. Even for something like the R35, those parts are graded on a weight scale and then matched before being assembled. The quality and accuracy of the tune is more important to get right first.
Yer i didn't think it was a good idea , every tuesday night was quality ( wank wank ) control meetings. It's was a joke. ( this might give it away ) they always got to rear crank shaft seal leaks and said ( we will skip that ). W.T.F . Quality would say take it of then the foreman would get reemed for to much scrap comming off the line so we where told to put it back on ( l.o.l ). I know longer buy australian built cars. I personaly believe cars wouldn't be made in Australia if it wasn't for the tax payers funding it with hand outs and tax breaks. Cheers Dave
Thanks for all the input guys but I'm still having a prob getting my head around the fact that it is still a rotating mass of parts and so as long as all the same parts are the same weight, then it should be balanced as the counter weights on the crank are only to offset the reciprocating action of the piston and rod. The way I see it, the lighter the better..quicker revs
You do realize that the OE equipment is graded and has a wide variance on weight between components which they consider "in specification". Nissan isnt going to spend that much time in balancing out every rotating assembly for every engine. Thats not cost effective nor production oriented what so ever. You can continue to tell others that balancing an engine whether it be street or race isnt important but I will tell you it most definitely is. Be it as it may, well balanced assemblies last twice as long as an unbalanced assembly. Its a fact. I'm not here to argue with you but I would certainly be careful in how you explain and tell others about critical assemblies such as crankshaft/rotating assembly balancing. And all these engines you speak of that rev as high as you say they do, you think their assemblies aren't balanced? I highly doubt it and if so I'd wager a bet on what their bearings look like and so forth. Theres a definite reason why engine builders go through such detail to ensure assemblies are done properly. Street or race makes no difference in ensuring the assemblies should be balanced. Thats all Im going to say about this as I dont feel like getting into an online pissing contest. So I'll end it in saying to each their own. Your dollar will turn into your holler.
/ Most VG`s last 20 years. Your saying they would have lasted 40 years if they had done it better from factory? But if its a fact..? wow.. 40 years! Your both spot on the money, your talking about 2 different things.
The answer without opinion is: The crank has weights on it that are sized according to the stock pistons & rods. If you replace either with an item of differing weight then the engine is out of balance. A balanced engine is a happy engine & should last longer & go better than an out of balance engine. With my own personal opinion: My eng bottom end was put together by a bunch of muppets a few years back, it didn't get balanced. It took approx 30-40000Kms before it died & the cause of death was not related to balancing, there appeared to be no ill effects from having pistons a few grams lighter than stock. The engine performed well, sounded good, didn't shake or vibrate, it never broke the crank or cams etc & it hit 8000RPM several times during burnout displays & drag racing etc. My new build is balanced though, for all the money that goes into a VG30DE(TT) build saving a few bucks should not be the reason to not balance the motor. Once the motors going & in the car it's to late to change your mind & balance it, it bugged the crap out of me for the last four years or so knowing my motor most likely was out of balance & could one day have an issue because of this. Fortunately it blew up due to another issue (word used loosely).
I am all for Balanced Assemblies. Even with the Flywheel added to the Crank that is going to be run. You get less Rotational Vibration out of a Balanced Assembly. Nothing can argue with that. That being said...Balancing is better. If you do not want to or can not afford to Balance everything then throw it together and run the piss out of it. Your Engine will fail faster than a Balanced Assembly. That is just my opinion though. It was Balanced from the Factory for a reason.
It isn't balanced from the factory the same way a builder balances an engine. It's a very rough graded balance.
