Replacing a crank....
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From: Phelps, NY
Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Replacing a crank....
Hey guys, well after some searching on here, I've come to a crossroad. First of all, the 350 in my Bird needs the crank/ bearings replaced. Only thing is, money is tight so I want to do this as cheap as possible with out having to guess if the engine will hold up or not. Now, I was told if I replace the crank with a brand new one, it would need to be balanced? I would love to avoid a machine/ engine shop right now, lol. Is there a way around needing to balance the engine? What about taking a crank out of a similar engine and installing new bearings with it? I remember while searching I came across a thread on balancing, but some said it's not "required" and others said it is, so idk. The engine would need to survive some track visits and those moments where you randomly wanna have fun. I want to get going on this asap so any help/ info would be greatly appreciated!
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Re: Replacing a crank....
On a street driven engine, the balance isnt going to matter as much as people tell you it will. Its not exactly cheap to balance, at least not at most places. At least 150 bucks usually. I put crank kits in cars all the time, no vibrations, no issues. Dont worry about balancing a patch together engine.
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From: Mesa AZ
Car: 87 Firebird, 90 bird coming soon
Engine: 355 Chevy Vortec Heads TPI, LT1 inj
Transmission: 700r4
Axle/Gears: 2.77 posi 9-bolt
Re: Replacing a crank....
Can your current crank be turned? I just had one done here in AZ for $75. Then install new bearing to match the amount of undersizing.
Joined: Feb 2002
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From: N. Illinois
Car: 92 GTA/ 00 TA
Engine: 383/350
Transmission: 700R4/T-56
Re: Replacing a crank....
Do this.
Balance DOES matter on a street engine. I listened to somebody before and followed that advice. 2000 miles later I was tearing it apart again.
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From: Phelps, NY
Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Re: Replacing a crank....
Alright, sounds like having the crank turned would be a lot better choice. This may be a dumb question but, having it turned and installing the appropriate bearings means no need for balance because it's the same crank right? I'm gonna be pulling the motor here sometime soon hopefully (if the good weather streak holds). A neighbor and his brother are gonna help me because I've never done anything like bearings before and don't wanna screw it up. How do you tell what are the appropriate bearing sizes to use? Do you just match up their size up with how much it was ground down?
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Re: Replacing a crank....
Dollars to donuts that assembly isnt balanced anyway. Work in a machine shop. Take factory rotating assemblies and rebalance them when a customer pays for them. They arent balanced for crap.
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Joined: Feb 2002
Posts: 3,462
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From: N. Illinois
Car: 92 GTA/ 00 TA
Engine: 383/350
Transmission: 700R4/T-56
Re: Replacing a crank....
In my case it was a rotating assembly bought from PAW. The engine would shake so much that I finally tore it back down. I found that my crank bearings were already wearing through.
I brought it to the machine shop and they said that they'd never seen one this bad before.
So a balance job and new bearings fixed my vibrator.
I brought it to the machine shop and they said that they'd never seen one this bad before.
So a balance job and new bearings fixed my vibrator.
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From: Philly, PA
Re: Replacing a crank....
Vipr- I think your experience is probably in the minority, although I agree it can happen.
I've done LOTS of motors without balancing. I probably built my first 10-15 motors years back and I didn't even know what balancing was yet! Also, the 383 in my Malibu is on it's 3rd build with it's 3rd different set of pistons. The different piston sets have varied by more than 25g each from the lightest set to the heaviest set- never did a rebalance, all 3 itterations of the motor ran just fine with no vibrations and it still runs strong today. It's a sub-6000 RPM motor.
I will agree that turning down the journals and using matching bearings is the way I'd go in this situation, unless the crank is too far gone to save.
I've done LOTS of motors without balancing. I probably built my first 10-15 motors years back and I didn't even know what balancing was yet! Also, the 383 in my Malibu is on it's 3rd build with it's 3rd different set of pistons. The different piston sets have varied by more than 25g each from the lightest set to the heaviest set- never did a rebalance, all 3 itterations of the motor ran just fine with no vibrations and it still runs strong today. It's a sub-6000 RPM motor.
I will agree that turning down the journals and using matching bearings is the way I'd go in this situation, unless the crank is too far gone to save.
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From: MD
Car: '88 IROC-Z medium orange metallic
Engine: L98
Transmission: 700R4
Axle/Gears: 3.27
Re: Replacing a crank....
You are comparing apples to oranges here people. There is internal and external balancing. You can install a new crank into an externally balanced engine without having the assembly balanced without issue because there is a weight on the flexplate and balancer.
If there is no weight on the flexplate or balancer then you have an internally balanced motor and you must have the crank balanced to match the rods/pistons. This will have to be done any time you change the rotating mass.
If there is no weight on the flexplate or balancer then you have an internally balanced motor and you must have the crank balanced to match the rods/pistons. This will have to be done any time you change the rotating mass.
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From: sunny so cal.
Car: 1990
Engine: 305
Transmission: 700r4
Axle/Gears: stock
Re: Replacing a crank....
what about his stroking the engine with a different crank? should he balance that then? i heard that if you change pistons that effects the balance too.
that a crank for a 350 is set up for heavier pistons while a crank for a 305 has the same stroke but it is set up for lighter pistons so the balance would be off from one to another.
the same for using a 400 crank in a 350 or 305, the balance is different. with a 400 i heard that you would have to use pistons that the skirt does not come down as far sio it will not hit the crank. i think you will have to use different connecting rods to pistons that connect at a different height to the pistons.
all that diffference in weight has to make some difference.
that a crank for a 350 is set up for heavier pistons while a crank for a 305 has the same stroke but it is set up for lighter pistons so the balance would be off from one to another.
the same for using a 400 crank in a 350 or 305, the balance is different. with a 400 i heard that you would have to use pistons that the skirt does not come down as far sio it will not hit the crank. i think you will have to use different connecting rods to pistons that connect at a different height to the pistons.
all that diffference in weight has to make some difference.
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From: Phelps, NY
Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Re: Replacing a crank....
You are comparing apples to oranges here people. There is internal and external balancing. You can install a new crank into an externally balanced engine without having the assembly balanced without issue because there is a weight on the flexplate and balancer.
If there is no weight on the flexplate or balancer then you have an internally balanced motor and you must have the crank balanced to match the rods/pistons. This will have to be done any time you change the rotating mass.
If there is no weight on the flexplate or balancer then you have an internally balanced motor and you must have the crank balanced to match the rods/pistons. This will have to be done any time you change the rotating mass.
So pretty much when I pull the motor, if I find it's externally balanced I can just go buy a new crank and such and just throw it all back together, if it's internal, then it would need balancing. I'll have to see what the crank looks like when we pull it apart to see if it can even be turned down. What are the odds of it being external vs internally balanced? The motor is the common 3970010 casting 69-80 Chevy 350 out of a truck.
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From: Pigeon Forge ,TN
Car: Firebird
Engine: 2.8 v/6
Transmission: t/5
Axle/Gears: open/3.42
Re: Replacing a crank....
I've built many engines to stock specs and never balanced them because they were for daily drivers and if they were going to thrash on them then I would have considered balanceing them to take the abuse . If you just want to daily drive this car or get on it some then just do as the others said and turn the crank a little to clean it up and reassemble it with new bearings and have fun . Also if your engine is stock no matter if it is external or internal balanced you could buy a new crank and bearings and reassemble it without a problem .
Last edited by 89-bird; Apr 17, 2009 at 08:53 AM.
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From: sunny so cal.
Car: 1990
Engine: 305
Transmission: 700r4
Axle/Gears: stock
Re: Replacing a crank....
so now we have 2 issues.
as long as it is externally balanced, its not necessary to do anything to the cran?. if he gets a stock 400 crank to make a 383 and it is externally balanced, no balancing is necessary even if he has to get new rods and pistons?
the 2nd issue is - is his car externally balanced and how do you know until you tear it down to get to the flex plate?
as long as it is externally balanced, its not necessary to do anything to the cran?. if he gets a stock 400 crank to make a 383 and it is externally balanced, no balancing is necessary even if he has to get new rods and pistons?
the 2nd issue is - is his car externally balanced and how do you know until you tear it down to get to the flex plate?
Last edited by tony_cogliandro; Apr 17, 2009 at 09:53 AM.
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
Take crank, rods, pistons, and block to a good respectable maching shop.....they should be able to turn the crank....and you can re-use your rods, but you need to have them checked for roundness....probably will need re-sized...you have to take pistons with you too cause they pistons are pressed onto the rods and need to be removed by maching shop....also take you block to and have it cleaned and checked for cracks (very cheap), and have them look at it because it might need line bored....the maching shop should know how to do all of this....what will happen probably is they will turn crank, resize rods, check block, and give it back to you...if your reusing all the stock componets, a lot of machine shops will not require balancing since it was balanced when it came from factory and your not changing piston or rod weight....this is the cheapest route....if you buy a new crank or a whole rotating assembly, you can buy them already balanced. But I would just take you factory stuff down if your trying to save $$....hope that helps....
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Re: Replacing a crank....
You are comparing apples to oranges here people. There is internal and external balancing. You can install a new crank into an externally balanced engine without having the assembly balanced without issue because there is a weight on the flexplate and balancer.
If there is no weight on the flexplate or balancer then you have an internally balanced motor and you must have the crank balanced to match the rods/pistons. This will have to be done any time you change the rotating mass.
If there is no weight on the flexplate or balancer then you have an internally balanced motor and you must have the crank balanced to match the rods/pistons. This will have to be done any time you change the rotating mass.
If you are putting together your stock engine, or mild engine, and are not going to replace pistons or do any other machine work, either turn your crank or get a crank and install it.
If I had a dollar for every time that I have put a crank in a SBC or any GM v6 without tearing down the whole engine and rebalancing I could probably retire a few years earlier.
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
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Last edited by 91interceptorZ; Apr 17, 2009 at 04:26 PM. Reason: -
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
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Last edited by 91interceptorZ; Apr 17, 2009 at 04:22 PM.
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
-
Last edited by 91interceptorZ; Apr 17, 2009 at 04:23 PM.
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Re: Replacing a crank....
okay you guys are way off......it doesn't matter if it's internal or external balanced....if you change the weight of ANYTHING (i.e. rods/pistons) it will need to be rebalanced.....you HAVE TO BALANCE if you stroke it....your changing rods and pistons when you do that....if you re-use the stock crank rods and pistons that came with you motor, you don't have to re-balance it. 400's are externally balanced, 305-350's are 'internally' balanced. which on a 400, the weights are in the harmonic balancer and the flywheel/flexplate, on a 350 the balancer is zero (no) weights, there are weights in the crank itself, and there is still a weight on the flexplate/flywheel. You said you didn't have much $$....it cost a couple grand to do a stroker by the time you buy a crank, pistons, rods, maching work on block, etc.etc. Supreme Member
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Re: Replacing a crank....
In my case it was a rotating assembly bought from PAW. The engine would shake so much that I finally tore it back down. I found that my crank bearings were already wearing through.
I brought it to the machine shop and they said that they'd never seen one this bad before.
So a balance job and new bearings fixed my vibrator.
I brought it to the machine shop and they said that they'd never seen one this bad before.
So a balance job and new bearings fixed my vibrator.
If all the bearings were torn up and wearing through, I would guess there were other problems with that engine. Probably from the very begining. There are extreme circumstances, such as when you take 8 mismatched rods and a crank and eight mismatched pistons and put it together, though it usually works for people too. As far as just replacing the crank, its not going to cause any problems.
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
[
Last edited by 91interceptorZ; Apr 17, 2009 at 04:24 PM.
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Re: Replacing a crank....
you need to re-read my post.....I said if he REPLACES rods/pistons with different ones (new or aftermarket)........THEN it needs rebalanced....if he re-uses STOCK items...it does NOT.........Go ahead and put a non-balanced motor together and you'll be rebuilding it again soon...I don't half-a** motors...you can do them cheap...but still do it right or it will cost you in the long run
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
.
Last edited by 91interceptorZ; Apr 17, 2009 at 04:24 PM.
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Re: Replacing a crank....
you guys don't read well........STOCK REPLACEMENT.......what does that mean.......STOCK REPLACEMENT, like a stock crank out of another car maybe.......let's play an example here....I buy a NEW scat crank, and some different brand rods, and some KB pistons , and then throw it together...that's supposed to run good....whatever...if your a professional mechanic I wouldn't ever go to you, to me that's cutting corners that is easily not cut...you probably don't measure bearing clearances, or degree cams either....that's stupid..no offense..people can build whatever they want however they want, it's their car, but I do everything to specs and don't take chances...I've NEVER had a problem with one of my motor builds, why, cause I do them right the first time.....if he steals another factory crank out of another motor....then yes you don't need balancing, I agree with you, but if you start mis-matching parts, or putting new parts in/different brands, then you DO need balancing....the machine shop I go to here balances motors for around $100...it's not expensive, and he races pro-street. You said backyard racer crap...that's what you do.....just throw some junk together and hope it works......good luck with that. I understand saving a $$, but you can't rub two pieces of poop together and get flowers. He can make his own desicion...like I said it's just my opinion..
#1 you have been saying that the replacement of a crank requires the balancing of the engine. If you meant the replacement with an aftermarket, fine, you are right, but you never said that until now.
#2 You have no idea of what I do or how I assemble an engine. To be honest I dont assemble that many SBCs anymore I am too busy doing 5-8K dollar engines in new cars most of the time. As an ASE Master tech I end up doing most of the crank kits and auto trans failures in our shop.
#3 Yeah 100 bucks sounds right, but that usually doesnt include the ultra expensive unobtanium metal that is used to balance with(I used to do that in a machine shop, I daresay I know how to do it, maybe better than you).
#4 Yeah, I'm a real backyard racer myself. I have put together tons of engines from spare parts and stuck it in a car or truck to play around with, most of us have and do, its called a hobby.
Thank you for taking the time to tell me how I do things, as you obviously know me so well. You were wrong, sorry. About a lot of things.
Werent you the guy that said that 3.8s used SBC 350 rods and pistons, etc?
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
there, now read the only post I left on here #15....it says replace stuff and NO NEED to rebalance it.......
and yes I said the vortec v6 use the 5.7" rod and 4.000 bore piston....
and yes I said the vortec v6 use the 5.7" rod and 4.000 bore piston....
Last edited by 91interceptorZ; Apr 17, 2009 at 04:33 PM.
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Re: Replacing a crank....
At least there isnt a lot of conflicting info being beaten around. And no, I wasnt talking about the vortec, all 4.3s use that configuration, I was referring to the 3.8s.
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From: boise, ID
Car: 91 B4C "police special service"
Engine: L98 494hp
Transmission: tko-600 on order
Axle/Gears: 3.23 true trac
Re: Replacing a crank....
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From: Phelps, NY
Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Re: Replacing a crank....
Well, I called one machine shop earlier on they quoted $205 for turning the crank down, and they said probably $250-350 for balancing. Sounds way off what I've seen other people say. I'm trying a different place tomorrow to compare with. As for the purpose of the engine, I just want it running good again. I'm not on a "strict" budget, I just don't wanna dump a lotta money for something I don't need to as I have bigger plans for the car in the future and they don't involve this engine if you get what I mean (I just want it running decent while I save up for something else). The car isn't going to be raced daily, it won't see more than 5,500 rpms, like maybe a blast here and there, and possibly the track just for fun once or twice. I wanna get it going as cheap as possible while doing it right the first time, if that makes more sense, which is the only reason I ask, I like to be at least 95% positive before I do something, especially something like this. Thanks for the ideas/ opinions so far guys.
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From: sunny so cal.
Car: 1990
Engine: 305
Transmission: 700r4
Axle/Gears: stock
Re: Replacing a crank....
if he replaces the crank can he get by with the same pistons if he finds he needs to be 30 over?
http://www.chevymania.com/tech/383.htm looks like he will. and new connecting rods too, and new pistons and lots more stuff.
here is a crank http://cgi.ebay.com/ebaymotors/SB-Ch...Q5fAccessories
here is a whole bunch of them internally balanced. http://shop.ebay.com/items/__gm-400-...nkshaft?_rdc=1
and another https://www.kmjent.com/cart/product.php?productid=1176
http://www.chevymania.com/tech/383.htm looks like he will. and new connecting rods too, and new pistons and lots more stuff.
here is a crank http://cgi.ebay.com/ebaymotors/SB-Ch...Q5fAccessories
here is a whole bunch of them internally balanced. http://shop.ebay.com/items/__gm-400-...nkshaft?_rdc=1
and another https://www.kmjent.com/cart/product.php?productid=1176
Last edited by tony_cogliandro; Apr 17, 2009 at 10:51 PM.
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From: Phelps, NY
Car: 87 Firebird Formula, 97' GMC Sierra
Engine: LT1, 4.3 Vortec
Transmission: T-56, 4L60E
Axle/Gears: 4.10 Posi, 3.42 Posi
Re: Replacing a crank....
if he replaces the crank can he get by with the same pistons if he finds he needs to be 30 over?
http://www.chevymania.com/tech/383.htm looks like he will. and new connecting rods too, and new pistons and lots more stuff.
here is a crank http://cgi.ebay.com/ebaymotors/SB-Ch...Q5fAccessories
here is a whole bunch of them internally balanced. http://shop.ebay.com/items/__gm-400-...nkshaft?_rdc=1
and another https://www.kmjent.com/cart/product.php?productid=1176
http://www.chevymania.com/tech/383.htm looks like he will. and new connecting rods too, and new pistons and lots more stuff.
here is a crank http://cgi.ebay.com/ebaymotors/SB-Ch...Q5fAccessories
here is a whole bunch of them internally balanced. http://shop.ebay.com/items/__gm-400-...nkshaft?_rdc=1
and another https://www.kmjent.com/cart/product.php?productid=1176
Sorry Tony, but I think I'm confused about this. I noticed those cranks were 400 one's, are you saying I should go stroker? or did you think that's what I was talking about with the crank? Or am I just very confused altogether? lol.
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From: Pigeon Forge ,TN
Car: Firebird
Engine: 2.8 v/6
Transmission: t/5
Axle/Gears: open/3.42
Re: Replacing a crank....
Just go to the parts store and buy a new crank and bearings and put a new oil pump in while your in there and you will be fine to run your engine up to 6,000 rpm without destroying it .
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