I've just finished installing my newly rebuilt engine, and it definitely seems to be out of balance. It feels like it's running on 6 cylinders, even though every cylinder if firing. I have a 1-piece rear main seal block (86+), and I installed a 3.75 stroker crank, which according to my machinist, requires an externally balanced damper that is 8" diameter. Anyway I installed the larger damper on my engine and used what appeared to be the same flexplate that was on my engine when it was a 350. The machinist said that this was the right flexplate for my application, even though every 400 motor I've heard of has a 14" flexplate??? He insisted that this 350 or stock looking flexplate would work, since we tried originally to use the 400 plate, which didn't bolt up. What should I do now? This guy is telling me to use parts that don't work and my whole engine could be screwed up because of it.

 

Did you have the rotating assembly balanced?

If the crank you bought was an externally balanced 1 piece seal crank you need the stock flexplate that fit the one piece real seal cranks, (it has a weight on it) from a 350 and a 8" harmonic dampner from a 400.

If the crank you bought was for internally balanced 1 piece seal crank I don't know which flexplate you would run but you would need a neutral balanced dampner on the front.

Either way, it HAS to be balanced because the crank isn't balanced at all when you buy them new and would be WAY off.

Are there any holes drilled into the crank throws for balancing?

 

No the rotating assembly was not balanced, I'm not looking to build a high-rev race motor.

Honestly I don't know if my crank is externally or internally balanced, my father purchased it and doesn't know either. I do know that the stock 12 3/4" flexplate bolts right up to my crank and that the bigger 14" 400 plate didn't. I'm wondering why I was told to use a 400 f.plate and an 8" balancer originally only later to be told that I need the 350f.plate instead, because the 400 plate doesn't line up. If in case I need to use the stock flexplate, do I need to put the stock size balancer back on? Does anybody with an 86+yr. 383 know????

 

Did you put the engine together without balancing?

I just put mine together and I had to balance the whole assembly. You need to take it apart and take it down a shop to get it balanced. You need to take the crank, 400 balancer, 400 flexplate, conn. rods, pistons, and some shops even ask you for the rings. I had trouble finding a 400 balancer and flywheel because everyone kept trying to give me parts for an old school 400 2 piece crank. You have to look for aftermarket parts for 86'+. Try CAT performance.

 

what is the crank out of who makes it. ??

 

you didn't balance it??????? i doubt that motor will last any time with all the vibrations it's puttin off.......

balanceing is key......... it like taking a 3 blade fan and cutting one of the blades off, it shakes and vibrates like hell...... when you balance a motor you are matching the weight of the rods,pistons etc to the weight of the counterweights on the crank.......

dude, i hate to tell ya this but, it's teardown time.........

good luck and i hope it works out for you....

 

DOH!!! (In honor of Homer Simpson) Well I've gotta be the dumbest motherf'er in the world for not knowing that I needed my motor balanced. I guess that's what happens when you don't have things done yourself. I left my dad in charge of talking to the machine shop and working on the bottom end. No one at the shop ever mentioned that a 400 rotating assembly needed to be balanced with the damper and flexplate. After talking with Summit and a few race shops and obviously after asking you guys, I've been told that the engine needs to be torn down and balanced. That plain sucks! I'll probably have the engine pulled out tonight, after I just finished putting it in two nights ago. At least the engine sounded awesome for a whole two seconds and it revved up super quick. It's gonna be awesome when I get done right.

Anyone know if there's anyway I can reuse head gaskets since they've only been compressed on the engine for four days? I'd hate having to buy new $40 Fel-Pros again. But oh-well if I do.

 

running reworked rods brand new pistons and scat crank at 7000 rpms with a Fluidamper and there was no balancing done and no problems here yet.. crossing my fingers... lol

 

I doubt that the crank is internally balanced. You will need an externally balnced harmonic balancer and an externally balanced flex plate. No the original 350 flex plate will not do. Call Lingenfelter Performance Engineering @219/724-2552. They have the flexplate that you need.

You will need both of these items even if you tear the motor down.

www.geocities.com/dzperf

 

Reusing your old 350 flexplate is the first area of screw up. BIGTIME! The 400 flexplate is A LOT different than your old 350 flexplate. How far off are you? Oh, only by about 6 OUNCES or so, that's all (that's a lot)!

I have built many low-buck motors and NEVER balanced them- including several 400s. You can get by without balancing but you MUST have the appropriate flexplate and balancer on a 400 or 383! The amount it's off by is just too much.

 

383 are externally balanced....

the flexplate is different you cant use the 350s and you got another dampner..thats a plus.

 

i agree with Damon that balancing isn't always necessary. im sure it helps out a lot if done properly but i cant really notice a difference I just always make sure to use a brand new flexplate with a decent harmonic balancer such as fluidamper or the cheaper streetdamper because of the silicone in the balancer it helps remove a lot of the harmonics in a motor that a OEM balancer cannot. im not sayin its not a good idea to get it done but i never had any problems with my unbalanced motors and i treat them like $hit.

 

My 383 isn't externally balanced. SCAT make a crank now designed to be internally balanced with a 1 piece rear main. Took alot of work to get it balanced correctly though, no mallory jut lot of weight off, mostly because my bob weight was pretty low, about the same as a 302 Ford. But yes you defintly need to get that thing balanced. It would probably be cheaper to go external, depending on the crank of course, but it is possible to use your flexplate. I used my flywheel for the T-56.

 

The bottom line here is, you need an externally balanced balancer and flexplate.

JAY87GTA - Was your 180hp with the 383?

www.geocities.com/dzperf

 

I dont know if that was a bash at him or what but just because you balance a motor doesnt really make that much of a difference in horsepower maybe slight but not a truly signifigant amount. Im running 12's on mine and I have a buddy running low 11's in his Malibu and we both have unbalanced motors and I know theres people out there ridiculously faster than us out there on unbalanced motors. I think its a really good idea to get it done if you can for a reasonable price but ive never considered it because of the prices and I dont feel any instability with mine at 7000 rpms so why mess with it? If I was turning 9000 you betcha itd be balanced.

 

camarojoe, The guy wasn't a balance shop was he ? I actually got caught in the same type of mess with an old timer machinist. I argued with this guy over and over but he had a good reputation and being that I am a mechanic and have the facilities I took him for his word and I put it together. What a mistake ! It vibrated like a bitch, The crank was lite 140 grams front and rear total and had to be replaced. Tore it down and started over with less than 100 miles on it. all new like I wanted the first time. I learned right then. If your going to deal with a machine shop on the lower end make sure they do it all right there.

 

90Formula,

It seems I'm going through the same thing you went through exactly.

I don't know what to think anymore. I've been told a hundred different things by a hundred different shops. Some say the crank needs weight drilled out, some tell me that the counterweights need weight added, and some, like my machine shop guy, don't know **** at least when it comes to flexplates. Right now I have a stock internally balanced, lets not get technical here, flexplate and I was told by summit that this is what they use with their stroker kits??

I just want a general idea of what needs to be done so I can learn something, and yes I do know the engine will probably be coming right back out after about 20 miles. So what I would like to know right now is who here with a 383 (cast crank for 1pc RMS, OEM 8" balancer, 400 rods or 5.7 rods, pistons don't matter) is using what flexplate on their setup and what if any balancing was done to their engine? Was weight added or removed from your crank? Also to you guys who posted above who said you don' t balance your engines, could you give me all the specs on your stroker motors?

In a few days I may pull the engine back out but that's if my "*******" balancing method doesn't work. This method is welding wheel weights on the oposite side of the original winged weight on the flexplate in an attempt to counter-balance the crank, since I'm assuming the crank and balancer are too heavy for the flexplate. I'll know something later today, most likely the engine will be coming back out though. :lala:

On a side note to any newbies, always check your rocker arm to retainer clearance when installing new RR's or new heads. I found this out the hard way last week when my engine sounded like it blew up. The forks on my self-aligning crane gold rr's ended up smashing on the retainers after a few minutes of running the engine, because the tops of the valves are about the same heighth as the tops of the reatainers. The valves weren't opening all the way in other words. So much for those weak *** aluminum rockers, or maybe I should blame my upgraded valve spring package. Nahh. those rockers sucked, I'll be going with a set of real rr's, the pro magnum series next time. Hopefully they'll fit under my new moroso centerbolt v'covers.

 

I dont balance my motors like I said but I have a 355 which balancing is a little less crucial on. On a stroker motor you might wanna balance it... for the simple fact that running higher RPMS on a stroked motor makes it a little harder on the bottom end. I know you already have everything but if I woulda been in your shoes I would have put a slightly bigger cam in the block and went with a 350 or went bigger and got a 400. Really the 383 does put out a lot of torque but all you are doin really if you look at it is adding cubic displacement. Im not discouraging you from gettin your motor balanced but from my experiences all of my motors have been AOK at 7000 RPMS and generally motors are nowhere near balanced when they come from the factory they are just mass produced.

 

No, the 180 was on my old worn out motor. Haven't updated my sig in awhile. Still running the break-in on the new motor and going through the obvious tuning procedures.
I think that when you are using a re-habed crank that was balanced at the factory or whatever and was in a motor like that, then the balancing isn't as crucial. But when usuing a brand new crank that was never balanced it's essential IMO. My crank for instance was 180 grams off in the front and 60 in the rear. My machinist told me 1/4 of a gram is like 80 some pounds of imbalance at 6k RPM.

 

There are other combinations to stroke a 350 to 383 but here's a brief description of the main parts I used.

http://members.sigecom.net/smaster/383parts.htm

Keep in mind that none of these parts had ever been assembled in an engine. If it hadn't been balanced I can only imagine how far off it would have been. Scat says balancing is REQUIRED to use the crank I used.

HTH

 

Here is what is required. If you do an engine rebuild and change the rotating weight mass in anyway then the crank needs to be balanced to the weight of the pistons and rods. It does not really matter much if it is externally or internally balanced when the combination changes then it is balance time.

The reason I had 100 miles on my car was I drove it to and from work tring everything from dampners and pressure plates and even more money. I got frustrated and ripped it back out. Wanna know the worst part. I am a 44 year old auto technician with almost 30 years experiance. I am a drivability tech these days but when the original machine shop told me no balancing needed. I argued with him and our service manager and heavy duty tech agreed with him. It took a guy that runs sprint cars to tell whats up. He said " If it does not vibrate after changing piston weight then your extremely lucky. If you change anything in the rotating assy at all it needs to be balanced "

2 ways you can go here..
1: spend more money trying things that will or may not work.
2: pull it out and take the crank, rods, pistons, 1 set of rings, dampner, flywheel and attaching bolts for both to a balance shop and have it done right. I did all new brgs and rings and he mods I couldn't afford the first time. looks, runs and sounds great now.

 

Thanks again for all the help guys. The engine will be back out of the car this Mon. I'll probably get a Fluidamper balancer when I rebuild again, because I've read and heard it's better than the OEM piece. Other than that, I'm going to have my current setup balanced and put back together. I'll have the engine dyno'ed as soon as it gets put back together and when it' s broken in, which should be a few months from now. Later.

 

The only thing we are gonna conclude to whether you must always balance your rotating assembly or not is It's like Jenny Craig: Individual Results May Vary. Because my assembly is brand new Sterling Pistons. reworked stock rods on a brand new cast Scat 9000 series crank, Streetdamper damper balancer and a B&M Flexplate. Then slapped it all together and 500 miles later I was pulling it up to 7000 rpms. I feel my motor is safe unbalanced whether it makes sense to some people or not. I feel that as long as you have something truly muffling the harmonics in the motor (such as a good damper) it will be okay. I just really stress though on having proper bearing clearances and having decent rod bolts to spin higher RPMS.