Internally / externally balanced assembly

I Purchased a rotating assembly for my Corvette (’90 automatic transmission) .The car is stock except for k&N filter, airfoil, and no precats and an hi flow cat. converter.
The rotating assy is not here yet in Italy… I’m waiting Fedex…… with the package….
The rotating is:
Eagle cast crank (1 pc rear seal)
Eagle SIR rods
KB flap top pistons +.030 (1.560” compr. Height)
Sealed pwer moly rings
Clevite main and rod bearings.
I purchased this 1 piece rear seal assemby with the option “balanced”.
Now the tech question:
I don’t know if the assy is internally balanced or externally balanced.
I don’t know if a L98 ’90 engine is internally or ext balanced.
I don’t need to know if an internally balanced assembly is best than an externally balaned, I need only to know if I can install the balanced assembly with my stock 12 ¾” 153 th. Flexplate and with the stock 6 ¾” balancer without knowing the kind of balancing procedure of the new rotating assembly.

Another question…_
What’s a SFI aprroved harmonic balancers? Whats means SFI?

Thanks.
Beppe.

 

All chevy 350's are internally balanced. It's only when you change to stroker cranks like 3.750 that some are sold as externally balanced and then you have to have a matched damper and flex plate.

SFI Is a quality assurance higher rpm rating. It means that the parts have been tested a verified to meet higher standards. SFI parts are required safety equipment by different racing organizations. I use SFI rated damper and flywheel because I have a 7000 rpm motor and I Auto-X race.

 

Not true. The older ones (pre one-piece rear seal) are internally balanced. Some (possibly all?) of the newer style 1-piece rear seal 350's are externally balanced. LT1 and LT4 engines are externally balanced. I'm not sure about L98's.

 

Who is right? :confused:

 

Mark is right. I didn't consider the new style motors. L-98 and older blocks are internally balanced. If a shop is sending you a balanced set of piston, rods, and crank and they say that it is balanced it would have to be internal or else they would be selling your the matching damper and flex.

 

Beppe,

You neglected to state the stroke or size of the rotating assembly you have on order. One would assume it is a 383. Here is a little back ground. All 1985 and eariler 350s (3.48" stroke) are internally balanced. All 400s (3.75" stroke) are externally balanced. The 400 used an un-balanced damper and an unbalanced flywheel/flex plate to externally add the weight need to balance the assembly. The 383 (3.75" stroke) is based on the 400 crankshaft. By nature it would be externally balanced like the 400. Some crank and rotating assembly suppliers make provisions for internal balancing. Due to the length of the stroke, this usually costs more. Most often an internally balanced assembly is offered at a more expensive price, rather than as an option. Whether an assembly is an internal or external type of balance, doesn't assure that balancing has been done. It merely refers to the type of balance and parts it will take. If you paid extra for balancing, I would assume yours would be balanced, which ever type you purchased. Double check with your supplier if you have any doubts.

When Chevy went to the one piece rear seal in 1986, the flywheel flange of the crankshaft was made smaller. Rear counter balance was lost in the process. One piece seal 350s, including L98s have a small "unbalance" weight on the flywheel/flex plate to make up for the loss of the compensating weight of the two piece seal crank rear flange. It is my guess that this practice continued on, in to the LT series engines, but I don't know that.

Comments and corrections are welcome. Good luck.

 

I'm ordering the Hardcore Racing Rotating Assembly #HCR-216-86005 from Summit Racing Catalog. It shows internally balanced.....I'm tearing down my 383 Max Velocity Plus Beck Racing Engine and installing these parts. My questions would be.....after cleaning and checking the block for any problems...will this rotating assembly drop right in without having to do any additional machining?.....Can some one recommend a good small block build up instruction manual or book so I can do this build up properly????? Changing heads to aluminum and going to a roller cam......Thanks :seeya Cappy

 

3.48" stroke! 4.030 bore = 355 ci
Doing some seaRCH ON THE NET I think that a L98 is mid internally and mid externally balanced.
The oem replacement Flexplate is defined " with weight" (153th) 12 3/4", and the front balacer (6 3/4") should be "neutral balanced".
The rotating assy I purchased has in the decription of the product the word: "balanced" without sayng if ext or internally...
An important Think:
The kit is eqipped with a 168 Th flexplate (1 piece pattern)
.Beppe
Beppe.

 

Cappy,

I don't find that part number in my Summit book. If it is another 383 rotating assembly, no machine work should be required. Because the rods are different than the ones in your current 383, I would check the bottom of the cylinder bores and the pan rail for clearence. Also, because of the rod, and more specifically, the cam change check for sufficient rod bolt to camshaft clearence. Even if this isn't a 383 to 383 swap, these are the critical areas to check. A little grinding MAY be necessary, but no real machine work is called for, here. Good luck.

 

Beppe,

You have ordered a stock stroke rotating assembly. The notation "with weight" in the description of the stock flex plate, alludes to the need for weight on the rear of the one piece seal 350s, I mentioned above. This is basically an internally balanced engine. The ad didn't mention "internal" or "external" because the method of balance is stock. Since it says "balanced", surely, it is. If you can catch them before they ship, you might see if they will substitute a 153 toothed flex plate for the one in their kit. If not, your old flex plate should work, just fine. Good luck.

 

CFI-EFI,
Part number is HCR-216-86005.....Hope this is a direct bolt in to my engine....I'm not sure what you mean about watching for the cam clearance? However I'm sure I'll be able to figure it out. After installing each part I will turn engine by hand to be sure no parts are coming into contact with each other.....I would like to hook up a 1 HP electric motor to the engine after installing internal rotating assembly, heads, cam, lifters, etc......then running engine on the electric motor for about an hour to make sure all the oil is flowing properly and parts are working as they should.....Would this be a good idea or is BUBBA playing with my head....... :seeya Cappy
BTW.....Please recommend a good book on small block high performance build up....Thanks again :seeya Cappy


[Modified by 8T1-7T9 BIONIC VETTE, 10:25 AM 7/21/2002]

 

This looks like the same part number in your origional post. I don't find it in my book or on their web site. I must be doing something wrong.

Depending on the specific rod and also the specific camshaft used, the rod bolts can hit the cam in 3.75" and longer stroke engines. Go easy before you ruin an expensive camshaft.

I have never heard of anyone doing this. I would NEVER try it with a flat tappet cam. You MIGHT be OK with a roller. Especially with a flat tappet, all the assembly lube will get wiped away. You want the engine to fire on the first rotation. Then take it to 3000 rpms immediately, for the first half hour, to break in the cam. A good oil primer attached to a half inch power drill should be sufficient. Prime until you get oil to the rockers.

There are a lot of good publications on the subject. HP Books puts out a good "How to Hot Rod The XXX Engine" series. I am partial to "Chevrolet Power" available from your Chevy dealer.

Good luck and have fun. I'm about two jumps ahead of you on my next project engine. I hope to have it in and terrorizing the strip, next spring.


[Modified by CFI-EFI, 7:35 PM 7/21/2002]

 

Thanks for the good info......I never thought to take her to 3000 rpm to break in the cam......Why do they do that?.....Do roller cams need to be broken in?......Guess I better purchase a good book somewhere and keep questions going on the forum to stay up on new tech tips to keep me out of trouble.... :seeya Cappy

 

Cappy,

3000 RPMs is incorrect. I should have proofed my own writting more thoroughly. It should say 2000 RPMs. The reason, is that during nornmal opperation, the cam receives only maginal lubrication. The main source of oil to the cam lobes. is oil that is "slung" from the crankshaft. At 2000 RPMs, the oil pressure is up and the speed of the crank is sufficient to ensure an adaquate supply of oil for the cam's first experiences in a tough life to follow. Although it's not common, a lobe can be "wiped" from a camshaft during a prolonged cranking on the first start up. On the first firing, you want that engine to start, NOW! It is my belief that a roller cam requires no such break in. Double check with your cam grinder when you purchase your cam. In my case, it's an old habit that may prove hard to break. Still, I feel that light loading, under power, is the best way to initially break in an engine. You will likely get as many answers to the "how do I break in my engine" question, as people you ask. It is a highly debated topic. You now have your FIRST, response. Study, read, ask questions, read some more. The better informed and knowledgable you are, the better equipped you will be to form your own opinions. Good luck and have fun.

 

CFI-EFI,
That explains it for me....Now I know the cam needs oil immediately or it will fry the lobes off without oil.....Good answer....now I know, and everyone else who was afraid to ask. :D I also went by a proffessional machine shop and asked more questions...I learned about choosing a small block for boring....He said look good at the cam ring casting collar....sometimes it will be fat on one side and slim on the other....This means the block was off cast towards one side during casting, and the walls are thin on one side and thick on the other. They prefer the hole be centered and even all around.....He showed me a bad cast and a good cast block...and sure enough there is a difference. Thanks again :seeya Cappy

 

You're welcome. I, as most others on here, are always willing to lend a hand to those with questions. Keep up the learning and have fun. "More Power To You!"

 

CFI-EFI, thanks for your good infos, I need a last good info from you...
Yuo said: 'The notation "with weight" in the description of the stock flex plate, alludes to the need for weight on the rear of the one piece seal ..'
Where is this weight??? . A weight can be relevant to the balancing procedure only if this is 'not weight centered '. Where is this wheight?

...Now i'm sure, The suppliers will send me a 153Th. flexplate and they said they balanced the crank with the 153 th. flexplate.
Beppe.