Anyone ever had their 401 or 425 balanced before they put it together? The guts of the 425 I am putting together for my '65 GS are at a very reputable performance shop in the next town south of here and they called me up today with a problem. The engine is a 425 with a stock crank that has never been turned, the balancer and pulley that came on the engine, stock rods that came with the engine (reconditioned with ARP bolts), original pistons (low mileage engine that didn't need boring), and the correct skylark GS manual transmission flywheel. The problem the guy called about is that he says it will require adding 90 grams of heavy metal to the rear crank throw weight to balance the engine out. He has the flywheel on it correctly with the dowel hole aligned. With it on there that way, the machined out place in the back of the flywheel is 180deg. opposite of the rear crank throws, so rotating the flywheel any would just make it worst. This all sounds really strange to me since that flywheel was on the original 401 in the car and had no vibrations in it at all --ran very smooth. Is the crank out of this 425 just that far out of balance? I took the guy the flexplate that came off of one of the 425's I took apart and he is going to put that on tomorrow and see what that does just to see how it changes things. That will answer if it is a problem with this flywheel or a problem with the crank. Anyone ever run into something like this before? If it turns out to be the flywheel, I plan to order one of the billet steel flywheels that Carmen sells.
Same Problem Here Brian, I had the same problem with mine. I have a 66 GS flywheel that I had balanced to the 425 with new (heavier) Egge pistons. It was way out of balance with he flywheel index and crank lined up. I had a sail added to the back of the crank that fit inside the flywheel. The sail on the crank required some clearancing of the block and rear main. Neither the machine shop or I realized it would need further clearance since they did not assemble the engine. I was not happy when I discovered it did, but, in retrospect, it was only a little bump in the road. It only took an hour or so to fix with a grinder. One other tip is to have you shop balance the clutch plate to your rotating assembly as well. Cheryl
Brian, the only reasonable explanations would be that the balancer or the flywheel is off, (or you bought real heavy rod bolts!)... either it's not the correct balancer, it lost one of it's weights, or the flywheel is wrong. Here's an explanation from Tom T on flywheel balance: >>>all I can tell you for sure is that the 401/425 flywheels (or flex plates) are approx. 4 1/2 ozs. out of balance, both standard & auto<<< And here's a pic of the balancer from my stock '66 401. It shows the pin weight pressed into the outer ring at the 4:30 position:
The guy from the shop called me back this morning and with the flexplate I took him installed on the engine, it comes out within less than 10 grams (it is a nailhead flexplate that was on the T-400 behind this engine originally). So the problem is obviously in the flywheel. Instead of modifying a cast iron flywheel and possibly compromising the integrity of it, I am going to order one of the billet steel nailhead flywheels that Carmen/Poston sell and have it shipped straight to the machine shop. If with that flywheel it is still way off balance, then they can just machine the appropriate amount out of the new steel flywheel and I won't have to worry about it cracking on me at some point down the road. The guy said that to rectify the out of balance issue that it would require taking more weight out of the same end of the flywheel that already has the pocket machined in the back of it, so the pocket is in the correct place, it just isn't large enough. Does that sound like a good plan to everyone? By the way Cheryl, I have a centerforce clutch and I have been told by several different places that you can't put them on when doing a balancing operation because the flyweights will move around and compensate some for any out of balance condition and throw off what is trying to be accomplished. I gave it to the shop along with the rest of the engine and they told me the same thing too. I have the same type clutch in my 300 and had it balanced without the pressure plate and it is still smooth as silk even though it was balanced without the pressure plate. From what I have seen, the centerforce pressure plates are well balanced when new.
Brian, when I had mine balanced they tried to feed me that crappola too. I told them thank you and sent it out somewhere else. The secong guy removed the balancing pins from the balancer and put them in another spot and it came perfectly into balance. I think that is your problem. I was lucky and was able to find an "old school" place that does balancing.......sounds to me like they just want the extra money for an additional operation. Think about it.......that crank would have had to been out from the factory. I used EGGE pistons, also. This guy: Rogers engine rebuilding woodhill, NY 607-458-5777.....probably the only thing on my motor that was done right the first time.:bglasses:
I know about the pins for the front balancer, but that won't help here--it is out too much. It is out by 90 grams, and putting a pin in every hole in the balancer wouldn't add up to 90 grams. This guy has been balancing engines for 25 years and he has actually done a nailhead before, just not one with a manual trans flywheel. He said the front end of the crankshaft with the balancer installed is only out by 9 grams, which is what I would expect and he can rectify that easily with the pins in the balancer. I ordered the billet flywheel and if it is still off this much with it installed, he can just mill more material out of the pocket in the back of it instead of adding heavy metal to the crank (which neither he nor I wanted to do). We didn't want to mill on the cast iron flywheel either because of the risk of weakening it.
Flywheel balance Brian, I had a similar problem with my 401. I bought one of the seel flywheels from T/A performance that was suppose to be for both the 401 and 425. This flywheel was way out of balance! It vibrated bad at 3000 rpm. To cure the balance problem, I placed the original flex plate on the flywheel and rotated the flexplate 180 degrees to cancel out the inbalance just to see how out of balance the new flywheel was. Needless to say, it was way out. so there are some weight differences between the 425 and 401 or the company that makes these new billit flywheels isn't balancing them correctly.
I ordered a flywheel from Poston this morning--Carmen was out of them and Poston had one on the shelf. The goal will be to make all the modifications to the flywheel and leave the crank alone. Jeff, you are the first one I have heard about having this issue on a 401. The flywheel I have now is the one off of my 401 and I never noticed any unusaual vibrations in it. Did your car come with a manual trans? I am wondering if maybe there is a different crankshaft for the manual transmission cars than the automatic cars. The crank I am using is the one out of the 425 I am building and it came out of a Riv. with a T-400.
Good Luck Brian, let us know how it turns out....this will most likely come up again in the future. It seems like many of the replacement nailhead parts 'aren't quite right'....Too bad. Things should improve as these problems are brought to light... Cheryl, what exactly is a 'sail'? I envision a 1/8" plate sandwiched between the crank and flywheel, and of an eccentric shape to provide additional balance weight??? Interesting and novel idea.... How's the '66 coming along?
Flywheel balance Brian, my 63 Wildcat was originally a dyna-flow auto trans car but the crankshaft was the same for both manual or auto. If I'm not mistaken theres only one company that acutally makes the steel flywheel for a nailhead but several people sell them. There is a difference between dyna-flow cranks and T-400 cranks. The dyna-flow crank has a bigger flywheel registering hole and a larger pilot bearing bore. Niether of which will effect balance. I had the registering hole enlarged to match my dyna-flow crank. The flywheel I bought from T/A performance was not balanced for my 401.
More on Flywheels Brian, The back of the stock flywheel and the aftermarket flywheel are a little different. I attached a picture of the aftermarket below. I think you may just have to remove more metal from the same side as it is removed in the picture (if I follow where it needs to come off from your description). That would make sense since the sail was added to the other side of the crank on mine to make the stock flywheel balance. With 425 pistons being heavier then 401s, I think they would require a different balance than a 401. The reciprocating masses are not the same, and the weights used on the crank to balance the assemblies are not the same. Anyone ever use a 425 flex-plate on a 401 with success (or vice versa)? Once the flywheel was balanced to the rotating assembly, my Borg and Beck clutch plate was balanced to that assembly. I can see how the weights on the Centerforce would disrupt that process. Walt, The sail is a piece of 3/16 plate that is butt welded to the block side of the crank flange. It is about 2 tall, and is parallel to the back of the flywheel. The machinist figured out how much weight was needed, welded a piece of about that weight to the crank in the correct location, and then ground it down a little as part of the finish balance. Sorry to say the 66 is behind a few other projects this spring and summer. I had to put the engine in the engine bay to save space in the garage, but it's just resting there for now! Cheryl
I'm confused..I thought a clutch plate should have a neutral balance, since it is not always in the same position relative to the crank. Frank
Your right Frank. The clutch plate should have a neutral balance. Mass produced objects (engines included) have the potential to be in or out of specification. Tolerances are less stringent for regular use, and, face it, things can get past the inspectors. If I am going to go through the expense of having an engine that should be in balance from the factory balanced, then it is not a bad idea to make sure the clutch plate that should be neutral is neutral. In my mind it is along the same lines as checking bearing clearances. Cheryl
Just an update for everyone: The billet flywheel arrived at the shop from Poston and it made the engine out of balance 70 grams in the opposite direction that the factory flywheel did! I had them drill the appropriate amount out of the flywheel and leave the crank counterweight alone. They also had to take about 9 grams out of the balancer to get the front end balanced (that is normal). I am heading out at lunch time today to go pick it all up so I can put it all together this weekend.
Well, that's good news Brian! I'm sure one of us is going to run into the same problem in the future....now we'll know the solution... Interesting that the 'front-end' of the crank is balanced seperately from the flywheel end...I never knew they did that! but now that I think about it...it makes sense. Have fun with the build!
I picked it all up and it doesn't look like any big deal--he just drilled two holes about 3/4" in diameter and 3/8" deep in the back side of the flywheel, directly opposite to where the balancing holes were drilled in the flywheel at the manufacturer. Short block starts going together tomorrow. All I am waiting on now is the big valve heads from Carmen and the headers to come back from being Jet Hot coated.
They will with the appropriate machine work. They are .060" bigger in diameter I think. The heads also have some mild porting done on them as well. With the cam I bought, the big valve heads, headers, and 2-4s, I should be at 400 hp.
