cyrus77

iTrader: (4)

Mercruiser 420 HP 454 balance questions

I got a 1987 Mercruiser 420 engine. Very happy about finding one. I took it apart and found it has TRW pistons .030" over so it has been rebuilt. It has;
a weighted harmonic balancer (I believe stock part number)
a weighted flywheel 3973457
So I was shocked to find the crankshaft 3967416 forged has a some Mallory metal (tungsten) added to heavy the counter weights and the rods have had metal removed from the bottom.

Does anybody know for sure if this is stock? Whats going on?

picklenjim

Does the crank have the complete part number at the rear of the crank or does it just have the last 4 numbers at the front. The old originals only had the last 4 numbers at the front and were used in the '70-'71 LS6 & LS7 engines along with the flywheel you have, 14" with 11" clutch. Then they started making the crank again using the same number but the crank had a smaller counter weight on front and the complete part number is at the rear of the crank. That flywheel when used with the newer crank caused vibration. Don't know the history behind yours but apparently somewhere along the line someone had it balanced up. I wouldn't worry about it just keep those parts together. The removing of metal from the rods s typical of a balance job.

cyrus77

iTrader: (4)

Complete number at rear.

What do you mean balanced up? I figured the engine as it came would be balanced. Why would mallory metal be used? Did Mercuiser racing use it?

cp5899

iTrader: (1)

Mallory is used to balance the crank if a good bit of weight is needed on the crank to balance the rotating assembly.


I'm not sure if the mags are balanced from mercruiser or not? I'm about to balance my 502 mag so I'll know in the next week or so. When I balanced my 330hp 454 it was not balanced, but it wasn't a mag. Perhaps the mag gets balanced from merc.

endeavour32

iTrader: (4)

I do not think the Mags or the 420's for that matter were balanced..

picklenjim

Just tweeking the balance of everything. Good idea to have everything balanced on a build just for piece of mind. Would suck to fire a new engine you just put together and have a vibration and the balance be in question. Helps preserve the life of the crank bearings too. Hard to tell what or why things were done unless you know it's complete history. You know it's been rebuilt.

cyrus77

iTrader: (4)

No one mentioned it, but I was concerned that they offset ground the crank to get a little more displacement. It seem like the only reason to add so much Mallory.

picklenjim

Doubt that. To increase the stroke on that crank they would have had to weld up the throws and then regrind it offset. Then when you add the mallory they would have so much in it that they could have just bought a nice aftermarket stroker crank. Also would have had to buy pistons to use with it. Put the crank in the block and one piston and measure the stroke.

MER Performance

I would be concerned, on a rebuild with +.030 TRW pistons not seeing some type of changes. 7/16th rods would definitely need some material removed on both ends to match. The weight of the stock pistons should be close to std. the amount of holes drilled in the crank from stock balance to now could easily affect what is there now. Mallory, added depending on diameter would be added depending if the heavy side was 180 degrees from the counter-weight. You would have to add weight, just to bring the counter weight around for drilling.
I can not give an answer, relating to the part numbers your have unless I looked them up, I agree; with prior post. I have seen, lazy balance work from others, drilling the flywheel, balancer, welding material to the leading or trailing edge of the counter weight. Tungsten added by drilling 90 degrees to crank and welded in. Instead of parallel, drilled, reamed and pressed in.
Sounds to me it was done correct. If you have a balance card, that would help or you will be faced with pressing off pistons, possibly galling the wrist pin by removing it. You will have to know the rotating weight and reciprocating weight of the rod, plus the pin, piston,rings and rod bearing. If you have run the engine already and feel no vibration, by 2500-3000 rpms or the engine doesn't move across the floor, I would say; you are good.
Example: I had 2 engines come in with problems, not even expecting the balance to be out. Put 1 on the dyno, @ 3000 it vibrated the engine and stand across the floor. I fired up the other engine in the boat and could feel it. Can not tell you how many grams it was out, since the engine was so wrong, we had to start over. Long story!

ezstriper

very unusual to see mallory used in a base engine like this....no not factory