Auto-Marine engine balance question.

tmcboat wrote: Hi All, In 2016 I bought a 1984 ford marine 5.8 liter engine and installed my pmc 1973 28oz flywheel and a new 6.53 inch 28oz. 3 bolt harmonic balancer    so I could use my pmc 3 bolt pulley. When we started the engine up we notice a slight wobble in the harmonic balancer- about 1/32 inch. I didn't think much of it and the boat runs good and has about 110 hours on the engine but still has the slight wobble in the harmonic balancer. . My PMC engine has a drive shaft tied directly to a volvo penta stern drive. I have read 2 blogs. One says that PMC used the 28oz flywheels and 28 oz balancers up till the late 1980's. Ford auto/not marine engine switched to a 50 oz flywheel and 50 oz. balancer after 1981-I hate to think that I have to pull the engine and lower unit to install a 50 oz flywheel and 50 oz harmonic balancer when the engine runs good now. I am going to pull the harmonic balancer and use a dial indicator to see if the crankshaft end- snout the balancers fits on is out of round. Your thoughts and suggestions please thanks, tmcboat

See the answer somebody gave in your other post

Keno, didn't even notice you had your flux capacitor set and 1.21 gigawatts flowing!! haha!!!
I also have those same holes in my flexplate for me car....its kinda interesting. I would tend to agree with your assumption on that.

SN, don't mention it man.

But don't worry about marking the flywheel it will only bolt on one way, as far as clocking goes. It will look close but only fit in one orientation. One thing that might make it easier is mark which side faces out. The flywheels do have a slight off set front to back. When put on wrong on a car the trans wont seat but I couldn't tell you about a boat. So I will definatly be marking that. Or just look as to what side the counter weight faces.
Ryan

Keno, thanks for the pics. That makes sense that its acutally caste into the piece.
Ryan

i pulled that 460 apart and on the front once i pulled the harmonic balance off there was a big counterweight also keyed behind it. next then the front seal, i would say it weighed roughly 2 pounds...not the seal, the weight lol

Keno, Joe, Thank God you guys chimed in I was going crazy! That�s exactly what I was trying to find out. Interesting point about the timing cover and cold water lift pump. I didn't even think about that. And yes it is a belt driven fresh water pump. And I was defiantly going to swap oil pans and pickups. Gaskets are already in stock actually!

Eric, Brass plugs absolutely. But I'd put money that is a stock crank in Daves motor. They have to drill holes in the crank from the factory. Its normal to have machining tolerances and those tolerances need to be corrected by proper balancing. The flexplate/flywheels don't have dowels or eccentrics. The bolt pattern on the back of the crank is drilled in such a way that the flex/fly can only be bolted on one way. The only thing that I can think of off hand that has an eccentric is the fuel pump, driven off the front of the cam. Timing is done on the balancer, which utilizes a woodruff key to align the balancer to the proper orientation on the crank.

Dizuster...I don't even know where to begin with you.

Brass cast plugs also, I could see the crank 3 pics up needing balanced with the FW and HB, because of the swing and the extra weight added for swinging that crank, I dont think that is a stock crank, the flex plate does not look to be dowel pinned or have an ecentric to time it to the crank

davidg wrote: Anyway guys, help me out here. What does 28 or 50 ounce balance (or imbalance) mean? I also saw the term inch/ounce, or ounce/inch. Not sure what those mean. Can someone explain what those numbers and terms are.

It means exactly what it sounds like, the combination of the flywheel(or flex plate) and the harmonic balancer are 28 or 50 in oz out of balance because the crank rods, pistons, etc need the extra weight for the entire rotating assembly to be balanced. Either to keep the rotating weight down, or some other design concern the stock cranks didnt have big enough counterweights to allow the engine to be internally balanced so it could use balanced flywheels and balancers. So what really happens here is the engine minus the flywheel and dampener is not balanced, in fact it is off balance by 28 in-oz. The flywheel and balancer are also off by 28 in-oz total but 180 degrees different than the engine, and when put together all are in harmony.

In a race situation internally balanced is better.. but in a skiboat boat, any balance is good balance.

Inch-ounce is what is sounds like an ounce of weight located one inch off center.

Ken....I like the line about staying at the HIE. I was about ready to use that today in one of my posts on this subject but didn't. I am not an engine expert, BUT.........

Anyway guys, help me out here. What does 28 or 50 ounce balance (or imbalance) mean? I also saw the term inch/ounce, or ounce/inch. Not sure what those mean. Can someone explain what those numbers and terms are.

I do not recall any kind of weight on the flywheel at all. Take your trans and bellhousing off your Supra and see what it looks like. Either way, it should work, right?? It works with your current set up.

I think the biggest difference you may find is, as folks have pointed out, is the larger clearance between the piston and the cylinder wall. But, it may be just fine.

Ryan.....attached is a picture of the crank in my boat. I assume it just has the normal counterweights found on standard production engines.

What is stopping you from just using the Mustang engine? It is balanced already. It is standard rotation. You have a flywheel that was being used for marine purposes from another 351. Just bolt that on, and your damper, and go. I would want to be safe as well, but, I don't see what is stopping you at this point??

davidg wrote: Ryan; There were no weights that I could see, or had to add. I also know that there were no weights on the crankshaft as I just assembled the engine a couple of weeks ago.

FYI - These are the weights on the crank that I was talking about that need to be drilled for either lightening or adding mallory metal..

Since nobody wants to believe me,
I pull some outside sources and site them here.
http://www.rpmmachine.com/engine-balancing.shtml
It won't let me copy the paragraph i want, but scroll down to "internal/external"
Just about half way. But heres an excerpt...
"If you're rebuilding an engine that is internally balanced, the flywheel and damper have no effect on engine balance and can be balanced separately. But with externally balanced engines, the flywheel and damper must be mounted on the crank prior to balancing."

http://www.carcraft.com/howto/ccrp_0803_engine_balancing/index.html
page 2.
"Internal vs. External Balance
Packaging is also an important issue. During the design of the 400ci small-block, a major engineering hurdle was insufficient real estate inside the small-block crankcase for the larger counterweights demanded by the 400's supersized 4.125-inch piston. This was especially difficult in the rear of the engine because the rear crankcase area on a small-block Chevy is restricted by the placement of the oil filter. The solution called for external balance weights placed on the harmonic balancer and flywheel/flexplate. One advantage to external weights is that they are generally lighter because they are positioned at the extreme ends of the crankshaft. The disadvantage is that these offset weights impart their own twisting forces back into the crankshaft, which is not good. This same situation occurs with the 454ci big-block Chevy, which is also the only production big-block that uses external weights to balance the engine."

"Small-block Fords have always been externally balanced, but because Ford is a name synonymous with change, the Blue Oval engineers altered the amount of the external balance when the engines morphed to a one-piece rear main seal. Early small-block Fords used 28 ounce-inches as the external weight amount, changing in 1981 to 50 ounce-inches. Like small-block Chevys, parts can interchange between early and late engines, but to guarantee smooth engine operation, the crankshaft, balancer, and flexplate/flywheel must all be kept within the same balance family."

to help you better understand, when i build a stroker 383, you use a 350 cube block and a 400 crank, i have to buy a 400 FW and A 400 HB, and send them out to have the three parts balanced together, to make them as one....that is what is considered an internally balanced engine. you cant use the 400 FW or HB on a 350 crank. but you could take the FW from a 350cube and slap it on a 265,283,327,305,307 because they are externally balanced engines
I will then weigh each piston, rod, and grind them for perfect weight within a gram or so of eachother so those parts are balanced
this is a weight balance not a reciprocating balance

Dave I too think thats the case, under 5k you do not need to balance any of the internals because they are close...when you spin them up past that mark you need precise weights of the pistons, rods etc.
i think Ryan refers to internally balanced as this process.
such as a 400 sbc, its a special harmonic balancer, flywheel and its all bolted together and spun on a balancing machine WITHOUT the pistons and rods, thus this what is meant by an internally balanced engine. you cant use a 350 FW on a 400....but you could use that FW on any other SBC"s, those parts such as the 350 crank is balanced by itself along with the FW and HB.