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Discussion Starter #1 (Edited)
This engine (302 from early 70s) has holley 4150 series carb and mild cam (with 280 duration .471 lift) and balanced crankshaft (with flywheel and front dampener only) done at the motor shop. I installed new pistons keeping the OE connecting rods.

The problem is it vibrates badly. After only several test runs intake manifold bolts tend to release although they are properly torqued to 25 ft.lbs.
The vibration also occurs when the car is not moving.

I suspect the crank may be imbalanced as I gave 50 oz flywheel to the motor shop who machined it to 28 oz. Or could it be another source of this vibration? What about new pistons?
 

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This engine (302 from early 70s) has holley 4150 series carb and mild cam (with 280 duration .471 lift) and balanced crankshaft (with flywheel and front dampener only) done at the motor shop. I installed new pistons keeping the OE connecting rods.

The problem is it vibrates badly. After only several test runs intake manifold bolts tend to release although they are properly torqued to 25 ft.lbs.
The vibration also occurs when the car is not moving.

I suspect the crank may be imbalanced as I gave 50 oz flywheel to the motor shop who machined it to 28 oz. Or could it be another source of this vibration? What about new pistons?
50 oz flywheel on 28 oz balance is a no no and will cause the problem you are having. It is not pistons. Make sure flywheel and Balancer are both 28 oz and I bet you fix your problem. Do not drive this car or run the engine anymore until this is resolved.
 

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OP said he had the 50oz flywheel REMACHINED to 28oz. So, that shouldn't be his problem unless they did it wrong or not at all.

As mentioned, the engine needs to go back to the "motor shop" as they made some kind of mistake. Probably mismatched balancer or flywheel wasn't properly machined.
 

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Discussion Starter #6
Can somebody post a photo of 50 oz flywheel machined to 28 oz?

And is it possible to install the flywheel to other than balanced position? There are some six bolts and I guess if the flywheel is somewhat rotated that is not good.

Not sure about the pistons and what is "bob weight". The motor shop balanced just crank without pistons; they said a small difference in piston weights, up to 3 grams or so should not affect the balance.
 

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Flywheel should only clock one way.

I tried to have a 50 oz machined to 28 oz also. All they did was put it on a flywheel surfacer and removed 22 oz. from the front side of the flywheel. I didn't bother to argue with them.
I did install it breifly and started the car, I didn't notice any vibrations. But I never drove it that way. I ended up buying a new 28 oz flywheel to be safe.

Jet
 

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67gtman - Did you pay to have this engine fully balanced? If so then they need to balance the whole rotating assembly... That includes the pistons. Somethings seems wrong with the balance.
 

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Discussion Starter #9 (Edited)
I brought to the shop 28 oz crank, front dampener and 50 oz flywheel telling them to make it balanced and they need to machine 22 oz from the flywheel. This shop does mostly freight truck engines and very rarely work on american v8 (this place is in Europe). Thus the guy seemed that he did not know what I was talking about but he said they have a balancer and they'll make it working. He gave me whole assembly claiming it has been balanced and for street use pistons should not cause noticaeble misbalance.

But now after second look the flywheel by far does not look like 28 oz flywheel as shown on the attached picture. There is only one hole about 3/4" diameter drilled from the 50 oz weight. ALthough the crank journals are leveled -.020" (with undersized bearings) this should be machined more. Any thoughts?

flywheel030203-2.jpg

jetfix - this is strange. yet I still don't know how to properly machine the 50 oz flywheel to 28 oz. I guess not like you are saying; rather continuously machine from the weight edges until the flywheel is 22 oz lighter I guess.
 

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I figured that they would have machined the material from one area, not all the way around.
They left it outside and I picked it up after hours. And didn't want to deal with it. So, It was easier to order a new one with a removable weight for any future changes.

Post a pic of what yours looks like if you can.

Jet
 

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Discussion Starter #11
From now on I don't trust anybody who tells me >>this thing is balanced<<. I'll add photo once I get to it maybe this weekend.
Does anybody know where exactly to machine the 50 oz wheel? My problem is I don't have 28 oz wheel, thus have to tell the machinist what to do. Are 28 oz and 50 oz wheels exactly the same only the weights' width is different?
 

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Well considering your location, I'm sure it's hard to find a good trusted shop....:):)
 

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Discussion Starter #14
So below is a flywheel that is supposed to work with the 28 oz crank and dampener. Is there any chance for this flywheel to be balanced?

reg0016.jpg

again can anyone advise how to machine it to be 28 oz? it won't be as I guessed before as this weight has approximately 550 grams or 19.5 oz (after measuring it and assuming it is steel with density 7.85 grams per cubic centimeter)
 

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That flywheel has not been rebalanced to 28 oz

you need to find a shop that knows how to balance an engine, the one you used sure doesn't.

I'd also suspect the damper was not correctly modified either.

IMO it may be better for you to just buy the correctly balanced parts and avoid the shops in you area.
 

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Not sure about the pistons and what is "bob weight". The motor shop balanced just crank without pistons; they said a small difference in piston weights, up to 3 grams or so should not affect the balance.
This is a bad sign.

It's impossible to balance a crank without the pistons. The machine shop needs ALL the parts of the engine that spin and reciprocate. They need the crank, rods, pistons, dampner, flywheel, rings, bearings, and even the clutch pressure plate.

They weight all the parts, the big and small ends of the rods seperately, do all the math, then bolt the flywheel and dampner to the crank, and load up "bobweights" that are attached to the crank throws with the correct amount of weight, and do a spin balance. When that is done, the pressure plate is attached, and it is re-spun, and weight taken out of that until it is balanced. (some shops have a seperate fixture for pressure plates)

You can't just "assume" the pistons will weigh the same, as those weights are ALL OVER THE PLACE when it comes to the aftermarket. There is a variance with the rods as well. Flywheels and dampners... can't assume anything.
 

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Im guessing you wanted to just rebalance the flywheel to 28 ounze and just use stock replacement pistons/rods.....If they used a crank balance machine they still would have to use bob weights to get the flywheel to the correct weight. It sounds like they balanced the crank, balancer and flywheel as a unit with no piston/rod bob weights....Hope they didnt drill or cut the crank or you may need a new one...
 

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Discussion Starter #19
Now I am little confused
So when you buy new pistons for 1968-1996 windsor and new 28 oz flywheel, these two are not "bolt on" parts? It is my understanding that some of you suggest that the engine is likely not to run properly when not balanced in a motor shop?
 

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Hello there.
As stated Yes the aftermarket piston/rod/cranks weight can vary widely.
The ONLY time that you can re-assemble a engine assembly without balancing is when you put all parts back in that came with the engine originaly. For example you just needed some bearings and a crank polish and a light re-hone with a "bottle brush" You havent changed out the pistons or rods etc.

But you DID change out the engine components. So if you have a early model engine that originally had a 28 oz balance factor then you need to replace the flywheel and balancer with 28oz parts.

Not sure why you gave him a 50oz flywheel to start with, but its obvious thats one of the major problems.
Replace it with a 28 oz.

Sorry to say that (as stated already) that if your "machinist" cut anything out of the crank then hes screwed it up also IF HE "balanced" the assembly with that flywheel attached. Youd need a new crank, However its difficult to say if he did.

Hate to say this but you may need to buy a whole new assembly. Im not sure of your financial situation but if your like most of us then that will be tough or youll have to wait. BUT there are complete balanced setups in a package deal out of the states. Just "drop" it in your block
Good luck
 
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