Flywheel Weight

[Paul]

I recently changed the clutch in our n/a daily driver due to the old one being quite rough.

I know that the n/a flywheel weighs in at about 33lbs and that the turbo flywheel weighs about 22lbs. This, I think, accounts for some of the turbo engine spunkiness, especially at low speeds.

So, I decided to lighten the flywheel while I was facing it by about 5 lbs. This somewhat surprised me with a better than expected improvement in acceleration.

Minor down side is need to be a bit careful on takeoff to avoid stalling engine, especially if you start in second gear.

Food for thought.

Paul

[JoeIsuzu]

Minor down side is need to be a bit careful on takeoff to avoid stalling engine, especially if you start in second gear.

That would be me, about 95% of the time.

I'd be curious to see Isuzu's rationale for the lighter turbo flywheel. It seems any argument for it would also apply to the NA engine.

Jack

[isuzu Specialities]

That is a beautiful lathe

For every 1lbs of weight you remove form a engines rotating assembly you must add 1.78oz of weight to your harmonic balancer. Doing so will to prevent the main and rod bearings form walking all over the place. Also prevents harmonic resonance for tearing apart your engine.

The more mass of an object the longer & more difficult it for it to accelerate its mass. By reducing the weight of the flywheel permits the engine RPM to rise faster. I am currently building a high performance 4ZE1 that I expect to get over 300HP out of. I have reduced the weight of the pistons, crank and flywheel to a total of 27Lbs down form 61Lbs. It's a fine line when doing this to any engine... too light and the engines rotating assembly won't have enough inertia to permit the engine to idle. 20+ years ago i did just that with a chevy 305 V8. the rotating assembly was 3lbs too light for it to idle.

dam... that is a gorgeous lathe

[Paul]

I wasn't aware of the need to adjust the balancer. I did just check the Isuzu parts book and sure enough there are different p/n's for the balancers on the n/a and turbo engines.

Given the modest (I think) change I made, I will ignore this risk and see if anything bad happens. Truck has 287k miles now. Maybe let you know.

Glad you like my lathe. Taiwanese, bought 40 years ago and been a friend ever since.

Paul

[isuzu Specialities]

sure enough there are different p/n's for the balancers on the n/a and turbo engines.

Truck has 287k miles now. Maybe let you know.

Paul

Assuming that 1/2 way decent maintenance was carried out for most of the vehicle life time the engine will start to act tired right about 250 to 300K miles. However run very well with acceptable drivability to 400k-ish miles.

Running a engine with the incorrect harmonic balancer weight will shorten whatever potential life is left in your engine by 50%. The thrust bearing is first to fail. 278K miles or not I would highly recommend installing the appropriate balancer.

[Paul]

sure enough there are different p/n's for the balancers on the n/a and turbo engines.

Truck has 287k miles now. Maybe let you know.

Paul

Assuming that 1/2 way decent maintenance was carried out for most of the vehicle life time the engine will start to act tired right about 250 to 300K miles. However run very well with acceptable drivability to 400k-ish miles.

Running a engine with the incorrect harmonic balancer weight will shorten whatever potential life is left in your engine by 50%. The thrust bearing is first to fail. 278K miles or not I would highly recommend installing the appropriate balancer.

Do you have a suggestion about how to add weight to the balancer as there is not likely a balancer in the Isuzu catalog for this?

Also, I have never heard the phrase 'bearings walking'. Can you describe this for us?

Thanks - -

Paul

[isuzu Specialities]

The average 4-cylinder engine are under 2.4L. This is due to the harmonic resonance being extremely difficult to cancel out. It's simply the nature of the design. 3 ways manufacturers combat this is to limit the RPM, make the rotating assembly heavy &/or use of a balance shaft.

Isuzu uses heavy rotating assembly & low redline.
(Side not Isuzu is the only engine manufacturer to build a 5.2L 4-cylinder engine.. wow!)

When the harmonic resonance becomes to great it literally vibrates the crankshaft at a very high frequency. This vibration smashes the crankshaft into the bearings and plows into the hard facing of the bearing. The evidence of this looks a lot like a lathe cutting tool chatter on a work piece.

This constant high frequency rapid hammering of the bearings expands the steel bearings & that expansion needs to go somewhere. It can't really go outward due to the block casting, so it moves the bearing laterally across the crankshaft. On connecting rods the bearing will twist the rod on the crank.

I'm not 100% sure what harmonic balancer is needed on your engine. I know that lighter rotating assembly = higher resonent frequency and more substantial weight is required to cancel it out. The rule of thumb is 1.78oz for every 1 Lbs of weight removed. Some research on balancer weight & shaft size to fit your crankshaft is needed. A good starting point for potential balancers to consider are Mazda G series, Mitsubishi 4G series along with Peugeot 504.

[Paul]

Thanks for the response.

While some of these things may happen to a degree. I am going to let it run as is and hope for the best. I do definitely like the difference in acceleration.

Paul

[Halden]

Paul, have you noticed if it seems a little noisier or any increase in NVH? I talked to a VW friend about this and he mentioned people have been lightening flywheels on those for years and have never seen any issues. People are putting thousands and thousands of miles on after doing this). I'd imagine there is a pretty big margin for error here.

One of the big engines I maintained had a viscous damper. The fluid was supposed to be changed and tested on some schedule, but it was absolutely never done. Made a lot of horrendous sounds when cold. Bearings looked new after 30,000 hours, save for some scratches from dirt from my predecessor. Damper apparently had sounded like this for 60,000 hours...

[Paul]

Halden - -

No, no change in NVH, of which diesel PUPS have plenty. As I noted earlier, one needs to be careful to give enough throttle on takeoff, especially if you're a 2nd gear takeoff person. But, after takeoff, the acceleration is noticeably improved.

Paul

[DieselJeep]

All inline 4 cylinders have a zero balance. Two up, two down.
On reason the tend to vibrate at idle. The block trying to sway opposite the equal " dumbbell" of weight rotating during ignition.
If you look at the harmonic balancer, there is a zero balance, ie. No offset weight off to one side as in a v8.

I haven't researched the engineering involved, but with a zero balance flywheel, and zero balance harmonic balancer, on a zero balance engine, I'm fairly certain you should not have to add weight anywhere. Esp with a 30lb flywheel on a 112 Cid 4 cylinder.

The flywheel primarily stores inertia.like lumbering forward at idle.

I have thought about shaving the entire horizontal bell off if I were to build a. 4FB1 diesel Pontiac T1000. I already found the perfect turbo.. Losing half of the mass of the flywheel would be fine and absurd once the launch was sorted.on tiny car tires? Whew! However, as I need all the inertia, mass and torque possible with heavy 31" tires off road tires, and a transfer case, and extra axle grunting over obstacles, not on this one. And when I get over 5psi boost, with all that rotational mass that could easily be TWICE a 4x4 pup, you don't notice. Scares the wife. Retired neighbor swore I spun the 31's on my way yo that delicious 5400 rpm redlibe.

I do agree that there would be a point of no return, shaving every once off it wouldn't idle. Especially on a v8 with one cylinder out of phase.But I'd bet the flywheel shaved into a flat plate for a drag application would idle fine.

[DieselJeep]

All inline 4 cylinders have a zero balance. Two up, two down.
On reason they tend to vibrate at idle. The block trying to sway opposite the equal " dumbbell" of weight rotating during ignition.
If you look at the harmonic balancer, there is a zero balance, ie. No offset weight off to one side as in a v8.

I haven't researched the engineering involved, but with a zero balance flywheel, and zero balance harmonic balancer, on a zero balance engine, I'm fairly certain you should not have to add weight anywhere. Esp with a 30lb flywheel on a 112 Cid 4 cylinder.

The flywheel primarily stores inertia.like lumbering forward at idle.

I have thought about shaving the entire horizontal bell off if I were to build a. 4FB1 diesel Pontiac T1000. I already found the perfect turbo.. Losing half of the mass of the flywheel would be fine and absurd once the launch was sorted.on tiny car tires? Whew! However, as I need all the inertia, mass and torque possible with heavy 31" tires off road tires, and a transfer case, and extra axle grunting over obstacles, not on this one. And when I get over 5psi boost, with all that rotational mass that could easily be TWICE a 4x4 pup, you don't notice. Scares the wife. Retired neighbor swore I spun the 31's on my way to that delicious 5400 rpm 4fb1 redline.

I do agree that there would be a point of no return, shaving every ounce off it wouldn't idle. Especially on a v8 with one cylinder out of phase.But I'd bet the flywheel shaved into a flat plate for a drag application would idle fine.

Esp on a zero balance engine with equal ignition pulses, and full timing and fuel control of mechanical diesels.

Just have to Rev it like a gasser to not stall on take off.