Torsional vibration, harmonic balancers, custom machining

62Ranchero200

62Ranchero200

Famous Member
I spoke with Ricky Hults at ATI Racing yesterday about harmonic balancers. He told me that the risk of running a machined-down harmonic balancer would depend on the HP output and RPM range of the engine.

The primary issue that harmonic balancers are designed to address is torsional vibration. Overly simplified, torsional vibration is the flexing of the crankshaft in the direction of rotation, due to the power stroke. The risk is that with too much flexing, a crankshaft can experience metal fatigue, crack, and eventually break.

From online articles (for example, atiracing.com), it appears that in rough terms (not engine specific), less than one degree of torsional vibration is desirable, between one and two degrees is acceptable, and over two degrees is considered dangerous. These guidelines vary according to the length of the crankshaft, the construction of the crankshaft, the specific output of the engine (HP per cubic inch), the RPM range of the engine, and perhaps other factors such as whether a manual or automatic transmission is used (I think torque converters probably act as torsional vibration dampers, since the viscosity of the trans fluid probably damps torsional vibrations to some degree; whereas a solidly engaged clutch may not, depending on the construction of the clutch).

We have zero information from Ford as to how much torsional vibration is acceptable for the components of our Ford Sixes, nor any way to quantify the damping factor of stock harmonic balancers (although Ford engineering guidelines on these topics presumably existed when these engines were being actively designed). Even less information is available on how much more torsional vibration a modified Ford Six might generate and how much damping it might require.

There is also no reasonable way for an individual to directly measure torsional vibration on their engine. I thought that perhaps Autometer or a similar company would make vibration gauges - surely they would be useful in some forms of racing with high output, high RPM engines, like NASCAR engines, as predictors of component failure - but it appears that no one in the automotive aftermarket does.

The complete lack of information on this topic bothers me greatly - torsional vibration and harmonic balancers are truly the proverbial "black boxes" that we know nothing about.

Of course, we could assume that Ford's wise, all-knowing engineers designed harmonic balancers with exactly the needed amount of damping for the worst operating conditions that could possibly occur on these engines :roll: , and that reducing this damping by even the smallest amount would provide insufficient damping, allowing torsional vibration over the threshhold of metal fatigue and eventual breakage. But we need to remember that this is an assumption. Some engines could have been "overdamped" in an effort to "err on side of caution". This is the reason why "out of the box" carburetors are often excessively rich - the manufacturers are "erring on the side of caution", since running rich may cause poor performance, but rarely damages engines, while running lean has been known to damage engines. We're not terrified to modify carburetors, because air/fuel gauges are available, and even without those it's possible to read the plugs. Also, many engine part decisions are made based on economies of scale: if the same or a similar part can be used across engine families (for example, SB6 vs BB6, or SB6 vs SBF), the part becomes cheaper to produce.

Engines are often stroked to provide greater displacements - 200s to 221, 302 SBF's to 347, 350 SBC's to 383, 460 BBF's to 521 - and the stock harmonic balancer is often used on the stroker engine for a low-budget build, if the external balance is correct (internally balanced /28 oz /50oz for SBFs).

I wonder if anyone on this forum has any information about torsional vibration on our Ford Six cranks - specifically, US 250's - and about the degree of damping provided by the stock harmonic balancers. Would machining the second (front) pulley from a stock 250 harmonic balancer (in an effort to gain clearance between engine and fan) mean certain destruction?

EDITS:

The rotating assembly has been statically and dynamically balanced
The engine features ARP main studs
The engine uses "early" 300 rods, which I expect are heavier than 250 rods
The engine uses very short custom pistons, which I expect are lighter than stock 250 pistons
This combo uses an automatic if that makes any difference (if torque converters damp torsional vibrations)

Thanks,
Bob
 
7th picture down shows the updated 1994 cranshaft for the Aussie 250, still with a 1.247" crank spigot, but a 3 element harmonic balancer.


My personal view is that back in the mids 60's when it was redesigned as a 250, Ford Dearborn reworked the stock 200 style crank main bearings to larger , reworked the thrust bearing and crank spigot for sound durablity reasons, and that they alone are enough to ensure that any US 250 crank is gonna be a heck of a lot stronger than the Aussie one. A big, thick 1.375" crank spigot will soak up a lot of crankshaft whip, and ensure that the harmonic balancer doesn't need to be extra special.


The Aussies and Argentine 3.1 and 3.6 liter 188's and 221's, and the later Aussie 250's are fine without the thicker snout..its just not an issue. But the Dearbrn designed crank is a lot meatier, and its a factor in its favour. Extra weight on a six cylinder crank always helps dampend out critical vibration.


From personal experience, the counter weight situation, and the total weight of the crank define the rpms where crtical vibrations occur. On the early steel crank the Australian small six cylinder Holdens used were 13 pounds heavier, and removed the 4400 rpm resonance and allowed it to rev to 7000 rpm without crtical vibrations. Later, Holden made a heavier cast iron crank which weighed 13 pounds extra, and the same 5300 rpm crtical vibration got rasied up to 7500 rpm. The extra amount of metal on the nose of the crank woudn't have been added for no reason. I know Dearborn have an emplty box rule, and that if they had the patterns, then going to that big fat snout would have been pretty cheap, but it wouldn't have been done for nothing.

Whittle your balancer/dampener down, for clearance, and I'm sure you'll be fine.





viewtopic.php?p=244499

xctasy":352qyrox said:
Development Path of the X-flow after 1982.

There is a lot of talk about the OHV, Single OHC and Double OHC x-flow engines, and claim and counter claim as to what works best on dollars verses power. Despite the vast changes, there are some really amazing similarities which allows the later stuff to fit the earlier engines.

Here is a very basic picture list of major changes in the X-flow engines from the first alloy head to the latest Barra 190.


Alloy head EFI, released late 1982, was a replacement for the lethargic 4.9 Cleveland 4-barrel and much more verile 5.8 4-bbl.



The EFI was technically a 149 hp version of the 131 hp 2-bbl Alloy head six. In practice, earlier 2-barrel 4.1 Sixes were rated at 141 hp, but Ford de-rated the carby engine 10 hp and 4 lb-ft on release! So the extra 18 hp and 15 lb-ft growth in torque was largely a 'paper' increase.

Fords last 4.9 was rated at 188 hp and 262 lb-ft, while the 5.8 was rated at 200 hp and 306 lb-ft. The 4.1 EFI easily shut down any 4.9 by 0.4 seconds on the quarter mile, 16.9 verses 17.3 seconds. Auto 4.9 LTD's had trouble breaking 18.8 seconds on the quarter mile, the LTD did 17.7 seconds.

A 4.1 4-speed carby was 17.6 seconds, while the 5.8 Police Interceptor was 15.8, the heavier Ghia ESP 16.1 seconds. When old 5.8's were still doing top whacks of 120 to 124mph, the EFI's 110 hp showed a significant loss of traditional Ford V8 performance.

Private car builders like D i c k Johnston , Advanced Induction Systems and Mike Vine added versions with carbs or EFI with anywhere from 217, 255, to 348 hp. At 3 to $4000 a kit, verses the old 750 buck 4.9 or 5.8 option, there were few takers.







Power for the 1985 XF variant was lifted to 162 hp DIN net at 4000 rpm, and 246 ft-lbs at 3000 rpm with 8.8:1 compression. The additive was the wilder 264 degree cam in place of the stock 256 degree item found on all cooking model Falcon. This was up 31 hp and 17 lb-ft on the Weber 34 ADM equiped carby version, still sitting at about 131 hp. On the base Falcon GL S-pack 4-speed, the quarter mile acceleration was still 17.6 seconds with a carby, but down to 16.3 seconds with EFI. Top speed was 109 mph wih carb, and 115 mph with EFI.




AIT did a 350 HP twin turbo version of the XF EFI, and then added X-Trak 4WD. Sadly, the project faltered.


A 5-speed T5 gearbox was a late addition. Magazine reports showed quarter mile times around 16.6 seconds on the lightest Falcon S pack.


Ford Dearborn, having seen Ford Australia was the most profitable wing of the Ford global empire, was happy to allow the Max Gransden and Bill Dix design another local Falcon, this timne with an OHC I6.

Two version were made, a base 161 hp CFI item, and an upmarket Multipoint EFI version with 186 hp. AIT devised a 240 hp Turbo version, but Ford opted out at the 11 th our due to transmission and drivetrain durability issues. Shame! AIT then went bust


1988 to 1991 EA 3939 cc Central Point Injection (out of a taxi with the very common propane carb).




The 3939 cc 238 cube OHC engine was more undersquare than the OHV. It had a rev limit of 5000 rpm, up 500 rpm from the 85 XF, up 200 rpm form the 82 XE. Pistons were undersized 68 thou, deck height 160 thou lower. Despite this, the engines were still a weighty 518 to 540 pounds, up from 481 and 537 for the carby and EFI OHV x-flows.

The OHC block has heavy gussets to add strength.


The rocker ratio was now 1.8:1, rather than 1.73:1 as with the earlier OHV X-flow

Four bolt bellhousing different to the ohv X-flow.

Starter motor nested under the true left side of the engine in the space previously occupied by the OHV camshaft.

Although the block was different, the crank and oil pump, 4.08" bore spacings and 5.88" con-rods were the same as the last OHV X-flow's, and it was made on the same machines and same Geelong plant that had been in operation since 1962 building 170 cube sixes.

The early EA variants had 3-stage automatics, then after 1990, BTR 4-stage. BTR 5 speeds were a common option.

The EB Series 1 variant had the same engine as the upmarket EA's. Then the EB II got a 20 thou over bore, bigger valves, a wilder cam and 243 cubes for 3984 cc's. The CFI version was scraped, and the MPI version had 198 hp and 257 lb-ft of torque.


The 1992 XR6 version had extensive blue printing by the Tickford engineers. Valve springs were 10% stiffer, head was a selective casting with smallest ports and alterations to cam timing and a better exhast system. No headers, but the engine was strong with 216 hp, and 269 lb-ft, a growth of 9 and 5 % respectively.
The rev limit was still 5000 rpm, but power was at 4600 rpm rather than 4500 rpm. Quarter mile times in this version were the quicker of all factory non turbo XR6's, 15.6 seconds. It was faster than the 221 hp 5.0 XR8. Despite power increases and spec upgrades over the years, these genuine Tickfords were standout performers.




In 1994, the EL crank got reworked to 12 counterweights (Holden XT5/XT6's had 12 counterweights in 1980, so not cutting edge). All Ford small I6's have had 8 counterweights since 1960 to 1993. The harmonic balancer was changed to a two element item.

The bearing clearances were tightened up.

Peak revs increased to 5500 rpm, up 10% or 500 rpm.

The bellhousing pattern was similar, but has 9 bolts instead of four bolts.

Compression was increased from 8.8:1 to 9.3:1. Every EFI since 1982 had 8.8:1 C/r, so a 6% rise required a the return of the piezo electric knock sensor last seen on the 86 to 88 OHV Falcon I6. This reduced ignition advance.

Engine mounts became hydroelastomeric, part silicone fluid, part rubber.

Serpentine drive for solid mounted ancillaries


A changed cam profile was employed

Waste spark triple coil ignition had no distributor on the EF. It reapeared on the EL!




In additon, the start of the 12 year reign of the Dual Resonance induction system, still going strong on the 2006 BF, made its appearance on the 1994 EF. The peak power increase was only about 6% for power, and 3% for peak torque. However, in the used range between 2500 and 3000 rpm, power increase was 9%, or 20 lb-ft. The runner changed from long path to short path at 3500 to 3700 rpm.



The power growth was form 198 hp to 210 hp, and from 257 lb-ft to 263 lb-ft. After 12 years, the base Falcon engine exceeded the last 1982 4.9 and 5.8 Cleveland V8's for claimed engine power. Stock automatic Falcons were hard pressed to dip below 16.5 seconds on the drag strip.

The XR6 EF power climbed to 220 hp, and 270 lb-ft, and yielded excellent 15.2 second quarters in 5-speed form. A 66 pound growth in weight was a 2% increase...exactly equal to the 2% power increase over the earlier EF.

XR6 automatics were significantly slower, and there was a large variance, with some 4-stage auto versions slower than 16.5 seconds over the quarter. Noticable was the gruffness of the engine with the BTR auto, despite plastic sump and NVH reduction techniques. The manual XR6 was still a great performance car for a cheap price, but the Supercharged XU6 Commodore with a 235 variant of the GM 3800 engine could yield mid 15 second passes with a 4-speed automatic.

The EL was a minor variation on the basic EF engine, but had many internal changes. Some of the XR6 engine mods found there way into the Fairmont Ghia. The XR6 stayed at the same power as before.


Sprintex and Whipple blowers were seen in the 1997 EL
The ill fated AJ-6 kit is still avaliable as a swap into the later AU's. The kit works best with the EF or AU distributorless ignition module. Most EL's had the EB/ED distributor. There kit will fit the OHV if the EF/EL/AU serpentine drive is used.

.

There was a reputed running change to the larger 2.65" main bearing AU crank and 6.06" rods with shallow pistons, and the 2:1 rocker ratio head late in the EL models life. The new AU represented a 700 million dollar investment by Ford Australia, and a complete re tool of the plant to suit the needs of the 21 st century.

With the AU came a huge rework of the basic engine. Variable valve timing was now optional, with power going to 231 hp, the 211 hp base model, the 198 hp LPG version, and the 220 XR6 and the 225 hp Ghia engine. It needed it, the portly optional IRS soaked up 154 pounds, requiring an extra 5% more power just to offest the weight gain.

Rev range was now up to 5700 rpm.



The Barra 182 and 240 Turbo found in the BA Falcons were the real hits for October 2002.

The block was revised.
The crank was reworked to accomodate a narrower single row simplex chain instead of the earlier duplex chain.
The water passages were changed
The oil pump was shifted to the front, using a modern g-rotor pump.
A windage tray and moved pump allowed a safe 6000 rpm rev limit,
the stock 6.06" conrods got a new part number and an extra oil hole for gudgeon pin lubrication,
new pistons to fit the four valve per cylinder twin cam head


The rev range allowed just over 1 hp per cubic inch, with 244 hp at 5000 rpm with 280 lb-ft at 3250 rpm. With 6 pounds of intercooled and turbo, the 240 T had 322 hp at 5250 rpm and a mamouth 332 lb-ft from 2000 to 4500 rpm.

Barra 182



Recent upgrades are the Barra 190 with 255 hp, the 362 hp 270 Typhoon and Tornado. Various dyno tuned engines with better cranks, pistons and rods have rated up to the 1200 to 1500 hp mark!


Showing the options open to us all, a gentleman called Mark, who's TE Cortina has the later EF OHC EFI unit on his ohv X-flow. Not a direct bolt-on, but Dynoed250 has shown you can fit any later EB EFI stuff on the earlier ohv engines, so there is no limit.

Click to expand...
 
62Ranchero200":2zliq2mr said:
I wonder if anyone on this forum has any information about torsional vibration on our Ford Six cranks - specifically, US 250's - and about the degree of damping provided by the stock harmonic balancers. Would machining the second (front) pulley from a stock 250 harmonic balancer (in an effort to gain clearance between engine and fan) mean certain destruction?
Click to expand...

Ford has specific parameters for acceptable crankshaft torsional vibration - usually expressed in terms of "degrees double amplitude"; in other words peak-to-peak twist degrees. To measure it requires special instrumentation be afixed to the end of the crank. This is a costly undertaking and not one normally found in your corner dyno shop.
I have machined all the pulley grooves off a stock damper to reduce weight but still retain a modicum of crankshaft twist control. It survived high speed operation on a drag car.
 
THE FRENCHTOWN FLYER":16yx3ur1 said:
62Ranchero200":16yx3ur1 said:
I wonder if anyone on this forum has any information about torsional vibration on our Ford Six cranks - specifically, US 250's - and about the degree of damping provided by the stock harmonic balancers. Would machining the second (front) pulley from a stock 250 harmonic balancer (in an effort to gain clearance between engine and fan) mean certain destruction?
Click to expand...

Ford has specific parameters for acceptable crankshaft torsional vibration - usually expressed in terms of "degrees double amplitude"; in other words peak-to-peak twist degrees. To measure it requires special instrumentation be afixed to the end of the crank. This is a costly undertaking and not one normally found in your corner dyno shop.
I have machined all the pulley grooves off a stock damper to reduce weight but still retain a modicum of crankshaft twist control. It survived high speed operation on a drag car.
Click to expand...

Greg , iron or steel crank ,stroke?
 
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