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Brattons NEW & Improved Float A Motor...any comments or Opinions? Heard these were very good now, Better Fit, new material, anyone have a set or any opinions, been "thinking" of installing as I drive all the time in the A :confused::confused::confused:
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? opinion: still a float-a-motor.
a well-restored car such as yours doesn't need them. |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? I have float-a-motors in my 160B, stock mounts in my 40B.
To decide you need to understand a little background stuff- Inline 4 cylinder Otto-cycle engine running vibration is attributable to three sources: 1) Primary dynamic imbalance of moving parts. THIS MAKES THE ENGINE WANT TO GYRATE AROUND THE CRANK CENTER. Ford did a good job of keeping this below the noticeable threshold, something many rebuilds do not achieve. If you have a dynamically balanced rotating assembly comprised of weight-matched parts in your engine this is not an issue. Contrary to layman belief, crankshaft counterweights have nothing to do with this running balance. Henry’s un-countered cranks were in very close dynamic as well as static balance. Adding counterweights does nothing to make an already dynamically balanced assembly ‘smoother’. The counterweights do two things: a/reduce crankshaft bending force against the main bearings, and b/add mass forward of the flywheel, reducing crank wind-up or twist by storing and slowly releasing the pulsed piston power. This second part, b/, DOES reduce overall vibration, but that fits into category 3) below. The primary dynamic vibration frequency is 1X (equal to) RPM. 2) Second order harmonic imbalance. THIS MAKES THE ENTIRE ENGINE VIBRATE UP/DOWN. This is caused by non-linear and mis-matched piston acceleration/deceleration profiles between pistons traveling up and those traveling down. Four design factors contribute to this: a/connecting rod length (infinity is best but impossible). b/ Ratio of bore to stroke. (Over-square is best, A’s are under-square). c/ Different crankshaft torsional load during the four Otto cycle strokes, causing opposing stroke pistons (two go up as two go down) to impart mismatched cancellations. (less horsepower is better, negative cylinder line offset is better). Model A’s that are ‘modernized’ to give more HP deliver more second order vibration. A’s were designed with positive (+0.125”) cylinder offset to produce more useable torque at a lower rpm. That added second order vibration. The only way to effectively reduce second order imbalance in an I-4 is with an opposing weighted countershaft geared to the crankshaft. Even then, the I-4 design is never perfect at all speeds and power output levels. The second-order vibration frequency is 2X RPM. 3) Torsional pulsation about the crankshaft axis. THIS MAKES ONE SIDE MOUNT PULSE UP WHILE THE OTHER SIDE PULSES DOWN. If you had an infinite number of cylinders there would be none. Adding rotational mass to the crankshaft and flywheel reduces this but a compromise must be made. More mass = sluggish engine acceleration. A four cylinder engine delivers a torque pulse every 180 degrees of crank rotation. The torsional vibration frequency is 2X RPM. ARITHMETIC: Remember physics? You need to sum all the vectors, both in magnitude and time. That’s what your butt actually feels! Adding #2 & 3 above, the left side engine mount will always transmit more ‘up’ force and the right side more ‘down’ force, in pulses twice the engine RPM. Parts of #1 will add to the 2&3 up/down/ and parts of #1 will force the engine sideways, back and forth between the frame rails. MODEL A ENGINE MOUNTS: Stock design permits very limited up/down movement with very little frame loading if the rubber has not age-hardened and the assembly is not over-tightened. Side thrusts can compress the large flat rubber sheet very little and flex the frame alternately left, then right. Part of the forward driving force of the vehicle is delivered to the frame through the top of the rear spring to the rear crossmember, part is delivered through the two side engine mounts. The design was an adequacy compromise for slightly less than 40 horsepower. As soon as Henry upped it to 50 horsepower (the Model B) engine mounting changed. The range of movement was changed and a third element was added in '32 to transfer rotational load to the firewall. Applying more than 40 HP to stock mounts passes exponentially more vibration during acceleration. Float-a-motors permit more movement in both vertical and side directions than stock A mounts if the rubber donuts are not too hard or over-tightened. That’s a big ‘IF’, but achievable. To facilitate dampening up/down pulses a third element, the rear tranny support with a rubber pad, is added. Failure to use it will shift the paradigm. Float-a-motors will always damp more side thrust toward the frame rails than stock mounts, but at a cost. There is less driving force delivered to the frame at the attachment point, as it flexes slightly forward, increasing the driving load on the rear spring/crossmember. Setup is critical. The donuts may need to be shimmed or trimmed to achieve the proper engine height and tilt. Proper loading on the third transmission support element needs to be present. The mount donuts need to be unequally tightened left/right to achieve maximum dampening during acceleration. The instructions do not explain how to judge, measure, or do any of this. Will your frame bend if you replace stock with floats? All 80 year old A frames bend from the pounding force of the engine and transmission mass at the side mounts. The relatively tight stock mounts make both frame rails react in tandem. Float-a-motors uncouple this but the loading is actually reduced at this point if the transmission third support rubber pad is properly loaded. The force is moved to the center cross-member. Without the trans mount (often omitted) the total loading is the same but uncoupled, permitting the right frame rail to see more total downward load when the car bounds over a bump than with stock mounts. A’s originally hammered over unpaved roads. That degree of accumulated repetitive stress is no longer the norm. Got all that Mark? There's a test at the next club meeting.:cool: |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? good lesson, mike k. thanks.
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Is that a "yes" for the F A M?
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Quote:
Quote:
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Mike, I think that is the best, most scientific explanation of the rear motor mounts that I've ever read. I will have to read it a couple more times to fully comprehend but it is very informative. I'll have to bookmark this discussion.
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? MikeK,
Could you explain in detail how to load the third trans mount and the donuts? How much pressure should go on the third mount and how does one unequally load the donuts?? Thanks! |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Great post, Mike. My entirely personal feeling about FAMs is, I drive my Model A to experience the Model A, so I have original motor mounts. If I wanted to drive a sofa I'd buy a Buick. :p
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? I agree with Ray.
BTW, we still have more snow forcast for this week. If this global warming keeps up I'm going to have to put tracks on my Model A's so I can use them most of the year!:D |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Quote:
Thanks. |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? I'm confused, Mike. You seem to suggest that motor mounts that allow the motor to move are bad. By that logic, bolting the motor directly to the frame should be best. Is it a matter of compromising between isolating the motor's vibrations from the frame while yet providing a firm connection for force transmission?
Steve |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Mike: Great dissertation.
FWIW, I did not notice any discerable difference in vibration by intalling either FOM, or a counterwieghted crank. I did cut out the center section of the front mount, using the ends independent of each other. In view of Mike's comments about left and right loading, I am not sure if this makes any difference and may result in more right side loading. Also, I thought I saw an article in an old Model A Times that the best front mount was the stock mount. Not using the rear trans pad seemed to result in more "bounce" at the trans, and without it the rear FOM donuts eventually squish down. FOM's do make pulling and installing the engine easier. |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Dog:cool: here,
Ole' Bill just informed me that I'm 'sposed to memorize ALL this RED LETTER/SPECIAL FONT dissertation for future reference:eek: I tole' him that we only have to recomember that Model A's shake & buzz & vibrate & bounce on pot holes & rub-board roads!:D Chief said sumptin' about wearin' TIGHT shorts?????????????? Wish I had known Chief, heard that he was a real Dog:cool: guy!:D Buster T.:cool: |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? UrhuggH! Shoulda kept my mouth shut. . . OK,
1) FAM's yea or na? I purposely did not answer this. IMHO(emphasis on the 'O' If you're bone stock and your engine is balanced to Henry's spec, if you have fresh rubber, spacers, etc. in original mounts, your teeth shouldn't be rattlin'. If you're bone stock and buzzing, either your original mounts need attention or your engine is not in dynamic balance. Just fix it. If you have significantly higher CR and a cam creating stronger power pulses, if you do a lot of low end 1st and 2nd gear driving, if you don't drive lots of crater potted roads, or if you don't mind that dirty word 'modified' hung on your otherwise bone-stock A, you can get a ride that buzzes the mirrors signifigantly less with FAM's if set up correctly. 2) I also agree with 700rpm, Tom W, and Buster T (who only wants to hang his head out 'cause he probably just stands on the seat anyway..) If you want the A experience, use the A mounts! You'll notice in my original post that only one of my two A's is FAM. My roadster has everything Henry's way right down to the fasteners and finish. 3) Bill Lee- my statement "crankshaft counterweights have nothing to do with this running balance." Try this LINK and be sure to click on the blue links within the document! In a perfect world crankshafts would be made of a material the cannot bend or flex, totally rigid. If you strike something and it rings like a bell, that's because it is flexing back and forth. A spinning crank imparts multiple centripetal loads along the crank axis from the rod journals spinning. The opposite side journals can be drilled or weighted with tungsten to bring the crank into balance both static and while rotating (dynamic balance) BUT as the speed increases the 180 degree opposing crank journals, which are obviously not directly across, impart their centripetal force at a different point along the axis. If the crank were infinitely rigid it would stay straight. It is metal, and despite being built like a brick poop house, it flexes, making the centerlines through each main bearing go out of alignment. Just 0.002" flex will impose an excruciating load on the main bearings as the block attempts to keep things in line. Counterweights place some opposing centripetal force at other points along the axis, reducing the flex to an off-axis deflection that does not exceed the bearing clearance and excessively load the oil film. Normal car cranks are counterweighted about 40-60% of perfect, sufficient to keep crank deflection forces within the load limits of the main bearings. A stationary engine that runs one speed only with no need to quickly accelerate, like a big diesel generator, will have a near 100% counterweight design. 4) Steve S- If i gave the impression mounts that allow the motor to move are bad, I didn't mean to. The problem is absorbing the vibe energy (as heat into the rubber) without transferring mechanical displacement into the frame. Like anything in physics, 100% is nice on paper but impossible to achieve. More available mount displacement (the FAM's) permit the elastomer to convert more energy to heat, and also give more displacement for it to act as a spring and simply rebound when on the opposite side of a pressure wave rather than passing the vibration force through to the frame. THE PROBLEM is how much movement can your setup tolerate. Engine movement changes control rod settings, flexes wiring, fuel, vacuum and exhaust lines, and imparts a varying mass CG to a moving vehicle. 4) How much load on the FAM tranny mount: I didn't go into it because it depends on variables such as the magnitude of the 2nd order vibes your engine produces and how hard you usually drive the engine. For me in a 160B with 760g pistons, a very high 160psi compression, a Stipe RR340, and other variables my engine 2nd order buzz is best controlled with either about 100lbs static on the crossmember rubber or less than 10 lbs! A stock engine may do best with 25 or 50. I don't know. How did I measure it? Indirectly by first putting the rubber in my Rimac valve spring tester and making a pressure vs height graph for the rubber I had. Differences in durometer, size, and contact pattern makes it impossible to just post a 'one fits all' chart. In all cases the FAM kit has no positive retainer system for the rubber block. You need to secure it or else going over one set of rough RR tracks or a big swooping dip and bump will cause you to lose it. 5) How to unequally load left/right mounts: Again, sadly, IT DEPENDS. The more HP (actually torque) you produce, the greater the reactive rotational force of the block trying to raise one mount while compressing the other. On the compression side you're kinda screwed because the FAM donuts are not available in different durometers. Here you just want to take all the slack out and the give the bolt/nut a very few (1? 2?) extra turns to prevent the discs from riding out of their seats. The left side, which attempts to rise as engine torque increases, seems to do better if it is somewhat more compressed. For me with my engine and driving style, 3 turns on the left and 1 1/2 on the right give the best overall result. Your ideal point may be completely different and with the opposite bias! One thing I will say here- unless the new FAM kit has a grade 5 bolt, a nylock nut, AND enough bolt length to add a SAE washer top and bottom, replace the hardware. ONLY install the bolts from the top with the nut on the bottom. 6) The optional FAM front mount: Worse than stock if your engine has dynamic balance errors, better than stock if you have enough horsepower (torque) to make the front of the engine slam the stock mount sideways, grinding the center bolt against the front crossmember. Got a hot OHV or an actual track speedster? If not you probably don't need it. It has the same overall effect as considerably tightening the rear mounts. 7) Land yachts: If you're looking for that deuce and a quarter ride (Electras were our family cruisers when I was a kid, too. I know that ride!) buy a 225. Make sure you have original springs and delco pleasurizer shocks, the HD aftermarket junk will make it ride like an M1 Abrams. You need the bias tires, too. Now cruise all day @ 6mpg. I think I'm done here. Good luck, no I can't second-guess what will work for you. Hopefully some of you will now understand why some people love 'em others hate 'em. If you just put the kit in, it is like rolling the dice. If you just ask someone for advice based on their experience, it's like rolling the dice. The odds are against you. Feel lucky? |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Mike, thank you VERY much for the link describing the forces involved. I have started reading the material but it will take a lot to wade through it.
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Mike could you amend this....
b/ Ratio of bore to stroke. (under-square is best, A’s are over-square) A's are under-square. |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Quote:
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Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Mike,
Thanks for the info. |
Re: Brattons NEW & Improved Float A Motor...any comments or Opinions? Most of this technical stuff posted above is over my head. However I did install the Floating mounts at first I had them too tight so had vibration I backed of some and it rides better. The instruction that came with mine did not explain very clearly how to install the rear trans mount maybe it is supposed to be obvious but I took me a while and some trial and error to figure it out. I did note that the trans mount is not secure except for the way it sits on the cross member but all in all no complaints.
I guess now I need to check if the trans mount is still there after a bumpy ride so I guess I learned something from Mikek's explanation |
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