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fpe 5.8 with the shakes...

Old 02-26-2005, 11:34 PM
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johnfly
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Default fpe 5.8 with the shakes...

fired up a buddies 5.8 today "brand new" let it idle for a min or so. and it sounded great but when we started to advance the throttle a bit the motor started to shake badly........ we killed it immedietly double checked everything. prop balanced...26x10 bolly..tried to lean the low end some.... no help. checked the prop hub, and solid stud that locates the prop both within .003 inch. the set screw that screws into the solid stud does have some run out and will be changed but about 80% of the prop rests on the solid portion that runs true.... do the 5.8's have a vibration just above idle ?????? does it diminish with more throttle ??????
for reference the motor was mounted to a big.... steel table " THE TEST STAND" lol...... any thoughts. thanks.
Old 02-27-2005, 12:54 AM
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Antique
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Default RE: fpe 5.8 with the shakes...

Worst single cylinder shaker I ever tested was the A&M 5.8 with the A&M crank...Totally unusable...Next was a small Homelite, or the Big Roper...
All singles shake, some worse than others...All shake at low rpms, and get better at higher speeds where the impulses get closer together...If the FPE uses the Sachs 5.8 crank and cylinder you won't get it any smoother, run it up to about 5500 and see how it does...Soft mounts make it worse....
All engines have small variations in the weight of the parts, so if one gets put together with all the weights on the wrong end of the tolerances you could get a shaker..There is no way to balance a single, unless someone can re write the laws of physics...You can sometimes get it smoother in a certain rpm range, but total balance is impossible...
this is why some single cylinder motorcycle engines run a balance shaft, to try to counteract the unbalance..It works pretty well to a point.......
Old 02-27-2005, 08:54 AM
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Diablo-RCU
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Default RE: fpe 5.8 with the shakes...

Does this engine have an ignition that retards the timing at low rpm?
If not, maybe it would help smooth things out.
Old 02-27-2005, 08:20 PM
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ParticleMan
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Default RE: fpe 5.8 with the shakes...

I have a low run time Sachs 5.8. It's one with the good crank. I maidened the plane that it was on this weekend. Honestly it doesn't shake that bad. Nothing like you're describing. I would say where the vibration is the worst is at lower idle. As the motor peaks out it gets very smooth. I don't think anything of it, I've seen BME twins shake just as much at idle.
Old 02-27-2005, 09:23 PM
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johnfly
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Default RE: fpe 5.8 with the shakes...

ok.... first off i'm not talking about a common 2 stroke single cylinder type vibration!!!!!!! I mean this thing is mounted to a .25 piece of steel that is welded to a .625 plate that is approx 2 feet by 4 feet.... the .25 piece is also reinforced with 2 90's that help hold it square....... "we ran a bme 100 on it with no problem, but it was a twin"
when i say it shakes ........................ i mean at 2500 rpm the prop hub is moving about a half of an inch !!!!!!!!! its a blurr.......
that in my humble opinion isn't a typical 2 stroke vibration........
we ran the motor again today but changed the mount to a 2x4 steel tubing .25 wall thickness with the "firewall" being .5 plate welded together to make the shape of a "T" it still vibrates very noticably at 2500 rpm but the shake wasnt there so we advanced the throttle to full power and it went away...so from idle to 2300 it is smooth from 2300 to 26~2700 rpm it shakes the table... then smooth again to full power or 5800rpm with the bolly 26x10.......... it sounds strong as heck...... but we are thinking that the firewall in his hanger 9 edge 33% will not be up to the task of holding on to this in the 2300~2700 rpm range.......
I have never run this big of an engine but i am a machinist and familiar with balancing high speed spindles and to me it acts like a harmonic vibration..... ?????? I am out of ideas he is calling fpe tomorrow to see what they say.. he just doesnt want to tear the nose off his airplane before its airborne....allthough that may be spectacular it would be costly.
Old 02-28-2005, 06:26 AM
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H. Wayne S
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Default RE: fpe 5.8 with the shakes...

Worse thing you can do is solid mount an engine to steel.
Go ahead and mount it on the plane. WITH the wings attached. The fuse and wings absorbe the shake & rattles.You will be amazed at the difference. Engine will smooth out.
Old 02-28-2005, 12:22 PM
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SLINGSHOT-RCU
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Default RE: fpe 5.8 with the shakes...

We have two FPE,s both run great. We had one that did what yours is doing and it was the timming. We set it at 28 deg and now it runs great. FPE,s dont shake that bad.
Old 02-28-2005, 08:55 PM
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evfast
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Default RE: fpe 5.8 with the shakes...

HHMMMMM....... Im fixing to purchase an F.P.E. 5.8!


later
Old 02-28-2005, 11:25 PM
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johnfly
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Default RE: fpe 5.8 with the shakes...

UPDATE................well my bud got ahold of fpe today and the tech told him to definetly NOT mount this motor to a steel plate..... and that if we ran it very much more we would likely wipe out the bearings....(good call wayne)
the fpe tech said to mount it in the plane with the wings attached and run it..
this motor is really awesome and i didnt mean to discredit fpe in any way... starts easy and all i can say about full throttle is "WOW"
5800 RPM OUT OF THE BOX and with no tweaking on the mix....bolly 26x10 prop.
hopefully others will read this thread and find out also that you shouldn't mount a big motor to steel.... as it allows no flex to absorb the power impulses. the tech told my friend that he mounts them to a 2x6...and that he tries to run every engine... so kudos to fpe and it sounds like the motor is ok... we plan on checking the timing to see where it is at and then mount it to the plane and light the fire..
thanks for all the advice... oh and "evfast" if u need power...... go ahead and get the 5.8 fpe.... it is an animal... but just dont mount it to steel to test run it........ completely our bad.
fly fast or fly vertical.
Old 03-01-2005, 12:52 AM
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Antique
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Default RE: fpe 5.8 with the shakes...

I would like to know how running an engine on a steel plate mount will wipe out the bearings
Where do some of these things come from ?
Anybody ever see it happen ?
When Walker Machine started making 4.2 Sachs conversions they ran a 4.2 for 1000 hours full throttle 24/7...Only part with out of tolerance wear was the piston rings...I very much doubt they bolted it to a 2x6...
I know the mechanic (Carlos Gregada) that put the Walkers together, I could find out what the mount was made of....
Old 03-01-2005, 07:01 AM
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H. Wayne S
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Default RE: fpe 5.8 with the shakes...

Any constant vibration produces a harmonic buzz. This harmonic buzz travels through the item producing the vibration like a sound wave and will focus on the weakest point in the structure.
The item producing the harmonic vibration is the crankshaft.The weakest point in the structure are the bearings supporting the crankshaft. If left unchecked these harmonics will get stronger and stronger and move faster and faster untill the weakest point fails.
Solid, hard mounting an engine to a steel plate intensifies these harmonics,there is nothing to absorb them. The buzz will get so strong and fast it will destroy the weak point. The bearings,
Thats the reason you have a "Harmonic Balancer" on your car engine.

People get this stuff from engineering, testing and application.

By the way, I are one of them engineers.
Old 03-01-2005, 11:25 AM
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Antique
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Default RE: fpe 5.8 with the shakes...

I "aren't" one of "them" inginears, couldn't spell it yesterday either...
The harmonic is only from 2500 to 2700, how could running the engine on a steel plate possibly wipe out the bearings if the engine is not run in that range ?
I guess I'll have to change my steel plate mount for my 289cc twin racing engine to a 2x6 so the bearings won't get wiped out during testing...NOT....
Old 03-01-2005, 07:47 PM
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johnfly
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Default RE: fpe 5.8 with the shakes...

rc ..... comparing a twin to a single and then talking about vibration hurting the twin.....
kinda like comparing apples to oranges...... secondly because the vibration is the WORST at around 2600or so .... the solid mount and the increased intensity of say "full throttle" could be masking vibration that is still present but not perceptible to the eye or ear and could possibly still be of enough intensity to wipe out the bearings.
but hay dont take my word for it ..... mount up a single to the old steel test stand and try it....... the proof is in the puddin.
Old 03-01-2005, 09:16 PM
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Antique
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Default RE: fpe 5.8 with the shakes...

Back around 1991 when the Giant Scale races started at Madera I converted an A&M 5.8 Sachs...The owner put it on a steel trailer on a steel mount for testing..The A&M 5.8 was/is the KING of all vibrators..He couldn't believe the vibration..Mounting that thing on a plywood and balsa wood airplane would have resulted in complete destruction of the airplane..If anyone here remembers the A&M 5.8 Sachs they know what I mean...Mounting a vibrator like that on an airplane and hoping that the vibration would be absorbed by the plane is folly....I put a Sachs crank in that engine using the original bearings eliminated the problem, and as far as I know the bearings are still in the engine, they were not "wiped out" by running the engine on the steel mount..I subsequently changed many A&M 5.8 engines to the Sachs crank..Never replaced the bearings, never saw a bad one...If a vibrator like that can't wipe out the bearings it can't be done..Walker Machine ran a 4.2 Sachs (probably on a steel mount) for 1000 hours on a steel mount..NO measureable wear on anything but the rings.....
I agree to disagree...
Old 03-01-2005, 09:45 PM
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Diablo-RCU
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Default RE: fpe 5.8 with the shakes...

A lot of motorcycle engines have used and continue to use solid mounts. I've owned a few big single cylinder ones that didn't have balance shafts...580cc Triumph MX, and Yamaha 540cc Enduro. Both of them started as 500cc engines that wound up with big bore piston kits. No bearing problems. I believe the harmonic balancer on the crankshaft of a V8 or straight 6 serves to keep the crank from failing from the twisting vibration you find in a long crankshaft. Short stout cranks like we have in model engines and motorcycles don't need a harmonic balancer on the crankshaft. Flexible crankshafts cause the problems.
Old 03-02-2005, 06:56 AM
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H. Wayne S
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Default RE: fpe 5.8 with the shakes...

Six plus years of scholastic education and 34 years of applied education and all of it wipped out in two days. Ain't life grand.

Twisting vibration?


Outa here !
Old 03-02-2005, 06:49 PM
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Default RE: fpe 5.8 with the shakes...

Twisting vibration is called torsional vibration by the engineers, but it means the same thing. If I said torsional vibration, two thirds of the folks reading this wouldn't know what I was talking about. Every power pulse of the piston tries to twist the crank one way, every time the piston compresses the mixture tries to twist the crank the other way. The crankshaft has a natural resonance frequency (where it sings like a guitar string). Bad things happen if the power pulses are in tune with the resonance frequency of the crank. The harmonic balancer dampens out these vibrations. Like a guitar string, you can change the resonance frequency of the crank by changing the diameter (stiffness). But, this has nothing to do with the type of engine mount. Crankshaft torsional vibrations are not damped out by travelling through the engine mount. It's the torsional vibrations that will damage the crank and the bearings.
Old 03-02-2005, 07:56 PM
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Default RE: fpe 5.8 with the shakes...

So everybodys toughts on the F.P.E 5.8 is?
Old 03-02-2005, 09:33 PM
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Antique
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Default RE: fpe 5.8 with the shakes...

What's not to like ? ANY engine with a Sachs crank and cylinder is good....The only difference is the machined case and mount.....
FWIW..I talked the the manufacturer of my racing twin today, he said the stiffer the mount the better it is for the engine...Quickee and Formula 1 racers go to great lengths to make the mounts as stiff as possible, stiffer mounts seem to make more rpm...Defense rests
Old 03-03-2005, 08:29 AM
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Default RE: fpe 5.8 with the shakes...

OK Rcign1, diablo and others. I know this is a sachs 5.8 post but it's winding down to a sachs crank and parts. Lets address this. What do you folks think about a sachs/dolmer 5.0 twin? Besides being heavy, any views??? Thanks Hooker53
Old 03-03-2005, 09:34 AM
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Default RE: fpe 5.8 with the shakes...

It all comes down to the crankshaft..Unless someone made a crank with a different stroke there's no way to make a Sachs 5.0 twin..Closest thing is a 4.8, made from two 2.4 Sachs cylinders...I have a Fox 4.8, and there are others out there..It is a very good twin if made by the right company, they are not all the same..I have a 4.8 made by A&M here somewhere...They made it with two different 2.4 cylinders..The crank is put together so loose that they drilled and pinned the parts, and when the owner crashed the plane the crank twisted and became unusable..Worst (almost) twin I ever saw..
I haven't run the Fox, but I don't anticitpate any crank problems..If Brison makes one I would trust that one also..Not so with Air Hobbies, do a search......There is another twin, made by Spehar using the Sachs 2.4 cylinders and a crank from Echo..Outstanding wormanship...Another uses the Horner case and crank..Good also....
Old 03-03-2005, 11:31 AM
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Default RE: fpe 5.8 with the shakes...

Thanks rcign, I will find a twin for this 35 % giles 202. I bought a A/H 4.8 twin some time ago but I'm having sec thoughts on the darn thing. Thanks again and really app your knowledge and help the past few years!!!! Hooker53
Old 04-05-2005, 05:48 PM
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Default RE: fpe 5.8 with the shakes...

WOW..... mounted the 5.8 to the 33% edge and fired it up ........need i say ........ ppprrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
smooth as glass..... allthough it shook violently when hard mounted to a metal bench. FPE. said "not to mount it to somthing that solid" OK i may be hard headed but i am capiable of learning. so i think in the future, test runs need to be done on wood.
hard to argue with sucess. thanks to all that commented, I know some will disagree but hay what fun would it be if we all had the same ideas and beliefs.
just wanted to follow up on this thread... JB.
Old 04-05-2005, 07:04 PM
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Default RE: fpe 5.8 with the shakes...

RCIGN, Ralph, when are you going to learn that all your years of trial and error and experience don't mean anything to all the RCU experts. Golly Gee let the guy put that shaker in a plane and watch how long it takes to start shedding parts. Maybe even set it to music.
"might a been the firewall, might a been a wing. might been a tail surface goinin, now look at the mess I'ts in" (some country song)
My test stand is 1/4 thick base bolted to the floor, welded to that is a 4"diameter pipe with 4 1" gussets 12"long verticle, pipe is 1/2" thick wall, 40"long to a table 6x12x1, which has a firewall 6x6x5/8".
It don't take long to find if a prop, crank or ignition isn't right. I would strongly suggest to the 5.8 owner to check his timing, trouble is the hub is keyed to the shaft and the last time I checked if you wanted to check the timing, FPE said send it in. Maybe that has changed.
Now yu'all member Ralph, experience don't mean nuthin on these forums. he,he,he,he
Old 04-07-2005, 04:07 PM
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marzo91
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Default RE: fpe 5.8 with the shakes...

Yes, What the engine is bolted to makes a HUGE difference. Even small singles vibrate badly if mounted to a steel mount, or a mount clamped in a vise. Try this at home. Run your plane with, and without the wings. Without the wings it will vibrate more than you can imagine. I taxied my Brison 3.2 for two tanks without the wings on. The tail shook so badly, it broke the outer Robart hinges on the horizontal stabilizer. Thought I had a serious problem. Called Brison, they told me to bolt up the wings. The difference was unbelievable. Now smoooooth as silk. Waaay cool, now.

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