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Old 01-08-2016   #1
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vibration / balance

hi all
i have a problem with engine vibration, its rev related, its a 650.
i dismantled the engine and sent the rotating assembly for balancing.
the guy in the shop called to tell me my rods and pistons are much heavier
then what he saw before on a 500 so he can't balance it without adding some
"heavy metal" to the crank's weight.
as far as i know the 500 and 650 rods and crank are the same??
can that be fly wheel assembly error?
any ideas?
thanks
Michael
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Old 01-08-2016   #2
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Re: vibration / balance

Hi
I had heavy metal set into my crank and flywheel to balance it when my engine was built - this is quite usual.
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Old 01-08-2016   #3
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Re: vibration / balance

really?
i'll tell him to do it then, thanks!
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Old 01-08-2016   #4
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Re: vibration / balance

Hi Mike;
As per Andrew's comments, this is not an unusual procedure. I have a (physical , because it no longer seems to be 'on-line') copy of the 'Forza 500' article regarding crank-shafts. Would you like a copy of this article? If you do, contact me direct with your address and I will put a copy into the post for you. I am away until about Thursday (emergency 'baby-sitting little Grand-daughter')--but will post it as soon as back at home.
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Old 27-02-2019   #5
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Re: vibration / balance

hi again, its been a long time since i started looking into the vibration problem...
what iv done so far with zero affect: dynamically balanced engine with new pistons flywheel and clutch, new camshaft and rocker assembly.
new gearbox mounts and engine mount.
now the vibration is a bit worse if anything..
the only thing i can think of is the engine mount, do i have to use the 126 one, or can i transfer the old 500 one?
thanks
Michael
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Old 27-02-2019   #6
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Re: vibration / balance

Hi Michael,
That sounds very frustrating. Which engine mount do you currently use? If you want to swap between 500 and 126 engine mount you have to change the rear panel as well (Fiat 500 or Fiat 500R)


Back to the original balance issue, was this engine vibrating much worse than other 500/126 engines?


Michael
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Old 28-02-2019   #7
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Re: vibration / balance

hi , i am using the original 500 mount as per bottom photo transferred from the old 500 engine .
yes , vibration is worse , you can't make out object in the rear view mirror..
its only rev related, not speed
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Old 28-02-2019   #8
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Re: vibration / balance

Maybe disconnect the rear engine mounting and support the engine on a trolley jack with a block of wood and rubber mat under the sump. Then run the engine and see if this period of vibration disappears, this way you'll know if the problem is with the rear engine mounting or lies elsewhere.

This is how I tracked down a vibration issue on a Fiat 600 - someone had inserted a thick washer in an attempt to reduce engine movement.

AL.
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Old 28-02-2019   #9
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Re: vibration / balance

Quote Originally Posted by Mike r View Post
hi , i am using the original 500 mount as per bottom photo transferred from the old 500 engine .
yes , vibration is worse , you can't make out object in the rear view mirror..
its only rev related, not speed
Are the rubber bushes in the hinged part of the mounting in good condition,
i.e. no metal to metal contact?

Can you feel this vibration through the gearstick? (although iirc the gear knob has a rubber insert, I wonder why....).

AL.
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Old 28-02-2019   #10
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Re: vibration / balance

as i remember i replaced the rubber bushes not long a go ..
ill try disconnecting the mount as you suggested and check bushes at the same time.
thanks
Michael
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Old 01-03-2019   #11
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Re: vibration / balance

I've been mulling this over the last few days. This is not an issue I've had before so I thought I'd try and think it through


Assuming the engine is good -


If the engine or gearbox mounts are loose/worn or slack, the engine will move around more within the engine bay. The vibrations caused by revving won't be transferred to the body as well.


If the engine or gearbox mounts are too tight or something else is causing the engine/box to bind, the engine will be tighter to the body, not able to move. More vibrations from revving will be transferred to the body.


As far as the engine mount is concerned -
  1. If the spring is worn it will be softer, the engine will move about more freely = less vibration transferred to body.
  2. If the bushes are worn, the engine will move about more freely unless there is metal to metal contact, but it would rattle and look very worn.
Does the engine move around too much or too little? Do you know anyone local with a 500 to compare how much their engine moves? A quick comparison can save you a lot of head scratching!
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Old 01-03-2019   #12
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Re: vibration / balance

Quote Originally Posted by Mike r View Post
hi , i am using the original 500 mount as per bottom photo transferred from the old 500 engine .
yes , vibration is worse , you can't make out object in the rear view mirror..its only rev related, not speed
The Irish solution to the rear view mirror vibrating would be to try rubber-mounting the mirror

AL.
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Old 01-03-2019   #13
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Re: vibration / balance

bushes and spring are new, but spring looking low, could cause engine to touch body..have to check that!
also have a lowering block of 18mm to give more room above engine. but i don't think its a problem .
Michael
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Old 01-03-2019   #14
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Re: vibration / balance

A few more thoughts.

Some other members on here have fitted a replacement engine mount spring and found it was stiffer?, resulting in vibration being experienced that wasn't present before.

I checked out the workshop manual (available in the Download section of F.F.).

This lists 3 possible causes of engine vibration.

1. Loose generator bolts.

2. Blower (i.e. fan) blade assembly out of balance.

3. Incorrect clearance of rear engine mounting rubber..........

Good move to check for possible metal to metal contact in the rear mounting.

The problem I mentioned earlier re. vibration on a Fiat 600 was caused by someone inserting a washer into the mounting to reduce engine rocking. This washer meant that there was no clearance on the rubber buffer contained inside the mounting which is only supposed to come into action when the mounting is compressed i.e. like a spring assister.
(I'm aware the mounting on the 600 is different to that on the 500, but the principle behind it's operation is, I believe, similar).

Another point is that sometimes replacement engine and transmission mountings are not always made from the same stiffness (Shore No.) of rubber as used in the original parts.

When fitting any new mounting, engine or trans., its considered good practice to loosen all mountings, rock the engine trans. unit about, allowing it to find it's natural positiion, then tighten all mountings. Same as when fitting an exhaust system. Incidentally, the 500 trans. mounting frame/crossmember has slots where the trans mountings attach to allow a little adjustment to prevent pre-loading the mountings.


If you still have vibration problems, I'd suggest disconnecting any item which might be transmitting vibration into the cabin, one item at a turn until the vibration disappears. You could start with the gearchange rod (although it has rubber in the coupling adjacent to the trans.), then the clutch cable (is there any difference in vibration when the clutch pedal is pressed?), followed by the speedometer cable and any other items that might be the culprit.


Another item to check is the rubber? covered plate at the rear end of the tunnel where the gearchange rod., clutch cable, handbrake cables etc. exit the car interior and connect to the engine/transmission - could anything be wrong here, causing the vibration issue?

Is it possible that your lowering plate is the root cause of the problem? Maybe this is putting something under strain resulting in the transmission of vibration into the passenger cabin? It might e.g. be twisting the trans. mountings? Or trying to bend the gearchange rod? Or forcing the gearchange rod against the cover plate mentioned above?


If it was my car, I think I'd try removing the rear engine mounting, supporting the engine on a jack at its normal installed height not where it's at with the 18mm lowering block in place. If the vibration disappears, then try lowering the engine by 18mm and see if the vibration recurs - which would indicate that lowering the engine caused the problem.

Remember that all parallel twin cylinder engines vibrate, usually very badly - just try an old Triumph or Norton motorcycle vertical twin.....

There's a number of different types of imbalance, you can't eliminate all of them (although the inclusion of balancer shafts in the design can work wonders), some of these forces vary with speed, some in direction and whether the engine is delivering power or is on the over-run. The best anyone can do (manufacturer or engine balancing specialist) is try to get the worst out of balance forces to occur where they won't be too intrusive or damaging. e.g. smooth at idle speed, no severe vibration at engine speeds used normally.

Some Fiat models incl. 4 cyl. ones had a habit of breaking throttle return springs due to vibration, Fiat's solution was to fit a rubber insert to dampen out the harmful vibrations. As I suggested earlier, it might be worth trying to rubber mount the rear view mirror is if it's shaking is your main cause of concern?

AL.
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Last edited by F123C; 01-03-2019 at 23:33.
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Old 02-03-2019   #15
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Re: vibration / balance

is there a measurement for Incorrect clearance of rear engine mounting rubber??
its a good idea to compere to the one i have!
thanks
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