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Author
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Topic: Random engine vibration
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-14-2002 10:12 AM
  
Since my conversion from C4 to T5 I have experienced engine vibrations kind of like a knocking (at fixed RPM)whether driving or stopped. What makes my problem weard, is that it is random: some days the vibrations can't be felt some days they are there ! Every parts involved are new. I have gone through ALL options and I am down to 3 possibilities in order of probability:A- Engine internal balance issue, but it should'nt be random ! Unless the centerforce dual friction clutch (that I have installed) has its diaphragm weights moving around leading sometime to an unbalanced situation. Anyone's seen this before ? Pure speculation on my end nothing factual. B- A random plug/Ignition malfunction on one cylinder. (The engine seem to loose some power when the vibs are felt) C- This one is far fetched but I try anyway: One or several cylinders not receiving even A/F mixture, a carburation malfunction. Any input would be valuable
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maxo
Journeyman Posts: 53
From: Fresno, CA
Registered: Jan 2002
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posted 05-14-2002 03:30 PM
I hear/feel the "same?" thing and have been trying to figure it out since I put my rebuilt 289 in. Everyone who has heard it thinks it is something else, I and a few others think it has to do with the flexplate? (auto) but have't got into it yet to see for sure
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65 coupe 289 - thinks it's a cobra 
http://mustangsandmore.50megs.com/maxo.html www.angelfire.com/retro/green65mustang/ [This message has been edited by maxo (edited 05-14-2002).]
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SteveLaRiviere
Administrator Posts: 30261
From: Saco, Maine
Registered: May 99
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posted 05-14-2002 03:35 PM
Pierre, Ford engines earlier than '82 had 28 oz. imbalance for the balancer and flywheel. Were you sure to use a 28 oz. flywheel? If you used a 50 oz. flywheel, there's the source of your vibration.------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
MCA Member # 47773 "Doubt is not a pleasant condition, but certainty is absurd."
- Voltaire
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-15-2002 05:09 AM
Maxo,
Did you have a dynamic balancing done to your engine during rebuilt ? Is your problem random as well ? (one day on, off the next).
Specialists that have witness my problem, also tend to think of the flywheel but can not explain the randomness part. They recommanded to rotate twice the pressure plate 1/3 of a turn and test drive it each time. In your situation you could rotate the converter housing 3 x 1/4 (in three separate steps since you have 4 bolts). It is a lot of work but it is cheap Steve,
I had done extensive research about this conversion and ironically vibrations were my worst fear ! So I paid very close attention to use 28 Oz products(Damper is "streetdamper" for early SB and flywheel is also "Centerforce" 28 Oz - 157 teeth). But I did not have a balancing job done. I tend to think that any random problem like this should not be related to an internal engine part(damper to flywheel) since there are no parts which position's will fluctuate over time !! It is either balanced or not. The only possibility may be with the pressure plate (centerforce dual friction style)that has little weights around its diaphragm to increase pressure with G forces at higher RPM. These weights are normaly loose and could be sometime misaligned (supposition?). I want to eliminate all options before tearing down my engine and send it to a shop for a full balancing job  !!!
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SteveLaRiviere
Administrator Posts: 30261
From: Saco, Maine
Registered: May 99
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posted 05-15-2002 08:54 AM
In that case, I would look very close at the ignition. As for your Centerforce theory, can you make the vibration stop or change by the clutch pedal? ------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
MCA Member # 47773 "Doubt is not a pleasant condition, but certainty is absurd."
- Voltaire
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-15-2002 11:16 AM
Vibrations seem to remain the same with clutch pedal depressed or not. If the weights are "locked" off balance, pressing the clutch doesn't change anything. I usely have to wait a few hours (engine turned off) for the problem to go away. I can sometime feel the vibs for several days in a row  and sometime vice-versa !!!As for the ignition:
Next time I experience the problem I will check with my timing light that there is a spark on all plugs. How can I find out if a spark is weak though ?
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SteveLaRiviere
Administrator Posts: 30261
From: Saco, Maine
Registered: May 99
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posted 05-15-2002 11:26 AM
You need to find someone with an scope, and check out the 'spikes' which is the electrical signature as each cylinder fires. That may show you something. I've found intermittant skips that way many times. What you may not see or feel could really show up there. Have you compared the resistance of all your spark plug wires? No engine sound accompanies this does it? Like a lifter tick or such?
Another thing to look at is a vacuum gauge. That could point out a sticky valve for you.
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'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
MCA Member # 47773 "Doubt is not a pleasant condition, but certainty is absurd."
- Voltaire
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-15-2002 12:02 PM
Steve,The scope sounds like a good idea. I will rent one. As for noises, there doesn't seem to be one but I will listen carefully next time. Spark plugs wire resistance range from 700 ohms to 900. Mallowry unit is new For the valves, all engines parts are new but I'll look into it anyway. I guess if this is the case I should hear something.
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SteveLaRiviere
Administrator Posts: 30261
From: Saco, Maine
Registered: May 99
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posted 05-15-2002 12:36 PM
Just throwing ideas at you. Good luck!  ------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
MCA Member # 47773 "Doubt is not a pleasant condition, but certainty is absurd."
- Voltaire
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V8 Thumper
Gearhead Posts: 2830
From: Orange, Ca. United States of America
Registered: Dec 2001
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posted 05-15-2002 08:35 PM
Here's a shot in the dark... how are your motor/trans mounts looking? The random/un-predictable symptoms have got me stumped [This message has been edited by V8 Thumper (edited 05-15-2002).]
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-16-2002 02:15 AM
Uhm.....I looked at the motor mount and they look OK. I have reved (spelling OK ?) the engine and it does not seem to move but how can I make sure ?
The trans mount was part of the T5 kit and is new.
I have also looked into possible contact between gear box/exhausts & tunnel, nothing there either.
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bluestreek
Gearhead Posts: 1017
From: Athens,GA
Registered: Jul 2001
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posted 05-16-2002 09:56 AM
Maybe this will give a clue... The only thing that is turning when the clutch pedal is depressed, is the flywheel and pressure plate. When the clutch pedal is not depressed and the tranny is in neutral, the tranny input shaft, clutch, and throwout bearing are also turning. You did install the correct pilot bearing in the crankshaft?? Right?
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-16-2002 10:06 AM
Yep, did install that, first bought a pilot bushing but eventually went for a pilot bearing.
As for the clutch, whatever its position, the problem is there (when it is "on")
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bluestreek
Gearhead Posts: 1017
From: Athens,GA
Registered: Jul 2001
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posted 05-16-2002 10:36 AM
You mentioned "fixed rpm".. What rpm does it happen at and does it go away when you change rpms??
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-16-2002 11:15 AM
1800 (strongest)& 2500, higher than that it will vary. These vibrations go away between above frequencies yet I can tell that the engine is not as smooth as in the "Off" phase.
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ccode67
Gearhead Posts: 1335
From: douglasville,ga,usa
Registered: Mar 2001
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posted 05-16-2002 01:02 PM
As a way of ruling things out, remove all the belts and try it, maybe a bad fan blade, power steering pump, alternator, water pump, air conditioner clutch, at least you will eliminate all these from the search.P.S. Don't let it overheat.
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Stuart MCA #48902
M&M #1091
67 stang 5 speed, 351W, Edelbrock Performer RPM package
91 f-150 xlt
98 explorer xlt sohc v-6
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Pierre
Gearhead Posts: 349
From: France
Registered: Apr 2002
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posted 05-17-2002 05:06 AM
Since I feedled around with the spark plug wires (mesuring resistance or potential bad connections 10 days ago now), the problem did not reoccur Ignition wires, eventhough new, are the only pieces that I hadn't checked 
Thanks all of you for your valuable inputs, I have a few days worth of testing now in the even this comes backI'll keep you posted
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