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Old 11-04-2013, 04:06 PM   #1
Peter J
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Default New vibration

Hey Guys,
I've checked the old threads and some close but no cigar. I've got an engine vibration since I rebuilt it with all new rods, pistons and rings. All from different dealers but all where bought as sets. It runs quiet and has plenty of power. No vibration prior to the rebuild and the engine was not removed so the flywheel was not disturbed. I only have about 50 miles on the engine so far so I guess my question is should I put some more miles hoping it will wear in or should I tear it back down and weigh the componants?
Thanks for your thoughts

Peter
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Old 11-04-2013, 05:04 PM   #2
Chris in CT
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Default Re: New vibration

Hi Peter,
Did you not weigh-off the rods and pistons? If not, you have your answer. Good Luck!
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Old 11-04-2013, 05:06 PM   #3
Patrick L.
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Default Re: New vibration

The vibration isn't going to fix itself. The parts probably should have had the weights checked and adjusted.
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Old 11-04-2013, 06:34 PM   #4
Peter J
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Default Re: New vibration

I was sort of afraid that would be the answer. I'm suprised that their would be enough weight variance to set up a vibration with all new parts. Oh well, a winter project.
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Old 11-05-2013, 11:40 AM   #5
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Default Re: New vibration

Could I weigh the whole assembly e.g. piston and rod? I've got the shims where I want them and would like to keep them together if I could. I've never replaced these many new parts at once so that's why I'm sort of in the dark on this.

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Old 11-05-2013, 03:19 PM   #6
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Why not keep everything with the correct hole. Just separate the rod from piston, weigh and adjust each, assemble, weigh and adjust again so they are all the same and put them back in their respective hole. The bearing clearance won't change.
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Old 11-05-2013, 03:36 PM   #7
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Default Re: New vibration

Quote:
Originally Posted by Peter J View Post
I was sort of afraid that would be the answer. I'm suprised that their would be enough weight variance to set up a vibration with all new parts. Oh well, a winter project.
Pete
Actually you'll be quite surprised as sometimes a set of pistons is out the window in regard to balance. Same goes for rods can't assume anything unless they say balanced then still don't believe it.
You'll notice in the photos above that pistons are out 6.6 grams.
This weight is out of the box and juggled wrist pins to get the best weight before metal removal.
Sometimes they're really good and then really bad.

Rods we try to keep them together as sets but lately alot of the threads are being damaged by people unknowingly overtightening the nuts.
We have to weight match the rods best we can before we even can pour them. To make the balancing work easier.
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Old 11-06-2013, 11:21 AM   #8
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Default Re: New vibration

I guess the next question would by how close should they be to each other to make they play well together. I figured I'd do what Patrick suggested. With only 50 miles on them, the pistons can still go anywhere their happy and leave the rods where I originally adjusted them.
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Old 11-06-2013, 11:49 AM   #9
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Default Re: New vibration

Peter,
I think the previous posters have probably predicted the cause but there is another possibility....varying fuel charge. Did you do anything to the valves that would give you a slight loss of seal on an intake valve? A leaking intake valve could interrupt/change the fuel charge to the adjoining cylinder served by the same port. This could cause a rotational variance and result in a noticeable vibration.
Good Day!
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Old 11-06-2013, 05:24 PM   #10
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Default Re: New vibration

Dave makes a point. I kinda assumed the valve lash was correct, compression checked and everything found satisfactory.
But if you take the engine apart, I think you'll be surprised when you start weighing things. Using a good scale, my opinion is that everything should be the same or no more than 2 grams difference. I weigh pistons with rings and pins. I find it hard to weigh each end of the rod but some folks do that. Then re-weigh with everything installed. Just be careful removing material, its really hard to put it back on once its ground off. [ smiley face]
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Old 11-06-2013, 08:53 PM   #11
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Default Re: New vibration

Peter: the reciprocating parts Rods and pistons should be less than a 1/2 gram if you're able to do so. The engine will vibrate at 2 grams or more.
Ford balanced these engines and on average a stock crank is usually around 2-3 grams.

You'll find the biggest out of balance on the rods since they probably didn't come from the same engine and the next culprit is the flywheel and clutch assembly.

I would suggest balancing the clutch and flywheel as a unit and you may be amazed to see it from 10 -20 grams out of balance.
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Old 11-07-2013, 03:20 PM   #12
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Default Re: New vibration

Valves are all new and proper clearance. Plugs are all ash colored so was running good. I wonder if the dynamics of the engine would have changed enough to make an out of balance clutch/flywheel ass. now be prominant that I couldn't feel earler?? Anyhoo, I have the engine out and now in the process of putting my B engine back in. I put the A engine in when I tried to sell it last summer (no takers by the way).
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