Engine balance problem?
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Engine balance problem?
I am hoping someone here can help. I have a 71 351W that will not idle without turning the idle up to about 2000 RPM. The engine runs so rough that you think it will come apart at idle.
The history of the engine is this. It has about 25,000 miles on it and was running great when it was pulled. It had been balanced to a 28oz flexplate and harmonic balancer. When I recieved the engine the harmonic balancer was missing and the flexplate needed to be replaced from a 164 tooth to a 157 tooth. That left me with neither of the components that were with the engine during the build.
I have the vehicle in a shop at this time, and they want to pull the engine, tear it down, and send it in to be re-balanced. I just can't believe this is the only way to solve this problem.
Have any of you had similar problems or do you have any suggestions I might try first? Thanks for any help you can provide.
The history of the engine is this. It has about 25,000 miles on it and was running great when it was pulled. It had been balanced to a 28oz flexplate and harmonic balancer. When I recieved the engine the harmonic balancer was missing and the flexplate needed to be replaced from a 164 tooth to a 157 tooth. That left me with neither of the components that were with the engine during the build.
I have the vehicle in a shop at this time, and they want to pull the engine, tear it down, and send it in to be re-balanced. I just can't believe this is the only way to solve this problem.
Have any of you had similar problems or do you have any suggestions I might try first? Thanks for any help you can provide.
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Both the balancer and the flexplate are 28oz and both are new. The flexplate is made by Scat, and the Balancer was purchased through Wild Horses for a 351W I don't know the make.
I used the firing order from the Chilton manual for a 351W not a 289/302 one.
I used the firing order from the Chilton manual for a 351W not a 289/302 one.
Cargo Master
Joined: May 2007
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From: British Columbia
Rough running engine
It seems unlikely that even with the wrong balance an engine would run as roughly as you say just idling. I'd suspect wrong firing order or bad carburetion. Perhaps one of the carburetor idle circuits or transfer passage is clogged. Compare the balance weight on the new vs old flexplate to see if they are very different.
Let's see if I can copy and paste images of the parts:
Well it doesn't work, so check this thread for the information:
https://www.ford-trucks.com/forums/4...confusion.html
Assuming the imbalance is correct, it seems a little bizarre to try to correct a rough running engine by taking it apart and rebalancing it. For starters, even if the wrong harmonic balancer and flexplate were installed, the engine does not need to be rebalanced, the correct harmonic balancer and flexplate would merely need to be installed.
As Conanski advises, check the firing order again for sure. The cylinder numbers are cast into the intake manifold over each intake runner.
Let's see if I can copy and paste images of the parts:
Well it doesn't work, so check this thread for the information:
https://www.ford-trucks.com/forums/4...confusion.html
Assuming the imbalance is correct, it seems a little bizarre to try to correct a rough running engine by taking it apart and rebalancing it. For starters, even if the wrong harmonic balancer and flexplate were installed, the engine does not need to be rebalanced, the correct harmonic balancer and flexplate would merely need to be installed.
As Conanski advises, check the firing order again for sure. The cylinder numbers are cast into the intake manifold over each intake runner.
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Thanks guys for your help. It's nice to hear that tearing the engine apart might be premature.
As for the engine mounts, they are brand new. As for the firing order, the wires were re-routed to the 289/302 style and it ran even worse.
As for the engine mounts, they are brand new. As for the firing order, the wires were re-routed to the 289/302 style and it ran even worse.
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Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
Perhaps the timing is off then or the wrong flexplate is on there. ive seen that happen more then once.
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Often times if you can't get the motor to idle at low RPMs, this is indicitave of a vacuum leak. If you can get the truck back, try running the motor at the lowest possible idle you can achieve, then spray suspect areas with a can of carb spray, listening for a jump in idle speed. This will pinpoint a leak. Sometimes it helps if you lean out the idle so that it can just barely run, then the jump is easier to notice.
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Thanks everyone for the help. The problem was finally diagnosed and it was the carb all along. It turns out that is was so plugged up that the mech said he had never seen a vehicle run so bad without something major being the cause.
This is a great site with a lot of very helpful people. Thanks again!
This is a great site with a lot of very helpful people. Thanks again!
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