Motor mounts were checked before install, and looked OK - no cracking or separation. They were also torqued to factory specs.
I would have the driveshaft balanced and then maybe have the tires checked for balance.
All testing was done in park
Do you have the spark plug wires set up for the correct firing order?
351W is 1-3-7-2-6-5-4-8, 289/302 is 1-5-4-3-6-2-7-8
yes, checked firing order twice.
There is nothing wrong with using the C4, they are a good transmission, better than the FMX or C6. I have one in my 70 cougar and my 70 mustang, both behind 351 clevelands.
I didnāt think the 351 ever came with a 157 tooth, generally larger vehicles and larger motors alway came with the larger flywheel/flex plate. Sounds to me, it has something to do with the 289 flexplate, but I am guessing.
I donāt think so. I have used lots of C4ās behind 351Wās and I never used anything except the proper flexplate for a 289. Whether the flexplate is proper or not is a question.
If the installer missed putting on the reinforcing ring when bolting the flex plate to your engine it can cause problems. But nor usually a vibration. Unfortunately, you cannot see this part when the engine or transmission is installed.
This is that part.
Reinforcing Ring - Flex Plate - Small Block - Used ~ 1967 - 1973 Mercury Cougar / 1965 - 1973 Ford Mustang ( 1967 Mercury Cougar, 1968 Mercury Cougar, 1969 Mercury Cougar, 1970 Mercury Cougar, 1971 Mercury Cougar, 1972 Mercury Cougar, 1973 Mercury Cougar, 1967 Ford Mustang, 1968 Ford Mustang, 1969 Ford Mustang, 1970 Ford Mustang, 1971 Ford Mustang, 1972 Ford Mustang, 1973 Ford Mustang ) at West Coast Classic Cougar :: The Definitive 1967 - 1973 Mercury Cougar Parts Source
You could also check to see if the motor plate was installed. Unlike the reinforcement ring you can see this if it is installed. Just look at the back of the block. it should be in between the engine and transmission.
Spacer Plate - Engine Block - 289 / 302 with C-4 Transmission - 157 Tooth - Used ~ 1967 - 1968 Mercury Cougar / 1965 - 1968 Ford Mustang ( 1967 Mercury Cougar, 1968 Mercury Cougar, 1967 Ford Mustang, 1968 Ford Mustang ) at West Coast Classic Cougar :: The Definitive 1967 - 1973 Mercury Cougar Parts Source
To tell if you have a FMX transmission look at the main case, if it is cast iron then it is a FMX. The C4 is aluminum. Good luck, vibrations can be hard to fine and even harder to diagnose without being there.
Royce, are there two different size flexplates for the C4 ? One at 157 and one at 164 tooth.
Iāve never used any that were not 157 tooth.
unbolt the torque convertor to diagnose engine or trans. I th nk its the trans, probably torque convertor
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Thanks for all the advice and suggestions. After talking to several machine shops and an engine balancing shop, the consensus is that it is most likely an internal imbalance, caused by the new oversize pistons and non-original crank.
So I will pull the engine and send the rotating assembly including the flexplate and damper to the balancing shop. I will report back in a month or so and let you know what happened.
I had this exact same problemā¦ 351W uses a 28oz 157 tooth flexplate with C4ā¦ Will use a 28oz 164 tooth flexplate with 4R70W ā¦ I spent over a year to find out the new Torque Convertor was my problemā¦New Torque Convertor was completely out of balanceā¦ Determined it when I put the Trans in with no Torque convertor, just the flexplateā¦ Started the engine and vibration was goneā¦ Put my factory Torque Convertor in and all is wellā¦ In my case I have the 4R70W trans attached to 351W after I rebuilt my engineā¦ Tore the engine down twice going threw what I thought was a engine out of balance issue as wellā¦ Hope this helps youā¦
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if the tires and driveshaft are not moving because it in park how could either cause vibration?
have you pulled plugs and checked them to see if any are fouled or possibly not firing?
The initial post says the car was on jack stands so I imagined the car was in gear not in park.
unbolt the torque convertor firstā¦very unlikely its the engine. Iāve thrown together a few cheap engines an never had a vibration.
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Throwing together a cheap engine is not the same as having a block bored and adding oversized pistons. I gather the cheap engine used the same rotating assembly. I believe it is an over balance situation. The combined piston weight is not equal to the crankshaft counterweight. Therefore the vibration increases linearly wIth RPM as described. IMHO
Iām kind of late to the discussion, but a couple of quick thoughts. First, have you confirmed that the front balancer is correct for a 351W, and that the outer ring has not slipped? Second, are you 100 percent certain the builder used a cam with a 351/302 H.O. firing order?
If those check out, Iām definitely more suspicious of the torque converter than the engine internals. Anyway, just my two cents. Good luck with it.
Iām late to the conversation too, but you need to know the order of the vibration. In other words the rpm of the vibration for proper diagnosis. Obtain a sirometer used to measure Briggs and Stratton engine rpm and find out hz. We need to know if itās a first or 4th order vibration. If first order, thatās crank balance or counter weight issue. If 4th order, thatās exhaust or engine/trans mount failure/ground out. Also, before you go much further, check engine oil level and verify not overfull. Overfill can cause a 1st order engine vibration.
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