hi all,, i have a rebuilt Y 292  that vibrates through the car at about 30-50 MPH.  all the usual machining was done including line honing the block and crank and cam would spin well by hand.  rods and pistons facing right way  ,, changed the balancer again,  static balance on flywheel and pressure plate, pulled gearbox apart and replaced all internals ,,, no difference.  it does this in the shed and foot on the clutch or off  makes no difference. to cut a long story short i  am wondering if there is the remotest chance that by putting the cam counter weight in  ( which it did'nt have )  have i created a vibe??  i would'nt think so but this problem has got me stumped.  any thoughts are welcome.  no pics because nothing to see. yes  i have a new water pump

You can rule out the fuel pump concentric counter weight as being the source of your vibration assuming all the pieces were installed in the correct order.

Performing a compression test on all the cylinders will help to verify that the vibration is not being caused by something as simple as a dead or weak cylinder.  You don’t mention if you had the rotating assembly balanced during the rebuild as that would have caught an issue with the connecting rod and/or piston weights not being uniform or out of sync with what the crankshaft was originally balanced for.  You do mention a static balance of the flywheel and pressure plate but that could still be the source of your vibration depending upon how that balancing operation was performed.

In one instance, found a distributor that had a miscut lobe that was causing a timing change for two cylinders thus creating a vibration.  Another distributor fixed that one.

Beyond all of that, the pressure plate would be a good place to start as they are at the top of the list for being the root cause of engine vibration issues.  Running the engine with the pressure place removed may help to determine if that is the problem or not.

Here are a couple of pictures of a crankshaft that was recently balanced showing the additional holes that were required to compensate for the lighter than stock pistons that were used.

  

  

Other thoughts on this are always welcome as these are just the tip of the iceberg.

Lorena, Texas (South of Waco)

Is this a high pitch buzz or low pitch knock ? Does it change pitch at different RPM ?
Does this vibration change depending on what gear you are in ? Do you have an RPM gauge ?
Clutch/flywheel is biggest possibility if it is RPM dependent, others are the piston assembly, one or two could be very different weight also to a smaller degree if a couple of rockers are a different ratio, and, the cam weight less noticeable.
Accessories attached or not ?
If it is NOT RPM dependent then it is not from the engine and something in the suspension or drive-line.



1936 Ford 3W Coupe : 56 T-Bird 312, 47 Packard 3 speed, 40 juice brakes.
1968 Merc Cyclone FB GT 390, Getting a better front clip!
1977 Ford F-250 Supercab RWD Explorer Long box.
1976 Chev Camaro RS LT
Future rebuild : 1949 Ford F-1

If it does it "in the shed", I don't think you're going 35-50 mph, so it must not be road speed that induces vibration. 

in the shed means at a stand still and 30-50 out on the road is the same result at approx same revs.

pretty sure it is revs related as at idle speed it is smooth ,when going through the rev range it vibrates like an out of balance harmonic balancer ,, but that  has been changed.

thanks Ted for the thoughts. today after staring at the piece of junk for a while i put the new water pump ( it was hard to mount) in the lathe  and spun it so the shaft was turning as in motion.  after putting the dial gauge on it the shaft runs true , but the hub for mounting the fan to had 28 thou run out! i have now trued it up but am still concerned it may not be the problem.  i had this same problem on a water pump may years ago .  i might get lucky. tomorrow  i am removing the cam and look for anything i can see.

Simply running the engine with the belts off will rule out the possibility of the water pump and other belt driven accessories being the source of the vibration.

Lorena, Texas (South of Waco)

just done that

Update on vibration?


South Australia