Tweet
The engine in my 62 has been recently rebuilt by a reputable machine shop here in town. Including balancing according to the receipt. Assembled by person or persons unknown. (all done at the direction of previous owner)Engine has about 3000 miles on it at this time. It has a vibration that kicks in at about 2100 RPM per the dash tach. It is not load related. It starts to smooth out above 2500 RPM. I had a professional mechanic who is very familiar with SB Chevy engines look at it and he said it seemed to be a harmonic vibration, possibly related to the somewhat radical camshaft. He also stated that the harmonic balancer appeared to be from a later model 350. !!!???? He set the timing at about 38 total and 14 initial. The engine seems to run best at this setting. The vibration had seemed to perhaps be timing related, but after trying about a million different timing settings, I have decided it really isn't. The distributor is newly rebuilt and has been set up on a Sun distributor machine prior to installation. I didn't notice this vibration when I bought the car and I think I would have. I first noticed the vibration after I disturbed the timing during the installation of a new tach cable. The car had a Mallory tach drive distributor, and I had to loosen the dist to get the tach cable to line up. The tach drive was on the wrong side of the distributor, so it was in a bit of a strain initially. I finally got everything to line up, and had the timing set approximately where it is now. I don't have a dial back timing light, so there was a bit of guess work here. It now has a proper 990 FI dist. The other area I have not addressed is plugs and wires. The wires and plugs are new, but the are not necessarily routed properly, and the front wires are tied together in a manner that could cause a cross fire. I cannot see or hear any arcing. However, if the problem were ignition related, I would expect it to occur under a load or at least be more pronounced under a load . Such is not the case. Could the balancer be the culprit? How do I tell? Any other suggestions?
-
-
Re: 327 engine vibration
Sure sounds like you've got a mis-balanced engine Ed. This is just one of the many problems that can surface with an improperly modified installation. At certain RPM there is a so-called "natural resonant" frequency, the harmonics of which can cause undamped "run-away" vibrations unless mechanically checked. That is the purpose of the harmonic balancer.
My machinist uses a progressive balancing procedure. He starts with balancing balancer alone and then with the reciprocating assembly. Next he attaches the flywheel and rebalances followed by a rebalance with the pressure plate. This assembly as a whole still has a resonant frequency but with the correct balancer the harmonics are dampened.
Spend a couple of hours and pull the engine. I'd recommend a rebuild using STOCK components. I don't think your cam or unshrouded 2.02 heads are helping you at all.
Dale Pearman -
Re: 327 engine vibration
I wuz afraid you wuz gonna tell me that. I have gotten the same recommendation from other quarters as well. Just trying to eliminate other possibilities first.Comment
-
Re: 327 engine vibration
Ed, sorry to hear about the vibration problem. Have you tried puting a timing light yourself on the balancer and with a screw driver or assistant run the RPM range up and down to check for a loose balancer,wobble w/timing light. Do this with the car parked and see if it makes any difference.
I had a worn out keyway in a balancer and it nearly cost me an engine. I never notice the vibration but I did notice prior to the costly repairs the balancer had a wobble to it when power timing. Good luck,grr#33570Comment
-
Re: 327 engine vibration
No noticable wobble in the balancer. What I DO see once in a while is a 10+ degree jump in the mark, sort of like a cylinder was occassionally crossfiring. Also, this balancer apparently does not have a retaining bolt; at least I can't feel one. I would guess that the crankshaft is not drilled and tapped for one. Did the 327 cast cranks not have bolts? I don't know what this engine has for a crank, I'm just guessing. I had hoped it was a steel one, but I know they are tapped.Comment
-
Re: 327 engine vibration
Of all the 327 cranks I have dealt with, none have had the front of the crank drilled and tapped for balancer retention, cast or forged, in the small journal size. Just my experience for what it's worth.Comment
-
Re: 327 engine vibration
I must have been thinking about 350 cranks then. See what happens when you get old?Comment
-
Re: 327 engine vibration
My '63 SHP forged crankshaft is drilled and tapped for a center bolt to sevure the 8" balancer. The 250 and 300 HP engines also had a forged crank, but I don't think they were drilled and tapped for a center bolt to mount their smaller balancers.
It sounds like you might have a parts compatibility problems here - perhaps running a balancer that was not engineered for your crank. Can you give us some part numbers and descriptions. I know that Joe can probably come up with the factory crank/balancer combinations. Don't pull that engine yet!
DukeComment
-
Re: 327 engine vibration
That's sort of what I was wondering when I posted this. I suspect the engine is made up out of parts out of God knows what. Ultimately,Dale is probably right, but I'd rather pull the engine down the road at my leisure and convenience.
I will probably have to get the balancer off the car to get a part number, so hold that thought for a couple of days. I also wonder if the flywheel could have thrown a weight? There was a loud noise from under the car while accelerating a few weeks ago that I never could find an explaination for. It sort of sounded like a rock being thrown off a tire, except it was awfully loud. Looked under the car and didn't see anything I could attribute it to. ???!!??Comment
-
Retainer Cap Screw
The bolt ( cap screw retainer) securing the harmonic balancer to 327 crank shafts started appearing around 1962 serial number 7585 (earliest unmolested observation). That would corrispond to March 1, 1962.
Dale PearmanComment
-
Live and Learn ( N. M. ) *NM*
Comment
-
Re: 327 engine vibration
A couple of other areas to look at might br the timing chain/gears. If the timing will jump ten degrees, that would be suspect. The other area I would chech would be a broken exhaust spring. Is there a ticking sound at idle?The light at the end of the tunnel has been turned off.Comment
Comment