Bb Engine Vibation Need Help!

[Bob H.]

I seem to have developed a vibration in my 427. It can not be felt when revving but when letting off the gas. Also, if held at high idle (1500rpm) it almost feels like an engine miss. It is very slight but I don't want the engine to come apart ignoring it.
Could a broken valve spring or bad wire cause this? My first thought would be not if it happens when backing off . Seems to idle finne and runs great.

I don't seem to be able to feel it when traveling at speed and backing off. It is only when the clutch is depressed.

There are no noises, just the love taps put out by the solid lifters.

Anyone have any ideas or how to proceed diagnosing this??

Bob

[Tom H.]

Re: Bb Engine Vibation Need Help!

Bob:

Have you changed or repaired anything on the car recently that could have caused this. I would start with the simple stuff.

[Bob H.]

Re: Bb Engine Vibation Need Help!

Hi Tom:

I haven't done anything recently. I changed the plugs primarily because I wanted to see what they looked like and all look about the same and ok.

I just went out and started it and holding it at 1500rpm's I can feel it shake almost like is isn't firing on a cylinder. When I let off you can feel the vibration as well but not at idle. (850) I can't tell any difference in power when getting on it but with so much torque, maybe I am not noticing it.

[Tom H.]

Re: Bb Engine Vibation Need Help!

I'd start with plugs and then look at wires and boots. Bet you'll find the issue. What plugs are you running ??

[Bob H.]

Re: Bb Engine Vibation Need Help!

just installed 45xls's. used my timing light and went on each wire and they "appear" to be firing ok

[Tom H.]

Re: Bb Engine Vibation Need Help!

Can you see any "fireworks" if you turn the lights off in the garage and visually inspect around the wires with the engine running ????

[Terry M.]

Re: Bb Engine Vibation Need Help!

I seem to have developed a vibration in my 427. It can not be felt when revving but when letting off the gas. Also, if held at high idle (1500rpm) it almost feels like an engine miss. It is very slight but I don't want the engine to come apart ignoring it.
Could a broken valve spring or bad wire cause this? My first thought would be not if it happens when backing off . Seems to idle finne and runs great.

I don't seem to be able to feel it when traveling at speed and backing off. It is only when the clutch is depressed.

There are no noises, just the love taps put out by the solid lifters.

Anyone have any ideas or how to proceed diagnosing this??

Bob

In the old days we had oscilloscopes that would show the spark patterns (they were often made by Sun, so they were commonly called Sun Machines -- although other manufacturers also made them) so one could more easily see if each cylinder was developing an equal intensity spark. In the hands of a skilled operator (isn't that always the case) one could readily find, or rule out, some causes of these kinds of issues. Some of us have these machines in our garages, and some of us even know how to use them. A local Chapter is where you could make such connections.

Some shops still have an old Sun Machine gathering dust in the corner, and a real good diagnostics shop will have the modern equivalent in a hand-held unit. Loose spark plug wires or a bad spark plug will show up easily on these machines. I just put this forward as a diagnostic option for you.

[Dick W.]

Re: Bb Engine Vibation Need Help!

In the old days we had oscilloscopes that would show the spark patterns (they were often made by Sun, so they were commonly called Sun Machines -- although other manufacturers also made them) so one could more easily see if each cylinder was developing an equal intensity spark. In the hands of a skilled operator (isn't that always the case) one could readily find, or rule out, some causes of these kinds of issues. Some of us have these machines in our garages, and some of us even know how to use them. A local Chapter is where you could make such connections.

Some shops still have an old Sun Machine gathering dust in the corner, and a real good diagnostics shop will have the modern equivalent in a hand-held unit. Loose spark plug wires or a bad spark plug will show up easily on these machines. I just put this forward as a diagnostic option for you.

I just obtained an old Sun 1120 this week. The former owner wanted $300 for it. I worked on him for two years, he called me and told me just to come get the d**ned thing out of his way. BTW, it works like a champ. I just hope I remember what I was taught when I attended a couple of week long schools that Sun conducted.

[Bob H.]

Re: Bb Engine Vibation Need Help!

I know some one that has one. I checked for fireworks after dark tonight but didn't see anything.

[Bill I.]

Re: Bb Engine Vibation Need Help!

Bob, I stand to be corrected on this, but, it is my understanding that a timing light ONLY shows that voltage is going to that plug wire, it DOESN'T mean that the plug is really firing. Bill.

[Mike H.]

Re: Bb Engine Vibation Need Help!

What about pulling one plug wire at a time and look for the one with no RPM drop, that's the one to look into further. If you can't find a ignition problem run a comp. check. I had a little naging problem like that and had "0" comp. on No.7.
CORDially Mike

[Paul H.]

Re: Bb Engine Vibation Need Help!

I know some one that has one. I checked for fireworks after dark tonight but didn't see anything.

I was chasing a similar stumble, around 1500 RPM's in my 65. After changing out most of the normal suspects I checked the wires at night for a light show. Didn't observe anything. I changed the plug wires anyway. Problem solved. If they are older it wouldn't hurt to change them.