C2 300 HP Harmonic Balancer on 340 HP 327

[Peter L.]

I have a recently restored 1963, 327/340HP, 4 speed convertible (on the road since June of this year) and I have been having trouble with the engine "lugging/lunging" at lower RPM's (under 2000) in first and second gear. I have had the carb (correct 3461S) rebuilt, and re/checked and supposedly it is not the problem. In looking over the engine (which was rebuilt as a 340 HP, by Musi Speed Shop when he was still in NJ with hydraulic lifters, per my request), I just realized that there are two different harmonic balancers, one for 300 HP and lower, and one for 340 HP and higher. The one on my engine is the original (6" diameter), which is a 300 HP type. The engine shop never suggested the original was incorrect, so I never knew about it till looking closely at all aspects of the engine. Could this be the problem? What effect does having the smaller 300 HP balancer on a 340 HP engine have?

[Loren L.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

If I recall correctly, the timing mark on the 8" balance is pretty much dead on line with the woodruff key slot, Is it the same on the 6"?? I'm intrigued by the "rebuilt as a 340 HP.....with hydraulic lifters" - does that mean he installed the pop-up pistons? What hydraulic cam was used and what are the timing specs for it? It's September now, have you fouled out one or two sets of plugs since June?

[Peter L.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

I spoke to the engine rebuilder about a week ago, and he lost all records from back then (originally re-built in 2012) to a flood. His recollection is that the cam was whatever he could buy meant for a 340 HP, 327. He could not remember exactly what he put in from 4 years ago. We dyno tested it, and it produced 340 HP and 345 HP on two successive runs, at 5500 RPM max. The reason I had him put hydraulic lifters was so I wouldn't have to listen to the solid lifters when they needed adjustment, nor would I have to get them adjusted ever. (I have no intention of running this car over 5500 RPM, at was meant as a really nice driver.) I have no idea what a pop up piston is, but I have left a message for the engine rebuilder about that, and should hear back from him in a day or two. I have about 550 miles on the engine, and have not changed plugs at all. The engine runs rough on start up at idle for about a 30 to 60 seconds then it smooth's out and runs very nicely at idle (once the choke drops out, the idle is around 900 to 950 RPM). One of the shops I had look at this adjusted the timing to 8 degrees BTDC, at 900 RPM, which is supposedly factory spec.

[Timothy B.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

Peter,

unhook and plug the vacuum line to the vacuum advance control and drive the car to see if it's better. While you have your head in the engine compartment look at the vacuum advance and post the numbers that are visible and if the distributor has a small aluminum tag see if you can see that part number.

The problem could be the factory vacuum advance control, it could also be a lean surge condition caused by the camshaft overlap.

[Bob R.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

Peter
You asked if the smaller balancer would cause the problem you are having I doubt it would. I had an issue with my 63 in lower gears lugging and lunging and i believe the problem was from the carburetor. Over the years someone had changed the metering rods and jets in the carb probably someone hot rodding and the result caused the problem. When I changed back to original spec the the problem disappeared.

[Joe L.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

Peter
You asked if the smaller balancer would cause the problem you are having I doubt it would. I had an issue with my 63 in lower gears lugging and lunging and i believe the problem was from the carburetor. Over the years someone had changed the metering rods and jets in the carb probably someone hot rodding and the result caused the problem. When I changed back to original spec the the problem disappeared.

Bob and Peter------

I agree. I don't see any way that an incorrect balancer would cause the problems you describe. In fact, even a significant engine balance problem would not cause that kind of problem.

Having said this, though, understand that if you reconfigure an engine, especially if pistons, connecting rods, and/or crankshaft is replaced, then the entire reciprocating assembly including the aforementioned parts + balancer + flywheel + clutch needs to be custom balanced. However, even if this was not done and the engine was reconfigured with respect to the components I mentioned and an incorrect balancer installed, I would not expect the kind of problems you described. You need to look elsewhere.

[Edward J.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

Pete, there's always a lot of posts about the 340 shp dist. vacuum advance as being a chronic problem, as per Duke a regular here you will likely want a B28 vacuum can, My 63 had what I call a trailer hitching effect at low speeds( bucking), and the B28 can fixed this problem and improved the running of car at all speeds.

[Timothy B.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

Peter,

I just want to add something about the carburetor and the trailer hitching you experience.

With a hot idle speed of 900-950RPM the primary throttle blades are well into the transfer slot and are open to far at idle. This can cause issues because much of that fuel for idle speed is coming from the transfer slots vs. the curb idle ports A/F emulsion screws. As a result the A/F emulsion screws (idle fuel supply) are not open as far as they would be if the primary throttle blades were closed with small transfer slot exposure. At higher cruise RPM under high vacuum conditions less overall fuel is available because the A/F screws are not open as much as they could be and you can get a trailer hitching effect.

The original carburetors are calibrated for the stock camshaft and your cam specs could have more valve overlap thus needing a richer fuel mixture. The above may or may not help but it's important when tuning a engine to run correctly, set the carburetor for the correct primary throttle blade/transfer slot exposure. At that point if the idle speed is to low, additional air for idle can be supplied by PCV valve or other means and all IDLE fuel supplied by the curb idle ports which are controlled by the A/F emulsion screws.

If the vacuum advance is not the problem and the above does not help then your carburetor is to lean IMO and the idle circuit needs to be tuned which is a different discussion.

I hope I explained myself OK

[Stuart F.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

As Tim probably recalls; I dealt with a "lean surge" condition with my 340 hp engine (even with a B28 vac) for over a year trying to sort out the problem which only occurred when I tried to use a rebuilt 3461s carb on it (my replacement 3721 ab carb worked fine). I tried everything you can imagine including all of Tim's ideas about jetting and transfer slots until, while checking at the latter, I looked at the transfer slot exposure and noticed that one side had more exposure than the other. Turned out that the shaft holes for the primary throttle shaft were worn so badly that the throttle blades did not fit the same and over exposed one side more than the other. I sent the carb to the carb rebuild shop here in Florida and instructed them to just rebush the primary shaft. That cured the problem.

Stu Fox

[Stuart F.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

One other thought about the OP's problem; are you sure just where your timing is? Remember the timing tab on a 340hp is meant to be used with an 8" balancer and even then it would be about 1.3 degrees too low from actual. I would suggest you put a timing tape on the balancer so you really can see with a timing light where it is at. Also, no 300hp engine spec should idle so fast. Even my 340hp runs best at 750 rpm at idle.

Stu Fox

[Duke W.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

It's a problem when you have a rebuilt engine and no documentation, so you don't really know what the internal configuration is, but you can maybe figure it out by taking some measurements and reporting the results. It's no longer a 340 HP engine, but something else, which is currently unknown.

You will need a Mity Vac or similar vacuum pump tool, which is about 25 bucks at Harbor Freight.

What is the number on the VAC and at what vacuum level does it start to move the breaker plate and reach the limit?

With the Mity Vac teed into the VAC signal line, go through the idle speed mixture adjustment procedure in the shop manual with a target idle speed of about 750 and report idle vacuum. If idle quality is unacceptable at 750 find the minimum idle speed you find acceptable and report that speed and vacuum.

If the engine is wearing the original unmodified distributor, max centrifugal is only 24 @ 4600. The proper total WOT advance is 36-40, so it needs 12-16 initial. The curve is also very lazy and lighter springs to bring it in quicker will noticeably improve low end torque. Get a dial back timing light and measure it.

Until you can provide us with the measured data as outlined above everyone is just guessing.

Duke

[Peter L.]

Re: C2 300 HP Harmonic Balancer on 340 HP 327

Guys,
I want to thank you all for your info and advice. This week has been hectic and I have not been able to try any of the suggestions above, and I will be away from 10/1 thru 10/13, so I won't be able to do anything for a few weeks. When I get back, I intend to dive into this with the advice above, and will let you know what I find and how I fare.
Thanks again,
Pete Loscalzo