1960 352 question

[jwinkler]

The motor's actually in a 1960 T-bird - I had the opportunity to spend a few hours driving it yesterday, and noticed what appears to be throttle-induced knocking.

I'm the guy who has the fire-breathing-but-but-from-the-wrong-end 351W in my CR, and in trying to figure that problem out learned that it's an excessively lean mixture that causes the mix to ignite at the wrong time (or wrong place).

Thinking about this when driving the car, I noticed that there was a break-over point with the throttle that changed as RPM increased. If I floored it from a stop, I'd get horrific knocking, but if I rolled on the throttle I could keep opening it up without causing any knock.

This makes me think that the root of the knocking is maybe a carb problem and that I could maybe address it with richening the mix. Of course, I'll have to research that one - the carb came with the motor and car (4bbl Autolite, I think).

And a quick BS-meter question. The car's been worked on by a mechanic who specializes in old Fords, and while he's done great work, he's said a couple of things that don't sound right. First, he said that the motor couldn't handle conversion from downdraft to PCV, although later relented and did the conversion (the car is mostly only driven on Sundays by a little old lady (my Mom) who has trouble breathing, and the fumes from the downdraft were overwhelming).

So for the "real or BS" question - he also told her that this motor couldn't handle modern 93 octane gas (apparently due to all the modern additives), but that strikes me as wrong since I'm guessing the additives are mostly the same across the octane spectrum, and the only difference is the relative willingness to combust. Anyone here care to corroborate or debunk this? I'm guessing that switching to "hi test" would also help the knocking.

Thanks,

JLW

[TerribleTed13]

JLW,
The older engines needed leaded fuel to lubricate the valve seats.
I had a 1965 F-150 with a 352 2V carb it ran great on cheap fuel
(85 octane). How many miles are on the engine? Has it been rebuilt replaceing the valve seats to hardened ones so you can use unleaded fuel? Check the timing chain to see if it has "jumped". Maybe you have a lot of carbon build up on the intake valves from "little old lady" driving habbits. An old mechanics trick I know to remove carbon is; get the engine up to operating temp. and slowly pour a can of "Classic coke" down the carb. 1 can in about 60 seconds. Holding the engine at about 2000 RPM. I remember the dwell reading was very critical. Useing a dwell meter the engine didn't run very well but useing a match book cover or feeler gauge (.016 or .015 I forget) to set the points the truck ran great. Hope this helps.

[Excaliber]

I'm not getting a good feeling about your mechanic. The knock is really simple and it's two things:

1. The timing is to advanced, plain and simple.
2. "Modern" gas, UNLEADED will be fine, use Hi Test if you don't want to change the timing. The T-Bird's were not high compression engines, thats why I suspect it's a simple timing issue. NOT carb.

Now the tricky part is: You can't trust the harmonic balance to be accurate on a car that old. SO correct timing may not be that easy. I would simply back off the timing a little at a time until the knock is gone AND the performance is acceptable.

So why is unleaded gas OK with an old car like this? Lead is a lubricant to the valves, specifficaly the valve seats. At SUSTAINED freeway speeds for a LONG period of time using unleaded fuel on an older motor could cause valve related damage.

Sunday driver, little old lady, NON sustained speeds unleaded fuel will NOT be a problem.

Now go fill up with some good unleaded Hi Test and get back to us.

As mentioned above dwell meter can be deceiving and give you bad results. Match book thickness is indeed close enough. Coke down the carb works, but so does plain water. That was actually a GM warranty procedure for their big 454 "putt put" owner engines.