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SBC 350 Rattle When Accelerating

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Discussion starter · #1 ·
I have a 67’ with a rebuilt 350. The cam is a pretty lumpy comp cam and the car progressively started running, starting rough and I was hearing ticking from under the valve covers . I noticed a spark plug cable on backwards which was no big deal, but when I removed the vacuum advance hose off the distributor, I noticed the distributor was loose. It was probably out around 10 degrees advanced. I rotated the distributor back to where the engine ran great and tightened the clamp down. I know I need to get a timing light.

Now that the distributor is back where the engine runs great again, I hear what I recognize from past vehicles as a timing chain rattle when I accelerate at the bottom of a gear (5 speed) but I’m not sure if that’s what it is. There is still a slight ticking coming from under the valve covers. Did the loose distributor cause damage to my lifters/rods. What could I look for? Thanks for the help!
 
#3 ·
What you're hearing is pinging also called detonation. Lugging the engine in 5th gear and then trying to accelerate without downshifting will do that. Especially when you don't know where you set the timing at. Very dangerous for your engine.
 
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#4 ·
I would stop driving it until you get timing issue sorted out. I broke 2 forged pistons & split 2 cylinders, one of them about 3" to detonation on a .030 over 350 many years ago. Very risky to continue driving it.
 
#5 ·
Pull a valve cover and check to see if the valves need adjusted.
 
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Discussion starter · #6 ·
SY1 said:
I would stop driving it until you get timing issue sorted out. I broke 2 forged pistons & split 2 cylinders, one of them about 3" to detonation on a .030 over 350 many years ago. Very risky to continue driving it.
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I finally got around to timing the engine. After removing the vacuum advance and plugging the hose, I set it at 12 degrees initial and 36 degrees total advance timing at 2500 rpm’s. The “pinging” is still there albeit much less noticeable. If I retard the initial timing any further, the engine wants to stall out. Is this slight pinging something I may have to live with or is there anything else that I can try? Full disclosure, I just bought the car as a fan of the cars and I am no gear head but I am very willing to learn. Thanks!
 
#8 ·
you need to get your vacuum advance under control as it sounds like you're adding to many degrees of advance with the vacuum. read Dave Rays posts on vacuum advance limiters. continuing to drive, even with slight pinging, will cancel pistons in short order. you could always keep it as it is and just run 116 octane leaded fuel, should be fine like that
 
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#10 · (Edited)
OP

while your title says you here a "rattle when accelerating"....the terminology neeed may be "detonation" after reading your post again and describing what you did relative to timing because your distributor was loose so you by hand adjusted t until the engine ran better, in your view, but still had the noise which under the condition to induce the noise sounds like detonation.

Your 12 degrees initial timing and 36 at 2500 rpm is good in a general sense but when you connect your VA you now have too much timing. As mentioned, you need to control your VA to not allow to much timing to come in with the mechanical timing. Dave Ray wrote a good "how to" which involves using a detent "stop" plate mounted to VA arm. Unfortunately, those are not available to buy anymore but homemade versions can easily be done following Dave's 411. Ideally you want 10-12 degrees of base timing + 10-12 degrees of VA added when VA is plugged in which gives you 20-24 degrees of timing at idle with VA plugged in. BUT you need to confirm how much mechanical timing you have by itself and if it comes in to soon you would need stiffer springs in dizzy. Dave's 411 goes over all of this

Stock VA, IIRC per some of Daves notes, had a small piece of vacuum hose over the "L" part of the VA rod to limit its pull. Just adding that may be a quick fix relative to how much VA your VA can provides. You can simply add this by pulling the dizzy cap and putting on about a 1/8" long piece of vacuum hose ID size of the VA rod end.

In the interim you could just back your timing down a few degrees like 8-10 initial to see if that eliminates the "pinging" sound under load acceleration. I assume you are using 93 octane. Here in CA we only get 91 so my total timing is only 34

I would also confirm your timing mark on your damper is accurate. If it's an aftermarket damper and is keyed hub the marking is right ASSUMING the position of the pointer is right (different ones for different diameter dampers). You can buy an inexpensive piston stop tool and use it to confirm TDC to confirm your pointer and damper in fact are aligned correctly which they need to be to accurately set timing. Some aftermarket pointers are adjustable to set them dead nuts using a piston stop tool to confirm TDC
 
#11 ·
I don't see where the OP has mentioned the amount of timing the vacuum advance is adding yet he's getting advice to limit it. In his last post he said he removed the vacuum advance and plugged the hose. He needs to run vacuum advance. Also said the engine wants to die with less that 12* initial timing. That's why he needs vacuum advance. What octane fuel are you running? What distributor setup? IMO 36* all in at 2500 rpm is too fast for his assumed street car setup. I have more questions than answers. I think this is a combination of timing and carb tuning.
 
#12 ·
allanjs said:
I don't see where the OP has mentioned the amount of timing the vacuum advance is adding yet he's getting advice to limit it. In his last post he said he removed the vacuum advance and plugged the hose.
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My take on OP's post Al is he unplugged the VA and blocked it to check his timing for base and then at 2500 rom but otherwise had VA connected.

So with 36 degrees at 2500 without VA "maybe" with it he is seeing too much timing as under load he appears to have detonation...if we understand his noise to be detonation

So yeah it would be helpfull to see how much VA is actually being applied if connected and when it drops out and mechanical takes over. IMHO, depending on which VA can is being used, some form of controlling how much VA is applied is crucial especially on modified motors for street use.

OP appears to have a modified "lopey cam" motor may need a few things addressed relative to base timing, VA, "total" timing and likely carb adjustments which could include jetting, etc changes

Also knowing how much vacuum the motor makes at idle

I think most of us are interpreting his "rattle when accelerating" as detonation...although without hearing it...could be misfire do to ignition. I think the fact he found a lose distributor and just adjusted it back by ear leads me to suspect timing issues...and VA, if used, is part of the equation
 
Discussion starter · #13 ·
ilikeike said:
Do you know the compression?
Maybe try some race gas just as a test.
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I don’t know the compression as the guy I bought it off got it from an auction online from the guy who resto’d it in Huntington Beach California. He had no knowledge of the engine build other than it’s a bored 30 over 350 with trick flow heads, comp cam and hypereutectic pistons. It’s has the edlebrock AVS2 carb as well. I always run 91-94 gas depending on the station I end up at. The car ran flawlessly when I got it in May until a few weeks ago when it wasn’t starting too well and was stalling out on very hot days. That’s when I noticed after looking around that the distributor was loose and had most likely moved quite a bit. Based on the driveline components (Borg Warner World Class T5 transmission with a Ford 9 in the back with an Eaton third member with 410’s along with strange axles) along with the truckarm center drive, mini tubs with 325 tires and the wilwood disc conversion, I suspect the guy built this car for racing around because it rips pretty good and handles very well. It wouldn’t surprise me to find out the compression is a little higher than normal on this engine build. I’m trying to track the original owner down for some more info. From the paperwork I do have, his name is Bob Woodward in Huntington Beach, California if you or anyone on the forum knows him I would love to get a hold of him.
 
#14 ·
OK, school time,

PINGING is noisy

DETONATION is silent

What we have NO idea of is the quench distance of this engine, too little, the mixture gets blown out of the detonation areas, going dead lean, too much, mixture migrates out, same detonation.

As noted, 12 initial is not bad for a stock engine, but one with a "lumpy" cam should need upwards of 16 initial, plus 10 vacuum advance, for an idle timing of 26 or so degrees.

IF the quench distance is out of the .039 to .045 correct limit, timing and curves will not help, the engine will ping and more than likely, silently detonate pistons out of the engine.

There is a way to check quench with the heads on the engine, if anyone wants the process, ask here, and I will outline it, simple to do, helps get these situations ironed out.
 
#16 ·
OK, school is in.

First, cold engine. Disconnect battery

Figure out which piston you want to check, and remove all the spark plugs.

Pull the vale cover for that bank of valves

Select the two push rods for the two valves of the cylinder you want to measure. Pull those two push rods (we do this to insure that we do not have a valve cut the measuring media inside the cylinder

Using a socket and breaker bar to turn the engine over by hand, rotate the piston down and partially back up the bore, but not all the way up

USING DEAD SOFT PLUMBER'S SOLDER, .090 THICK, curve the end of the solder so it fits into the plug hole, and literally curves to the front, or rear of the bore, NOT the top or bottom of the bore diameter.

Then, BY HAND, slowly rotate the crank to move the piston up and through its TDC, and down the bore.

Carefully remove the solder. Use measuring device to measure the thickness of the compressed solder.

This is the quench distance for the cylinder

The reason we do not try to use the top or bottom of the piston top is that the piston rocks over at both BDC and TDC, which would not give an accurate measurement

I have done this so many times, it isn't funny. One time, I couldn't find my solder, my Ford loving neighbor took it to repair his plumbing, the rat.
 
#17 ·
David Ray said:
OK, school is in.

First, cold engine. Disconnect battery

Figure out which piston you want to check, and remove all the spark plugs.

Pull the vale cover for that bank of valves

Select the two push rods for the two valves of the cylinder you want to measure. Pull those two push rods (we do this to insure that we do not have a valve cut the measuring media inside the cylinder

Using a socket and breaker bar to turn the engine over by hand, rotate the piston down and partially back up the bore, but not all the way up

USING DEAD SOFT PLUMBER'S SOLDER, .090 THICK, curve the end of the solder so it fits into the plug hole, and literally curves to the front, or rear of the bore, NOT the top or bottom of the bore diameter.

Then, BY HAND, slowly rotate the crank to move the piston up and through its TDC, and down the bore.

Carefully remove the solder. Use measuring device to measure the thickness of the compressed solder.

This is the quench distance for the cylinder

The reason we do not try to use the top or bottom of the piston top is that the piston rocks over at both BDC and TDC, which would not give an accurate measurement

I have done this so many times, it isn't funny. One time, I couldn't find my solder, my Ford loving neighbor took it to repair his plumbing, the rat.
Click to expand...
Awesome, very nice easy to follow explanation. So I assume you haven't had any issues with the solder not staying in 1 piece doing this? As i was read, I was visualizing trying to fish a bit of missing wire out of a plug hole, that won't be fun at all.
 
#19 ·
Nice to know that I shouldn't use a lead solder, and, not put it into the engine, and not turn the engine slowly with a socket and breaker bar by hand, because I have done these steps for more than a couple of hundred engines in the last 50 years, and have had a lot of others do exactly the same, with not once having the solder break off, separate, get destroyed, because we all were CAREFUL and did it slowly as we went along.

But, I'll take the sage and expert advice, stop doing this inspection process, by recommendation from a source that has, no doubt, tried it, and ended up breaking the solder, from not doing it right,
 
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