So my motors been making a little top end knocking sound. More noticeable at low RPMS. Went away as the RPMs went up.

The motor was running little rough too so I pulled things apart Monday night. I went for the obvious for the rough idle first. Pulled the cap and the screws on the rotor loosened up and it was just about ready to fall off. The cap contacts were all chewed up. I figured it might be screwing the firing all up so I might figured maybe the knocking was related to this. I replaced the points, cap and rotor, got it back together, set the dwell, set the idle, set the timing.

Still making the knock

I took it for a "beat on" type ride around the block. As it tach'd out I started hearing what sounds like detonation....

The timing was set a 7.5 degrees, I run 93 octane so the only thing that could cause it would probably be a slipped damper.

I get back home and the knock at idle is LOUDER THAN EVER. It sound like it's coming from the top end in the front of the motor and the oil pressure is fine so I start removing spark plug wires, #1, #3, #2, #4. No difference.

I go under the car with it running, knock is definitely coming from the top end .

For whatever reason I put my hand on the power steering pump....knock, knock, knock, . I try wiggling the shaft, doesn't seem loose. Took the belt off and with no tension on the pulley it's clearly loose.

I tightened the nut back up, put the belt back on, fired it up.......no knock

Take it for a ride.....no detonation, get back home, no knock

I'm one happy guy tonight...................

 

I like happy endings!



- Eric

 

way to narrow it down, Good job!!

 

I knew you'd take in the gutter Eric

J/K

I thought about it when I posted it and figured it would generate a couple choice comments.

 

Hey, go with what you know, I always say.

- Eric

 

Only 7 degrees of timing? I'm happy for you that the knock turned out to be nothing, but I just understand the timing. Are you sure you are checking correctly? Sure the timing light is right? Even with 10.5 and 93 octane you can run more timing and wake that thing up.

 

Dave,

I know I can probably run more. I'm still trying to get comfortable. It's plenty fun for me and my 4 and 10 year old girls.

The factory setting for a 68 455 is 7.5 degrees. It's a 70 motor & I'm guessing it's the same.

While we're on the subject, how do you check for total advance at 3000 RPM's? Timing tape on the balancer? Obviously the timing marks only go to 10 degrees.

Thanks,

 

Almost pulled a motor once because of a bottom end tick. Would come and go and Thats what was driving me nut's! And it would follow the RPM up and down! Finally one night I had it running before I was about to pull it and check for the last time, as its running I noticed the oil dipstick wasn't all the way seated, as soon as I push it in all the way. Tick tick tick. That one moment of OCD saved me hours of tearing apart a perfectly good motor for no reason at all.

 

The timing of the '70 engine could be different as the cams probably are depending on the original engine specs. The easiest way to lock the timing at 30 degrees is with an adjustable timing light. That type if light will have a **** on the other end from the light bulb. Set the **** at 30 and rev the engine to 3,000 rpm. First loosen the distributor hold down nut enough to allow some movement for adjusting. With the engine at 3k and the light at 30, adjust the distributor until the mark on the balancer and the pointer line up. Lock the distributor back down and it is now set at 30. Or buy a piece if timing tape, but be certain you get the tape for your size balancer---you will need to measure your balancer first. Once you have the correct tape apply it to the balancer (make sure the outer edge of the balancer is clean and grease-free so the tape adheres properly) loosen the dist. bolt, rev to 3000, then turn the dist. until the 30 mark and the timing tab line up. Then tighten the locking nut. Two things also need to be done---you must unhook the vacuum advance hose and plug it so there isn't a vacuum leak. Second is mark the balancer with white crayon or chalk at the "0" and the "30" mark. Even if you use the tape, mark the balancer, because most of the time the tape isn't as wide as the balancer. The white line is much easier to see when making the timing adjustment. Another trick I have found over the years, is to try to do this when you are in the shade or later in the day, it is a little easier to see the light flashing on the balancer---I don't mean midnight but try to do it out of the sun glare. Another little trick is once you set the timing at 30, mark the bottom flange of the dist. and the manifold together, and notice and remember what direction you turned the dist. to advance or retard the timing. I say to do this because the next time you can adjust the timing without the light. If the reference mark is there at 30,you can turn the dist. a little one way or the other to raise or lower the timing a little. Notice how minute the degrees are on the tape and that's how much you will need to change the timing without the light.
I know this answer is a little long, but the process isn't hard once you do it a few times. Oh yea, one more thing---make sure you hook the vacuum advance hose back up and make sure the advance works! It's easy to check and easy to replace if it is bad,
Good luck and let us know how you make out. Changing that timing will surprise you with the added performance.

 

I thought to check total advance you need a dial back timing light, so you can dial it back xx degrees until you get to a marked reading on the tab and then you know.

 

Not really, I describe above how to with a regular timing light and the balance degree tape. The dial type light is a little easier, but if that light is not available, the tape is a whole lot cheaper than a new timing light.

 

Thanks Dave,

I researched it a little before I posted the question. I had a pretty good idea of what I needed to do (that's why I asked about the timing tape). I appreciate the answer because, believe it or not, when you do a search NOTHING like your little dissertation above comes up.

My timing light is a simple strobe with no dial back. The cam is new. It's a Comp Cams DE 42-208-4 with Speed Pro SPE 369P pistons , but everything in the ignition system is stock. The balancer is stock and I'm pretty sure it's 6". That seems to be the standard Olds size.

My next project is to install an analog MSD 6AL which I understand changes the total advance required. Just so everyone understands, I'm not trying to get any more performance from the MSD. I bought it used for decent price because I wanted a Rev limiter.

 

I hear ya on the rev-limiter. That is good insurance, especially if you have a stick. I should practice what I preach, because I have two SBO 4-speeds and don't have a rev-limiter on either one. My racing days are behind me, but I do like to play a little and really should have one on each car. Keep us up to speed on your progress.

 

Personally I give any engine I tune as much timing as it will tolerate.

 

Out of curiousity, how do you determine how much timing it will tolerate? Thirty five years ago I'd crank the timing up on my SBO a little at a time until it pinged and then backed off a little until it stopped. From everything I've read by the time you hear pinging the damage is already being done.

FWIW that car roasts it's tires from a rolling start right through second gear and chirps third if I hit it right. (I don't do it often)

I've got what appears to be sciatica in my right leg. It doesn't really hurt but it causes my calf to cramp when I point my foot......like when I mash the accelerator to the floor...... thus the need for a rev limiter

 

Agreed. Dyno. Tune for the max HP. The engine will tell you when it has too much before it starts knockin or pits the combustion chamber. Read the plugs, use your ears and common sense and a bore-scope once in a while if in doubt. Obviously 50-60* for most engines is too much. You have to take your octane and driving style into consideration too. 89 back off. 110 crank er up. Never had a problem. Most of the time I dont use a timing light rather I use a vac gauge and my butt dyno.

 

I finally borrowed a dial back timing light. I was running 7.5 initial and 25 total at 3000 rpms. I bumped it up to 9 and 27.5 and it's running great.

Can I really take it to 30 degrees?

Here's a pic of roasting through 1st, the slight skip across the intersection is shifting to second and I took it until I wasn't comfortable spinning & it started to go sideways a little. It felt nice and put a big smile on my face

 

Mike - Try setting the initial @ 12 & see if engine will tolerate it under load and hot cranking. If it does, bump it to 14 & retry, if good you can end it there. Ideally you should probably get 34-36 total in by say 3000rpm but that may take some recurving. I know way back before I understood total timing I always set the initial just beyond the end of the timing tab which I think was around 12-14 & they always ran well.

 

Kind of caught this thread late but I am glad it turned out to be nothing. I have story you'd appreciate....

I had a friend call me and asked me to come look at his car. He had a 83 Toronado with a 307, 80k miles and a bad knock. It was coming out of the bottom of the motor. We borrowed ramps and crawled underneath. Turned out the motor was fine, but the flywheel inspection cover was warped (made of plastic) and it banging on a raised part of the flywheel with each revolution the engine made. Once removed, the noise went away. Sometimes you get lucky.

 

On the subject of timing. Once total mechanical timing has been set, how do you figure out what additional advance is allowable via the vacuum module. I understand you can get different amounts of advance in the modules, so for instance what was stock? Both specs. total mechanical and additional vacuum for a mid sixties big block? What are others running?

 

Original vacuum and mechanical advance specs should be in the Chassis Service Manual.
Old Motor manuals have them, too, in a very nice table.

Here's the basic layout of what you do:

• Set the maximum mechanical timing so that it doesn't ping at full throttle, usually somewhere in the 34-36° BTDC range at 3,000 to 3,500 RPM.
  Use an aftermarket advance tuning kit to set it so that it is "all in" by 3,000 to 3,500.
• Set the "bottom end" of the timing so that the car starts easily
  (that is to say, if the span of the mechanical advance unit is wide enough, the engine will be retarded enough to start easily, but if not, such as with HEI, you may need to extend the range a bit with mechanical modifications or an advance tuning kit (which may be able to increase the mechanical range).
• Set the speed of the mechanical advance with an aftermarket advance tuning kit - take it out for full-throttle runs through the RPM range - if it pings at a particular engine speed, but not once it winds out past the RPM where it reaches full advance, you may need to use a stronger spring on one side to hold it back from full advance for just a bit longer.
• Start working on the vacuum advance - you will need a vacuum gauge in the car so you can see where it pings.
  • Drive it around and listen carefully for pinging at part-throttle
    (generally at low RPMs when going up hills at 40-60 mph).
  • An aftermarket adjustable vacuum advance can is useful for this exercise, even if you later decide to use a non-adjustable can.
  • Follow the advance can's directions to advance incrementally until you hear ping, then retard a bit.
  • The vacuum gauge will tell you where it pings and where it does not.
    If it pings at the highest vacuum settings, you may benefit from reducing the range of the vacuum can (usually with an included stop), and then re-adjusting.
    These things can usually give you over 20° of advance, which, if you already have 36° mechanical, can put you way over 50°.
    It's tough to get this just right, because you're timing it at a time when it's got some load on it, and is also running at over 3,000 RPM, so it pretty much puts you on the highway, where it's hard to hear pinging - I recommend driving close to concrete barriers on your left during uphill runs with minimal throttle deflection (to keep the advance unit fully deployed), so that you can hear the sound from the engine reflected off the concrete.
  • Once you've got the highway-speed, uphill cruising pinging dialed in, you can go back and fine-tune the vacuum advance spring pressure to get the most advance under partial vacuum conditions.
  • At this point, you can measure the settings that you've obtained with the vacuum advance, and buy a non-adjustable unit that is close to those settings, if you wish.

- Eric

 

Thank you , a wonderful description as to what should be done. I'm surprised at the amount of vacuum advance but will give it a try. I surmise it might help with fuel economy at least when taking trips. Am I correct that tan adjustable model has 2 controllable aspects 1. how much advance is dialed in (total # of degrees) and 2. at what vacuum it begins and ends and to some extent how fast it happens?

 

The two variables on the aftermarket adjustable vacuum advance cans are

• The amount of spring pressure on the diaphragm (which adjusts how far the diaphragm moved under a given vacuum, and just shifts the same line left or right on the graph), and

• The place where the diaphragm starts - the stop they provide pushes the diaphragm "forward" (advanced) in notched steps of 1-2° at the beginning of its travel (it doesn't cut it off at the far end), which means that when you adjust it, it advances your base timing as well, which means you probably have to readjust your timing when you mess with it. (This can also be a good thing, because if you encounter bad gas, you can turn the stop one or two clicks and retard your timing by a predictable amount without getting out the timing light - it'll still ping at part-throttle, but not at full throttle).

You can also use any method your ingenuity can come up with to make a stop for the "high" end, if you prefer.

- Eric