Timing: Power & Rattle v. No-power & no rattle

[Austin C10]

About a month ago, my 1972 Chevy started experiencing some rattling on acceleration. Initially it was only when I got on the gas pretty hard. But then it was every time I touched the accelerator. I experienced a pretty significant loss in power, too.

After tuning it up, I took it to my favorite shop (I'm just not in a position to be messing with timing right now) and they adjusted the timing making it real quiet. They said that the harmonic balancer was old and had slipped, and that the most quiet setting was about 10 degrees above top-dead center. But this pretty much sucked the life out of her. No jump at all. On my way to take it back to the shop, I had a total electrical meltdown: short and the fusible link burned up.

Does anyone think that the timing adjustment could have played a role in that short? I didn't think so, but it is an odd coincidence.

Anyway, they replaced the harmonic balancer and re-adjusted the timing with a timing advance to give back some power. Well, the acceleration rattle is back. The shop owner said that the engine is old, and that I can have one or the other: proper timing with no noise and no power, or pre-explosion and some pep, which I assume is going to kill the engine. Should I buy this? I mean, the harmonic balancer is new, so is the vacuum advance. Why can't top dead-center of 10-12 degrees give me full power and no noise?

[Sport/Truck]

You probably have some carbon buildup on your old motor~ and that will help cause pre-denotation (pinging/knock). There are several products that can help with this. Some of the better ones are SeaFoam & Mopar Combustion Chamber Cleaner. Here is a link on how to use it~ I’ve used it with great results on my VR4 Galant. http://www.neons.org/howtos/MoparCleaner.shtml
I the link to the procedure I used isn’t working at this time~ but you can try it later (I’m sure you can Google MCCC and find some more info.) http://www.outreach.psu.edu/users/res122/DSM/
There are lots of good info on SeaFoam on this site too~ just do a search for it.

After you get the carbon cleaned off you can test by advancing you timing to where it was knocking at. It should be better if non existent.

One thing you can do for the long term is water injection. This will clean as you drive and allow a bit more advance on your timing. You can Google water injection and read more.

AFAIK the electrical short is totally unrelated……
Hope this helps,
s/t

[Longhorn Man]

You tried running a higher octain of fuel? That's all the hi test is for, to prevent spark knock.
I hear ppl whine and b!tch about spending the extra money on hi-test... but there's 2 things to look at.
1. Hi test will ALWAYS be cheaper than new pistons.
2. at the typical 10 cents more per grade, and your trucks's 20 gallon tank, the most you'll spend extra is $4. Seems trivial to me.

The pre-ignition you are hearing WILL end up damaging your engine... if it hasn't already.
You must get rid of the spark knock.

[Sport/Truck]

I wasn’t sure if the high octane would work if the engine is carboned up. Probably would help.
I’m assumed the motor was not knocking before and is not a high compression engine. Is this a true assumption?
s/t

[Billla]

There's something not quite right here. Do you have an advance-capable timing light? "Messing with timing" is really, really easy - really 10-12 degrees should be a completely workable initial timing, so I suspect an advance problem.

This has been rehashed a million times here, so Search is your friend Job 1 is to ensure you have an accurate TDC mark, then to check your mechanical and vacuum advance.

IMHO, the shop owner's comments were complete B.S.

Sport/Truck, I agree that it could be carbon - I honestly haven't seen it myself but too many other folks have told me about it to dismiss as myth Water injection IMHO is completely unworkable for a street-driven engine.

Octane could also be the culprit if this is a modified engine - but shouldn't be required on a stock one.

[Longhorn Man]

Bill, you are right, on a stock engine, it shouldn't be needed. I wasn't thinking stock.
Another possibility, is being way too lean, that would cause this too.

like bill said, verify the ballancer is right. They coulda added a later one for a long water pump, which would have the markings in another spot, making this one no good for setting the timing.
Bring it to top dead center on the #1 stroke, and see if the make is in the right location.

[mnunn454]

Sounds to me like the vacuum advance/retard isn't working.

Is the vac adv hose connected, and to the right place? When you pull a vacuum on it, does the breaker plate inside the distributor move? If it does move, does the plate stay in one place, or does it slowly "leak down" and return to its original location? If it's bad/leaky, it'll need to be replaced.

If the vacuum adv is fine, I'd check to see if the spring and flyweights under the rotor are all working smoothly and normally.

Let us know what you find.

[Austin C10]

Originally Posted by Sport/Truck

I wasn’t sure if the high octane would work if the engine is carboned up. Probably would help.
I’m assumed the motor was not knocking before and is not a high compression engine. Is this a true assumption?
s/t

The knock just started a month ago and prompted this visit to get it diagnosed. Not high compression.

Originally Posted by Billla

There's something not quite right here. Do you have an advance-capable timing light? "Messing with timing" is really, really easy - really 10-12 degrees should be a completely workable initial timing, so I suspect an advance problem.

This has been rehashed a million times here, so Search is your friend Job 1 is to ensure you have an accurate TDC mark, then to check your mechanical and vacuum advance.

IMHO, the shop owner's comments were complete B.S.

Sport/Truck, I agree that it could be carbon - I honestly haven't seen it myself but too many other folks have told me about it to dismiss as myth Water injection IMHO is completely unworkable for a street-driven engine.

Octane could also be the culprit if this is a modified engine - but shouldn't be required on a stock one.

I'm assuming the harmonic balancer from the dealer fit the engine. I'll find out how they got it and also confirm that even though they replaced the advance, that its actually working.
I'll do the carbon cleanout before taking on the timing myself if things don't work out on my final visit to the mechanic. As far as the timing light, its a $40 model from O'reillys

Originally Posted by Longhorn Man

Bill, you are right, on a stock engine, it shouldn't be needed. I wasn't thinking stock.
Another possibility, is being way too lean, that would cause this too.

like bill said, verify the ballancer is right. They coulda added a later one for a long water pump, which would have the markings in another spot, making this one no good for setting the timing.
Bring it to top dead center on the #1 stroke, and see if the make is in the right location.

I'll double check.

Originally Posted by mnunn454

Sounds to me like the vacuum advance/retard isn't working.

Is the vac adv hose connected, and to the right place? When you pull a vacuum on it, does the breaker plate inside the distributor move? If it does move, does the plate stay in one place, or does it slowly "leak down" and return to its original location? If it's bad/leaky, it'll need to be replaced.

If the vacuum adv is fine, I'd check to see if the spring and flyweights under the rotor are all working smoothly and normally.

Let us know what you find.

New cap and rotor, not sure about finding the breaker plate while I've got vacuum.

[Billla]

The traditional question when things start is "what changed" - was there anything else that changed at that time?

The balancer can fit the engine...but it's possible that the timing mark is off. IMHO, you'll ALWAYS need to verify TDC before doing anything else. There are cheap, easy tools for this - basically a brass bolt that screws into the spark plug hole - let me know if you want a walk through, or use the Search function.

When you say "they replaced the advance" - what advance did they replace - the vacuum advance? If this is the case...what's the P/N for the advance unit?

The timing light you've got is OK, but one with adjustable advance is better if you can borrow one. Typically timing marks only cover about 12 degrees - and you'll have 32-36 degrees of mechanical advance.

It's good advice to check the free play in the advance weights. It is possible to check the vacuum can if you have a mytivac; otherwise it gets interesting

[Longhorn Man]

just unplutg the hose from the cab/intake, stick it in yout mouth and suck on it, when you have the vac aplied like that, stick yout tounge over the end of the hose. If the vac can holds vac, then it'll stay on your tounge, if it just falls off your tounge, then it isn't holding vac.

[GREASEMONKEY72]

FWIW, running a higher octane fuel in an old engine with some carbon build up does help, i went from 87 to 89 in my truck and it made a big difference and after i seafoamed it i was able to go back to 87 and keep the same performence

[57sailplane]

heres my 2 cents,

im not saying this is correct because i dont no if it is hard on a motor. but when i worked at a junk yard all the cars that came in halfways runing shape we had to tune up using old plug wires old plugs that were regaped.. now i was working on a 79 camaro that the boss wanted to keep the motor if it ran good. it was missing teribly when it came in i got here running mostly cause the plugs were all fouled badly.. when i got better plugs in the motor it ran great but rattled like you say.. the boss being the old head that he was. told me to keep here runing with more throttle as he trickled a cup of water down the carb.. i tell you what that thing blew out white, blue, and black smoke and soon there after the rattle was gone and boy did that motor run.. now i don't think it could hurt the motor but im not sure.. he said its like steam cleaning.. the water boils that carbon right out, not sure what else...

[Longhorn Man]

yup, that works great, but ppl are scared of it.
You d@mn near need to TRY to hydro lock an engine.
Dumping tranny fluid works good too, but it stinks... do it outside.

[Billla]

Originally Posted by Longhorn Man

just unplutg the hose from the cab/intake, stick it in yout mouth and suck on it, when you have the vac aplied like that, stick yout tounge over the end of the hose. If the vac can holds vac, then it'll stay on your tounge, if it just falls off your tounge, then it isn't holding vac.

Yeppers - I was thinking more along the lines that it could be the wrong vac advance can, so with a mytivac you can plot the Hg vs advance curve.

[71tahoe]

I scanned through and didn't see anyone suggest making sure the vacuum is ported and not direct. If it is direct it can give you too much advance too early.

Also, if your balancer slipped and they replaced it, did they inspect the timing chain and gears? I'm not sure if it could cause the problems you're having but a valve train out of sync could make it hard to diagnose.

[57sailplane]

about that balancer slipping anyways. has anbody seen one slip. im mean your going to have to sheer off a 3/16 key to slip the balancer and im not sure what would make it slip anyways. it would have to be somthing real jaring.. unless they are talking about the balancer came undone.. like the actual rubber faled... got me on this one..

[71tahoe]

I've seen the rubber piece fail on my cousin's truck but have only heard of a partial failure where the outer ring slips a little.

[Billla]

Originally Posted by 71tahoe

I scanned through and didn't see anyone suggest making sure the vacuum is ported and not direct. If it is direct it can give you too much advance too early.

Also, if your balancer slipped and they replaced it, did they inspect the timing chain and gears? I'm not sure if it could cause the problems you're having but a valve train out of sync could make it hard to diagnose.

The only thing ported vacuum affects is vacuum at idle; agree that a stock engine doesn't need additional advance at idle - but this would not cause too much advance on acceleration as the butterflies are open at that point.

If the timing chain slipped, there would be a lot more going on I honestly don't buy that the elastomer failed and the outer hub moved - I hear it happens, but I've never actually seen one...

[71tahoe]

Originally Posted by Billla

The only thing ported vacuum affects is vacuum at idle; agree that a stock engine doesn't need additional advance at idle - but this would not cause too much advance on acceleration as the butterflies are open at that point.

If the timing chain slipped, there would be a lot more going on I honestly don't buy that the elastomer failed and the outer hub moved - I hear it happens, but I've never actually seen one...

If they set it at 10-12 deg with direct vacuum unhooked, then normal idle with the vacuum hooked up would start advanced beyond 10-12. Could that affect accelerating under load from idle?

Also, I agree about the slipped balancer. I've only seen total failure due to high RPMs.

[raws67]

What about a flat cam? With todays oils maybe its flattened the lobes and not letting the engine bleed off enough compression? Just a thought

[Sport/Truck]

So have we found a solution for this yet?
s/t

[Austin C10]

Originally Posted by Sport/Truck

So have we found a solution for this yet?
s/t

Not yet. I'm still working my way through it. I just had the truck delivered to me in Redwood City CA where I relocated last week and started a new job, so I'm slammed on that front.

I tried burning out the carbon with some SeaFoam in the tank and down the throttle body through the carb. I got lots of smoke (on my way to the highway, some fart smeller drove by me in their Subaru and yelled out an audible "Peeeyew" ) but no change in the rattle/pinging on hard acceleration. A previous reply mentioned a more detailed decarboning, so I may give it another shot.

I've read about "pre-explosion" and "pre-detonation" (I found an excellent post mentioning both). Is there a difference between the 2 and how do I tell which I have? At this point, I've got less pinging/rattling, but I think that the timing delayed too much sucking away the power I'm used to. So I've got the worst of both: still a little pinging (especially under load) and not much acceleration.

My plan is to keep the board posted and to ask questions as I implement suggestions. I'll find TDC first.

Thanks so far!

[57sailplane]

man.

i hope its a timing issue. its sounding more and more like a cam issue or an over lean issue. when a cam flatens it alows the intake to close sooner making your engine a higher compresion motor dynamically.. which in turn results in pinging. does your engine have mechanical choke. if so try opening it slightly to pull more fuel. if the pinging goes away or you get more power then its a lean or cam problem... i would mess with the timing and such first.. whats got me is the pinging with retarded timing..

[eedgell]

As far as valve trane goes, low oil pressure can cause the effect of a flat cam. The low pressure if it exists is usually due to bad cam bearings. A worn timing gear and chain will cause timing to be all screwed up. You can set them and they seem to change, and they accually do at rpm. If the engine has miles on it, and all else fails check the cam and timing chain/gear.

[Sport/Truck]

Yes, I think there are the same, It’s basically the fuel igniting before it’s supposed to.
I hope you can figure it out.
s/t

Austin to Redwood CA!!??

Holy real estate batman! Most people are moving out of CA!