Jump to content

Retarding ignition timing.


WPVT
 Share

Recommended Posts

I'm still wrestling with a 1954 Dodge truck engine that clatters at speeds above 40 mph. I discovered that retarding the spark to 8 degrees after TDC initial timing, makes the noise goes away. I've checked centrifugal advance, vacuum advance etc., and all seems well. I tried timing by vacuum method, and with a timing light, and both ended up about TDC. That setting makes for a noisy engine, though. and retarding the spark seems to cure the noise problem.

 

Is retarding the spark masking the sounds of a worn engine ? I have decent compression, good oil pressure, and the engine runs well. It's just noisy above 40 mph and retarding the spark makes a big difference.

Link to comment
Share on other sites

Thanks. The 218 flathead has a convenient port on top that permits one to insert a wire and check for actual TDC. That has been done and agrees with the timing pulley. 

My question is whether retarding the timing can help with noise from mechanical wear. It stands to reason that a retarded ignition would produce less power, but also put less strain on the engine. 

Link to comment
Share on other sites

First you need to be sure the mechanical advance in the distributor and the vacuum advance diaphragm are working properly. If the mechanical advance is sticking your timing will always be off one way or the other.

If all is well in there set it where it sounds the best and leave it, as long as power feels good. 

Link to comment
Share on other sites

This is quite strange or may be not. The old gasoline for those old engines is obsolete. You are dealing with high teck gas today. The engine has to move up to to today's dose of gas. Today's gasoline "explodes" much faster and therefore the engine should be timed at something like 8 degrees BTD. May be I am wrong. To check for worn distributor/chain remove the distributor cap and rock the fan back and forth and look at the rotor for  lag.

Link to comment
Share on other sites

10 hours ago, Oldtech said:

First you need to be sure the mechanical advance in the distributor and the vacuum advance diaphragm are working properly. If the mechanical advance is sticking your timing will always be off one way or the other.

If all is well in there set it where it sounds the best and leave it, as long as power feels good. 

Thanks. Both vacuum advance and centrifugal advance seem to be working properly. I've also verified that the crankshaft pulley timing marks are accurate as well. At speeds above 40 mph the engine is very noisy and "clattering".  If I retard the spark to 8 degrees AFTER TDC initial timing, it quiets right down and sounds fine at 50-55 mph. As to power, I don't have much to compare it to. I'm on the old Dodge forum and nobody there seems to have this same situation on their flatheads. So I keep thinking I am missing something. 

 

Link to comment
Share on other sites

In 1975 I rebuilt a olds 455 in a high school auto shop.  I did the top end and another student did the crank.  After we got it together i could not get it to stop rattling unless I kept the distributor retarded 8 degrees. Of course it had very little power.  Of course it was my car and some of my older car friends started helping by changing springs in distributor, they even tried changing the jets in the carb thinking it was all of a sudden running lean.  It was my car and it drove me nuts so I pulled the engine and guess what , my buddy ordered the wrong main bearings, he assumed that the engine had a standard crank and it was not, he claimed he read the plastigauge correctly, he did not! Lesson learned the hard way, engine was a front wheel drive Toronado , so no pulling pan off to look around.  Actually I learned a lot of lesson at 17 years old, some I am still working on,

  • Like 3
Link to comment
Share on other sites

6 hours ago, ramair said:

In 1975 I rebuilt a olds 455 in a high school auto shop.  I did the top end and another student did the crank.  After we got it together i could not get it to stop rattling unless I kept the distributor retarded 8 degrees. Of course it had very little power.  Of course it was my car and some of my older car friends started helping by changing springs in distributor, they even tried changing the jets in the carb thinking it was all of a sudden running lean.  It was my car and it drove me nuts so I pulled the engine and guess what , my buddy ordered the wrong main bearings, he assumed that the engine had a standard crank and it was not, he claimed he read the plastigauge correctly, he did not! Lesson learned the hard way, engine was a front wheel drive Toronado , so no pulling pan off to look around.  Actually I learned a lot of lesson at 17 years old, some I am still working on,

I suspect that retarding the spark puts much less strain on engine parts and so might quiet the noise of loose parts. I'd like to be sure, though, before I tear down an engine that seems to run well otherwise. Your story tends to bolster my theory.

Link to comment
Share on other sites

To me is sounds like time to pull the pan and plastigauge all of the bearings. Taking advance out of the engine will make a rod knock go away.  Both on distributor models and electronic ignition engines with a knock sensor. 

 

Electronic ignition with a knock sensor and a bad rod or main bearing will make the engine run very poorly and possibly hard to figure out why it is running poorly.  Quick check is to just pull the knock sensor wiring.  If the engine stays quiet might need to look elsewhere.  If you get a noise, problem diagnoised.

Link to comment
Share on other sites

Some of those lessons at 17 we never forget. I too have similar memories in auto shop class back in high school.  Many, many years later those early  lessons still guide me today. 
 

Your theory about bearing knock is a good one. Knock the engine power way back. Inefficient combustion. No hard, firm torque on the crank.  Sure I bet that would indeed cut down on the bearings knocking. 

  • Like 2
  • Haha 1
Link to comment
Share on other sites

What was interesting to me is the sound was so unlike any bearing noise that I have ever heard, it was more of a crackle or ping sort of like when you go up a steady mountain climb And you have to much spark advance.  If the car had a oil pressure gauge on it I would have seen a reduction in pressure after the engine was test run, instead I did saw the “IDIOT light” went off so good to go, Right! Remember the improved Murphy’s law, if there is a 50/50 chance of something going wrong, 9 out of 10 times it will,

Link to comment
Share on other sites

On 9/14/2021 at 7:20 PM, Larry Schramm said:

To me is sounds like time to pull the pan and plastigauge all of the bearings. Taking advance out of the engine will make a rod knock go away.  Both on distributor models and electronic ignition engines with a knock sensor. 

 

Electronic ignition with a knock sensor and a bad rod or main bearing will make the engine run very poorly and possibly hard to figure out why it is running poorly.  Quick check is to just pull the knock sensor wiring.  If the engine stays quiet might need to look elsewhere.  If you get a noise, problem diagnoised.

Thanks. No knock sensor here...a 1954 Dodge truck.

Link to comment
Share on other sites

I think what I have here is a worn engine, hence the noise at higher RPM's. 

Interestingly enough, I got it to quiet down, and still stay within specifications. They made some models without vacuum advance, so I disconnected mine, and set the initial advance at 2 degrees after TDC, as called for in the repair manual.

Then at 2600 RPM, I have full centrifugal advance of 11 degrees, minus the 2 degrees, which gives me a total advance of 9 degrees, instead of the 21 degrees it had.  That really quiets things down. Not addressing the root cause, but it works for now. It must be that on heavy duty models they de-tuned the engine in this way to enhance longevity. It will probably also use more fuel, but that's OK. 

Link to comment
Share on other sites

3 minutes ago, JFranklin said:

I agree that you should drop the pan and check the bearings and clean out all the sludge and make sure the oil pump screen isn't fouled.

Thanks. The engine will be rebuilt this winter, so the bearings, etc. will all get checked then.  

Link to comment
Share on other sites

6 hours ago, WPVT said:

I think what I have here is a worn engine, hence the noise at higher RPM's. 

Interestingly enough, I got it to quiet down, and still stay within specifications. They made some models without vacuum advance, so I disconnected mine, and set the initial advance at 2 degrees after TDC, as called for in the repair manual.

Then at 2600 RPM, I have full centrifugal advance of 11 degrees, minus the 2 degrees, which gives me a total advance of 9 degrees, instead of the 21 degrees it had.  That really quiets things down. Not addressing the root cause, but it works for now. It must be that on heavy duty models they de-tuned the engine in this way to enhance longevity. It will probably also use more fuel, but that's OK. 

Ya... 11 degrees isn't nearly enough at 2600.  21 would be normal. Could even use a bit more  

Link to comment
Share on other sites

6 hours ago, Oldtech said:

Ya... 11 degrees isn't nearly enough at 2600.  21 would be normal. Could even use a bit more  

Thanks. For the flat head Dodge, 21 total advance is for the standard 1/2 ton pickups with vacuum advance. It was interesting to learn that all of the heavier trucks run with 9 degrees total. 

I've heard that vacuum advance was primarily added to improve fuel economy, and this information bears that out. The engine runs well, but not as efficiently. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...