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Engine Timing and Valve Positioning

Started by racertb, November 11, 2014, 06:23:44 PM

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racertb

Hey guys:

Not running yet, still playing with it but I think I'm close.  Plugs clean and gapped, points clean and set to .20 and valves appear to be in correct position.    Firing order 1342, distributor turns clockwise.  She was kicking back a little (too advanced) so was using Ian's suggestion of using dash control to retard until it got close.  By that time, battery was done, so plugged in charger.  Haven't tried today, but possibly tomorrow.

I may have to re-position the distributor as well.  Will keep you posted.  If you think  of anything else I should try, please let me know. 


imoore

If the battery is a little weak it may cause it to back fire. due to slow cranking. I know with my engine in cold weather I do need to retard the timing a little otherwise she backfires. but once running I put back to full advance
1928 Q tourer (Holden bodied)
Several vintage stationary engine

29plycoop

A fully charged battery is important especially in this weather. Just to be safe you might check the spark at the spark plug. Pull one wire off at the spark plug and hold about 1/8 in. from a good ground while turning engine over and see if the spark is strong bright blue or a week flash. You might also check to see if the + wire at the coil is getting full 6 volts when you turn on the ignition switch. Happy Motoring! - Rich
Plymouth and inovation go hand in hand.

imoore

How is everything going. I hope you have succeeded and she is now running.
Ian
1928 Q tourer (Holden bodied)
Several vintage stationary engine

racertb

Hi Ian,

I took a break from the car for a while until this week and next to work on it. Been busy at work and now with the holidays, I'll have more time to play with it.

I'll keep you posted.  Thanks for asking.

Ted

racertb

Ok, got her running yesterday for about 5 minutes then cut her off...had to go finish Christmas shopping!

I celebrated that minor victory and have a lot more to do. I only rechecked TDC on #1 and looked at the valve positioning, especially on #4.  She fired up and without doing anything else, she ran real rough and I had to pull the throttle lever down to keep her running.  There was a steady "popping" from the exhaust.  I just wanted to listen and observe (again, a minor victory!)

I'm off for the next week, so I plan on getting back out there and putting the vacuum gauge back on it.  I believe at this point it the timing needs to be advanced.  I also think I still have a carb issue, but I'm going to hold off on that for now.

One interesting note that may not have anything to do with anything... I put the "old" distributor cap on (after checking for spark earlier at the coil wire)  just for grins.  I noticed the old cap fits a little tighter than the newer one I have been using because I can feel the old cap pushing down on the rotor button.  Don't know if this is significant or not... more to come.

Ted

racertb

Update... Got the distributor advanced and car sounds better, but still not great.  With vacuum gauge, needle fluctuating around 17hg.  Carb mixture screw backed out just about one turn.   This is the best I can do at the moment with just playing with the distributor and carb adjustment.  Still a miss out of the tailpipe.

Since the car is on jack stands (I wanted to keep it off the tires since its been down a while), I ran it through the gears up to about 30-40 mph.  It sounded better at the higher speeds, but still coughed through the carb occasionally at lower speed acceleration.

I will post a video soon hoping for some feedback...


chetbrz

Hi Ted,

I haven't put a vacuum gauge on my 29 but I did use it on my 1948 Flathead six when I first fired it up after a valve job and new timing chain.   At slow idle the Vacuum was at 21 inches of mercury and rock steady.   See picture below. 



http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

racertb

Thanks Chet, let me know if you ever put on the '29.  I had it around 18-19hg max, but purposely backed  it down a little.  After adjusting the mixture and idle on the carb, I called it a day.  This is about the same as it was before when it quit on me.   I would think that if my cam gear was bad, the car wouldn't be running.

I need to figure out the fluctuation issue, whether it's valves or something else.

chetbrz

Ted,

Maybe a poor valve seat or a weak valve spring or possiably a sticking valve.  Wasn't your motor recently rebuilt.  If so was the cam shaft reground or replaced?  Slop in the timing chain can give you that needle shake.   You have been all over the normal timing stuff.

Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

racertb

The motor was rebuilt in the mid-80's when my Dad had the car, so I don't know exactly what was done to the motor.  I just know it was rebuilt. I think the receipts are somewhere in a box so I could see what was done or not done to it.

I was also wanting to look at my spark plug gap as well to see if it might help he miss...I heard some Model A folks like a slightly bigger gap for a smoother idle.   Any thoughts on this?  I realize this won't help any possible valve issue, but just trying to see what else I can do with what I have to work with.

I also can work on the carb since I have a new kit and float for it, but might hold off on that for now.

racertb

Check this out from the Plymouth Bulletin regarding 4cyl Spark Plug Gap and Timing:

http://plymouthbulletin.com/smf/index.php?topic=327.0

chetbrz

#28
Quote from: racertb on December 23, 2014, 10:31:01 AM
Check this out from the Plymouth Bulletin regarding 4cyl Spark Plug Gap and Timing:

http://plymouthbulletin.com/smf/index.php?topic=327.0

It's worth a try.

BTW I always set timing advanced as far as possible without pinging.  If it pings retard it until it stops (pinging).  This might require a test drive. Since your engine has no timing marks I thought you were already doing this by ear ?  Full advance should be with the spark control cable all the way in.  Pulling on the spark control cable will then retard the engine for starting.  Much easier to start the engine while the timing is retarded.  Once started, your timing should be advanced to the run position, (Cable pushed all the way in).

Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

racertb

I've got the plugs gapped at .030 and advanced the timing up to 20hg on the gauge.  Turned the motor off and re-started.  I could tell it was a little too advanced because she cranked a tad slower and the starter kicked back a little.  I backed the timing down slightly to 19hg and she started up fine.   I suppose I could advance kit to 20-21hg and use the dash control to retard when starting as you suggest.  I believe that Model A owners do  it that way as well.