My old school 340 upgrades and results.

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It is chrysler I believe. It has light advance springs and adjustable vac advance.
 
Here is a pic of the Mallory type that you can adjust the mechanical advance on. They were made by Mallory for MP, they came in the electronic ignition kits for while. The old fill and file stock type work as well, just takes a little longer to get the advance set where you want it.

MoparPerformanceDistributor.jpg
 
gtsdude said:
Here is a pic of the Mallory type that you can adjust the mechanical advance on. They were made by Mallory for MP, they came in the electronic ignition kits for while. The old fill and file stock type work as well, just takes a little longer to get the advance set where you want it.

View attachment 1714931671
Click to expand...
Yes it is the model shown. Adjustable mec advance. However I installed it as it was set up and no improvement. It doesn't like the initial advance set at 20 so it can get the 34 degrees that it likes on top. It goes to a really lopey idle which is fine but it doesn't like starting there. I tried different timing settings and no change. Starting to think maybe it is the valve Springs. I have another coil I can try but it will be tomorrow.
 
Right now I reinstalled the original distributor. To use the other distributor I will have to lock out the mechanical advance. I did notice that the timing twitches a bit when it breaks up. Watching the vacuum Guage it does bounce a bit when it breaks up. Not sure if it is conclusive though.
 

At least you narrowed it down some, that was a good deal on the dist. Maybe pull a couple valve springs and have them checked. I would check the installed height of the springs you are taking off so they can check the pressure at that height.
 
They sell a tool to check them in the car, moroso has one for $90 bucks, comp has one about $300
 
I think I found the problem. It is going to turn out to be valve springs. Today I took the valve covers off and removed the rocker arms. I used my special custom high tech valve spring pressure checker. I reached in and put my palm on the valve spring and pushed. I found 2 very weak valve springs one marginal. I pressurized the cylinder with air and removed the valve spring. I found the inner spring broken. I removed the inner spring and recorded some measurements to get replacement springs. Now just need to buy some. I didn't take the other 2 springs off for inspection because I figured it doesn't matter at this point. It needs springs.
 
For the record this is the exhaust spring on cylinder 3. Intake spring on cylinder 2 is weak and so is exhaust on cylinder 8
 
Nice you found it, I just replaced valve springs on my 340 with X heads for a new cam, best bet is to measure installed height and then look for springs. Mopar specs the P5249847 for the 508/292
Single with damper
OD 1.50
Wire Diameter .207
103lbs @ 1.67
260lbs @ 1.27
Install at 1.67 to 1.68
depending on installed height, I would find some similar spec springs, not necessarily the MP springs, they are a little spendy.
 
I work at a Chrysler dealer and I already checked on the springs from Mopar. Yes they are spendy . They are also not available any more so that takes care of those. My installed height is 1.7according to my digital dial calipers. I know dial calipers are not Uber precise but I don't own an inside micrometer. As a generic figure I would like to see at least 120 seat pressure and over 300 open.
 
That should work, just need to shim them up, I found a NOS set of MP dual springs for my .557/296 solid cam. I also used a caliper to measure also, it will work.
 
I also have a set of 273 rocker arms and push rods for hydraulic lifters. Any performance to be had there? I had heard that the stamped steel rocker arms are actually closers to 1.4 ratio.
 
I would use them for sure, I have a set on my 340 also, I put comp adjusters with locking nuts so they don't back off. I have never done it, but you hear of pushrods poking through the stamped steel rockers. I think the factory rocker are all over the place as far as ratio goes, the 273's might not be any better for rocker ratio.
 
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gtsdude said:
I would use them for sure, I have a set on my 340 also, I put comp adjusters with locking nuts so they don't back off. I have never done it, but you hear of pushrods poking through the stamped steel rockers. I think the factory rocker are all over the place as far as ratio goes, the 273's might not be any better for rocker ratio.
Click to expand...
Previous owner of this particular area has had that happen with the push rod pushing through. Easy enough fix.
 
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I don't know about the mechanical rockers actual ratios but the stamp steel Hyd. rockers can be as low as 1.4, which give you a good reason to say "Hummmm" because the small block performs as well as it does with crap for lift.

You can have your rockers reworked and blue printed to the proper 1.5 if you wish.
 
What is anyones thoughts on valve springs with or without out dampers?
 
Broken valve springs will sure cause the issue you had. :)

If it's a 508 hyd, there are decent single springs with dampers that will control the valve. 99835 crane may work. I've run them with a 528 mechanical, shimmed a bit.

trick flow 16926-16 may also work
 
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Thanks for the part numbers. I was only asking about springs with no damper because when I very first started this detective work into the misfire/pop I was told by the original owner that he though the valve spring were weak maybe not broken. I went out and purchased a set of valve springs from my local machine shop. They sold me their in house brand valve spring which was a dual valve spring with no damper. It had the specs I was looking for but at the time I didn't want to run a dual spring. Didn't want to remove heads and machine plus they did not have matching retainers for a mopar. So I returned them and decided to take it apart to see what was inside. That is when I found dual valve springs already installed. I then decided that a good dual valve spring, even if worn would be night and day better than a factory spring which has no problem going over 6000. Yes I am aware that stock cam profile requires different spring control than higher lift long duration cams.
So now I am thinking I could go pick up those valve springs again. They are inexpensive. I am on a tight budget at the moment but if they are not going to work I will just wait and pay for better springs.
 
Ordered a set of the previous mentioned trick flow springs today. Now waiting for the delivery
 
340dartley said:
Ordered a set of the previous mentioned trick flow springs today. Now waiting for the delivery
Click to expand...

So it was springs! Looks can be deceiving. I'm curious how fast it does the 1/4 with new springs. You should be able to really run it out now. I bet it's got cam to go to 6000 or more.
 
did you pull the head, you'd be lucky if a valve didn't kiss a piston. that's a long time to be running an engine with a broken spring.
 
Didn't pull the head but I did take a look into the cylinder with a bore scope. There are no marks on the piston.
 
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