Valve adjustment 1951 Plymouth

[hep2jive]

Hey everyone I have a stock 1951 Plymouth. Engine rebuilt in 2022 I have 15k miles on her now. My mechanic does the valve adjustment and it was perfect until starts chugging, mainly uphill, around 35mph. Then I had him do another hot valve job it's good until it starts chugging again a few thousand miles later. I drive mainly at high speeds. 55mph for long periods of time... What would my adjustment be for that type of driving? Car idles nicely and this issue is intermittent then gets more frequent. Thank you!

[Sniper]

Sounds like you lock nut isn't locking like it should be.  This let's the lash open up. 

[hep2jive]

Thanks  hmm something simple I'm sure

[FarmerJon]

The service manuals call for .010 intake and .012 exhaust for cars that operate at high speeds for long periods of time.

I would have your mechanic carefully examine the tappet lock nuts, and maybe report what the clearances currently are (assuming it is back to chugging)

[Sam Buchanan]

Guess I'm a bit uninformed....but what exactly is "chugging"....does this mean "missing" or low on power or what? Thanks. 

[hep2jive]

38 minutes ago, Sam Buchanan said:

Guess I'm a bit uninformed....but what exactly is "chugging"....does this mean "missing" or low on power or what? Thanks. 

LOL chugging is misfiring. Abrupt hesitation a terrible feeling!

[FarmerJon]

Chugging uphill sounds like a lean condition, like a float set too low, but having the valves adjusted fixed it for a while? Strange.

When you had the mechanic adjust the valves the second time, did he make any mention of if they had opened up noticably? 

[hep2jive]

7 minutes ago, FarmerJon said:

Chugging uphill sounds like a lean condition, like a float set too low, but having the valves adjusted fixed it for a while? Strange.

When you had the mechanic adjust the valves the second time, did he make any mention of if they had opened up noticably? 

Yes it only chugged when accelerating or up hill intermittently but now becoming more frequent. The second adjustment he said some were mis adjusted. I drive often at high speeds for long periods of time maybe they just need to be set differently.

[FarmerJon]

But the issue has come back. I would have them document which lifters are out of adjustment this time, and if loose or tight. If it is the same lifters going out of adjustment,  they may need to be replaced or repaired. 

I last adjusted my valves in '22, about 5000 miles ago, and I regularly  drive 70+ on the highway, although usually only for 20-30 minutes at a go. I set mine at the .010 in, .012 ex, although a touch on the loose side (ie. May actually be .011&.013 but didnt have those gauges) I can hear them a little until it is up to temp.

[hep2jive]

My mechanic said the valves were right where they needed to be but I did replace the 180 tstat to a 160 that might have been a problem vapor locking? Didn't happen at high speeds only at 30-40 mph going slightly uphill.... I hope it won't do it again ugh. My mechanic did put the exhaust valves to 0.012 drove around a bit seems fine now.

Edited June 3 by hep2jive

[Sam Buchanan]

39 minutes ago, hep2jive said:

My mechanic said the valves were right where they needed to be but I did replace the 180 tstat to a 160 that might have been a problem vapor locking? Didn't happen at high speeds only at 30-40 mph going slightly uphill.... I hope it won't do it again ugh. My mechanic did put the exhaust valves to 0.012 drove around a bit seems fine now.

 

Sorry, but the thermostat doesn't have anything to do with fuel vapor lock............and your car should be very happy with the 180F thermostat.

Edited June 3 by Sam Buchanan

[Sniper]

That's a mechanic I would not use.  Anyone suggesting a 160 thermostat is someone that doesn't know what they are doing.

 

Sounds like something electrical is heating up and failing on you, had a coil do that with somewhat similar issues.

[hi_volt]

+1 on a possible coil issue.  I've had that happen on a couple of my classic cars where the coil secondary opened up.  A quick check of the resistance when hot wouldn't hurt.

[Sniper]

Heck just see if you got a spark when it happens. Maybe observe the color of it if it's orange it's weak if it's blue it's probably strong enough

[hep2jive]

Thank you. It only happens when driving. Idle smooth. It's done the same thing in 30 degree weather (30F} that hard choppy acceleration - while cruising. It's a new coil but maybe this one didn't like the heat. The 160 thermostat keeps the car much cooler maybe I won't have that issue again. I drove it around seems alright. Should I replace the coil?