Cylinders 3 and 5 running cooler

[darth_linux]

Got my distributor replaced with one from HalifaxHops after the "Rick E." unit I had self destructed. The engine fired right up, but there still seems to be an issue. I haven't driven it yet, but just getting it warmed up I can tell it's running rough. I put new plugs in it while the dizzy was out, and the plug wires are only 1 season old. Cylinders 3 & 5 are running cooler than the other 6. I measured the temp on the exhaust manifolds right above each port with an infrared gauge. All the cylinders were 650F at the manifold after a good 20 minute warmup, but cylinders 3 & 5 were only 550F.

I'm going to pull plugs 3 & 5 and take a look, but what type of failure would cause 2 adjacent cylinders to run cooler than the others? Worried about the engine needing a rebuild . . .

thanks!

 

[CBODY67]

Might be a carb issue, but I doubt it. Combustion gas temp is related to combustion chamber heat. Both of those cylinders should be feeding off of different sides of the carb, too. Maybe gap the plugs a bit wider on those two cylinders?

Don't think this can be related to the engine needing a rebuild, either. If no misses, then the compression rings are still working. Might get a borescope into those two cylinders to look at the tops of the pistons, to look for shiny areas where oil is washing off the carbon around the edges of the piston tops.

"Valves not sealing" would be evident at the end of the tail pipe. Negative pressure pulses when the "leaking valve" cylinders were on their intake cycle, as evidenced by holding a red shop towel loosely over the end of the pipe. It'll suck the rag into the pipe on that negative pressure spike.

Just some thoughts,
CBODY67

 

[413]

Swap some plug wires from a hot cylinder to cold cylinder and see if the cold cylinders move or stay the same.

Compression test is next. It can absolutely be related to internal engine condition, ring seal, blow by, valves not sealing, etc.

 

[david hill]

Before you do anything else, Hook up a vac gauge to the power brake booster and observe. Note the inches of vac at idle and 1500 RPM. Does the needle fluctuate and does it worsen at rpm increases. Then proceed w/ a wet dry vac test. Observe if you here excessive air in the Intake, Exhaust or coming from the crank case.

 

[Toolmanmike]

The first thing you should do is a compression test. May be a leakdown to further diagnose.

 

[halifaxhops]

Vacuum gauge will tell alot google vacuum gauge readings. Scope would definitely tell you what is going on but doubt there is one near you that knows how to be used.

 

[3175375]

Vacuum gauge will tell alot google vacuum gauge readings. Scope would definitely tell you what is going on but doubt there is one near you that knows how to be used.

View attachment 711658View attachment 711660View attachment 711659

Printed these out and will laminate. GREAT reference information!

Thanks!!!

 

[darth_linux]

Great advice everyone. Thank you. I'm gonna pull plugs 1,3 & 5 just to compare. These are brand new plugs that have only ONE run cycle on them (yesterday). Then I'll use the borescope to take a peak inside the cylinders. After that I'll get her warmed up and use a vacuum gauge to see what the needle is doing. If the vacuum is wacky, I'll certainly do a compression test and find out what the numbers are. I think those steps will give me enough data to either diagnose or fix what's wrong.

Thank you!

 

[darth_linux]

Before you do anything else, Hook up a vac gauge to the power brake booster and observe. Note the inches of vac at idle and 1500 RPM. Does the needle fluctuate and does it worsen at rpm increases. Then proceed w/ a wet dry vac test. Observe if you here excessive air in the Intake, Exhaust or coming from the crank case.

I've never heard of using a shop vac in this manner. Where does one put the shop vac tube, and where does one listen from/to? Thanks!

 

[darth_linux]

AND THE PROBLEM WAS . . .

#3 spark plug side electrode got bumped upon installation and had zero gap. It probably, kinda, sorta, worked above 1500 rpm, but at idle I don't think it was firing. It was basically black, while the other plugs around it had started to take on the tan color.

I gapped it to .0375", reinstalled it carefully(!) and she runs and drives like normal again.

I still feel a little hesitant to "get on it" after the distributor bushing disaster, but I'll break the plugs in gently, regain some confidence, and then this weekend I'll check the vacuum and re-time it. The timing is close enough for reliable driving but I'm not sure what it's on atm. Theoretically it should be the same as when I removed the other distributor since I changed nothing, but I still need to verify.

Thanks to ALL OF YOU for your tips and suggestions. Luckily it was just my own lack of care that caused the problem and nothing major.

Cheers!

 

[413]

Good,deal.

Warm it up and floor it! Shouldn't hurt anything, and if it does then it needed to be fixed anyway.

 

[Toolmanmike]

AND THE PROBLEM WAS . . .

#3 spark plug side electrode got bumped upon installation and had zero gap. It probably, kinda, sorta, worked above 1500 rpm, but at idle I don't think it was firing. It was basically black, while the other plugs around it had started to take on the tan color.

I gapped it to .0375", reinstalled it carefully(!) and she runs and drives like normal again.

I still feel a little hesitant to "get on it" after the distributor bushing disaster, but I'll break the plugs in gently, regain some confidence, and then this weekend I'll check the vacuum and re-time it. The timing is close enough for reliable driving but I'm not sure what it's on atm. Theoretically it should be the same as when I removed the other distributor since I changed nothing, but I still need to verify.

Thanks to ALL OF YOU for your tips and suggestions. Luckily it was just my own lack of care that caused the problem and nothing major.

Cheers!

Nicely done.

 

[67_300_Convertible]

Glad the fix to this is something simple and inexpensive.