I was bored and tinkering today and have recently bought a compression tester so I thought I would check my cylinders after fiddling with the carb and discovered they range between 95psi on Cylinder 6 up to around 112psi on Cylinder 4.

Which after some googling while at Canadian Tire to try and replace the two spark plug wires I wrecked leads me to believe I have severely low compression. Which isn't a complete shock but means I need to start planning to do the rings probably, which at that point I might as well pull the engine and do it right with a proper rebuild.

So on that note, does anyone know of a good post or youtube video with all the various gotchas to be aware of? Thankfully mine has almost nothing to it vacuum or electronics wise so it should be fairly simple but I think I'll start planning now so when the snow melts in March or April I can start tearing into it.

 

There should be other signs that it needs a rebuild. How much oil does it use? How much blow-by does it have? Blow-by would be smoke coming out of the breather on the valve cover. Any knocking noises? Hate for you to waste time and money and end up with the same compression numbers.

Things that can affect compression numbers;

Engine should be warm

All sparkplugs should be out.

The battery needs to be topped off with a good charge so it spins the engine fast.

You should tie the carb wide open so the cylinders can suck lots of air into them when checking compression.

 

You've done a compelling job of making me second guess my plan.

Oil usage is pretty minimal, I'd say the blow by is negligible honesty, a bit comes out because the valve cover breather just has some steel wool or something in it and vents to the atmosphere. I think it's more steam than oil though as I see some milkiness in the cap.
I wouldn't say any knocking noise, some noise that could plausibly be defined as knocking but sounds like it's coming from the fan not the engine.
Engine was warm, I had it running for better part of an hour while fiddling with the carb (about 18" vacuum after factoring in altitude at about 14* BTDC)
All spark plugs were not out, I was pulling them one at a time and gapping them then putting them back after testing each cylinder.
I think the battery was fine but I can't prove that.
I did not have the carb tied wide open, I was doing this solo so I just turned it over for 10 seconds or so then went and recorded what the tester had stored on it.


Edit: Addendum, I started down this path cause I'm getting around 12mpg and have seen people reporting upwards of 20 and if I could get around 17 I was going to call it a win. Then I saw people saying that the 4.9L should be >125 psi and some people saying 150. When it shows 95 and I saw people saying 90 was basically a dead cylinder I kind of just planned on dealing with the issue.

 

If it runs good and performs decent, I personally would just run it. Don't put too much value in those claiming 20 MPG, they are probably using bohemian arithmetic. No offense if you or anyone reading this is bohemian, it's just a term I use.

 

Here's a good read..
https://www.ford-trucks.com/forums/1...l#post19570746

You could just drive it. Even if a fresh rebuilt engine gets better gas mileage, how many years would the pay off be.

 

You make a compelling argument Jim. If I found a pipe to redirect the valve cap vent into the air intake like stock I probably wouldn't notice at all. I just got hung up on compression numbers.

 

Have you experimented with the timing? Bump it up a little bit at a time till you hearing pinging, and then back it off just a little bit. This will help fuel mileage and power. After a drive, go around and check all the wheels for heat. They all should be close to the same, if one is boiling hot the brake is sticking,, a common problem on these old trucks. You can also pump your tires up to the sidewall max pressure. This will give you a little rougher ride, but will help with mpg numbers.

 

AFR Gauge
Get one so you know just what the carb is doing.
My first carb ran rich the Ebay replacement was way to lean so I made it a little richer but think still pretty lean still.
I have not run the MPG numbers on this new carb but it has Tobe better.
Dave ----

 

I just recently started looking at AFR gauges. I did bump the timing from 10 to around 14 (I wish I got the dial style timing light but c'est la). I'm not sure what pinging will sound like honestly but after about where I have it the engine starts to stagger so I figured I've pushed my luck enough.
The brakes are all in pretty good shape, I did a fairly full rebuild on the last summer and I've tinkered a lot with them. I think I've gotten a bit to in my own head on this one and I feel like the Ebay carb runs rich but dialing the lean idle mix does very little until it chokes the engine out entirely.
I should maybe take another run at the Carter YFA and see if I was just an idiot before.

 

If you have the standard LT235/85R-16 , 80 psi is max. I don't think you'll gain many MPG running max pressure. I inflate my rears to 80 when hauling a wet cord of wood, increase fronts to 70 psi. But for normal unloaded or lightly loaded I use 55 psi. This maintains good handling and a comfortable ride and good even tire wear. I've run these tires for 400k miles so have a lot of experience with them. 80 psi will have your front wheels following rutted pavement like an Ohio train track wandering all over. For what 0.25 mpgs more? I get excellent mileage at 55 psi.

 

My standards are 235/75R-15 and it's around 44 psi.

 

How much is max pressure?

 

I'll have to check but it's south of 50psi.

 

Are you running LTs then max tire pressure is 80 psi

https://tirepressure.org/lt235-75r15

 

Try 50 to 55 psi see how you like it.