As mentioned in my hei conversion post. I replaced my spark plugs. At that time I decided to do a compression test and the results are in.

I must say it's better than expected but, not 100% healthy.

Although I found out I technically didn't' do the test right. Your suppose to crank the engine the same number of times on each cylinder. I cranked it until the needle quit raising. However, I do believe most of the them reached their peak around 2-3 cranks. The rear cylinders where like twice that if not more. Which I found interesting because I have a friend with a 1968 Plymouth Satellite that the rear cylinders also failed, the rest met the minimal 100 psi requirement.

The old spark plugs were crusty white... definitely running lean, no?

Short recap story, I bought this truck from my job at a technical school which was used for grounds keeping, maintenance and trash removal. It never left the campus grounds and idled all the time. Minimal maintenance was done on it, including regularly scheduled oil changes. Basically it only got "fixed" when it quit running. I enjoyed driving it on almost a daily basis so when it was retired (and replaced by a 1991 Ford F-250) I decided to save it from the clutches of the angry electromagnet in the sky. Drove it home.

I'd like to go through the whole motor some day. Get the sludge out, new rings, oil pump, etc. This isn't the trucks original motor it was a 360 crate long block setup for TBI that the school had sitting around when the original 318 died.

 

Did you crank with the throttle blades blocked open, all plugs out?

I would put new plugs in and drive it hard accelerating and decelerating with some one following to see what colour smoke comes out at each time.

You can get an adapter and push compressed air through plug, both valves closed at TDC and listen at exhaust, intake and valve cover tube or dipstick tube. This can show if valve or rings are leaking by.

 

Being that this truck has runaround at low speed for most of its life....
I think that compression difference might not be that bad.
As long as the engine is showing good Vacuum.... 18"
I think I would just work on putting a good tune up in it and drive it at road and hwy speed before getting to crazy with it. See what it acts like after a few 100 mile's?
Get the old dog so it will start, stop, and steer. and go run it for a while.
A few good additives to the oil and fuel will help clear out some of the built up gunk
Marvel Mystery Oil and Seafoam would be my go too's....
Then kind of decide from that point.

Just my 2 cents

 

No I didn't but, that does make perfect sense.

I just put new plugs in as part of my hei conversion that are gaped to .045"

Your talking about a leak down test, yes? I plan on doing that in the near future.

The last time I had a vacuum gauge on it to adjust the idle mixture the highest I could get was about 17" of vacuum.

I've been driving the truck since I think February. I alternate weekly between my two trucks. So, I've put well over 100 miles on it, but less than 3000 because I haven't done my second oil change yet.
I've done a little highway driving but, since both my trucks are former military M880s with 4.10 gears, the fastest I've pushed them is 55mph. The military rated them for 70mph but the motors scream loud enough for me at 55.

I've done numerous repairs on it (front end, brakes, drive lines, electrical, etc) So far it's proven to be quiet reliable. It hasn't left me on the side of the road yet (knock on wood). My plan is to use it exclusively this winter when the snow flys, to keep my nicer dodge out of the salt and snow.

I'm little wary of using any cleaning products in the oil, as I'm concern about sludge becoming dislodged and causing engine damage. I think a motor rebuild would be best. Which is something I would like to do someday but, at this point, I simply don't have the time.

This particular truck is sort of sentimental to me and kick started my love for old dodge trucks. So, I don't mind spending money to keep it going.

 

Nothing wrong with that.... Sounds like you catching up on what needs to get done...

 

Not a leak down test but a cylinder pressure test. Cranking with throttles closed can cause inaccurate numbers and can pull gas in washing the oil from the rings and giving a lower number. Best is to drive it to get hot pull in with everything ready and do the compression test quick while as warm as possible.

 

Alright Thanks. I'll remember that the next time I do this test.