Ford 4630 compression

[MGriff]

Hi everybody;just joined tonight after following forum for a year+. We have a Ford 4630 w/ non turbo 201" engine thats showing some age. Blow by and some oil use. Ran a compression check today with engine cold. #1 250 psi. #2 290 psi. #3 290 psi. Know it is a tough question but what psi does a "good" tight motor run. Just trying to decide if it is time for a rebuild or run it one more season. Thanks in advance.

 

[john_bud]

Diesel, right?

450-500 psi would be healthy.

You should run the test with the engine hot. Cold doesn't tell the whole story. Also a blow by test is useful.

 

[RickB]

Hot or cold, that's a tired motor. A leakdown test or hot compression test isn't going to make you feel any better.

 

[MGriff]

john-bud and RickB. Thanks for the answer. Hot didnt change it much. #1 270 psi. #2 290 psi. #3 290. You re right dont feel any better. Thanks again

 

[john_bud]

Hot or cold, that's a tired motor. A leakdown test or hot compression test isn't going to make you feel any better.

True, but it may show that the valves are leaking or the head gasket is bad. But, it's probably just time to bite the bullet and do an in-frame overhaul.

 

[MGriff]

I know these motors are prone to electrollis. We have always run the treatment in the cooling system but is there anyway to check that before we do the overhaul?

 

[Soundguy]

low compression and a pinholed block (or liner ) are seperate issues.

 

[john_bud]

I know these motors are prone to electrollis. We have always run the treatment in the cooling system but is there anyway to check that before we do the overhaul?

Leakdown test each cylinder with the radiator cap off. Look and listen for bubbles.

With the cylinders open, pressurize the coolant system and sniff look listen for anything getting into a cylinder.

If you can borescope the cylinders, a coolant leak will scrub it clean as a whistle.

 

[Soundguy]

a holed' cyl wall should make a few other symptoms.

steam from exhaust.

maybee pressurized cooling system.. etc..

 

[MGriff]

Thanks for the help. john-bud we will do your tests before we tear it down. It would be nice if it were valves/head but everything points to rings/cylinders. Just wanted to cover all bases 1st. Thanks again

 

[john_bud]

Odds are it will need a rebuild AND valves ... but it's good to know just how bad it is before you start.

 

[MGriff]

john-bud; I dont have a real leakdown tester so I pumped in 80 psi w/ air compressure. Motor was hot, each piston on TDC on compression stroke tranny was in gear so motor couldn t turn. In 60 sec lost an average of 20 psi. Could hear air leaking into crankcase. On a tight motor what would be a good leakdown result?