I have a 86 f250 6.9 with 360kms. all the glow plugs were faulty so I decided to do a compression test as I was pulling all the glow plugs out. IM hoping some of the experts here could let know what they think of my engine compression.

Cyl 1: 440psi Cyl 5: 400psi
Cyl 2: 420psi Cyl 6: 400psi
Cyl 3: 420psi Cyl 7: 460psi
Cyl 4: 400psi Cyl 8: 420psi

As I didnt have a remote starter i could watch the compression build up I just recorded the compression after turning the engine over 10times for each cylinder.

Let me know what you think.

Thanks

 

there right where it should be u got a good motor

 

so 460 is probably what all the cylinders would be in top condition?

do you think I need to worry about a cylinder head gasket going?

im considering buying a turbo set up but I dont want to ruin the engine.

 

Some 6.9s have tested at over 500 PSI, but those are rare. 400 is still fine, but what about cylinders 1,2,3 and 4?

Was the engine hot or cold?

Adding a turbo on an older engine will not ruin it, but if you're really concerned, keep below 7 PSI (even 5 psi makes a big difference that you will notice). Generally 10 PSI is still safe and some push higher, but with older head gaskets, there is a risk to start a leak. Blowing a head gasket is rare and if it does fail, there will generally be plenty of warnings signs.

Doing a head gasket job is a great time to put ARP head studs in (over twice the tensile strength of the stock bolts), but it is a pain and takes a lot of time and cuss words to get it done right.

 

I have cylinder compression for cylinders 1-4 posted in the original post.

the engine was cold. hasnt been running in a few days.

should I have done it warm? my manual says some ford engines should be warmed up where other engines will be tested cool.

 

Don't mind me.....

I'm thinking that if you had glow plug issues,then you may have some deposites in the engine due to previous startup attempts.

But even if not, a compression test after a good long run would probably get slightly better results. Its not unusual for these trucks to get a little soft if they aren't run hard for a long time. Its one of the reason they shouldn't be used as daily drivers. Or if you do drive them lightly, 'excercise' them on the weekend to prevent glazing.

But even if nothing changes, thats more or less right where my engine was when I put my turbocharger on. The only reason I rebuilt mine was due to a glow plug incident that left a few pistons with signature marks on them.

 

Looks decent to me. The important thing isn't so much the raw numbers as consistency. One or 2 cylinders 100 psi lower than the rest is bad. With all in the 4-500 range you should be fine.

Now, the correct way to check is it with a hot engine and all 8 glow plugs out. That way you get the fastest cranking speed and everything is warmed up.

 

Anything within 10 precent of each other is great. You are so close, even cold, I'd say your engine is great. Turbo should be fine. If you want to change head bolts to studs that would be good insurance. Good luck and let us know what you do. We always like to read on turbo's.

Chet