Compression test

[MustangGT]

Hi guys.

I just did a compression test on my 390.
How much variation is acceptable?
1. 176
2. 185
3. 185
4. 181
5. 155
6. 173
7. 168
8. 179

The sparkplugs on #1 and #8 is soaked with oil, the rest is fine.
I've just replaced the umbrella seals on the valves but havent started it yet so the sparkplug reading is before new seals.
Any comments?

Best regards
Morten

[ScotiaFE]

Those numbers look good.
#5 is a little low.
You could leak down to see were the loss is, but unless you are going to pull
the top off run it.
While your at it snug up the intake bolts a tad.

[jayb]

I agree with Howie, those numbers look good.  You'd like to have #5 up with the rest of them, but it's not so far off that it's a big concern.

[MustangGT]

Wow. Lightening fast replies! Thanks guys!

I took two more readings of #5 but it came out about the same, 157 and 155.
Sounds like I could just button everything back together with new valve cover gaskets and snug the intake bolts a little. Thats great.
Hopefully the new valve seals and restrictors in the oil passage will decrease the oil consumption a bit.
I'm just trying to keep this thing alive long enough for me to afford a new engine but saving up enough money is hard.

Again, thank you guys for your quick feedback!

[machoneman]

I'd add a quart bottle of SeaFoam gas additive (all major parts suppliers) to the tank, drive it for a tankful and re-try the #5 test. Bad valve seals often pump enough excess oil into the cylinders that the rings (one or all three) get gummed up. Can't hurt to try and it is darned good stuff for any gas engine.   

[MustangGT]

I've searched for Sea Foam and it seems like there is no norwegian distributor.
Just checked the intake bolts and while the 4 bolts on each corner where tight, the 3 + 3 on the sides could easily be tightened about 1/8 turn.

[rcodecj]

I don't like the seafoam additive. I added some and within a few miles my accelerator pump gaskets started leaking. I think they softened up the rubber.
The carb was fairly new and did not leak before that. I put a bottle in a full tank, and at around 1/2 tank it started leaking.
Maybe coincidence but I think it's destructive to the rubber parts on the carb.

[machoneman]

Try a marine engine shop as it's used primarily in fresh/salt water engines and gas tanks. Perhaps it is sold under a different trade name overseas. Have used it for years with various outboard engines, carburetor and EFI equipped. Also, many automobiles with Holley, Carter and other carburetor makes w/o any issues. I guess results may vary but it is clearly blended for air/auto/marine engine usage. Perhaps an e-mail through their website will produce an answer if it is sold local to your area.

http://www.seafoamsales.com/