Guide me in the right direction...bad compression

[kezell]

He is the story.....I was about out of gas so I pulled in a gas station...all they had was 87....so I said that I will just toss a few gallons in and drive to the next. Well that's where I went wrong.....I forgot about the low octane gas when a Camaro passed me...I down shifted and took off. Then at the top of 3rd I shut it down. I then noticed that I had a odd sounding exhaust, kinda like I dropped a cylinder. Just a flat sounding exhaust.
I got home changed the plugs and coils, same noise. Compression test is as follows.
All the passenger side read:
1-185
2-182
3-185
4-185

Driver side:
1-180
2-170
3-175
4-137 nearest the fire wall.

So I squirted a little oil in that cylinder and it jumped to 190.

Do you all think it is a bad ring or bad head gasket?
Car does not smoke, no water in the oil that I can tell yet.

Mods are:
Boost-a-pump
stock pumps
60lb injectors
ported blower, inlet, and tb
2.76 upper/ 4lb lower
Kooks long tubes etc..
2400 SCT MAF
Custom tune
and the rest of the supporting parts.

I know it was a bone head move and is going to cost me.
I found a head changing kit but can where can I buy factory piston rings at?

 

[Blueline]

I would bet you have damage to the rings/piston/ringlands....... good luck with whatever you do.

 

[eaglesnick]

I would bet you have damage to the rings/piston/ringlands....... good luck with whatever you do.

Agree with this, number 8 cylinder gets the hottest and is often the piston to suffer damage.

 

[Blueline]

Yeah OP I forgot to add in my post, your next step is a leak down test and bor -o- scope. Goodluck!

 

[kezell]

Thanks guys, I plan to pull it down in the next week or so to check out the damage. I will post back any related info.

 

[kezell]

Quick question.....Does ford offer a head changing kit or will I have to purchase it all seperatly? If so, any recomendations?

 

[Quick Strike]

If the compression increases when you add oil, there is something wrong with the bore/rings/ringland/piston combination in that cylinder. This should be confirmed with a leak down test as suggested. You will hear air escaping into the crankcase in that cylinder.

If this is the case, your next issue is if you can get away with just a slight hone and one new new stock piston/ring combination, or if you have done damage to the bore requiring an oversize. If you are in for one oversized piston, you are in for eight and an engine balance.

 

[kezell]

Well I pulled the head today and the head, head gasket, and valves all look fine. The bore looks the same as the rest.
Could I still have a ring issue? Or should I start by bringing the head to a shop to have tested?

If I do pull that piston, what should I look for?

 

[kezell]

I pulled the piston today and I cant find any cracks etc....What is the factory gap that the rings should have?

So far I have pulled the head and piston and cant find anything that stands out and says...pick me

 

[Quick Strike]

Piston diameter 90.180-90.191 mm
Piston-to-cylinder bore clearance -0.010/+0.026 mm
Piston ring end gap — compression (top) 0.30 mm
Piston ring end gap — compression (bottom) 0.50 mm
Piston ring end gap — compression (oil ring) 0.65 mm
Piston ring groove width — compression (top) 1.53-1.549 mm
Piston ring groove width — compression (bottom) 1.519-1.539 mm
Piston ring groove width — oil ring 3.031-3.055 mm
Piston ring width — compression (top) 1.47-1.49 mm
Piston ring width — compression (bottom) 1.47-1.49 mm
Piston ring width — oil ring 2.854-2.984 mm
Piston ring-to groove clearance — compression (top) 0.04-0.079 mm
Piston ring-to groove clearance — compression (bottom) 0.029-0.069 mm
Piston ring-to groove clearance — oil ring 0.047-0.201 mm
Piston pin bore diameter 22.0042-21.998 mm
Piston pin diameter 21.991-29.994 mm
Piston pin length 61.60-62.03 mm
Piston pin-to-piston fit 0.0058-0.0132 mm

 

[kezell]

Thanks man! I will take some measurements tomorrow morning.

So even though the piston/piston rings look fine...I can still have a issue?

Just wondering since this is the first time I have had low compression on a motor.

 

[Quick Strike]

I'd pay particular attention to the top ring grove width and piston ring to grove clearance. A little ring flutter from a loose or ringland with unseen damage would drop some compression. Are there any cracks/chips/wear in the rings (side or face), and does the ring tension seem OK? How is the bore cross-hatch compared to the rest? Are there any vertical scratches in the bore that catch a fingernail across them?