Low compression

[donmcgowen]

Markmurphie, here are the compression results. Added oil and gained 20-30psi. Pics are top to bottom cylinders 7, 8, and 6.

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[SolarFlare]

What's normal on these cars?

 

[donmcgowen]

200psi

 

[donmcgowen]

I bought a full set of pistons, rods, rings. When I get the energy I'm going to pull the motor, pull the drivers head and see what the damage is. Guessing ringlands from excessive detonation. Hoping I can just slap the pistons in and throw it back together as long as there is no head damage. But I need to open it to know what's wrong for sure. I had a complete motor and trans with 9k miles in the works for $3500 but seller backed out.

 

[ahl395]

I bought a full set of pistons, rods, rings. When I get the energy I'm going to pull the motor, pull the drivers head and see what the damage is. Guessing ringlands from excessive detonation. Hoping I can just slap the pistons in and throw it back together as long as there is no head damage. But I need to open it to know what's wrong for sure. I had a complete motor and trans with 9k miles in the works for $3500 but seller backed out.

Ouch, sorry to see.

What was the cause of the detonation?

 

[F1scamp]

With compression numbers that low and you thinking its the rings or lands from detonation, I would be surprised if the cylinder walls aren't scored. I would do a leakdown to verify it is going through the rings, and get a borescope down the holes and look at the walls. The factory shortblocks are surprisingly cheap from the dealer.

 

[Aaron@Jpcracing]

As a few guys have said you might as well do a leak down to figure out where the issue is.

Feel free to hit me up if you need any pricing on engine components

 

[hunterdg]

Are acceptable factory specs for compression and leakdown available on this forum or elsewhere? I see 200 psi above but searching for “leakdown” or “leak down” doesnt return any results.

 

[kcc0521]

I would guess you need to have the rotating assembly balanced for new rods and pistons. Where did you buy the parts? What pulley and fuel were you running? It might just be a head gasket?

 

[donmcgowen]

Just an update the ringlands on both cylinders were intact, but as soon as the piston came out, they just crumbled. No cylinder scoring. Anyway I had a new short block installed for free. Don't ask.

 

[Killswitch16GT]

Just an update the ringlands on both cylinders were intact, but as soon as the piston came out, they just crumbled. No cylinder scoring. Anyway I had a new short block installed for free. Don't ask.

You in Georgia???

 

[donmcgowen]

Illinois

 

[Crackerjack17]

Just an update the ringlands on both cylinders were intact, but as soon as the piston came out, they just crumbled. No cylinder scoring. Anyway I had a new short block installed for free. Don't ask.

I'm guessing the same thing happened to mine. I lost compression on the same two cylinders. I'm slowing working on rebuilding the engine myself. I have the engine out, but haven't taken it apart yet. I'll post some pics when I do.

 

[Tommy V]

Yep.same cylinders on mine as well,those seem to be the cylinders that go.first on this new block,always the drivers side.

 

[Barrel]

7 and 8 are where I was leaking coolant on my first engine. Blew out the head gasket.

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