Not the head gaskets,so now what????

SMOKEDYA · Apr 21, 2011

I was having some serious smoke/steam comming out of my catch can on my 351 turbo.So i did a compression test.Came up with 130ish PSI on all cylinders except 1 it read 35psi.This was on the driverside only since i didnt wanna take the down pipe off.So i looked at that plug on the cylinder that read 35 and it was black,the rest was goldenish brownish.Well got the engine pulled and BOTH the head gaslets are fine,but the on cylinder that tested low the valves are black the rest are normal,and the piston and cylinder wall looks fine on every cylinder.I cranked the motor over by hand and they all moved freely.When i was taking off the lower intake only 2 bolts were tourqed,the rest came out by hand.Could this be the cause of the low reading in 1 cylinder,or the reason for all the steam????I havent taken off the oil pan yet but will tomorrow.Also the oil looked perfect and so did the coolant.Dudes i'm lost at this Any help would be great!!!! peace

john

Rick 91GT · Apr 21, 2011

Did you do a leakdown test?

SMOKEDYA · Apr 21, 2011

Unfortunitly no i dont have a compresser peace

john

mrv8outboard · Apr 21, 2011

Well I was going to ask the same thing as the leakdown test would have given you the location of the compression loss. So you need to have the head checked and pull that piston and measure the bore and inspect it for cracks.

MarcMonteverde · Apr 22, 2011

leak down test. air coming from pcv system or throttle body is intake/ air from exhaust is exhaust

SMOKEDYA · Apr 22, 2011

I figured out i think i have a slightly cracked piston in that cylinder.

So now i know i need a new piston based off these numbers from on the piston what are the part numbers?Here are a few pics of the numbers they are on the inside of the pistons

There is also a 12 on it and also a C on it,then on the tops they are stamped 40 so i assume 40 over?peace

john

Rick 91GT · Apr 22, 2011

Is there any marks on the back of the tops, near the pin boss?

SMOKEDYA · Apr 22, 2011

Nope,only marks are what i stated..... these are just cast pistons. I was just courious on how to tell the CC of them?I think it's better to run forged pistons this time...So anyone have any idea what caused this?I see 9PSI and my A/F is in the safe zone by my wideband.....

Rick 91GT · Apr 22, 2011

Detonation is a big cause for cracked pistons, plus a cast piston is pretty cheap and wont take the pounding in a motor like that.

To tell the cc of the piston you have to pour fluid into the notches using a calibrated graduated cylinder, and keep it flat to a surface, I have a cc kit that I use for heads and adapted it for pistons.

If you need anything let me know if I can help 717-343-2108

90FoxBdy · Apr 23, 2011

Do you know the history of that block? Those look like the same markings from a cheap Recon remanufactured block i had. I did the same thing to the #4 piston with 8lbs from an s trim.

SMOKEDYA · Apr 23, 2011

90FoxBdy said:
Do you know the history of that block? Those look like the same markings from a cheap Recon remanufactured block i had. I did the same thing to the #4 piston with 8lbs from an s trim.

No i dont

Not the head gaskets,so now what????

SMOKEDYA

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