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Lost Compression in cyl 7&8 Mystery Solved!

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Crackerjack17

Crackerjack17

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HAHA... I Just did a weekend long track day at Circuit of the Americas with my Whipple car. Second day last session, I got a CEL for cylinder 8 misfires and cank posistion sensor. Multiple laps that had WOT pulls to 150 Plus. Doing my compression test tonight. Could be a fun build!
I never got any check engine light for misfires, just knock. And actually my car ran fine, besides all the blowby. It would be prudent to do the compression check obviously.
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Crackerjack17

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Im gonna do a full look over this weekend. Pull all the plugs and take a look and do the compression check. If it all checks out Im gonna keep on sending it!

I did some quick math.

I did 6 Sessions at 30 minutes each. 180 Minutes. 4 Minutes per lap so 45 LAPS total. Each Lap has 2 Long straits where i did wide open throttle pulls to 130 MPH Plus. So basically 90 HARD pulls over 130 MPH with half of those being to 150 plus.
That's what I'm talking about!! Getting your moneys worth. Lol. :headbang:
 

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Crackerjack17

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What did you clean the head deck with?
Paper towel. Haha. I scrubbed down the valves and pocket area with gas using a brass/plastic brush and some plastic pry tools I had to scrape away deposits around the valve seats. The head was perfectly smooth and flat. I did wipe it down with a rag and lacquer thinner and the block too before i put them together. Hit everything with compressed air and made sure no particles. Slid head over studs and hand torqued the nuts down in pattern starting at center. Then first round was 35ft/lbs, then 70ft/lbs, then 100 ft/lbs on the arp nuts. I forgot to take pictures of the bottom of heads.

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Darthmayxj

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Ohhh no.... here are my compression numbers

1 - 250
2 - 245
3 - 242
4 - 250
5 - 250
6 - 245
7 - 205 Wet - 300
8 - 205 Wet - 300


Obviously 7 and 8 have some ring issues. What do I do now!
 

Turbolag87

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Ohhh no.... here are my compression numbers

1 - 250
2 - 245
3 - 242
4 - 250
5 - 250
6 - 245
7 - 205 Wet - 300
8 - 205 Wet - 300


Obviously 7 and 8 have some ring issues. What do I do now!

Start saving for a new build...sorry too hear :(
 

Darthmayxj

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Start saving for a new build...sorry too hear :(
Ford service manual says a difference of 75 percent is bad. I'm at 82 but TWO cylinders are down. Would you guys go ahead and move forward with a short block and get it done or are my differences not that bad?
 
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Crackerjack17

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Ford service manual says a difference of 75 percent is bad. I'm at 82 but TWO cylinders are down. Would you guys go ahead and move forward with a short block and get it done or are my differences not that bad?
I am no engine expert, but if those two are showing a consistent drop compared to the rest then something is wrong and only going to get worse. I will tell you though, I could have simply put two new pistons in mine and opened up the other rings on the other pistons and put it back together. There is nothing wrong with my block. When I get the chance I'm going to pull the rings off those two pistons and shove them in the block and see what the factory gap is, out of curiosity.
 

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I am no engine expert, but if those two are showing a consistent drop compared to the rest then something is wrong and only going to get worse. I will tell you though, I could have simply put two new pistons in mine and opened up the other rings on the other pistons and put it back together. There is nothing wrong with my block. When I get the chance I'm going to pull the rings off those two pistons and shove them in the block and see what the factory gap is, out of curiosity.
I like the idea of just getting one put together and moving my heads to it. I figured ill do the fuel system, clutch and switch to e85 while im in there.
 
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I like the idea of just getting one put together and moving my heads to it. I figured ill do the fuel system, clutch and switch to e85 while im in there.
That's exactly what I'm doing! I am enjoying putting this together. But, I'm mad at myself :headbonk::frusty: now for not going ahead and getting it sleeved. Oh well, next one. Lol

Look at this motor porn. Cams are back in, timing chains on and ready to install front cover. :headbang:

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Darthmayxj

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That's exactly what I'm doing! I am enjoying putting this together. But, I'm mad at myself :headbonk::frusty: now for not going ahead and getting it sleeved. Oh well, next one. Lol

Look at this motor porn. Cams are back in, timing chains on and ready to install front cover. :headbang:

picture.webp
I've done multiple OPG installs now. I was worried that the cam phaser timing would be hard. Nope. Service manual spells it out barney style.
 
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Crackerjack17

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I've done multiple OPG installs now. I was worried that the cam phaser timing would be hard. Nope. Service manual spells it out barney style.
I wasn't sure at first either, but it's easy. And when you take apart the old motor you should follow the timing chain removal process because that sets the cams in the neutral position to where the are barely under any pressure from the valves. And make sure to take front "mega" cap that covers both cams off first! Because the cams are under some pressure, if you remove the individual cam caps first, it can put the cam on a bind and possibly destroy the front journals. Then the head would become a nice coffee table piece.

Putting it back together, put the keyway at the 5 o'clock position and go by the manual for timing chain installation. Eveything lines up. And, you can't put the phasers on wrong because they have a pin that only goes one way on the cams.
 

x_man586

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So is going F.I. on these cars a gamble? The engines weren’t meant for it.
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