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Discussion Starter #1
I broke #5 rocker arm last winter on an accidental overwind and am just now getting around replacing them. I decided to replace all the rockers with the Comp Cams Hi-Energy Rocker, Ford SB 1.6 3/8". I think I've got the hydraulic lifters adjusted correctly. While I was at it I decided to check the compression to make sure I didn't have some major internal issue. 1=190, 2=190, 3=190, 4=160, 5=195, 6=165, 7=165, 8=160

I always heard that up to a 10% variance is OK. If that is true I have issues.

The engine is a 347 with improved 351 heads Comp Cam, Headers and mild stuff. Less than 10,000 fairly easy miles. I'd appreciate comments if I should have concern with just putting everything back together and go cruising.
 

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Hard to tell without knowing how you checked the compression. Were all the plugs out and the throttle wide open? What cylinder order did you do the test in ie, were the four higher ones the first or last done? Seems odd that all your low and high ones have the very similar values.
 

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FFCobra Craftsman
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Your variance is more than I'd like to see but, since it's been down for several months I would drive it for a couple of weeks and re-check it. You could do a leakdown test to get a better indication of where the leak is. As Norm mentions, I like to figure a way to lock the throttle full open while testing. This way you aren't shooting a stream of gas into the engine for each cylinder. Also I crank the starter until the gauge doesn't rise any more.
 

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Discussion Starter #4
I did not have the throttle open. I checked in sequence 1-4, 5-8. I did 1-4 in a group and after a break to deal with a 2 year grandson I did 5-8 in another group. 7-8 were last and hard to get to. I did crank until the gauge did not rise. I can not find my last compression readings from a couple of years ago. Seems like 160 was the common theme back then, but who knows how many brain cells I've lost since then. I told my wife a few days ago that I wish a E-F gauge could be connected to my brain to see where I am at with remaining brain cells. I'd like to pull over right before it went below E. Cheery Monday morning thought..

Speaking of compression ratios, is there a relationship between compression readings and compression ratio, ie. 10-1, 10.5-1, etc?

Thanks.. Jim
 

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Yes. Higher compression ratio will produce higher readings. There is a formula to approximate the compression by bore, stroke and combustion chamber volume.
 

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Discussion Starter #6
BTW all the plugs were out.
 

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Discussion Starter #7
Bad News -- I blocked the throttle open and began the compression checks again. Because my tool cart was setting on the driver side I started with #5. The numbers in ( ) are the original readings. 5=220 (195), 6=190 (165), 7=185 (165), 8=190 (160). I thought maybe 20-25 increase may be because the throttle was open?

Then I noticed anti-freeze around and below the spark plug hole. With a few turns of the engine I could see a mist coming out of the #5 spark plug hole. There looked like seepage at the head gasket below #5. The other cylinders are dry. The leak at the head gasket doesn't make much sense unless the head is cracked?

I'm going to pull the head and see what is going on, but I don't expect good news. Any words of wisdom before I tear into the engine?
 

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Could be coolant leaking into the port. SBF will blow head gaskets pretty easily with detonation. Too much timing or lean mixture on that cylinder.
 

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Look for an intake manifold leak between the coolant crossover port and the #5 intake port. The coolant on the outside could simply have sprayed out the spark plug hole while you were cranking the engine for the compression check. Coolant in the #5 cylinder will have bumped the compression number on that cylinder. Check the other side too.

HTH

Norm
 
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Remove the thermostat housing and do a leakdown test o cylinder 5. Listen for air in the thermostat housing. Intake gasket failure is far more common than head gasket failure. Espacially on a low mileage, nicely driven engine.
 

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Discussion Starter #11
I did the leak down test on #5 and #1. The pressure held OK.

I re-did the compression tests with the throttle open. All the readings were higher than my original when I did not have the throttle propped open. Last settings.
1=200, 2=195, 3=200, 4=190, 5=220, 6=190, 7=185, 8=190

#5 is my problem cylinder and has the highest compression? The others all seem reasonably close.

I found an anti-freeze leak around the bottom of thermostat housing that may have accounted for at least some of the antifreeze I saw around #5. After I cleaned up all the antifreeze I didn't see any more accumulation around the plugs.

I replaced the plugs and wires last summer. The plugs taken out look worse than the ones they replaced. #1, #4, #8 are black. The other plugs are a light tan to white. I used Auto-lite 3924 plugs and new wires from O'Reilly. Again low mileage driven. Few trips over 10 miles of highway driving. Something is wrong, but what?
 

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Discussion Starter #12
I found an anti-freeze leak around the bottom of thermostat housing that may have accounted for at least some of the antifreeze I saw around #5. After I cleaned up all the antifreeze I didn't see any more accumulation around the plugs after my other tests.

I did the leak down test on #5 and #1. The pressure held OK.

I re-did the compression tests with the throttle open. All the readings were higher than my original when I did not have the throttle propped open. Last settings.
1=200, 2=195, 3=200, 4=190, 5=220, 6=190, 7=185, 8=190

#5 is the cylinder that had the broken rocker arm. It has the highest compression? The others all seem reasonably close.

I replaced the plugs and wires last summer. The plugs taken this time out look worse than the ones they replaced. #1, #4, #8 are black. The other plugs are a light tan to white. I used Auto-lite 3924 plugs and new wires from O'Reilly.

Again low mileage driven. Few trips over 10 miles of highway driving. Something is wrong, but what?
 

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Double check your #5 plug to make sure it is not wet with coolant. You could have an intake gasket failure at the area indicated in the photos. Both of these are of the #1 side but, #5 is exactly the same.

Good Luck

Norm
 

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Discussion Starter #14
Cobra Intake Gasket 3-21.JPG
Pulled the intake and as the following picture shows the gasket looks blown on both 1-5.
There was a little damage pulling the gasket but not much. #1 plug was black but it could have been antifreeze wet. It didn't seem to have to an oily texture. The other black cylinders (4, 8) had heavy carbon.

I've got the heads cleaned good, ready for new gaskets. Before proceeding I need to address an age old question about my intake manifold. As received in the donor car the intake is a gel coated single plane Victor Jr. Numerous recommendations over the last 10+ years on this website have recommended changing to a dual plane intake since the single plane is most beneficial in the upper RPM that I don't get to very often. Now that the intake is off this seems to be a good time to make a final decision. I am not sure what the deciding factor will be. If anyone has an opinion please let me know.

Norm thanks for your follow through on my latest issue. Jim
 

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Glad you decided to check things out and found the problem. I am no expert on single versus dual plane manifold performance benefits but, if you ever plan on changing to a throttle body fuel injection system like the Holley Sniper, keep the single plane manifold even if it’s just on the parts shelf. They are recommended for that application.

Norm
 

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Discussion Starter #16
Glad you decided to check things out and found the problem. I am no expert on single versus dual plane manifold performance benefits but, if you ever plan on changing to a throttle body fuel injection system like the Holley Sniper, keep the single plane manifold even if it’s just on the parts shelf. They are recommended for that application.

Norm
Progress is being made. After researching single/plain intakes yet again I yet again decided to keep the single plane I have. The dual plane would have made 15+ HP more in the RPM range I use, but so what. It was a challenge to find the proper intake gaskets. I finally remembered to search through my Cobra archives from 2008 and found the notes I made from the single discussion I had with the guy that built the 87 Mustang donor car. The one page of typed notes has info that I probably never would of found otherwise. The most important info was the info that the intake gasket was a Fel Pro 1262. From there I could verify it on the Internet and order it through my local NAPA store. It will be here Sat 4-3.

With the intake off I have great access to the push rods. I think I can run through the procedures on the Internet to get them set perfectly. Most were pretty close, but a few were a little loose.

I love the parts house guys. What kind of of vehicle, what's the year, what's the engine size. You can guess when you say the vehicle is a Factory Five Cobra and that it is a 1965 replica the stares begin. The engine is a 347 with 351 heads, etc.. The clicking on the keyboard stops. The next question is do you have the old part to look at. Spin, spin, spin.

Reading the builder notes again he noted the engine block was decked and line bored, Scat H-beam rods, Weisco flat top pistons, etc. Hopefully I can get it running again this spring and do my cruising. All in all it is fun. A little frustrating, but fun.
 

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If you use the same Fel Pro intake gasket, expect the same results. Google Fel Pro intake gaskets leaking. If you insist on using Fel Pro order the part number with an S. This has a steel layer in the gaskets.
 

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Discussion Starter #18
If you use the same Fel Pro intake gasket, expect the same results. Google Fel Pro intake gaskets leaking. If you insist on using Fel Pro order the part number with an S. This has a steel layer in the gaskets.
 

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Discussion Starter #19
I have no loyality to the Fel Pro gaskets. It has been the only one I could get a line on. I tried numerous times to get through to Edelbrock without success to talk about the dual plane intake and gaskets. Finally gave up and went to my notes and then to Napa. I'll check with Napa tomorrow and see if they can get the S suffixed gasket. Thanks for the info.
 

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I have these in my wish list on Summit. Have not checked against the port size on my manifold but one of these may be what you are looking for. The 1262's are 2.10" X 1.28" and the 1250's are 2.0" X 1.2". There is a good thread on SBF intake manifold installation that I have followed previously. Main trick is to use 4-5" of all thread in the 4 end manifold bolt holes in the head to line the manifold up and make sure it comes straight down on the gaskets/intake ports (studs would accomplish the same thing). I think the original thread was from Wayne Presley? Good luck with the install. Scott

 
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