Back Firing Engine Compression Test

Retro Jim

Retro Jim

Senior Member
Well I did a compression test on all 8 cylinder to see if that would help any . Well I thought the engine was rebuild not long ago and I am right .
Here is the cylinder results .
#1--150
#2--150
#3--150
#4--150
#5--140
#6--150
#7--130
#8--150

All spark plugs are clean with no carbon .

I would say it's didn't have a valve job or a terrible one done to the heads ! Maybe a bad guide , maybe a bad valve , bad valve or a bad seat IF they were replaced . I also think the intake gasket is leaking as well .

Jim
 
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OK...#7 being low would indicate no fire in the hole....gas washes the cylinder walls, pressure drops because there is no oil in and on the rings. Now I haven't gotten the books out....but....if I remember correctly #7 and #5 are one of those that stays cold with the 302 vs 351 firing order. Do the switch, it will prove out which cam is in the engine and eliminate one potential problem without having to open anything.
 
Jim, extreme shot in the dark here. You mentioned the driver side is the one that is missing & its a random misfire. Are the plug wires for 7 & 8 situated next to each other on the valve cover? I've only seen it once in 40+ yrs but it can cause a crossfire if they are run next to each other.
 
LOWRIDER said:
Jim, extreme shot in the dark here. You mentioned the driver side is the one that is missing & its a random misfire. Are the plug wires for 7 & 8 situated next to each other on the valve cover? I've only seen it once in 40+ yrs but it can cause a crossfire if they are run next to each other.
Click to expand...


No they aren't . I did find out the painful hard way that the coil wire was bad ! I was using a MSDII coil and I reached over to adjust the distributor and my are touched the coil wire and distributor at the same time and got a very hard jolt that went up to my shoulder ! Those higher voltage coils hurt ! I did change that wire but the other wire are fine .

Jim
 
Ford blue blood said:
OK...#7 being low would indicate no fire in the hole....gas washes the cylinder walls, pressure drops because there is no oil in and on the rings. Now I haven't gotten the books out....but....if I remember correctly #7 and #5 are one of those that stays cold with the 302 vs 351 firing order. Do the switch, it will prove out which cam is in the engine and eliminate one potential problem without having to open anything.
Click to expand...

The firing order for a 302 is , 1-5-4-2-6-3-7-8
The firing order for a 351w is , 1-3-7-2-6-5-4-8

So how will switching 5 & 7 work ?

Jim
 
Ford blue blood said:
Not saying switch the two....just that they will be cold, put the W order on it and see what happens....
Click to expand...

OH , OK . I was wondering if you knew something new I never heard of !

It's a 302 firing order !
The dist cap is NEW and it's the 2 nd one I have tested the engine with along with all the ignition parts .
I also had this problem posted on the HAMB main board and we all came up with the same conclusion that the intake gaskets are leaking . I sure hope that's the problem . I contacted the owner and he order the parts for me . He lives 1.5 hours away in another state so I tell him what parts I need and he pays them and ships to me . That is a better way and doesn't tie my money up until the job is done ! The he only owes me the labor ! I will post what happens when I get the intake gasket replaced !
Thanks for all the help !

Jim
 
Well I pulled the intake today and what a damn nightmare ! First off , there was 4 intake bolts that were hand tight , then there was a ton silicon around BOTH sides of the water inlets . The cork gaskets at the front and rear ...well they used the OLD ones and tried to fill the gaps up with about a 1/2 tube of silicon that was left from the water jackets !
So there is no question that the intake gasket was leaking ! Once I get the gaskets and get everything put back together , I will let everyone know how it turns out .

Jim
 
Jim that is great news...but bad as well.....one would have to wonder what else was "jake legged" when that motor was put together?
 
Can't wait for the engine to run correctly. I am Glad that you went into the engine, The suspense was KILLING me!!

:D:D
 
Distributor is fine !

Actually the engine looks like it was rebuilt by someone then someone else did the intake crap job to unload it . It has a new oil pump due to the oil pressure , new lifters , push rods and looks to have a new cam as well . Problem with that is , that cam wasn't broken it so it's not going to last . It really looks like I was the first one to get it running . The customer bought it from a guy that bought a gas station and it was left there by the last owner . So I have no idea what was done but seems to have a fresh rebuild under that intake !
Will see what happens when it's done .

Jim
 
BIG problem found now on backfiring engine !

Well I removed the intake and the nightmare has begun .
I did replace the intake gasket and as I was filling the radiator with water all the sudden the water started pouring out the intake gasket at the water jackets in the front . Now I know why the last person used a 1/2 tube of silicon on the gasket .
So I drained the water and pulled the intake . I used a steel straight edge on the heads and they were true . I then use that same straight edge on the intake and OMG , it looked like a motor cross dirt track . The intake is full of waves ! Both side is like that . Well I will have to find a sbf 2 bbl intake cheap someplace . That was the whole problem from the start . The last person trimmed down the front and rear cork gaskets on the intake and used a 1/2 tube of silicon on both sides of the side gaskets hoping that would hold .
Well the nightmare continues to go on and on !

Retro Jim
 
Nightmare should be over since you found the problem. 2bbl sbf manifold should be easy to find since so many get replaced with 4bbl.
 
But only if they keep them . Not long ago I took some to the scrap yard because everyone wants a 4 bbl . So here I am with a guy who needs one now and I scrapped some but didn't know he would need one . I couldn't sell them at the BIG Ford Carsile show in Pa. in June for $20 each so they hit the scrap yard . I had them for the last 3 years and got tired of dragging them to the shows trying to sell them .
Isn't that the way it always goes ! :eek:

Jim
 
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