Minimum compression to get 272 to fire?
Thread Starter
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Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
Minimum compression to get 272 to fire?
Hi folks - As some of you know by now, my '56 F500 sat for nearly 20 years in a field. The engine wasn't stuck, but I knew it wasn't going to fire with just fresh fuel and a new battery.
The compression in the 272 is very poor; and in 5 cylinders non-existent. The entire driver's side was 0 across the board.
The passenger was: 60, 0, 50, 60.
I took the plugs out and soaked Marvel Mystery Oil in each for 24 hours. I was able to do a compression test on the passenger side this morning before a downpour started.
The passenger side then read 120, 30, 70, 70. So we're making progress.
The question: What is the minimum compression needed for the engine to fire? I'm hope everything will loosen up with multiple fluid changes and clean fuel (with MMO added to both oil and fuel) once it's running. I keep reading that a few short trips with fluid changes in between really clean things up well.
The compression in the 272 is very poor; and in 5 cylinders non-existent. The entire driver's side was 0 across the board.
The passenger was: 60, 0, 50, 60.
I took the plugs out and soaked Marvel Mystery Oil in each for 24 hours. I was able to do a compression test on the passenger side this morning before a downpour started.
The passenger side then read 120, 30, 70, 70. So we're making progress.
The question: What is the minimum compression needed for the engine to fire? I'm hope everything will loosen up with multiple fluid changes and clean fuel (with MMO added to both oil and fuel) once it's running. I keep reading that a few short trips with fluid changes in between really clean things up well.
Postmaster
Joined: Jun 2014
Posts: 3,206
Likes: 3
From: Oakhust NJ Jersey Shore
You more than know that you have stuck piston rings, valves stuck and not seating, you can soak everything with marvel mystery oil, Tap on the valves with a rubber hammer, gotta get everything moving again, If you can get to 125 psi you can get her running.
Thread Starter
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Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
Yup, very aware of the condition the motor would be in for sure. Glad to see a target number. At least one cylinder is back from the dead. I'll do more soaking and tapping.
I'm curious to see if any of those driver's side cylinders come up. any increase means something is working. I'll update after this afternoon's test, presuming the rain stops.
THANK YOU!
I'm curious to see if any of those driver's side cylinders come up. any increase means something is working. I'll update after this afternoon's test, presuming the rain stops.
THANK YOU!
Lead Driver
Joined: Nov 2002
Posts: 9,680
Likes: 1,251
From: Jefferson City, MO
My build thread has info and questions on my compression and trying to get my Y-block started.
Here is where that discussion starts.
https://www.ford-trucks.com/forums/1...l#post11985687
Here are compression numbers:
Cylinder Before After oil After Valve Lash
1 55/0 0 125
2 60 85 115
3 60 75 95
4 75 95 125
5 55 65 85
6 55 90 100
7 65 100 105
8 65 95 105
The third set of numbers are most likely the compression I had when it finally started for the first time.
Here is where that discussion starts.
https://www.ford-trucks.com/forums/1...l#post11985687
Here are compression numbers:
Cylinder Before After oil After Valve Lash
1 55/0 0 125
2 60 85 115
3 60 75 95
4 75 95 125
5 55 65 85
6 55 90 100
7 65 100 105
8 65 95 105
The third set of numbers are most likely the compression I had when it finally started for the first time.
Thread Starter
|
Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
My build thread has info and questions on my compression and trying to get my Y-block started.
Here is where that discussion starts.
https://www.ford-trucks.com/forums/1...l#post11985687
Here are compression numbers:
Cylinder Before After oil After Valve Lash
1 55/0 0 125
2 60 85 115
3 60 75 95
4 75 95 125
5 55 65 85
6 55 90 100
7 65 100 105
8 65 95 105
The third set of numbers are most likely the compression I had when it finally started for the first time.
Here is where that discussion starts.
https://www.ford-trucks.com/forums/1...l#post11985687
Here are compression numbers:
Cylinder Before After oil After Valve Lash
1 55/0 0 125
2 60 85 115
3 60 75 95
4 75 95 125
5 55 65 85
6 55 90 100
7 65 100 105
8 65 95 105
The third set of numbers are most likely the compression I had when it finally started for the first time.
Dude. I just watched your "first start" video and I can't stop cracking up to your reaction when your old girl fired up! I can only imagine the feeling. I'm not there yet. But I'm hoping I can get the compression up. Thanks for the link to your thread by the way. Very useful!
Junior User
Joined: Mar 2015
Posts: 94
Likes: 0
From: UK
just been through your Youtube channel..your reaction to it starting for the first time was epic. I almost felt like i was there with you 
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Lead Driver
Joined: Nov 2002
Posts: 9,680
Likes: 1,251
From: Jefferson City, MO
Dude. I just watched your "first start" video and I can't stop cracking up to your reaction when your old girl fired up! I can only imagine the feeling. I'm not there yet. But I'm hoping I can get the compression up. Thanks for the link to your thread by the way. Very useful!
Calvin, be sure to take a video of your first start. I have a bunch of videos of nothing happening or backfires or some other odd situation before my first full start.
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Thread Starter
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Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
Joe I most certainly will post a video of the engine firing! I'd probably get just as excited as you did too I bet!
I dropped the oil pan today so I could clean out whatever goo might have been in the bottom of the pan and also wanted to get a god look at the lower end. Other than 3" of sludge in the pan I was so pleasantly pleased at how clean the engine was. Pistons looked shiny as did the cylinder walls that I could see. I was about to reinstall the pan with its new gasket and seals when I decided to do a quick check on the timing chain. The driver's side was tight but the passenger's side seemed uncomfortably loose. That concerned me. I left the pan off for now so I could take a look at the '56 truck manual. Seems 1/2" deflection or less is acceptable. I'm at more like 3/8" so I'm OK for now.
I dropped the oil pan today so I could clean out whatever goo might have been in the bottom of the pan and also wanted to get a god look at the lower end. Other than 3" of sludge in the pan I was so pleasantly pleased at how clean the engine was. Pistons looked shiny as did the cylinder walls that I could see. I was about to reinstall the pan with its new gasket and seals when I decided to do a quick check on the timing chain. The driver's side was tight but the passenger's side seemed uncomfortably loose. That concerned me. I left the pan off for now so I could take a look at the '56 truck manual. Seems 1/2" deflection or less is acceptable. I'm at more like 3/8" so I'm OK for now.
Thread Starter
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Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
IT'S ALIIIIVVVVEEEE!!!! BWAH HAHAHAHAHA!!!!
Well, Ethel has been resurrected! She runs! Kinda. After two oil flushes and a new oil filter, several soaking sessions of Marvel Mystery Oil I was only able to make a dent in the compression issue. I now have 120, 60, 90, 90 in the passenger side. It was 120, 30, 70, 70. Driver side was a big fat ZERO across all four cylinders. Now at 30, 60, 70, 60. It seems the Marvel is doing its thing. I imagine a few cylinders are simply not firing which is why it sounds so rough. Any suggestions or thoughts?
By the way my heart is banging from all the excitement!
By the way my heart is banging from all the excitement!
Thread Starter
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Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
THANK YOU! 
I believe if I remove the valve covers I should see a little oil seeping through the center of the rockers. Am I correct?
I'm not going to hurt anything running it for short periods while I verify these things am I?
I'm more of an antique Farmall tractor kind of guy. I'm learning as I go so forgive the questions that might seem silly to most.
I believe if I remove the valve covers I should see a little oil seeping through the center of the rockers. Am I correct? I'm not going to hurt anything running it for short periods while I verify these things am I?
I'm more of an antique Farmall tractor kind of guy. I'm learning as I go so forgive the questions that might seem silly to most.
Believe Nothing
Joined: Jun 2004
Posts: 7,514
Likes: 398
From: W. Central FL.
You have a very basic OHV V8 engine. If it is oiling enough, you will see oil being thrown off the rocker arms when the engine is running. Be sure you have oil at the rockers at both ends of the rocker shafts. Won't hurt a thing.
Thread Starter
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Laughing Gas
Joined: Dec 2014
Posts: 774
Likes: 11
From: Simsbury, Connecticut
All valves appear fine and aren't stuck. It took a while but oil is now circulating at the rockers. All good things. But man do I have one horrible driver side knock. That's the same side I have low compression too. Thoughts on this?