what engine is this? (Mercury)
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Senior User
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From: Lewisville, NC
what engine is this? (Mercury)
I have a Mercury engine in the 53 F100 I'm rebuilding. The compression is low (75 lbs. +/- 5 lbs) per cylinder. I'm going to test it tomorrow by squirting oil in the cylinders and see if the compression changes. I'm assuming a rebuild of some degree will be in order. My understanding is that this is basically a stroked 239 with slightly different heads to adjust compression.
How do I tell what year engine it is since it is not the engine that shipped with ? I have photos in my gallery of the numbers at the rear of the engine (21 and 57P 4) and the engine. It appears to be 24 bolt 8CM heads. Any information you can give me on this would be appreciated. The engine runs, but weakly. What information do I need to know to order head gaskets, etc.?
-Scott
How do I tell what year engine it is since it is not the engine that shipped with ? I have photos in my gallery of the numbers at the rear of the engine (21 and 57P 4) and the engine. It appears to be 24 bolt 8CM heads. Any information you can give me on this would be appreciated. The engine runs, but weakly. What information do I need to know to order head gaskets, etc.?
-Scott
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Joined: Oct 1999
Posts: 6,776
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From: Kalispell, MT
That's your garden variety 255 ci Merc flathead if the heads haven't been swapped. You can't tell for sure until you pull the heads and measure the stroke. (4" stroke is merc, 3.75 is ford) Both use the same parts except for pistons and crank.
It will probably run forever with the compression you have - flatheads are amazing engines. Fresh rebuild should be 110.
All you need to know to order rebuild materials is it a 49-51 8CM (or 52-53 = EAC) None of the other numbers you found mean anything. I've found parts counter guys choke on a range of numbers sometimes. If you run into that, tell them its for a 51 Merc car.
My first suggestion would be for you to contact Red's Headers, CA or Patrick's Antique Auto Parts, AZ for the right parts the first time. Both are top notch flatheaders and will treat you right.
It will probably run forever with the compression you have - flatheads are amazing engines. Fresh rebuild should be 110.
All you need to know to order rebuild materials is it a 49-51 8CM (or 52-53 = EAC) None of the other numbers you found mean anything. I've found parts counter guys choke on a range of numbers sometimes. If you run into that, tell them its for a 51 Merc car.
My first suggestion would be for you to contact Red's Headers, CA or Patrick's Antique Auto Parts, AZ for the right parts the first time. Both are top notch flatheaders and will treat you right.
Last edited by mtflat; Dec 28, 2005 at 09:47 AM.
Thread Starter
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Senior User
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From: Lewisville, NC
Heads say 8CM, so that's solved...
I understand the crank difference (stroke). Why are the pistons different - pin placement? I think that the heads are different as well.
Cutting to the chase, can I use the standard 239 head gaskets? I'd like to pull the heads to check the valves, etc. and de-carbonize everything.
Thanks for the information.
-Scott
I understand the crank difference (stroke). Why are the pistons different - pin placement? I think that the heads are different as well.
Cutting to the chase, can I use the standard 239 head gaskets? I'd like to pull the heads to check the valves, etc. and de-carbonize everything.
Thanks for the information.
-Scott
Lead Driver
Joined: Oct 1999
Posts: 6,776
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From: Kalispell, MT
Originally Posted by Narwhal
Heads say 8CM, so that's solved...
I understand the crank difference (stroke). Why are the pistons different - pin placement? I think that the heads are different as well.
Cutting to the chase, can I use the standard 239 head gaskets? I'd like to pull the heads to check the valves, etc. and de-carbonize everything.
Thanks for the information.
-Scott
I understand the crank difference (stroke). Why are the pistons different - pin placement? I think that the heads are different as well.
Cutting to the chase, can I use the standard 239 head gaskets? I'd like to pull the heads to check the valves, etc. and de-carbonize everything.
Thanks for the information.
-Scott
Short answer is yes, 239/255 use the same head gaskets.
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Joined: Sep 2005
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Sir: "...a rebuild of some degree..."??? How many times have I naively gotten into an old engine wishing for "some degree of a rebuild". On flatheads especially, there can be no such thinking, in my considered experience, as you seem to imply. Think you can get away without boring it out? Replacing cam? replacing valve components? unbolting the heads without a bolt or two snapping off? Think again. I would plan for a complete rebuild and, depending upon varying factors such as parts acquisition & if your machinist has a two thousand dollar boat or motor home payment coming up, sinking some big bucks into that block. Otherwise, just fire it up and see if there are any deleterious issues such as ominous noises or oil leaks, overheating, etc. Good luck.
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Bronx Tale
My first vehicle was a 53 Ford with a flathead 8, just do regular maintainance and use it!
Trouble will find you elsewhere!
Drive that great car of the best years of "Rock in Roll"
From Conners Street, New England Thruway,
"The Bronx New York"
White Castle Boston Post Road
Yankee Stadium
Now in Boulder City Nevada
Trouble will find you elsewhere!
Drive that great car of the best years of "Rock in Roll"
From Conners Street, New England Thruway,
"The Bronx New York"
White Castle Boston Post Road
Yankee Stadium
Now in Boulder City Nevada
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Fleet Owner
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From: NM
Given the low compression, I'm wondering if someone hasn't put Merc heads on a Ford engine. A lot of people mistakenly assume that all Merc parts result in a performance increase on a Ford engine. The Merc heads actually have a larger combustion chamber to compensate for their larger displacement (to give the same compression ratio). I wouldn't be surprised to find it's a 239 with 8CM heads, and just needs the right heads to restore compression!
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Fleet Owner
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From: NM
What kind of carburetor was on it? Was it a "teapot"? (Merc style carb) or the typical Ford/Holley model 94? While nothing but a check of stroke will absolutely verify it as a Merc, there are some other clues; What does the intake manifold have for a casting number? Is the oil pan a truck style (with large round clean-out section)? Also look on the intake manifold block surface, right rear, for some punched-in marks. They can sometimes be de-coded. On the other hand, all of these parts interchange. If you want to measure the stroke without pulling a head, try dropping the pan. You can measure from down there (on a cylinder) and clean out all the crap at the same time!
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Senior User
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From: Lewisville, NC
It was a "Ford" labeled Holley 94 carb, but the air horn doesn't match the oil bath air filter - I've had to shim it out about 1/16" to fit. The rest I'll have to check on.
Hard to tell what's original and what's not.
-Scott
Hard to tell what's original and what's not.
-Scott
Post Fiend
Joined: Jun 2001
Posts: 7,493
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From: Erie, pa
The only way to tell is by measuring the engine stroke.
The blocks are identical (within reason)
The difference is in the Crank and the pistons.
Everything else interchanges.
Unless you pull one out of a barn with o miles, the stickers still on it, and unworn (dry rotted) tires. It needs the heads pulled to be sure.
The blocks are identical (within reason)
The difference is in the Crank and the pistons.
Everything else interchanges.
Unless you pull one out of a barn with o miles, the stickers still on it, and unworn (dry rotted) tires. It needs the heads pulled to be sure.
Fleet Owner
Joined: Jul 2004
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From: NM
Mike, Can't really get a clean shot down the cylinder. Like I said, pulling the pan is not hard (on the trucks) and you can measure from the bottom of the skirt to the bottom of the cylinder bore (I can't remember if the skirt projects past the cylinder at BDC). Plus you get to see what shape everything else is in, maybe pull a rod cap, main cap, oil pump and screen, etc. No cost except for a gasket.
4TL8, I'm not sure I'd trust that one either!
4TL8, I'm not sure I'd trust that one either!
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Joined: Aug 2003
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From: Oakdale,Ca.
I wasn't sure if it was like the Mopar FH 6's I have or not.
I'd be the guinny pig on my FH V8's, but both are stuck and soaking in diesel. 5 gallons in each poured through the plug holes and intake...funny thing is there's none leaking on the floor.
Tells me at least the pan gaskets are still holding
I'd be the guinny pig on my FH V8's, but both are stuck and soaking in diesel. 5 gallons in each poured through the plug holes and intake...funny thing is there's none leaking on the floor.
Tells me at least the pan gaskets are still holding