Pistons not flush with block
Lead Driver
Joined: Oct 1999
Posts: 6,780
Likes: 558
From: Kalispell, MT
I'm not sure what you're measuring "to the crown"?
Van Pelt's measurements are for diameter of the bore in a stock engine.
In order to use the same block and con rods, a Merc crank that is +1/4" requires a wrist pin placed higher on the piston so that it sits lower in the bore.
Along the lines of ebear, I'm thinking you have a Merc crank with Ford pistons.
edit: I measured some of both I have in the shop. The Merc pistons measure 1 1/2" from center of the wrist pin to the shoulder (top of the deck normally) and 1 5/8" to the crown of the piston.
Some early Ford pistons measure 1 5/8" center of the wrist pin to shoulder and 1 3/4" to the crown of the piston. This makes the Ford pistons sit 1/8" higher in the bore.
Van Pelt's measurements are for diameter of the bore in a stock engine.
In order to use the same block and con rods, a Merc crank that is +1/4" requires a wrist pin placed higher on the piston so that it sits lower in the bore.
Along the lines of ebear, I'm thinking you have a Merc crank with Ford pistons.
edit: I measured some of both I have in the shop. The Merc pistons measure 1 1/2" from center of the wrist pin to the shoulder (top of the deck normally) and 1 5/8" to the crown of the piston.
Some early Ford pistons measure 1 5/8" center of the wrist pin to shoulder and 1 3/4" to the crown of the piston. This makes the Ford pistons sit 1/8" higher in the bore.
Lead Driver
Joined: Jul 2003
Posts: 9,372
Likes: 1,733
From: AKRON ohio
I'm going to guess as I'm not there to see everything nor am I a flat head guy, looks to me like it's a merc stroke that when assembled years ago they cut the tops of the pistons to the deck height desired for this engine. Is this a possibility?
If this is what they did, it was done to up the compression as if flatheads are like y blocks the piston sits down in the cylinder not at zero deck height
If this is what they did, it was done to up the compression as if flatheads are like y blocks the piston sits down in the cylinder not at zero deck height
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Cross-Country
Joined: Nov 2020
Posts: 89
Likes: 16
The real questions is where do I find pistons which are 1/8" shorter than the Ford pistons.
Measurements as I have them.
Width New - 3.209" Original 3.186"
Height New - 3.138" Original 3.065"
Center of pin to dome top - New - 1.750" Original 1.667"
Top of pin edge to edge of cylinder New - 1.278" Original 1.155"
I have the question submitted to Carpenter Ford and Van Pelt.
Thank you.
Measurements as I have them.
Width New - 3.209" Original 3.186"
Height New - 3.138" Original 3.065"
Center of pin to dome top - New - 1.750" Original 1.667"
Top of pin edge to edge of cylinder New - 1.278" Original 1.155"
I have the question submitted to Carpenter Ford and Van Pelt.
Thank you.
Fleet Owner
Joined: Jul 2004
Posts: 27,300
Likes: 1,059
From: NM
If what you need is Mercury pistons, Egge and others have them: https://egge.com/?year_id=34791&make...vpf-ymm-search
You could also sell the Merc crank, get a Ford crank and use the Ford pistons.
You could also sell the Merc crank, get a Ford crank and use the Ford pistons.
Thread Starter
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Cross-Country
Joined: Nov 2020
Posts: 89
Likes: 16
The stroke measures 3 3/4" but that is on top of the piston that is 1/8" too tall. The largest counter weight is 6" indicating a Merc crank. I've ordered a set of Mercury pistons from an outfit in Birmingham.
Thank you again for the advise.
Thank you again for the advise.
Fleet Owner
Joined: Jul 2004
Posts: 27,300
Likes: 1,059
From: NM
The piston wouldn't affect the measured stroke. 3-3/4" would be a Ford crank, I'm not seeing how that is possible. What is the distance from the edge of the piston to the deck, at bottom dead center?
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Tuned
Joined: Mar 2014
Posts: 319
Likes: 18
Pistons not flush
I've been rebuilding my 1953 239 flathead V8. New pistons came from Dennis Carpenter. Used 8BA control rods purchased used on E-Bay. The crankshaft was machined for the mains .010, rods .020 and cylinders .030. Once installed the piston heads are about 1/8' above block at top.
What have I done and what can I do?
What have I done and what can I do?
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