The Ford Barn

ursus · 09-23-2023, 01:23 PM

I acquired a stock Model B short block that was rebuilt and put in storage about 15 years ago. At first it was difficult to turn it over but after flushing out the cylinders with WD-40 I can now turn it through full revolutions with about 25-30 pounds showing on the torque wrench.

However, there is much greater resistance as the pistons are moving through the middle of the cylinders, which is the area of maximum side thrust. There is much less resistance when the pistons are at the top or bottom of a stroke. I pulled one piston and found the ring end gaps to be 15-18 thousands, nice cross hatch on cylinder walls, and both rod ends to be in spec.

Is it normal for newly rebuilt engine (rebabbited mains and rods, new pistons, rings, etc) to exhibit greater resistance as the pistons are moving through the middle of a stroke?

P.S. I only have experience with engines that were partially rebuilt, and never with a fully rebuilt unit that hasn't been run.

GPierce · 09-23-2023, 01:28 PM

The piston velocity is higher mid-stroke than at the top and bottom.

Big hammer · 09-23-2023, 01:31 PM

Also less mechanical advantage mid stroke, spark and gas make some noise!

AL in NY · 09-23-2023, 03:32 PM

ursus: 25-30 ft/lbs is perfect for a well rebuilt Model A short block.

Jim Brierley · 09-24-2023, 12:48 PM

Yes, it is normal in rebuilt, or older engines because the piston is moving fast in mid-stroke. It is caused by ring drag.

CWPASADENA · 09-24-2023, 11:14 PM

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Sounds good to me.

I would use regular motor oil to lubricate the cylinders, WD-40 is not a very good lubricant. On a freshly rebuilt engine that has not yet run, it will always be harder to turn the crank when the pistons are mid stroke and much less effort when the pistons are at the end of their stroke. Just oil everything really good, put everything back together and get it in the car. You may want to use some assembly lube on the cam lobes.

My opinion,

Chris W.

CT Jack · 09-25-2023, 08:07 AM

In your case resistance is a function of the engine rebuilder and time in storage. I would finish assembling the engine and run it on an engine stand. Initially, I would turn it over without the spark plugs and use break in oil. This would help to free up any corrosion on the cyclinder walls and get oil into the main and connecting rod journals. Then follow up with starting the engine monitoring the temperature. I would initially run for a short interval and not exceed 180 degree water temperature. Then progressively run longer and change speed. Also retorqued the head when cold. After running for a couple of hours drain the oil and install it in your car.

nkaminar · 09-25-2023, 03:40 PM

Depending on the pistons and rings, the engine will not loosen up until you have 1,000 to 2,000 miles on it.

CWPASADENA · 09-25-2023, 10:20 PM

When you first start it, do NOT just let it just idle. Run it at about 1000-1500 RPM, varying the engine speed every so often. You need to get the engine speed up to ensure the internal components and cylinder walls get plenty of lubrication.

My opinion,

Chris W..

09-23-2023, 01:23 PM	#1
ursus Senior Member Join Date: May 2010 Location: Oregon Posts: 1,375	Rebuilt Engine Piston Resistance I acquired a stock Model B short block that was rebuilt and put in storage about 15 years ago. At first it was difficult to turn it over but after flushing out the cylinders with WD-40 I can now turn it through full revolutions with about 25-30 pounds showing on the torque wrench. However, there is much greater resistance as the pistons are moving through the middle of the cylinders, which is the area of maximum side thrust. There is much less resistance when the pistons are at the top or bottom of a stroke. I pulled one piston and found the ring end gaps to be 15-18 thousands, nice cross hatch on cylinder walls, and both rod ends to be in spec. Is it normal for newly rebuilt engine (rebabbited mains and rods, new pistons, rings, etc) to exhibit greater resistance as the pistons are moving through the middle of a stroke? P.S. I only have experience with engines that were partially rebuilt, and never with a fully rebuilt unit that hasn't been run.

09-23-2023, 01:28 PM	#2
GPierce Senior Member Join Date: Dec 2014 Location: Germantown,TN Posts: 516	Re: Rebuilt Engine Piston Resistance The piston velocity is higher mid-stroke than at the top and bottom.

09-23-2023, 01:31 PM	#3
Big hammer Senior Member Join Date: Jun 2014 Location: Land of Lincoln Posts: 3,131	Re: Rebuilt Engine Piston Resistance Also less mechanical advantage mid stroke, spark and gas make some noise! __________________ Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done

09-23-2023, 03:32 PM	#4
AL in NY Senior Member Join Date: May 2010 Location: Southern Upstate New York Posts: 1,160	Re: Rebuilt Engine Piston Resistance ursus: 25-30 ft/lbs is perfect for a well rebuilt Model A short block. __________________ AL in NY

09-24-2023, 12:48 PM	#5
Jim Brierley Senior Member Join Date: Jun 2010 Location: Temecula, CA Posts: 4,091	Re: Rebuilt Engine Piston Resistance Yes, it is normal in rebuilt, or older engines because the piston is moving fast in mid-stroke. It is caused by ring drag.

09-24-2023, 11:14 PM	#6
CWPASADENA Senior Member Join Date: May 2010 Location: PASADENA, CA Posts: 1,885	Re: Rebuilt Engine Piston Resistance Sponsored Links (Register now to hide all advertisements) Sounds good to me. I would use regular motor oil to lubricate the cylinders, WD-40 is not a very good lubricant. On a freshly rebuilt engine that has not yet run, it will always be harder to turn the crank when the pistons are mid stroke and much less effort when the pistons are at the end of their stroke. Just oil everything really good, put everything back together and get it in the car. You may want to use some assembly lube on the cam lobes. My opinion, Chris W.

09-25-2023, 08:07 AM	#7
CT Jack Senior Member Join Date: May 2010 Location: Hebron, CT Posts: 432	Re: Rebuilt Engine Piston Resistance In your case resistance is a function of the engine rebuilder and time in storage. I would finish assembling the engine and run it on an engine stand. Initially, I would turn it over without the spark plugs and use break in oil. This would help to free up any corrosion on the cyclinder walls and get oil into the main and connecting rod journals. Then follow up with starting the engine monitoring the temperature. I would initially run for a short interval and not exceed 180 degree water temperature. Then progressively run longer and change speed. Also retorqued the head when cold. After running for a couple of hours drain the oil and install it in your car.

09-25-2023, 03:40 PM	#8
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,900	Re: Rebuilt Engine Piston Resistance Depending on the pistons and rings, the engine will not loosen up until you have 1,000 to 2,000 miles on it. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

09-25-2023, 10:20 PM	#9
CWPASADENA Senior Member Join Date: May 2010 Location: PASADENA, CA Posts: 1,885	Re: Rebuilt Engine Piston Resistance When you first start it, do NOT just let it just idle. Run it at about 1000-1500 RPM, varying the engine speed every so often. You need to get the engine speed up to ensure the internal components and cylinder walls get plenty of lubrication. My opinion, Chris W..