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Old 09-20-2020, 08:17 PM   #21
Greg Jones
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Default Re: Hard turning with new pistons

Herm Kohnke told me when using plastigage to put a spot of oil on the bearing then lay the plastigage in the oil. Then torque and measure. According to Herm if you don’t use oil you won’t get an accurate reading. In my experience I find he is correct. FWIW. I am sure others will disagree but I know what works for me.
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Old 09-20-2020, 08:22 PM   #22
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Default Re: Hard turning with new pistons

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Originally Posted by Greg Jones View Post
Herm Kohnke told me when using plastigage to put a spot of oil on the bearing then lay the plastigage in the oil. Then torque and measure. According to Herm if you donít use oil you wonít get an accurate reading. In my experience I find he is correct. FWIW. I am sure others will disagree but I know what works for me.
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Old 09-20-2020, 10:11 PM   #23
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Default Re: Hard turning with new pistons

I had a similar problem with an engine rebuild four years ago. Car would overheat and lock up when stopped, until it cooled down. Tried different rings. Checked ring clearances. Reassembled. Still stuck. After much discussion with the machine shop (very reputable), we determined that in spite of boring and honing to mfg specs, the pistons and rings were too tight. We pulled the engine for the third time, rehoned and increased the piston to wall clearance to .0045. Problem solved. Pistons and rings were from Snyder’s. Not their fault, the mfg specs were to tight.
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Old 09-21-2020, 12:02 PM   #24
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Default Re: Hard turning with new pistons

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mfg specs were to tight
Methinks that piston manufactures base there specs on modern engines that have water jackets close to the full length of the cylinder, whereas the Model A engine's water jackets are only part way down the cylinder.
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Old 09-21-2020, 12:18 PM   #25
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Default Re: Hard turning with new pistons

In reworking my old Ford tractor engines, I find the new engine seals are stiff as can be and really drag on the crankshaft. Could that be problem? Lot's of talk about presoaking or not on the seals. I usually put them in dry but then rub in assembly lube. A new type front seal helps a lot.
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Old 09-21-2020, 01:02 PM   #26
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Default Re: Hard turning with new pistons

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Quote:
Originally Posted by Greg Jones View Post
Herm Kohnke told me when using plastigage to put a spot of oil on the bearing then lay the plastigage in the oil. Then torque and measure. According to Herm if you donít use oil you wonít get an accurate reading. In my experience I find he is correct. FWIW. I am sure others will disagree but I know what works for me.



I'm not going to disagree.

Using oil is the way to use plastigauge.

But, you're right. There are some that disagree.
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Old 09-21-2020, 01:02 PM   #27
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Default Re: Hard turning with new pistons

Quote:
Originally Posted by Greg Jones View Post
Herm Kohnke told me when using plastigage to put a spot of oil on the bearing then lay the plastigage in the oil. Then torque and measure. According to Herm if you donít use oil you wonít get an accurate reading. In my experience I find he is correct. FWIW. I am sure others will disagree but I know what works for me.



I'm not going to disagree.

Using oil is the way to use plastigauge. And it needs to be fresh.

But, you're right. There are some that disagree.
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Old 09-21-2020, 02:27 PM   #28
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Default Re: Hard turning with new pistons

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Originally Posted by katy View Post
Methinks that piston manufactures base there specs on modern engines that have water jackets close to the full length of the cylinder, whereas the Model A engine's water jackets are only part way down the cylinder.

I have to agree. That was clearly the problem with my engine.
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Old 09-21-2020, 08:01 PM   #29
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Default Re: Hard turning with new pistons

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Using oil is the way to use plastigauge. And it needs to be fresh.
Ditto, especially the plastigauge, the oil can be old as stink as long as it's clean.
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Old 09-26-2020, 03:23 PM   #30
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Default Re: Hard turning with new pistons

Well I tore everything back down and put it together once again to find it was still too tight. I decided to look at my old pictures (Glad I take pictures every step of the way) to find I installed the caps on backwards. I'm not sure how I reversed the direction of the caps, but I did (I probably rotated the engine direction when the engine came back from being re-bored).
I didn't think it would make that much of a difference, but it did make a drastic improvement once they were on correctly. I was able to set the gap without the engine binding. It was still tight to turn once the pistons were connected but at least it turned without giving me a hernia.
Thanks for everyone's input
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Old 09-27-2020, 09:31 AM   #31
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Default Re: Hard turning with new pistons

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It was still tight to turn once the pistons were connected but at least it turned without giving me a hernia.
On a rebuilt/overhauled engine there is a lot of drag between the rings and the cylinder walls until the rings are seated.
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Old 09-27-2020, 10:09 AM   #32
Patrick L.
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Default Re: Hard turning with new pistons

Quote:
Originally Posted by pcpat View Post
Well I tore everything back down and put it together once again to find it was still too tight. I decided to look at my old pictures (Glad I take pictures every step of the way) to find I installed the caps on backwards. I'm not sure how I reversed the direction of the caps, but I did (I probably rotated the engine direction when the engine came back from being re-bored).
I didn't think it would make that much of a difference, but it did make a drastic improvement once they were on correctly. I was able to set the gap without the engine binding. It was still tight to turn once the pistons were connected but at least it turned without giving me a hernia.
Thanks for everyone's input



The caps do have to go on in the correct location and orientation. Usually punch marks are used to eliminate any mistakes.
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Old 09-27-2020, 11:49 AM   #33
Ernie Vitucci
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Default Re: Hard turning with new pistons

Good Morning...I have been involved with the building of a good number of Model A engines...not as the builder...simply as the humble helper...when an engine is put together properly, it can be turned over with a crank on the test stand fairly easily...builders with experience have their own clearance measurements based on experience...not necessarily the measurements that come with the parts. We start and run them a number of times...on the test stand...bringing the engine up to 160 each time. If the tolerances are correct...the engine will not swell to the point that it will not turn...if you are building an engine and it becomes too tight to turn after you shut it down, take it apart and hone it a bit more until it is happy...building these engines...in my humble opinion...is art...not science...Ernie in Arizona
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