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Old 11-25-2018, 09:03 AM   #1
marko39
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Default 38 221 engine questions

i opened up a 38 engine i have had for 40 yrs. to check its condition. pistons are steel and measure about 3.036. is that a stock piston for a 3.062 bore? cyl. bore measures about 3.077. what is the wear limit before boring is needed? last, i measured valve clearances and all are .004-.005 over spec. is this normal and what would be the probable cause? all other engines i had had tight clearances and valve stems had to be ground. thanks, Mark
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Old 11-25-2018, 09:19 AM   #2
JSeery
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Default Re: 38 221 engine questions

Something appears mixed up with your piston measurements. The piston would be within a few thousandths of the cylinder bore. The cylinder measurement also seems a little suspect to me. That would be a lot of cylinder wear and would have something like a .007 ridge.
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Old 11-25-2018, 10:49 AM   #3
rotorwrench
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Default Re: 38 221 engine questions

I don't think Ford made any pistons less than 3 1/16" unless it was a quality control problem. If it was that loose, it would have been one noisy oil burning mess. A bore of 3.077" is a lot of wear but it would have been with too small a pistons in it. Piston slap would have been bad with that much clearance.


I'd be wondering if those were even Ford pistons. Back in the day, shade tree mechanics were liable to install anything that would fit the bore. Clearance is too much at .005" over in my book. You have room to bore it oversize though.
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Old 11-25-2018, 10:55 AM   #4
marko39
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Default Re: 38 221 engine questions

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Originally Posted by JSeery View Post
Something appears mixed up with your piston measurements. The piston would be within a few thousandths of the cylinder bore. The cylinder measurement also seems a little suspect to me. That would be a lot of cylinder wear and would have something like a .007 ridge.
thats what i thought too. cyclinders have no ridge so engine was apart in the past. i was wondering if was bored .010. i checked a piston from a 39 sleeved engine and it was about the same dia. but bore measured .007 above stock. i was hoping someone had a stock piston they could measure for me. Mark
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Old 11-25-2018, 10:59 AM   #5
JSeery
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Default Re: 38 221 engine questions

A stock piston diameter is going to be the same as the stock cylinder diameter minus a couple of thousandths (as in .002 or .003). Same with an overbore, the piston should be within a couple of thousandths of the cylinder bore. It also depends on the material the piston is made of, steel pistons would have tighter clearances.

Last edited by JSeery; 11-25-2018 at 11:32 AM.
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Old 11-25-2018, 01:27 PM   #6
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Default Re: 38 221 engine questions

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thats what i thought too. cyclinders have no ridge so engine was apart in the past. i was wondering if was bored .010. i checked a piston from a 39 sleeved engine and it was about the same dia. but bore measured .007 above stock. i was hoping someone had a stock piston they could measure for me. Mark
I've come across the no ridge with steel Pistons . I forgot cause it's bee 30-40 yrs since I saw steel Pistons . So anyway the steel Pistons have the top ring VERY high on the piston , giving the illusion of no ridge . You'll need to run the piston down to bdc and take measurements with a good bore micrometer .
I found good NOS on e bay , cheap . Bearings , rings Pistons etc . I've done 2 21 stud 36 lb engines in the last year . On one I just rering end it and de sludged it . It runs great , it's was An engine I've been stepping over for the last 20-30 yrs . I was totally stunned after the tear down and rebuild .
Good luck
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Old 11-25-2018, 01:35 PM   #7
Karl Wolf
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Default Re: 38 221 engine questions

One can measure cylinder taper by using a piston ring.
Put the ring in the top of the bore, measure the end gap with feeler blades.
Put in the bottom and measure. To square it, use piston with no rings on it.
Subtract, and divide the difference by 3.1416.
(I just use 3.)
That is your taper

Karl
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Old 11-25-2018, 01:37 PM   #8
marko39
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Default Re: 38 221 engine questions

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Originally Posted by rotorwrench View Post
I don't think Ford made any pistons less than 3 1/16" unless it was a quality control problem. If it was that loose, it would have been one noisy oil burning mess. A bore of 3.077" is a lot of wear but it would have been with too small a pistons in it. Piston slap would have been bad with that much clearance.


I'd be wondering if those were even Ford pistons. Back in the day, shade tree mechanics were liable to install anything that would fit the bore. Clearance is too much at .005" over in my book. You have room to bore it oversize though.
i checked piston again this time with a digital caliper and got 3.059 . either my old mics. are wrong or its operator trouble. looks like a good block for a rebuild as i see no cracks and crank measured std. there was a shade tree mechanic involved somewhere in the past as oil pan rear is torch cut on bottom between the two tranny boltholes. he didnt want to drop the pan to remove flywheel. engine also has one 8ba valve and rest mushrooms.
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Old 11-25-2018, 03:38 PM   #9
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Default Re: 38 221 engine questions

If your original bore measurement is accurate (3.077") that's still .018" piston to wall clearance, which is still way too much, even for a forged piston.


Sal
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Old 11-25-2018, 04:05 PM   #10
G32
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Default Re: 38 221 engine questions

marko39;

Just wondering if your 1938 is a 21 or 24 stud engine?

Neat project!

Gene Iulsa
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Old 11-25-2018, 06:23 PM   #11
rotorwrench
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Default Re: 38 221 engine questions

It's rare to find an engine with only a .010" oversize in the more modern era. It generally takes more to straighten out the walls using a boring bar. Many of the rebuilders just went out to .040" OS as a matter of practice. Back in the days before & during the war, folks would hone them oversize and use the smallest oversize they could get. That may be a more likely scenario. They just forgot to get OS pistons. It probably didn't take long to find out that that wasn't such a good idea if they ran it that way.
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Old 11-26-2018, 08:29 AM   #12
marko39
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Default Re: 38 221 engine questions

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marko39;

Just wondering if your 1938 is a 21 or 24 stud engine?

Neat project!

Gene Iulsa
it is a 24 stud and was in my 39 tudor when i got it in 1977. i did start it back then but not for long as it had no exhaust and i pulled it because clutch rusted and i could not push pedal down . deceided to go with a 39 engine. i think i will try to find a new home for it now i know what it needs. Mark
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