Allis C compression value
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=159813
Printed Date: 14 Apr 2026 at 6:07pm
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Topic: Allis C compression value
Posted By: John426
Subject: Allis C compression value
Date Posted: 09 Apr 2019 at 11:39am
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Hi What is the compression ratio or the PSI compression for an Allis Chalmers C distillate On the web i see differents ratio from 70 PSI to 115 PSI . What is the correct one for distillate engine? Mine is the tractor number 50953 , i think that production date is last quarter of year 1947
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Replies:
Posted By: Leon n/c AR.
Date Posted: 09 Apr 2019 at 11:44am
| Several year ago when I checked our old B best I remember it was somewhere between 60-70 psi. |
Posted By: John426
Date Posted: 09 Apr 2019 at 11:48am
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I checked mine , i have 65 PSI on each cylinder, but my question is does it O.K or to low?
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Posted By: DrAllis
Date Posted: 09 Apr 2019 at 12:22pm
| If the compression is 65 psi on ALL four cylinders, AND it runs OK, why are you concerned?? The only way to correct it is to overhaul it. It sounds like it does indeed have the distillate pistons in it. You did check the compression with the throttle set WIDE OPEN didn't you ??? |
Posted By: CrestonM
Date Posted: 09 Apr 2019 at 12:53pm
| Are you all talking about the dished kerosene pistons? My "B" had those, and it had 90 psi in all 4 before I overhauled it with gas flat top pistons. |
Posted By: John426
Date Posted: 09 Apr 2019 at 1:39pm
| I have flat piston |
Posted By: AaronSEIA
Date Posted: 09 Apr 2019 at 1:51pm
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4.75 c/r is 99 lbs 5.75 c/r is 115 per the book. AaronSEIA
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Posted By: Gerald J.
Date Posted: 09 Apr 2019 at 8:50pm
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Should be mentioned in the shop manual: http://geraldj.networkiowa.com/Trees/Allis-Chalmers-G-B-C-CA-Service.pdf" rel="nofollow - http://geraldj.networkiowa.com/Trees/Allis-Chalmers-G-B-C-CA-Service.pdf Gerald J. |
Posted By: Dick L
Date Posted: 09 Apr 2019 at 8:57pm
Flat top pistons can also be low compression pistons when they do not come even with the deck when at TDC. |
John426 wrote:Posted By: steve(ill)
Date Posted: 09 Apr 2019 at 9:00pm
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Aaron............. not sure how they got those numbers...... atmospheric pressure is about 14.7 psi ................ if you had a 5:1 compression motor, you should get 5 x 14.7 or about 70 psi ................ if you had 6:1 compression, you would get about 85 psi..... I don't see how any of the small allis motors would put out 100 psi since then all had less than 7 :1 compression ...... ?????? ------------- Like them all, but love the "B"s. |
Posted By: AaronSEIA
Date Posted: 10 Apr 2019 at 6:49am
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I don't know either. Just quoting the AC service manual. The BE engine was 4.67 c/r at 84 lbs and the 4.92 c/r at 94 lbs. I'm assuming "compression pressure" is on a compression test gauge. I don't think I have an I&T manual to see if they say the same thing. AaronSEIA
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