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Charlie175 
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 Topic: Cylinder PSI
Posted: 30 Oct 2020 at 2:43pm |
Can someone tell me what the cylinder PSI was for these 226 engines: WD45 D17 (Did it change any over the years?) 170 175
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Charlie
'48 B, '51 CA, '56 WD45 '61 D17, '63 D12, '65 D10 , '68 One-Ninety XTD
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steve(ill)
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Posted: 30 Oct 2020 at 3:07pm |
This is what i have for the WD45 from the service manual... Seems to vary on compression ratios................ 4.75 , 5.25 , 6.45 ......... and 7.2 for the LP
Tractor DATA lists the D17 as 7.25 ............. 170 as 8.0 ............ 175 as 8.2
Edited by steve(ill) - 30 Oct 2020 at 3:13pm
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Charlie175
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Posted: 30 Oct 2020 at 3:27pm |
Thanks Steve, what I am looking for is if I did a compression test on each of these models, what is the PSI it would read?
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Charlie
'48 B, '51 CA, '56 WD45 '61 D17, '63 D12, '65 D10 , '68 One-Ninety XTD
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Brian G. NY
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Posted: 30 Oct 2020 at 3:35pm |
Seems most automotive repair manuals don't specify the compression pressure; only that the pressure should be between 10PSI between the highest and lowest cylinders. On the other hand, Allis-Chalmers did list the compression pressure in their manuals. Well, at least on some of their tractors. Taken from factory manuals.
Gasoline Low Octane Fuel L.P.G. Fuel Diesel WD 110 80 Not listed WD-45 130 110 " " 385 D-17 145 85 170 *385-425
*at low idle (600 RPM)
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steve(ill)
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Posted: 30 Oct 2020 at 3:58pm |
atmospheric presssure is 14.7 psi... so "theoretically", you take the compresion ratio and multiply by 14.7 psi to get the cylinder pressure... does not always work exactly that way.
6.45 x 14.7 = 95 psi
7.0 x 14.7 = 101 psi
7.2 x 14.7 = 103 psi
so they dont change much.. I think thats why they say " as long as they are within 10 psi ( and hopefully above 80 psi) , then you are good to go.
Those numbers you listed seem a little high... Not sure how you would get 145 psi on a D17 ?
Edited by steve(ill) - 30 Oct 2020 at 4:02pm
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Brian G. NY
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Posted: 30 Oct 2020 at 4:57pm |
[QUOTE Those numbers you listed seem a little high... Not sure how you would get 145 psi on a D17 ?
[/QUOTE]
The question is: how does Allis-Chalmers get those PSI figures? Seems their servicemen might have been disappointed after rebuilding an engine if they were not attaining the compression pressures the factory manual calls for.
It's been a long time since I've taken the compression on any engine but it seems that back in the day, a stock 2 barrel Ford 351 Windsor would produce 150 PSI pretty reliably. As I recall, those engines (prior to '72 or '73) had around 8.5 or 9.0 compression ratio. Maybe it has something to do with turning the engine over a few revolutions while performing the test. Anyway, the numbers I posted came out of the A-C Factory manuals.
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DrAllis
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Posted: 30 Oct 2020 at 5:30pm |
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D-17 at 145 psi.....170 at 165 psi.....WD45 at 130 psi...…..175 is 170 psi. All numbers from A-C Service Book.
Edited by DrAllis - 30 Oct 2020 at 6:28pm
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steve(ill)
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Posted: 30 Oct 2020 at 6:49pm |
Ford 351 Windsor would produce 150 PSI pretty reliably. As I recall, those engines (prior to '72 or '73) had around 8.5 or 9.0 compression ratio....
YES, and im sure DrAllis is right on his numbers... Like i said, "theoretically" you multiply by the atmospheric pressure, but that usually gives a low number.. I dont know why, but most on line explainations tend to think the CAM TIMING effects the psi greatly... Again, i dont really understand how that happens either..... some 9.0 CR motors put out 150 psi and some put out 180 psi... WHY ?
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DanWi
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Posted: 30 Oct 2020 at 11:07pm |
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Wouldn't it be higher because of the vacuum you create on the intake stroke would pack more air in then just static air pressure therefore giving it a higher reading, also the reason it would be affected by cam timing.
Edited by DanWi - 30 Oct 2020 at 11:07pm
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rw
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Posted: 31 Oct 2020 at 5:01am |
I think the calculation of atmosphere psi times comp ratio is a good thumb rule. It fails to take into consideration that as you compress the intake charge, it heats as it is being compressed and that raises the pressure the gauge shows. Cranking speed has some effect on the heat generated. The throttle plate and choke plate needs to be open all the way. rw
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jaybmiller
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Posted: 31 Oct 2020 at 6:05am |
I always used '15' as the atmospheric pressure. Easier to do the math..... Generally though you need 100PSI per cylinder and all the same. I KNOW that a rototiller with B&S 5HP engine will start and run with 40 PSI but as soon as you try to turn the soil, it STOPS !!! The 'all 4 within 10PSI' quickly shows if any cylinder has bad rings, guides or headgasket problems.
nuther 'easy math' trick... take the CC of the small engine /30 gives you approximate HP of the engine. UP here they sell engines by CC..guess 270 cc sounds better than 9 HP ?
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Ed (Ont)
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Posted: 31 Oct 2020 at 7:13am |
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Interesting thread. If I have time I may do my 45 this week.
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injpumpEd
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Posted: 31 Oct 2020 at 10:18am |
 steve(ill) wrote:
Ford 351 Windsor would produce 150 PSI pretty reliably. As I recall, those engines (prior to '72 or '73) had around 8.5 or 9.0 compression ratio....
YES, and im sure DrAllis is right on his numbers... Like i said, "theoretically" you multiply by the atmospheric pressure, but that usually gives a low number.. I dont know why, but most on line explainations tend to think the CAM TIMING effects the psi greatly... Again, i dont really understand how that happens either..... some 9.0 CR motors put out 150 psi and some put out 180 psi... WHY ? |
CAMSHAFT PROFILES, and Cam to Crank phasing, or timing.
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Coke-in-MN
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Posted: 31 Oct 2020 at 1:43pm |
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Compression is one way of finding if all cylinders are close - then a leak down test using compressed air can also be helpful if there is a difference - seeing if it will hold pressure or leak by valves or into pan - same with adding a few squirts of oil to cylinder to see if ring leakage improves with oil to seal rings .
Was just using that 30 number divided in to cc - seems my Norton Motorcycle is 750cc but rated at 65 HP with 9:1 compression - My 850cc (823 actual cc) Norton is rated factory as 60 HP with 8.5:1
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steve(ill)
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Posted: 31 Oct 2020 at 2:39pm |
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I think the "divide by 30" is a calculation for B&S lawn mower engines that run 3600 rpm.... As you speed up the RPM ( motorcycle), dual overhead cams, 4 valves .... you can get a HP out of 10 CC... some maybe even more.
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steve(ill)
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Posted: 31 Oct 2020 at 2:42pm |
there are 16 cubic centimeters in a cubic inch... High HP car engines use to get 1 HP per cubic inch ( 350 inch = 350 HP) .... using that number you would divide the CC displacement by 16.............
so lawn mowers maybe / 30...... cars may be / 16 ..... motorcycles can be / 10..... all depends on engine design and RPM rating.
and my 125 cubic inch ALLIS B puts out an AMAZING 22 HP !!! 
Edited by steve(ill) - 31 Oct 2020 at 2:44pm
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Charlie175
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Posted: 31 Oct 2020 at 6:23pm |
I did my 45 yesterday. Warmed up, wide open throttle, no plugs, battery charger on, I had:
1: 165 2: 160 3: 155 4: 165
I cranked until the gauge didn't move
It has a Z Code motor in it. So that puts me in 170 territory ratio wise.
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Charlie
'48 B, '51 CA, '56 WD45 '61 D17, '63 D12, '65 D10 , '68 One-Ninety XTD
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Ed (Ont)
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Posted: 01 Nov 2020 at 2:59pm |
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Great compression and good range from highest to lowest! That must be a good working engine! 😀
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Wispitfiremike
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Posted: 01 Nov 2020 at 7:59pm |
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Most small engine powered equipment are sold with CC's listed now not horsepower as I heard they got sued for not dynoing the listed power. Just dodging the attorneys looking for a buck.
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CTuckerNWIL
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Posted: 01 Nov 2020 at 8:19pm |
DanWi wrote:
Wouldn't it be higher because of the vacuum you create on the intake stroke would pack more air in then just static air pressure therefore giving it a higher reading, also the reason it would be affected by cam timing.
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Drawing in atmospheric pressure by lowering the piston, can't can't build more pressure. When the valve closes, and the piston hits the bottom of the stroke, you can't have any more than atmospheric pressure in the cylinder. 
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steve(ill)
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Posted: 01 Nov 2020 at 10:03pm |
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thats the part i dont understand Charlie.. Seems like no matter what you do with the cam or pistons,, the BEST you could get is Atmosphere x compression ratio ? .... but we know that is not right... somehow you get MORE than atmospheric pressure in the cylinder at BDC.. ... im wondering if multiple cylinders makes the intake manifold have a slight positive pressure ( above atmosphere)...... but i thought it was somewhat negative ?
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steve(ill)
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Posted: 01 Nov 2020 at 10:06pm |
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if a 7.0 compression ratio motor can get 160 psi at TDC, then the "atmospheric pressure" would be 160 / 7 = 22.8 psi ........ but "normal atmosphere" is 14.7 .... or 8 psi lower ?
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plummerscarin
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Posted: 01 Nov 2020 at 10:33pm |
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Well, how bout this:
The air/ fuel charge has momentum entering the cylinder. That momentum continues to fill the cylinder even though the piston has stopped its downward movement. Think multi car pileup on the freeway
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LouSWPA
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Posted: 01 Nov 2020 at 10:42pm |
plummerscarin wrote:
Well, how bout this:
The air/ fuel charge has momentum entering the cylinder. That momentum continues to fill the cylinder even though the piston has stopped its downward movement. Think multi car pileup on the freeway |
You got it! tuned headers, cam timing, etc can create a small supercharging effect. Of course, how significant that is the engines we are discussing here is another question
Edited by LouSWPA - 01 Nov 2020 at 10:45pm
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jaybmiller
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Posted: 02 Nov 2020 at 5:54am |
I've heard that the piston should be big diameter and rings 'thin' to get best power. tossing in say 40 thou over rings into a tired engine reduces power compare to say proper 10 thou rings. hmm... since the leakdown test can show less comp(bad rings,guides), it'd show more maybe with 'thick' oil in the sump ??
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Charlie175
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Posted: 02 Nov 2020 at 6:38am |
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Ram Air induction! :)
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Charlie
'48 B, '51 CA, '56 WD45 '61 D17, '63 D12, '65 D10 , '68 One-Ninety XTD
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