B Oil pressure needle bouncing, dirty inside gauge
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=200419
Printed Date: 15 May 2024 at 7:36pm
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Topic: B Oil pressure needle bouncing, dirty inside gauge
Posted By: resurrection20
Subject: B Oil pressure needle bouncing, dirty inside gauge
Date Posted: 20 Mar 2024 at 2:10pm
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Hi all, me again, See pix for details. Oil level is full (choke still on, lol). I was working my B pretty hard today and I looked down and noticed the oil pressure gauge was bouncing quite a bit. The white backing inside is peeling and turning brown and there seems to be a film on the inside of the glass. After reading quite a few forum posts... seems like it's just a bad gauge. My girl's really being needy lately!  
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Replies:
Posted By: Codger
Date Posted: 20 Mar 2024 at 2:30pm
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Old girls need love too as they say. Most likely a bad gauge with a compromised solder connection internally. That happens and reproduction gauges in both direct reading, or electrical are available to emulate the original(s).
------------- A career built on repairing and improving engineering design deficiencies, shortcomings, and failures over 50 years now. |
Posted By: resurrection20
Date Posted: 20 Mar 2024 at 4:25pm
| After I fired it back up, the needle was behaving. Of course, I don't trust it now. Better order a new one. |
Posted By: PaulB
Date Posted: 20 Mar 2024 at 7:21pm
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That is inherent in the small block oiling systems as they have a 2 vane oil pump which gives a pulsing oil flow. The good quality oil pressure gauges have a very small orifice into the gauge to level this out. Probably your gauge going bad. Don't get worked up over it. I be more concerned about your filter not having the proper restriction to maintain the needed oil pressure to the camshaft and crankshaft. ------------- If it was fun to pull in LOW gear, I could have a John Deere. If you can't make it GO... make it SHINY |
Posted By: Jim2
Date Posted: 22 Mar 2024 at 9:06am
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That's a nice looking piece of equipment for $500 just judging from the sheet-metal. You did alright! Have only run my tractor a few times around the yard but from what I can tell mine stays pegged at maximum while running. Then goes back to that line below "NORMAL" when the engine is off. Was thinking I'd just run it that way. Doesn't have numbers anyway and gives a pretty good indication that it has pressure, which is all a new gauge would show anyway.
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Posted By: resurrection20
Date Posted: 03 Apr 2024 at 2:31pm
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Thanks! It came with a spray rig on the back and 20 gallons of Roundup. If I used Roundup, it would have been a great savings. What I've learned from this forum (experts abound here) is that excessively high pressure can mean your oil filter is plugged up and all the oil is bypassing it. Or that little tube in the middle that shoots the oil into the filter could be clogged or the opening might not be wide enough Someone told me they could get pushed closed. The tube comes up and out to check all the orifices. Neither are the end of the world, but your oil isn't getting cleaned like it should. Or maybe you just have a messed up gauge. 
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Posted By: Jim2
Date Posted: 03 Apr 2024 at 5:28pm
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Will have to have a look at that. Tractor is sitting there with the timing cover and oil pain off right now in an effort to fix leaking front crankshaft seal. Found out when I pulled the oil pan that the screen had fallen out of the strainer and was lying loose in the bottom of the pan. Looked at the filter, but haven't changed it yet. Looks like new from the bottom. Didn't think to check to see if tube is plugged or to examine the orifice. That's a great tip!
We're getting hit with snow here this week. Planning to paint a few things before I button it up again, but will have to wait for better weather. Jim |
Posted By: steve(ill)
Date Posted: 03 Apr 2024 at 10:47pm
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there is a spring loaded ball (relief valve) in the pump that tries to maintain 15 psi going to the filter ( and dumps the rest down the hollow cam shaft)... If you remove the filter or the 1/4 inch tube, you will run too much oil back to the sump and will not be able to maintain the 15 psi setting ( hi idle).... If you PLUG the filter or the 1/4 inch tube then you have NO filtered oil dumping to sump and ALL of the oil is going thru the hollow cam shaft... and it SHOULD be maintained about 15 psi. Now if your motor / pump is worn out and you can only get 10 psi at high idle or have only 2-3 psi at low idle ... then plugging the 1/4 inch line or the filter SHOULD make all the oil go thru the cam and RAISE you pressure.. ( you might get 5-10 psi at idle ??)... but remember, the relief valve is trying to maintain 15 psi. at High idle. ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 03 Apr 2024 at 11:00pm
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Here is a picture of the pump on the back of the hollow cam shaft. you can see the discharge of the pump has the "RELIEF VALVE" that helps maintain 15 psi. Also in the second picture you will see there is a restrictor "PLUNGER" at the FRONT of the cam shaft that plugs most of the hollow cam and allows SOME of the oil to spray thru it onto the front timing gears.. If you take out that plunger, you will also LOOSE pressure in the system.   ------------- Like them all, but love the "B"s. |
Posted By: Jim2
Date Posted: 04 Apr 2024 at 8:35am
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Hate to ask too many questions on resurrection20's thread, but kind of wondering if anyone has thoughts as to what effect my strainer failure might have on oil pressure? I can't remember where, but saw someone else's strainer and it was pretty well plugged up. I'm sure that would impede flow and reduce pressure. Like I said, haven't looked at my filter tube, but seems like it may well be plugged just judging from the way the filter looked and the high reading at the pressure gauge. I'm thinking that I may want to drill a hole in the pickup tube to wire that strainer in place. . . . Anyone else make similar modifications?
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Posted By: steve(ill)
Date Posted: 04 Apr 2024 at 9:33am
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If you have access to a gauge with numbers... i would try that... The "most common" mode of "high pressure reading" is the gauge. ------------- Like them all, but love the "B"s. |
Posted By: Jim2
Date Posted: 04 Apr 2024 at 10:42am
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Don't know that I've got a gauge w/ numbers. If I did, would be doubtful that it would be sensitive enough for these low pressures. Just came back in from another look at filter, base, oil tube, etc. Pulled the 1/4" oil tube out, and it was as clean as a whistle--no dirt or debris of any kind and holes looked good as well. Only question that comes to mind is that the oil filter mounting base is full of oil. Shouldn't that just drain down into the sump? I'm wondering if there could be an obstruction *after* the filter that would be artificially raising my oil pressure? Could just pull it off and try to figure it out, I guess. Have plenty of time, so more inclined to watch some YouTube videos or ask you all rather than get into more trouble by digging into something that really isn't an issue at all. Likely overthinking this, but don't have a wealth of experience to draw on, so. . . . |
Posted By: steve(ill)
Date Posted: 04 Apr 2024 at 1:09pm
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The oil filter housing has a lip before it drains back into the crankcase... If you remove the filter, there will be a PUDDLE of oil about 1/4 inch deep or more in the housing base. If you REALLY have more than 15 psi of pressure, its Possible that someone changed the spring inside the oil pump last time they rebuilt it, with a "will fit".. -------------- In the PICTURE above you see item #12 and 13 are the "RELIEF VALVE".... lets not call it that.. Its more of a PRESSURE SETTING VALVE.. No matter what the valve is adjusted to, the pump puts out a given quantity of oil.. The 1/4 inch tube and orifice and filter are sized so that 15% of the oil goes thru the filter.. The other 85% of the oil goes thru the camshaft... If you TIGHTEN the spring on the "pressure setting valve", then you could get ( lets say 5 or 10) pounds more pressure inside the pump.... but the flow still remains about the same as the FILTER and the HOLLOW CAM always get a portion of the flow.
------------- Like them all, but love the "B"s. |
Posted By: Jim2
Date Posted: 04 Apr 2024 at 2:04pm
Thanks, Steve--that matches what's going on here. Seems like there's nothing to worry about.
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Posted By: resurrection20
Date Posted: 04 Apr 2024 at 2:56pm
Steve(ill) is the best. He's been answering my annoying questions since November!  
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Jim2 wrote: