IH 300U oil pressure

pwyld

Member
Hello All. About a week ago I was bush hogging with my IH 300U tractor when I notice I was losing power. I didn't have enough power to start the bush hog from a stand still. I looked at my gages and notice I had significantly dropped in oil pressure. I immediately drove the tractor back to my shop and shut it off. I did not seize the engine, but decided to pull the oil pump and examine it...according to the shop manual. Getting the oil pan off was a task in itself. I'll save that story for another day. I checked compression on each cylinder and got ~155 psi for all of them.
Now I have the oil pump off (se photo). I want to check it out if it is working correctly before I put it back in. There was a .004 thick gasket (#5 fig IH620-s ee photo). The gasket is suppose to be for the end play for the gears according to the manual (para 66A - see photo). I'm a little confuse with the diametral clearance they mention in the shop manual. I heard it for bearings but not for gears. I assume it's a term back in the 1950's that I'm not familiar with. Maybe they mean center distance variation...a more common term used in gear design today. I have no idea.
Anyway, I don't want to put the gear pump back on without somehow testing it first. I thought about making a fixture for it and driving it with my milling machine to test it out. Unfortunately, I have no clue what would constitute an acceptable working oil pump. I guess splattering oil all over my shop would be some kind of evidence the oil pump is working, but not exactly the way I would like to do it. What rpm should I turn it at. I can control it to whatever rpm I need, but then again, how much oil should be pumped out. Are we talking gpm, in^3/min or ft^3/min. There are no specs I can find.



I know I probably have the capability to fix it...even if I have to machine a new gear or part for it. However, my problem is I'm not a mechanic, so I don't know exactly what I should be looking for to fix.
Any help would be greatly appreciated.
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Check if the bottom plate is grooved where the
gears have been turning.

Since you have a mill, you can true up [flat]
the bottom plate & then assemble the pump.
Then check end play on the drive shaft.

Pressure on the pump is probably more important
than volume output right now.
Jim
 
I would think,if the oil pressure dropped suddenly,that the pump gears,or its body, would not be at fault.Maybe a gear slipping on the shaft,due to a sheared drive pin,or the oil pick up tube getting stopped up,or even a stopped up oil filter.Also,check the oil pressure regulator-maybe the spring broke.Also I
would pull the rod caps off-at least one-and check the bearing.
Another thought,was the engine running so bad, running at so low of an rpm,that it had idle oil pressure,instead of higher rpm oil pressure?Was it starving for fuel maybe?Good luck.Mark
 
Just FYI a plugged oil filter on that engine will not cause a loss of oil pressure. It would in theory raise it. That engine has a bypass type oil filter that only allows a metered portion of the pressurized oil to go through the filter and return to the pan. Most if not all early IH/ Farmalls through the 450 model were designed this way. Unlike most modern engines with "full flow" filter systems.
 
Thanks for the suggestions. I already replaced the oil filter about a month ago, so I don't think that is the problem. The engine was running fine when this happened. No low rpms. Plus my tractor does not starve for fuel. It's actually a gasoline guzzler. That problem for another day.

The base plate of the oil pump looks okay to me (see pic - base). I checked it out on a surface plate and its flat. If I need to resurface it I would do it on my surface grinder and not on the mill. A mill won't give you as good as a finish within .0001 accuracy like a surface grinder would.

The spring looks good. Its not broken The gears don't look worn or have damaged teeth. The gears do have an .0008 backlash which is +.002 above what the spec calls for. I don't see that +.002 would be the problem (see pic).

The end play from the base plate surface to the gears is .0005, which will require me to get a gasket ~.004 thick to keep it in spec (spec: .003 to .006).

I don't think the shear pin is broken. I still can drive the gears when I put some resistance on them.

Mark...I'm not following you with "pull the rod caps off-at least one-and check the bearing". Are you referring to the drive shaft on the oil pump? I fired compressed air through the pump and it doesn't seem to be clogged.

I'm starting to think I'm going down the wrong road. I can't find anything that would indicate the oil pump is bad.


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Pwyld,what I meant was checking the rod bearings-that is the crankshaft connecting rods.That was to check for damage due to low oil pressure.Also,you seem to be contradicting yourself-in your first post you said the tractor was running bad,and lost power,and so you looked at the oil pressure gauge which was reading low,and in this post you say it was running good.A 300u does use a lot of gas,2-3 gal an hr working hard.But if it started running bad,maybe it suddenly lost fuel flow.You said it did not have enough power to run the PTO,so was it making any strange noises,or sound like something was straining?Would the engine still rev up to high rpm when the problem occurred?Did it have power with the PTO off but not on?If it did indeed rev up,but would not make oil pressure,then you could have an internal pressure leak,or oil starvation to the pump,but your pump looks fine.If it would not rev up,maybe that it is what you need to look at first=low rpm/hot oil is lower pressure than full rpm pressure.
From what I see,your oil pump looks fine;your checks are all close enough that it would not have made a sudden loss of pressure.By the way-was your pump gasket intact?Let us know what you find.Mark
 
Hey Mark. Maybe I didn't articulate my words well enough. What I meant was the engine seemed to run fine during idle...before I notice the low oil pressure. It was only when I engaged my bush hog and released the clutch that's when I lost power and then look at my gages. It was then it would stall out. If I didn't engage my bush hog the engine seemed to run fine with no load on it. I was able to drive it back to my shop.

If I pulled on the throttle while in idle it would rev up, but I didn't engage my bush hog in that mode, since I didn't want a quick jolt on the bush hog or tractor. I haven't had this problem before, so I'm assuming there is something wrong.

I was always leery about my carburetor, so now you're making me wonder about my fuel system. Since it ate so much gas, I never consider a shortage of fuel. Not sure how that can be when it's a hog.

I didn't think of looking at the crankshaft. Thanks for clarifying that. I'll read more on that in my shop manual.

No...unfortunately my gasket is not in tact. I'll have to find a new one. I thought of using brass shim stock that I have laying around (I got from .001 to .002 thickness shim stock), but I'm not sure if that would be a good idea. I can easily get the tolerance using it, but I'm thinking I probably should just buy one at KIO auto. How much can it cost...lol
 
I would echo what Mark R has replied, check the con rod bearings. I doubt you will find serious damage but possible. Those engines will run with minimal oil pressure. The gauge may slightly move the needle at idle and barely come up above the minimum mark on the low scale of the gauge at full throttle and it will still run fine. It is good to see you have a manual, after you get it back together I would look at the section on the mechanical advance in the ignition distributor and determine if that is functioning properly as in not stuck.
 
What I meant about the pump gasket-was-was it ok before you took it apart?And was the oil pressure ok when/while you drove back to your shop?And was it only low when you put the load/PTO on? You may even have a PTO problem if that is the only time it loses power.Or the bushhog gearbox is seizing up.
I think I would probably put a new gasket on the pump and reassemble it,and start over.Mark
 
Ultimately, the low oil pressure has NOTHING to do with the lack of power. They are two separate issues.

155 PSI sounds unusually high and consistent for compression, unless the engine was recently rebuilt to professional tractor pulling standards. Are you sure you checked it correctly?

If you indeed have 155PSI of compression across the board you've got a fuel or ignition problem. Your perception about how much gas it uses (i.e. your comment about "gas guzzler") is not relevant to whether it is getting enough gas to run properly.
 
BarnyardEngineering...I used a compression gage and they all came within +/- 5 psi. I was told the engine was rebuilt and looking at the cylinder walls from underneath the oil pan location I don't see any real scratches or marks if that says something.
 
Hey Mark...I really can't tell you about the gasket. It seems to break off in flakes when I removed the base plate. When that happened I just took a razor knife and removed the rest off.

The oil pressure gage still was running very low when I drove it back to my shop. I was actually concerned about it, since I was expecting the engine to seize up and then I would have a real problem on my hands. However, it seemed to run okay, even with the gage reading very low.

I am agreeing to put the oil pump back on try what you mentioned in your last reply.
 
Well since the oil pressure was low,and the engine was achieving higher RPMs,then maybe you do have an oil problem.There could be some sort of leak,in the pressure side.Also maybe try another manual gauge to check the oil pressure.Make sure there are no restrictions in the oil pick up tube,or its screen.Another poster said a restricted oil filter would not lower oil pressure due to the oil flow set up,but change it anyway since you're changing the oil.Was the oil ok,or did it smell like gas,or was it over full,or, way under full?Diluted oil could lower the pressure.
But,unless the pump drive failed,or it lost oil supply,the pump just would not suddenly drop pressure.Keep us posted.Mark
 
It isn't necessarily something "sudden."

The loss of power caused him to look at the gauges, which is likely not something he normally does. The oil pressure could have been low for some time.

BTW, 1PSI for every 10 cubic inches is what I have been told as a rule of thumb for bare minimum oil pressure. If you were getting at least 16PSI at idle, you weren't harming anything.

Unfortunately, low oil pressure is almost never the oil pump. It's generally the more expensive alternative. The pump is the easy cheap thing to try, and should be rebuilt/replaced during an engine overhaul anyway, so you're not out anything trying.
 
To get diametral clearance First you have to get diametral pitch.
Heres a link http://commercialgear.com/pdf/Diametral-Pitch-Spur-Gears.pdf
 
Mark...I blew compressed air through the oil pump and it did not appear to have a stoppage. I think there is another tube according to my shop manual that may be clog. I'll need to look at that. Was that the one you were thinking of?

Barnyardengineering...you're right. I normally don't look at the gages when I'm running my tractor. Also, I did not run the tractor at idle when I did my compression test. I already had the oil pump out. What I did was bump the engine a few times per cylinder until the compression gage reading did not increase anymore.

Bhunt...yes I have heard of just "clearance". It is different for different pressure angle gears.
 
Diametral clearance in this case is measured from the tip of the spur gears to the inside edge of the oil pump casing this is a criticial area along with the endplay gap from top of the gears to the bottom of the pump cover this should be covered in your book with a specific tolerance for each.

Best of luck Byron
 
Well,I guess your usual oil pressure may be unknown,so where did it read when it was 'low'?
Has this engine been apart before? Maybe a blob of silicone,if any was used,could be blocking a passage/oil galley.I've seen it happen.Silicone is great stuff when used sparingly.Use your blow gun and try to blow thru the engine passage from the oil pump.Be careful-oil will spray every which way-mostly in your face.Oil should go to the cam and crank first.How did your rod bearing(s) look?
You may want to start a new post so we can follow along better.Mark
 
Bryon...that makes sense to me now. I don't know why I didn't think it was supposed to be the clearance between the housing and gears. I do have the specs on it and I will measure it now. Thanks.

Mark...I've replaced all the gages with an OEM equivalent (made in India). I was told by the second owner the engine was rebuilt. I had never taken it apart...guess I'll have to roll up my sleeves.

I'll try you idea of using compressed air to clean out through the engine passage. Thanks for the warning on the oil spry...guess I'll have to roll down my sleeves.

I'll have to take a pic of my rod bearings. I really don't remember what they looked like. I want to say okay, but it's been a while since I crawled under the tractor to look at them.
 

Yea I thought you said something about fabricating the gears new that's why I gave you the link.
Anyway looks like you got a lot of checks to do best of luck
Byron
 
Thanks Bryon. I did check the diametral clearance last night when I got home. The spec calls out for a clearance of .005 to .008.

Using a feeler gauge I got .010 max on the driver side (see pic with arrow). The driven side was well within spec (between .006 and .007).

Again, not being a tractor guy or engine guy is .002 out really going to make that much of a difference? I've worked with a lot of engineering drawings and in my experience how found that a lot of tight tolerances called out are usually unnecessary.

I'll give you a quick example. I have a buddy that I recently re-bored out a Sea-Doo engine block. He wanted the block bored out to the size for a new pair of aluminum pistons he bought. The spec with the pistons called out a clearance of .0040 to .0045 for a Sea-Doo.

However, when I measured the pistons I found that they themselves we out of out of round by about .013. There was no way, unless I machined the pistons, that I could keep that clearance all around with a tolerance of .0005. Make a long story short he said just use the largest diameter as my reference.

Hence, I wonder if .002 out makes that much of a difference with the gear pump. Maybe someone out there knows.

Bottom line, I don't want to put the pump back in until I'm very confident that its working fine. It was a real pain to take the oil pain off. There's a threaded screw just under the front stay rod, which was pretty much almost impossible to take off. You can't get a tool in that spot (see pic - with oil pan off). I'm not really sure how I'm going to get it back on again. I'll meet that challenge when I put the pump back in.

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Pwyld, when you do put it back together, if the oil pressure is still low, try a manual gauge(a test Gauge) and read it where the line comes out by the oil filter. I have a 300u that was my Dad's,been driving it since I was very little, and it always carried about 60# at high idle, and 30# at low idle. It has 7500+ hrs now, and 1 overhaul; oil changed about every 100 hrs.Remember pressure drops off a bit as the oil warms up.Mark
 
This is my personal opinion NOT an expert opinion I've never heard of an oil pump diametral clearance .002 out ever being enough to make a huge difference like you describe. On a personal note I have the same .002 diametral clearance tolerance issue as you on a different tractor similar pump and it had text book oil pressure.
The cover to gear tolerance yea its probably more critical.

Best of luck with it Byron
 
Bryon...I tend to agree with you. I don't think .002 out of spec is going to make that much of a difference for

As far as for the end play clearance (cover plate), well the pump gears are helical (see pic), which means there is an axial load on them. Measuring the driver gear I found it to project out .0342. The only thing keeping this gear from rubbing and scarring the base plate is the film thickness of the oil. For the driven side the pump gear is an idler and centers on a fixed pin.

Since these gears have to be opposite hands of each other, the driver will be pushed to the base plate and the driven will be pushed up into the housing. So much for keeping a spec of .003 to .006 base clearance.
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I think I remember somewhere some pumps you can shim the drive gear that is on the bottom at the camshaft and that will not allow it to creep up on ya that is If I understand you right.

Any way best of luck Byron
 
Hey Bryon...you're right. I can do that, but the original piece didn't have one which I'm assuming was not part of the original design. Anyway, I just was pointing out in my opinion that although there might be specific specifications called out you have to wonder sometimes if they are really true.

I had an engine guy come over who is a friend of a friend of mine who rebuilds tractors. He's telling me it's probably my main bearings, or something like that that's causing the problem.

In any event we made a deal on fixing it. He's going to tear down the engine and I'm going to do all the machining that is needed to rebuild it again. He's got the room and space, which I don't have, and I got the tools and machinery which he doesn't have.

As you might expect this might be a long project, since look how long it took me to just examine just the oil pump. The fall and winter are just around the corner here in Kentucky. My mind is now shifting to beer, pig roasts, firewood, hard cider, fishing, and hunting. The plan now is to have this tractor up and running by next spring, if I survive...lol.

Anyway, I want to thank everyone for their comments, suggestions and recommendations. I'll definitely will start a new Post when there's something interesting to talk about.

Thanks to everyone!!
 
(quoted from post at 00:42:18 08/23/16) Hey Bryon...you're right. I can do that, but the original piece didn't have one which I'm assuming was not part of the original design. Anyway, I just was pointing out in my opinion that although there might be specific specifications called out you have to wonder sometimes if they are really true.

I had an engine guy come over who is a friend of a friend of mine who rebuilds tractors. He's telling me it's probably my main bearings, or something like that that's causing the problem.

In any event we made a deal on fixing it. He's going to tear down the engine and I'm going to do all the machining that is needed to rebuild it again. He's got the room and space, which I don't have, and I got the tools and machinery which he doesn't have.

As you might expect this might be a long project, since look how long it took me to just examine just the oil pump. The fall and winter are just around the corner here in Kentucky. My mind is now shifting to beer, pig roasts, firewood, hard cider, fishing, and hunting. The plan now is to have this tractor up and running by next spring, if I survive...lol.

Anyway, I want to thank everyone for their comments, suggestions and recommendations. I'll definitely will start a new Post when there's something interesting to talk about.

Thanks to everyone!!

You know some spec like the pump cover can be a huge problem seen em put to thick of gasket and have to pull it for low oil pressure. Even some of the bearing specs are tight my rod bearings were .004 to .006 S/B ,001 to .003 the recommended tolerance mains .0015 to .002 they were all at .004 and still had textbook oil pressure. Your right about the specs I suppose these tractors are very forgiving through. Just put my new mains back in today there at at .002 now.
Well hunting and fishing is more fun anyway and the tractor still getting done..
Byron
 

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