Rene T
Site Team
soyjer,
You keep using the dimension of 1/3". Do you really mean 3/8"?
You keep using the dimension of 1/3". Do you really mean 3/8"?
Onan generator oil change
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blw2
Well-known member
Only the first few threads carry the load anyway, even with a straight threaded fastener.
Rene T
Site Team
blw2 said:
I beg to differ. On a tapered thread, if the entire male plug is engaged within the threads of the hole, that's perfect. Maximum strength and sealing. On a straight thread like a bolt, to achieve maximum holding power, the threads need to be engaged at least the diameter of the bolt. So if the bolt or plug lets say is a 1/2-20" thread, you need 1/2 thread engagement.
soyjer
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Rene T said:
I just took a closer look and maybe 1/4" is more accurate. The drain plug hole has 3 threads...about 3/16"... that are 360 degrees at the bottom, and then, above that, about 4 threads...about 4/16"....that are the ones that have the cut-outs in them. Assuming that the cutouts extend fully to the bottom of the oil reservoir, then that would mean that about 1/4" of oil would remain left in the oil pan if the cutouts were not there at all, or if a person was using a drain cock or other permanent plug that extended up and blocked the cutouts. If the cutouts are blocked then the only way to get the last 1/4" of oil and crud out would be to use the suction thru the dipstick/fill hole method. I just went ahead today and ordered the new updated drain plug with sealing washer that came standard with 4000 series generators starting with Spec L (mine is a Spec K). As a reward for telling Cummins Onan about the torque spec contradictory information, they are waiving the shipping charges (I didn't call every mom and pop shop, but nobody stocks these parts within 500 miles of me, that I could find...I guess they sell very few of them):
181-0490 Plug, Drain $5.50
181-0489 Washer, Sealing $5.50
Regarding the contradictory published torque values, it would sorta make sense that the old drain plug without a gasket/washer actually required 21 lbs-ft to stop it from leaking, but then around Spec L time it was determined that 21 lbs-ft was too stressful for the aluminum oil base, and so the drain plug was changed to an improved gasket/washer type drain plug (with Spec: L) that was then capable of achieving a good seal with a (less stressful to the oil base) 5-8 lbs-ft. But that still wouldn't explain why the Service manuals specified 5-7 lbs-ft going all the way back to 1997...way pre-Spec L. So where the 21 lbs-ft printed in all of the Operator's manuals for over a decade came from remains a mystery...as does why no one corrected it for over a decade. The contradiction still exists in the latest Operator's manuals (2012 or 2013). They are supposedly going to correct it in any future printings of the Operator's manuals, assuming that the generators involved are still being made, that is.
Rene T
Site Team
soyjer said:
At these prices, you're paying for shipping without knowing it. ;D
:'(
soyjer
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Rene T said:At these prices, you're paying for shipping without knowing it. ;D
Actually, the shipping on the washer alone from Cummins Onan national center would be $20 for 2nd day air which is the cheapest shipping national offers. The plug was available in S. California and they would have charged an additional $4-5 for the plug shipping. The washer shipping might have been cheaper if I lived on the East Coast instead of the West Coast.
Jacks Small Engines has them for less if you have to pay shipping:
WASHER SEALING 1810489 $4.98 $4.98
PLUG DRAIN 1810490 $4.98 $4.98
Estimated Shipping (Lower 48 states): $8.95
http://www.jackssmallengines.com/
Update: I just got an answer from Onan's email tech support:
From: [email protected]
Sent: Wednesday, January 21, 2015 9:05 AM
To: Jerry
Subject: Re: Re: A question for Cummins Power Generation
Dear Jerry,
The operator's manual is correct, 21 lbs ft. I do not know why it say 5-8 lbs ft in the service manual. The only thing I can see is it could be for the oil pipe plug, the plug under the oil dipstick.
Jerry's reply:
OK...what you are saying does make sense, based upon the wording in the manuals themselves:
The Parts manual refers to both plugs as ?Plug, Drain?, whereas the Service manual torque value is listed only for ?Oil Drain Screw?...and ?Screw? sounds somewhat more appropriate for the ?plug? under the dipstick hole that you are referring to. Additionally, in the Service manual, under the ?Oil Capacity*? specification, it is asterisk?d to this note: ?*See Periodic Maintenance in the Operator?s Manual for oil filling instructions.?, which would seem to imply that the Service manual doesn?t address the ?under the engine? oil base drain plug at all, instead referring the reader to the Operator?s manual, which specifies the 21 lbs-ft.
Why the California experienced Onan N. California engineer, and the technician, both told me 5-7 lbs-ft, I don?t understand, because they knew I was talking about the drain plug that is normally used to drain the oil during routine oil changes, which is the one referred to in the Operator?s manuals that specify 21 lbs-ft. They both said that 21 lbs-ft was way too high and stressful for that aluminum oil base.
My personal experience that prompted my phone calls to Cummins Onan was that, at 17 lbs-ft, the head of my drain plug was already ?bottomed out?, and so further tightening would just result in stripped threads or a cracked aluminum oil base. I pretty sure that my plug is the original, because I?ve seen pictures of the original in the original Onan parts bag, and it looks identical (no flange, and about 7/16? of threaded length above the head), and because my generator only has 400 hours on it. When I look up into the drain hole, the threads look pristine, and so does the drain plug, but yes, it?s always possible that during the previous owner?s ownership someone could have gone OVER 21 lbs-ft and damaged the drain hole, and I just can?t detect the damage visually.
In any event, I?ll get the new improved drain plug and sealing washer, and hopefully that will stop the oil leak out of that drain hole, because it employs the sealing washer:
181-0490 Plug, Drain
181-0489 Washer, Sealing
Do you know WHY the old washer/gasket-less drain plug was changed to the new drain plug with sealing washer starting with Spec L? The oil base part number didn?t change. Did other owners also have problems achieving a leak-less seal with the old drain plug?
Jerry
Jerry,
No idea on why the change but that's why we go from one spec to another.
They can change a washer or length of bolt, etc., and it's a new spec letter for the same model.
As for problems with the bottom drain plug\hole, I did not find any history on that part.
blw2
Well-known member
Rene T said:
Well brevity may be the soul of wit, but not always accuracy!
I was too brief..... should have written, "..... most of the load"
In a straight threaded fastener, a great majority of the load is carried by the first thread. A little less by the second..... a little less than that by the 3rd....... I know it's all the same helix, but it progressively carries less load....
This is why in critical applications, a nut should never be re-used in a bolted joint. The screw can be but the first few threads in the nut deform..... this is what I was taught anyway.
A tapered thread is different of course, and is not under the same tensile load, but my guess is that a similar thing happens.
In a theoretical world, sure the tapers would meet perfectly..... I stand corrected!
Rene T
Site Team
blw2 said:
I've always been taught that that if the pitch diameter and the root/minor diameter of the nut threads is the same pitch diameter and the root/minor diameter of the bolt threads, then the load applied will be equal on all the threads at the same time. https://www.google.com/search?q=parts+of+a+threaded+bolt&biw=917&bih=400&tbm=isch&imgil=U3j07EKsGhb-LM%253A%253Bib9Tj-IVcuBLxM%253Bhttp%25253A%25252F%25252Fencyclopedia2.thefreedictionary.com%25252FScrew%2525252BThread&source=iu&pf=m&fir=U3j07EKsGhb-LM%253A%252Cib9Tj-IVcuBLxM%252C_&usg=__-TgRSP5dJmrgHpExBsUTVTl6MWA%3D&ved=0CFIQyjc&ei=z0TAVMyFBeTjsATw-4LYDw#imgdii=U3j07EKsGhb-LM%3A%3Bfzpwxzo2JCQQ7M%3BU3j07EKsGhb-LM%3A&imgrc=U3j07EKsGhb-LM%253A%3Bib9Tj-IVcuBLxM%3Bhttp%253A%252F%252Fimg.tfd.com%252Farchitecture%252Ff0993-03.png%3Bhttp%253A%252F%252Fencyclopedia2.thefreedictionary.com%252FScrew%252BThread%3B200%3B288
blw2
Well-known member
true, but when the screw is loaded, it all deforms
Rene T
Site Team
blw2 said:
True but it deforms equally.
Great discussion Brad. I give up!!! :'(
blw2
Well-known member
check out this page....
https://www.fastenal.com/web/en/77/reuse-of-fasteners
but don't give up. You were correct to point out that this thread is about a tapered thread, which isn't under the same loading.
https://www.fastenal.com/web/en/77/reuse-of-fasteners
but don't give up. You were correct to point out that this thread is about a tapered thread, which isn't under the same loading.
carson
Well-known member
A great debate for Nuts and Screwballs. ;D
soyjer
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Gary RV Roamer said:
When I took a quick look at the above drain plug, I had noticed that it said 1/4"-18 NPT, but, at the time, I was trusting that the specification in the 2010 Onan Parts manual (981-0246) was correct, and it specifies a 1/4"-14 NPT oil drain plug. Not being well versed on NPT specs, I didn't realize that apparently there is no such thing as a 1/4"-14 NPT, and that the Onan Parts manual was simply wrong. The above plug is about the same dimensions as my existing plug, which depends solely upon the tapered thread for a seal, and won't seal at 17 lbs-ft even without having run the engine at all since the oil change, and that's why I want to go with a gasketed plug, which would be easy to find if it wasn't a tapered NPT thread. So to satisfy all of my requirements what I would end up needing is either:
1.) 1/4"-18 NPT drain plug WITH FLANGE AND GASKET, with the threaded part NOT LONGER THAN 5/16" (approx. 6 threads long), AND where the gasket gets compressed at the approximate same time that the NPT threads tighten up (see Rene T's posts regarding that),
OR
2.) Same as above, except longer, and then stack up multiple washers/gaskets until the gaskets get compressed at the approximate same time that the NPT threads tighten up (see Rene T's posts regarding that).
AND I'd be afraid to allow a plug to extend more than about 3/8" into the threaded part of the oil base, because I don't know how far a plug could extend without interfering with the oil dipper that reaches down and splashes oil up for lubrication (no oil pump on these 4000 series generators).
I have ordered Onan's new (with SPEC L) improved plug/sealing washer combination, which is supposed to work on pre-SPEC L generators because the oil base is supposed to be exactly the same (same part number), but I'll post here when I try them out and let everyone know if they work or not:
181-0490 Plug, Drain
181-0489 Washer, Sealing
This whole issue revolves around my reluctance to torque to 21 lbs-ft a brass 1/4"-18 NPT drain plug into an aluminum oil base (especially when it has 1/4" long "cut-outs" in the female threads to allow the oil to drain fully out, which gives me only three 360 degree threads to depend upon). I'm not vastly experienced in aluminum threads, personally, but two Onan engineers and technicians told me that 5-8 lbs-ft sounded like the right torque, and that 21 lbs-ft seemed WAY too high, despite the fact that Onan's email Tech Support is saying that the 21 lbs-ft specified in their Operator's manuals is correct. I'd rather err on the side of caution, rather than end up having to pay a shop to replace my oil base with stripped-out threads or a crack in it. I only wish that Onan had designed the oil base to use a normal NON-tapered thread oil drain plug with gasket, and also that they had designed it such that the threads started and ended BELOW the level of the bottom of the oil base, so that the oil drain "cut-outs" in the threads, which weaken the upper half of hole, wouldn't have been necessary.
Gary RV_Wizard
Site Team
Since you have the only Onan 4k oil plug leak problem that I have encountered in my many years here, I have to wonder if what you really need is a replacement oil pan? Maybe a previous owner did over-torque and damaged the threads or seat? Based on what I have NOT heard from our many members, most people with Onan 4000's just slap the oil plug in and have no worries. Apparently something is wrong with yours...
Rene T
Site Team
Good idea Gary. There may be a minor crack not visible to the naked eye and it may open up when you torque the plug.
WILDEBILL308
Well-known member
May be time to sell the coach and by a different one.
Bill
Bill
Soyjer, I don't have an on an but I have a 5kw Powertech. On the first oil change I replaced the factory plug for a fumoto valve and in over 8,000 hours I have never experienced any leaks. If you can find one to fit your model, it might be a simple solution
soyjer
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Gary RV Roamer said:
What you are saying makes sense. Although the generator and motorhome only had one previous owner, and the generator only has 400 hours on it, it is still quite possible that somebody didn't realize that it was an aluminum oil base (and with cut-outs in the threads, making it further vulnerable to damage from over-tightening) and just cranked the thing too tight. Wouldn't take much to cause the cut-out portion of the hole to spread and then cause cracking in the lower part of the hole where the three 360 degree threads are.
soyjer
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dan680fl said:
Good idea, except...don't know about the 5KW, but the 4K generator oil base is designed with cut-outs in the upper half of the threaded drain hole to enable all of the oil to drain out, so any plug or draincock or Fumoto Valve, etc., must come out during oil draining or about 1/4" of oil will remain in the oil base during oil changes. Odd design.
Rene T
Site Team
soyjer said:
Can you park the motorhome in such a way that the generator will be off level thereby possibly draining more oil?
