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Author Topic: Weird 671 Oil Pressure Readings  (Read 2623 times)
gus
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« on: October 02, 2010, 01:39:49 PM »

On my just-finished 1300 mi trip some interesting things happened.

First, the amount of oil thrown increased by 100-200% which is to say about one gal per 150 mi! This is mostly going out the front main seal as shown by some rags I tied on the stanchions which are only black on the fan side. The oil then drains down the engine cover onto the bumper, a real mess.

This has happened somewhat the five years I've owned the bus, but nothing like now.

The oil press shows around 30psi at 60mph after driving for about an hour or so when the oil is hot and the level is around 1/2 to 1 gallon below full. Before now it always showed 40-50psi.

The really weird part is that when I go through a small town and drive slow it shows 40-50psi when wound up in third gear at about the same rpm as when on the road in 4th at 60mph?? Then when I shift back into 4th and gain speed out of town it drops back to 30psi again?

Also, it does the same thing when I drive around a sharply curved Interstate ramp in 4th at 45-50 mph??

The coolant temp never varies between 165* - 170*F during any of these weird happenings and the engine runs like new.

My first thought is a destroyed front main crank seal and my second is a clogged oil filter cartridge, the original non-spin-on type.

Can this seal and the rear be replaced with the engine in the bus??

I would sincerely appreciate any insight into this mystery by you 671 users.

Thanks
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PD4107-152
PD4104-1274
Ash Flat, AR
Rick 74 MC-8
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« Reply #1 on: October 02, 2010, 02:44:33 PM »

Hard to tell for sure it may be as simple as voltage changes as in a bad ground and grounding Thur the linkage. or check if it drops when you are under hard acceleration. If a DD is like a Gasser The seal leaking maybe from a bad thrust bearing you might be able to check for excessive end play in the crank
I'm sure there will be some experts chime in on how to check for sure

                                                                               Rick 74 MC-8
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Rick59-4104
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« Reply #2 on: October 02, 2010, 03:31:07 PM »

 Hello Gus,
 Not sure of the name of the shop but I have heard one of the best DD shops around is up at Springfield Mo. Maybe someone will chime in with the name of the shop.. I know a member here from Oklahoma recently had some work done there..

Rick
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NW Arkansas
1959 GM 4104  No. 4115
1972 Grumman Kurbmaster Stepvan Conversion
1957 Airstream 13 panel Overlander
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« Reply #3 on: October 02, 2010, 07:35:59 PM »

  Put a mechanical gauge on the engine to verify the electric gauge. There is no other way I know of to verify oil pressure. You can run a line up front from the engine, just purge it of air before attaching the gauge.
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TomC
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« Reply #4 on: October 02, 2010, 09:09:59 PM »

Sounds like you should check your main and rod bearings.  Severe drop in pressure usually indicates this.  Sounds like you're going to be removing the engine anyway to fix the leaks, might as well dip into it to make sure all's OK.  Good Luck, TomC
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gus
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« Reply #5 on: October 03, 2010, 06:43:13 PM »

The reason I call the pressures weird is that they don't stay low, they sometimes show normal pressures as described in my first post??

It has a mechanical gage already installed at the engine, now I need someone to ride back there while underway to read it!

I was hoping Don Fairchild would chime in here because he surely knows if I can replace the main seals in position.
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lostagain
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« Reply #6 on: October 03, 2010, 07:12:32 PM »

Replacing the main and rod bearings, and thrust bearings is not hard to do. Take pan off, then oil pump off. Take a good look at the service manual for the procedure before you dive in.

Replace the front seal while your hands are greasy. You'd have to pull the engine out of the bus to do the rear seal.

JC
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JC
Invermere, BC
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gus
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« Reply #7 on: October 04, 2010, 03:11:31 PM »

JC,

Thanks. From reading a couple of DD manuals it appears the rear seal can be replaced by removing the trans or am I reading it wrong?

The manual also says the oil pan must be removed to remove the front cover, is this true? It appears to me the cover can be removed without removing the pan??

I'm hoping the bearings are ok but if I have to remove the pan I might as well replace the bearings too.

Does the crank have to be turned to remove/replace the front seal, my manuals don't even mention doing this.
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« Reply #8 on: October 04, 2010, 05:45:39 PM »

Rear seal: you have to separate the trans from the engine to get at it. So yes you could just take the tranny out, but it may be awkward. I would wait until you have more reasons to pull the engine and trans as a unit. Once you get to it, you could have it out in a day. You need a dolly to pull the engine onto.

I can't remember if the pan has to be off to remove the front cover. But removing the pan is not a big thing.

Turning the crank is not necessary to replace the seal, but you only need a big socket wrench on the front pulley nut to turn it if you had to.

I find if you study the manual first, then dive in, it is not rocket surgery.

JC
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JC
Invermere, BC
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« Reply #9 on: October 04, 2010, 06:31:28 PM »

Gus if i was doing the rear seal I would pull the tranny not the engine.  You can use an engine hoist for the tranny. Yet another reason to like a V drive.  Sounds like you have a little work to do. Good luck.
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Don Fairchild
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« Reply #10 on: October 05, 2010, 04:05:15 PM »

Gus;

You can get to the front seal buy taking out the radiator. Be sure to use a over size seal and wear ring on the front pully. You want to do the same thing on the rear if you pull the trans to do it. You dont have to drop the pan but if you tear the gasket you will drop the pan and change thegasket any way so why not pull it and get it over with, then as others have said now would be a good tine to drop the oil pump rebuild it and roll in new rod bearings and mains and thrust washers and rebuild the regulator and relief valves.

Hope that helps. You can call me at eight eight eight 473 three six 2 six


Don
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gus
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« Reply #11 on: October 05, 2010, 06:41:18 PM »

I've studied two manuals so far and have another one I'll look at but they are obviously written for mechanics who do this stuff all the time, not for shade-tree mechanics like me!!

At this point my plan is to remove the radiator and front cover and replace the seal only. If I see any sign of bearing play I'll go ahead and replace them also but I'm hoping not to have to do that. The rear can wait until I find out the results of the new front seal. I'm pretty sure the front is the big problem because of the oil all being on that side of the white rags I tied around the stanchion.

Don,

Why would I need an oversize front wear ring if it is replace by a new one? I thought an oversize seal is only used if the old ring is reused? (Isn't this seal actually undersized since the ID is less?) That part of the manual is a little confusing.

I may be using your phone number once I get into this a bit more, thanks.
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PD4104-1274
Ash Flat, AR
Rick59-4104
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« Reply #12 on: October 06, 2010, 02:05:15 AM »

 Gus,
  I am a little over an hour away, I am "shade-tree" myself but I would be willing to come over and be a tool hander and help anyway I can just to get the experience if you need the help. I run a big truck with mail Harrison to Little Rock Sunday PM thru Wednesday nights but am off the last part of the week and thru the weekend.
  I have a DD 671 Manual, I'll see if it is "followable" in the morning.

Rick
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NW Arkansas
1959 GM 4104  No. 4115
1972 Grumman Kurbmaster Stepvan Conversion
1957 Airstream 13 panel Overlander
Don Fairchild
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« Reply #13 on: October 06, 2010, 09:20:28 AM »

Gus;

It's not an over size wear ring it's an oversize seal with a wear ring. Hope that helps. If you can get the seal out with out removing the front cover then you don't have to worry about the pan gasket. I don't always have that luck. Hope you do. Call me if I can be of help.

Don

If you have a lot of hours or miles on that engine I would ask you to rethink the bearing change. We always changed bearings between 100 and 120 thousand miles. We also looked at the rocker arms for wear, changed injectors and did a tune up at the same time. Might be a little more on the front end but will save you big time on the back end.  Remember the fram commercial pay me a little now or pay me a lot later.
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gus
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« Reply #14 on: October 07, 2010, 06:41:25 PM »

Rick,

Thanks, I may take you up on that offer but it will be a while before I tackle it. At my age I could use some muscle!!

Don,

There is a method in one manual of drilling holes into the seal metal, inserting sheet metal screws w/washers and prying it out with a pry bar!! I am dubious of this method but it might be worth a try just to see if it works!! If it doesn't then the cover can be removed. The disadvantage to this method I can see is that it may be very hard to determine the condition of the wear ring. I also thought of using a slide hammer but that might jerk the screws out. It would allow more even pulling though.

I hate to get into bearing and other metal wear. Once you start into that there is no end before serious bucks are spent. If I see any sign of serious crank or bearing wear it would be simpler and cheaper just to buy another good engine since there must be a pile of them around.

When you replaced the valve cover and gasket in April '07 I should have had you inspect the rocker arm wear!! Are you still in Bakersfield?

 I have no idea of the engine mileage. I've put 50K on it in five years so I hesitate to put a whole lot of money into it now considering my age. I probably won't be able to drive it much more than four or five more years. If I park it now I've gotten my money's worth out of it in fun alone!!
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PD4107-152
PD4104-1274
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