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Old 08-28-2021, 06:27 PM   #1
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Engine oil Leak air compressor/hydraulic pump

New engine oil leak between air compressor and the hydraulic pump.

On my 1998 Alpine the air compressor mounts onto the front face of the timing case. There is a separate cast housing about 2 inches thick mounted to the other end of the air compressor. There is a gasket between the compressor and the cast housing. NO leak at that location.

The hydraulic pump is mounted to the other side of the cast housing. There doesn't appear to be a gasket at that interface. That is where the leak is.

It is NOT red hydraulic fluid. The tank is full and no evidence of hydraulic fluid leak.

There is a flat bracket bolted to the cast housing at the bottom front. The other side of the bracket is bolted to the side of the engine block to support the compressor, cast housing, and pump.

While searching for the leak I discovered that 2 of the 3 bolts connecting the cast housing to the engine block were missing. The remaining bolt was still tight.

I replaced the missing bolts and cleaned up the mess. I haven't driven far enough since the repair to determine if the leak is stopped.

I assume the compressor and hydraulic pump are driven by a common shaft and engine oil flows from the timing case through the compressor and into the cast housing in front of it.

I assume the hydraulic pump is lubricated by the ATF fluid it pumps.

The leak is small but it makes a mess on the back of the coach and front of the toad.

Do any of you folks have knowledge or experience with these components and how they are lubricated and sealed.

Thanks for any suggestions.
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Old 08-28-2021, 07:49 PM   #2
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Since you are referencing the engine, please tell us the engine make and size so we too know what you are asking.
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Old 08-28-2021, 08:31 PM   #3
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I had a similar leak on my Cummins C8.3L engine in about 2004. It was at the gear case cover and involved an unseen gasket that was slightly leaking. (Your leak sounds bigger.)

After getting a quote from Cummins West to involve $2,100 of my money to repair said leak, I posted my issue on one of the RV Forums.

I got this reply:

The fix was a small spray can of Permatex Form-A-Seal Leak Repair - NAPA #765-2650 @ about $5.00. I sprayed the area (couldn't even see the leak behind the pump) with brake clean several times (soaked it real good) and then applied the Leak Repair exactly as the directions said by letting it run down the crack from above the leaking area (actually used a watch to make sure the timing was perfect).

I did the above steps on my rig and it worked. The fix still is working about 70,000 miles later and I still carry a can of that stuff.

Might be worth a try for your issue?
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Old 08-28-2021, 09:37 PM   #4
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Quote:
Originally Posted by Ray,IN View Post
Since you are referencing the engine, please tell us the engine make and size so we too know what you are asking.
Ray,
Thank you for the response.
My 1998 Alpine Coach has an 8.3 Cummins- mechanical- no electronic engine control system.

Earlier version of the engine in your coach. But probably with different attachments/equipment- such hydraulic powered engine cooling fan-4 wheel hydraulic disk brakes- no air brakes.

Hoping that some one with identical system has had this issue and will respond.
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Old 11-12-2021, 05:58 PM   #5
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2005 Alpine Coach 400 HP Cummins
The air compressor mounted onto the engine has a plug (similar to an engine block freeze plug) on the bottom. It appears to be a press fit from the inside. Mine has a rust hole in it and it leaks about 1 qt. of engine oil every 1000 miles. Cummins estimates it to be a $3,000 repair. R&R with a new compressor. A friend of mine owns a cement mixing company (thus he has his own mechanics) & this also happened to his coach. His man R&R it with a rebuilt compressor ($750) & 9 hours labor. I have tried everything I can think of to stop the leak without success. There is a constant small oil drip. I called JB Weld & followed their instruction – did not work. Now I have JBW firmly there but the leak is somewhat reduced but because of the oil it did not seal totally – yes I cleaned it – electric wire brush – break cleaner – mixed the JBW until it was warm and pressed it tight & held until my hand just about stuck. Still leaking. I cleaned it all again and sprayed it with Permatex 82099 Spray Sealant (per there instructions) – still leaking. It’s very difficult to get to – laying my back, on the ground and reaching high up to the bottom of the compressor. I was considering grinding off the JBW and drilling & taping the bottom of the compressor – bolting a plate with a thick rubber gasket – but I do not know if the bottom of the compressor casting is thick enough. Cummins won’t discuss it. Well, it’s winter now and I’ll get back to it in March. Maybe the oil drip will have stopped and JBW will work this time – I’ll try that first. I am looking for a magic fix from someone much smarter than myself.
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Old 11-12-2021, 07:07 PM   #6
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There should be a gasket on the hyd. pump mount. You probably can't see it if a piece of it has fallen out. The gear train will pull engine oil up the gears for lubrication of the gears. There is a small oil passage on the compressor side built into the housing the compressor bolts to. It is to supply oil to the compressor crankshaft/connecting rods just like in the engine. The oil leaves the compressor via gravity through a drain hole in the compressor crankcase and the mounting surface. I would try the spray remedy first and see if that works.

tjshively, the problem with trying to stick a sealant to the bottom of the compressor is the oil keeps seeping out. It may not look like it but it is nearly impossible for it not to. Perhaps if you get the jbw off and let it sit all winter it will clean up enough to make it stick.
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Old 11-12-2021, 11:52 PM   #7
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tjshively and David 70

Thank you for your posts to this old thread.
David, you are correct There are 2 flat gaskets in the assembly. After cleaning the oil and accumulated grime off both gaskets are visible. #1 between the compressor and the case extension and #2 between the case extension and the hydraulic pump where the bolts were missing from the support bracket. It is the #2 gasket that is leaking.

After cleaning as much as I could I applied the permatex spray gasket maker around the gasket and let it cure. I drove about 40 miles and found that I still had a small leak in the same area. I zip tied an oil absorbent cloth below the area and towed my jeep about 700 miles over 2 days. The jeep got a few drops of oil on the front but the absorbent cloth appears to be dry- it certainly isn't saturated. That is a huge improvement.

You state that the oil should flow by gravity from the compressor back into the Cummins timing case. I assume that the compressor shaft has seals prevent the oil from leaking out of the case.

Should there be engine oil in the case extension between the 2 gasketed interfaces? Does oil in that space indicate a shaft seal failure? Or is that a design feature?

Thanks for your input.
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Old 11-13-2021, 02:42 PM   #8
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Engine oil Leak air compressor/hydraulic pump

2005 Alpine Coach (purchased new - I'm 1st & only owner)
There are NO flat gaskets to what I described. The leak is NOT between the engine & compressor - it is at the bottom compressor where there is a PLUG similar to a freeze plug in an engine block – but installed from the inside of the compressor – per info from Cummins. To be fixed properly the compressor must be uninstalled and a new plug installed from the inside. Again – per Cummins and they have never done one and don’t know if it is even possible. Cummins will only provide a warranty when installing a new compressor. The plug has a small hole where it rusted through – this is Cincinnati where we have salt on the roads. See attached photo.
Any ideas are apricated. Thanks Guys (or Gals)
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Old 11-14-2021, 12:52 AM   #9
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TJshively,

Can you visit a Holset compressor dealer and examine an unmounted compressor like yours to determine the thickness of the casting? And also determine the thickness of the plug and the clearance between it and any moving parts inside the case.

Since the plug is "replaceable" then you should be able obtain one to examine.

Can you drill and expand the hole to eliminate the rusted metal and then braze a metal plug into the hole? Or screw an expandable rubber plug into it.

There are some very good industrial tapes and epoxy putty plumbing products available that should be able to seal the leak.

I plugged a hole in an engine oil pan with an epoxy putty product several years ago and it never leaked again.

I'll try to find the name tomorrow and post it for you.
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Old 11-23-2021, 07:32 AM   #10
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I have a2002 40' Cummins 400. I also had a drip on the what we will call the freeze plug.
I did get a new plug through the Cummins rep. expensive 125.00 dollars. Got it at CIT in Morton IL. Used a special adhesive went in from outside ended up very easy fix. Pops in just like a freeze plug on an engine. I don't know if I still have the part number or not. Let me know if I can Help.
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