1975 20R Missing Oil Galley in Timing Chain Cover?!?! - YotaTech Forums



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1975 20R Missing Oil Galley in Timing Chain Cover?!?!

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Old 04-10-2018, 07:39 PM   #1  
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1975 20R Missing Oil Galley in Timing Chain Cover?!?!

I'm finding nothing online about this issue, hoping someone can help solve it. I posted earlier about blowing oil filter gaskets due to high oil pressure in my 1975 20R. Today I pulled the pump and found something really bizzare.

The oil pressure bypass 'plug' or plunger or whatever you want to call it seems fine but there is no connection between the oil pressure bypass galley and the block - the oil galley is not there on my timing chain cover which the pump seals against. When I look online at aftermarket timing chain covers they clearly have this oil galley that I don't have, which would connect to the high pressure bypass galley on my aftermarket oil pump. As far as I know the timing chain cover is original to my 1975 20R block but I don't know for sure. The oil pump is new, I replaced it. It's a 'Rock' 20090815 0P900' which came in a complete engnbldr rebuild kit for the 1975 20R.

Here is my oil pump. The small galley between the larger galleys on the right side of the photo is where excess oil pressure should 'spill off' when the pressure is high enough to push open the very simple spring-loaded bypass valve. That valve is on the right side of the photo, you can almost make out the plunger inside that oil galley (it's in the closed position, obviously) and the brass bolt/cap on top is what holds in the spring.



Here is where that pump mates to the timing chain cover. Note how there is no galley which connects to where excess oil pressure should be spilling out!


Now look at this timing chain cover from LCE performance which is the aftermarket part for my 1975 20R (https://www.lceperformance.com/20R-2...-p/1015009.htm) It clearly has a galley which would connect to the galley in my oil pump.



Was there an 'early' 1975 timing chain cover and oil pump with a different oil bypass? Unfortunately I didn't save the original pump from my rebuild so I have nothing to compare to.

In ALL OTHER RESPECTS from this missing oil galley the timing chain cover and oil pump I have look exactly the same as the 20R parts I can find online on lceperformance and enginetech. I've been running the truck like this for years, the only issue seems to be that I have to let the oil warm up before revving the engine or my oil pressure goes off the charts. Once the oil is warm the pressure is high but maneagable, I get 60-70 psi max when highway driving. The truck runs fine except if the oil is cold and I rev it too hard which blows the gasket on the oil filter and dumps all my oil out...

If someone has a timing chain cover from a 20R, can you look at it for me and describe exactly what is going on with that small oil galley that is located between the larger high and low pressure oil galleys where the oil pump bolts on? That is the one which is missing on my engine. I'm wondering if it's just a drilled hole that I could drill myself, in the photos it looks too clean to be a cast galley.
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Old 04-11-2018, 04:35 PM   #2  
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Was there a problem with the oil pump before you removed the cover etc?
Edit: Sorry just saw the reason. So . . .
Is this truck/engine new to you or have you had it for a while?

Last edited by L5wolvesf; 04-11-2018 at 04:36 PM.
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Old 04-11-2018, 09:23 PM   #3  
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Originally Posted by L5wolvesf View Post
Was there a problem with the oil pump before you removed the cover etc?
Edit: Sorry just saw the reason. So . . .
Is this truck/engine new to you or have you had it for a while?
I've been driving it like this for years actually just now finally dealing with it. I called 22re engineering and lceperformance today, the guy at lceperformance had heard of this one other time but not seen it. 22re guy pulled out a tc cover for me and confirmed that the high pressure bypass 'galley' is just an 8mm hole drilled thru the tc cover so I'm going to drill it out tomorrow and I imagine that will fix the problem. Very curious how this happened though. I don't think it was doing this before I rebuilt it with the same tc cover and a new oil pump. The only things I can think of are that the old oil pump was so worn that it couldn't build enough pressure and the missing galley is a mistake (could be an aftermarket tc cover) or that the truck had a weird tc cover/oil pump from a 'first few engines' era in early 75 or maybe it came from some other motor that wouldn't need a high pressure bypass like a forklift (lce engineering guy's idea).
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Old 04-15-2018, 07:55 PM   #4  
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Did you ever figure it out?
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Old 04-16-2018, 06:00 AM   #5  
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Yeah I was going to post something but I've been real busy. I did pull the timing cover and drill it out and it fixed the problem, oil pressure is now back in normal ranges. The timing cover did not look original to the truck and the casting itself had a fin on the backside exactly where I drilled the oil galley which makes me think it wasn't designed to have the galley. Also I talked to the previous owner and he never had this issue (before I rebuilt the engine and replaced the oil pump), I think maybe there were some early '75 20Rs that had a pressure relief built into the pump without a separate oil galley.

Anyway it's a pain to pull the tc cover but the fix itself is very easy if anyone else ever has this problem. After I pulled the tc cover I wiped some prussian blue around the oil galley on the oil pump and stuck it back on which showed me exactly where to drill, then I center-punched and drilled a 5/16 (8mm) hole (if you don't have prussian blue on hand I've found powdered chalk from a chalk line mixed with a few drops of water works pretty well). I tried to pull and replace the tc cover without pulling the oil pan. I've been told it's doable but it didn't work for me, I had leaks and had to redo it. To pull the oil pan you need to pop off one of the steering components so you can drop the drag link enough to wiggle the pan out. The easiest way to do it is to take the castle nut off the side of the pitman arm that connects to the truck and slide it off (passenger side of the truck, mounted to the frame). This avoids having to hammer on anything with a pickle fork and bust up the boots.

Still very curious if anyone has info on this weird problem, even the guys at lc engineering and 22re performance hadn't run into it.
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Old 04-16-2018, 05:34 PM   #6  
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Wasn't the 20r used in forklifts and such too? Wonder if that plays into it?
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