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· Master Story Teller & Fabricator
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Discussion Starter · #4 ·
I posted this thread because I was helping a friend with a fluctuating oil pressure problem and we were discussing how the oil flows in our engines. The conversation shifted to the oil bypass system, which I discovered I knew almost nothing about. I've known about the oil bypass built into some of our oil pump covers, but never really learned what it was there for. What I had no knowledge whatsoever about was that there is a second, primary, oil bypass device in the center of where you screw your oil filter to. Both work the same way by using a spring that presses on a ball that blocks a hole leading to a bypass passageway. The purpose of both is to bypass oil that can't get through a clogged filter, passageways, or other obstruction. They can fail and cause oil pressure to drop if the springs get weak, the ball doesn't seat well, bypass passageways are blocked with crud, etc. We can get rebuild kits for the ones in the oil pump covers, but apparently not for the one at the oil filter. With our engines having 50 years of wear and tear on them, a lot of engines appear to have issues with worn, weak, or gunked up passageways.

There's a mod. Now, I'm not advocating this "mod", I only heard about it yesterday and don't know what adverse issues doing this might cause down the road. The mod is to remove the pressed in cap with the bypass hole and the spring and ball, then tap the remaining opening for a 3/8" plug, and plug off the bypass, thereby disabling it. There is now no oil pass function at the oil filter, but you still have one at the oil pump. Theoretically, you could install the flat type of pump covers with no bypass function built into them and have no oil bypass in the system at all. The negative consequences would be that if your filter clogs oil won't get bypassed back to the crankcase. However, if your bypass springs are weak, or the balls aren't seating or get stuck, your engine can bypass the oil prematurely or all the time. This could be a cause of low or fluctuating oil pressure on some engines.

So, that's what I think I know about all this, so I thought I would share this knowledge with you guys and start a discussion about it.

Start talking.......
 

· Master Story Teller & Fabricator
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Discussion Starter · #5 ·
This post came in from one of our Euro colleagues:
<<< Simo Laakso contributed a good tip about a filter with a bypass built-in. For people like me who DO drive their Opels in the Winter(and use thick oil), this filter with a bypass might be an alternate option: "Valve where you screw the oil filter to is indeed an oil filter bypass valve. That will allow the oil to flow past the filter when it's either too cold and thick to flow thru the filter or the filter is blocked. This allows the oil pressure to the bearings etc to be good even if flow thru the filter is not enough. With light oil and in warm climate you might do fine with it blocked, but definitely not here in the north. However you can disable it and start using an oil filter that has a built in bypass valve! For example classic Volvo filter fits to CIH and has the valve." >>>
 

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1973 Opel GT
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Don’t skimp on the oil filter. Get one from a brand with a good reputation for building oil filters. Most oil filters in have them as a spring below the filter, pushing the filter against the threaded mounting plate. You want oil filters with a backflow check valve.
 

· Master Story Teller & Fabricator
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Discussion Starter · #9 ·
So, which hole or holes do you remove the bypass gizmo from and tap and plug? Both side holes? The recessed one? The not-recessed one? This is the only pic I could find of an unmolested oil filter area, anyone got a better pic?

Sleeve Gesture Font Art Wrist


It's hard to tell from this pic, but it looks like the not-recessed hole has the bypass freeze plug with the hole in it and the spring and ball behind it, as it was described to me, and the recessed hole seems to already have an allen head plug in it. So, the not recessed hole with the flange of metal around it?
 

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I am getting Jason Selby's engine parts ready to take to the machine shop, and I wanted to have the chain case prepped for cleaning and flushing.

I have removed the oil galley expansion plugs (mini-frost plugs) without a problem, and tapped the holes for 3/8" NPT plugs (as well as the smaller plugs in the head lifter/cam oil galley). But I have not removed an oil filter bypass assembly prior to now. Since this engine suffered a near-catastrophic lifter and cam failure, with LOTS of metal shrapnel throughout the engine, I want to ensure all the oil galleys are opened for a thorough cleaning.

The oil filter pressure relief ball sits behind some kind of steel seat, that appears to be pressed in. I tried a #6 reverse thread bolt extractor, and it screwed nicely into the relief ball seat. I thought it might be threaded but it won't (reasonably easily) screw out. I am reluctant to get too rough with trying to pull the seat out. What is the best way to remove it? I see that OGTS sells replacement seats, which seem to be simply expansion plugs with a centre hole, so I should be ok to damage the existing seat. Should I just drill it out? Or just get rough with a puller?
 

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...and to answer (however incorrectly) my own question, I just got the oil filter bypass ball seat out.

I tapped the inside of the seat to M10x1.5. I then made up a simple puller, using an M10 bolt, a couple of heavy washers, and a large (5/8") nut. The seat was sitting a mm or so below the oil filter base, so this apparatus allowed the puller to unseat the seat.

Once it was out a mm, I then threaded the end of my small slide hammer to a corresponding m10x1.5, threaded it in, two pulls, and out popped the seat.

It is likely reusable, if I dressed the ball seat edge. But I will order the replacement seat from OGTS:
So I have an option at reassembly.

As a comment, while I appreciate that the filter bypass may be redundant, I like the idea of a reliable oil filter bypass, should this engine get started on a cold Canadian winter.
 

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So, I see this is an older post, but I don't understand why plugging the oil filter bypass path would help. Or, asked a better way, how would a week spring cause low oil pressure there. Dosent the bypass and the normal route through the filter go to the same gallies? Or, through the filter or not, shouldn't it be the same pressure?
 

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So, I understand that. But dosent it flow to the same path after the filter? So the pressure should be the same if it goes through the filter or not ? The same bearing clearance and all? I have no reason to believe I will have low pressure, but I am a spot that if this works to prevent it, I will plug it. But I am just trying to understand. It seems like it would just allow dirty oil to flow. I think I am missing something simple but just can't see it.
 

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I believe it is often recommended to eliminate it because over time those springs got weak and would allow the bypass to open during regular operation, allowing dirty oil to bypass the oil filter. I could be wrong but I don't think it would cause low oil pressure.
 

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My understanding on my GT is that the relief never goes above 4.25-4.5 bars that’s when the ball in question opens always with a cold engine letting oil bypass the filter. When the engine warms up it seldom goes above 3.5. I’m pretty comfortable assuming that the oil always gets filtered under that 4 bars of oil pressure.

I can see why people block it off to ensure the oil always gets filtered but I don’t believe that this raises the or has any effect to operating oil pressure once warmed up. If it was malfunctioning could it cause the low oil pressure symptom? I’m in agreement with the last two posts, not sure that it would.
 
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