GM Block Mounted Bypass

[garageman402]

Hey, does anyone know the stock bypass rating of the OEM GM oil filter bypass valve? The one Summit has from Allstar (ALL-92000) has an answered question where "LORENS" says 45psi. Seems a little high to me. I have seen the valve become unseated in some vehicles & require replacement, but I'm thinking of just upgrading mine for the hell of it (spring maybe weakened, not sealing as well, etc.). I like the fact the bypass is in the adapter so oil doesn't flow over the dirty side of the filter during bypass.

Edit: Melling has the same adapter (MFA350) at Summit, the Melling Tech answered a question about PSI with 9-11. Is this pretty much what the stock setting is? I think I'd trust Melling over Allstar

Thanks!

 

[clinebarger]

They work off pressure differential.....9-11 PSI sounds right.

 

[PontiacHO]

Go with Melling. They’ve been in the oil pump-pressure business for 100 years.

 

[garageman402]

Go with Melling. They’ve been in the oil pump-pressure business for 100 years.

That's what I was thinking, but brands change over the years, some that were good, are now cheaply made, some that were cheap are now good, or have a better product lines. Melling is $19.95 (9-11 psi), Allstar $15.99. Summit has their brand in 2 versions, one $16.99 (15-17 psi), one $39.99 (14-17psi), & Chevrolet Performance has one, $68.99 with 17-18 bypass pressure. The bypass pressure questions were all answered by "Summit Racing Experts" or "Melling Tech Support". The Allstar question was answered by some random person named "LORENS"

So many brands (& price points), how do you know which is better quality?

 

[garageman402]

I just noticed the filter adapter is mounted with the bypass toward intake hole from the pump, seems like that would divert the flow to one side of the filter? Is this how it came from the factory? Maybe I'll flip it around so the oil flows across the whole filter. This is my '71 402 that has had a lot of work done before I owned it.

 

[ZeeOSix]

Edit: Melling has the same adapter (MFA350) at Summit, the Melling Tech answered a question about PSI with 9-11. Is this pretty much what the stock setting is?

The stock filter bypass valve (in the filter mount/oil pan) in my 2002 Z06 was 11 PSI. A fellow Vette board member did some actual measurements on one, and came up with 11 PSI when fully open. Cracked open a bit sooner than that, so that's probably what the 9 PSI in the "9-11 PSI" range spec is referring to.

 

[ZeeOSix]

I just noticed the filter adapter is mounted with the bypass toward intake hole from the pump, seems like that would divert the flow to one side of the filter? Is this how it came from the factory? Maybe I'll flip it around so the oil flows across the whole filter. This is my '71 402 that has had a lot of work done before I owned it.

The filter bypass valve is simply a check valve. It just flows oil around the filter when it opens due to too much dP across the oil filter. If it's put in backwards, it's not going to flow since a check valve is designed to only flow in one direction.

 

[garageman402]

The filter bypass valve is simply a check valve. It just flows oil around the filter when it opens due to too much dP across the oil filter. If it's put in backwards, it's not going to flow since a check valve is designed to only flow in one direction.

I didn’t phrase the question right. I meant turn the adapter 180°. The oil inlet hole from the pump comes from the block side of the mount, the bypass valve bulge is also mounted facing the same way. If I spun it 180° so the bulge is on the outside side, would oil coming from the pump flow more freely across the filter baseplate?

 

[garageman402]

The filter bypass valve is simply a check valve. It just flows oil around the filter when it opens due to too much dP across the oil filter. If it's put in backwards, it's not going to flow since a check valve is designed to only flow in one direction.

Here are some pics to illustrate what I mean. If I moved the adapter 180º the oil inflow would be less obstructed by the bulge. Is this how the factory installed it, or has this been altered?

 

[garageman402]

Another question: Gasket or no gasket? Some replacements come with gaskets, some without, saying they're not needed.

 

[Snagglefoot]

So which engines is this thread about?

 

[Fair enough]

I had to look up 1971 402, its something I havent seen before, but also don’t remember the filter mount on my 1971 Chev G30 with 350.
It looks like yours the filter inlet is on the block casting at the bottom, and the hole on the adapter contains a bypass to route the oil back to the filter outlet pipe. Maybe the whole adapter with the two bolts is the bypass valve? They sell them I looked it up on Rock.

It is the same engine as a 396 but larger. The adapter is tne bypass valve, saw the back of it on Rock. The oil would flow back through the filter outlet pipe inthe inside of the adapter. I would think it needs a gasket 100% because that separates the in from the out flow.

https://www.rockauto.com/en/moreinfo.php?pk=8311328&cc=1028124&pt=14022&jsn=8

 

[Snagglefoot]

I had to look up 1971 402, its something I havent seen before, but also don’t remember the filter mount on my 1971 Chev G30 with 350.
It looks like yours the filter inlet is on the block casting at the bottom, and the hole on the adapter contains a bypass to route the oil back to the filter outlet pipe. Maybe the whole adapter with the two bolts is the bypass valve? They sell them I looked it up on Rock.

The 402 is a big block Chevy engine that was commonly used in pickups. It specs a PH30 filter and if a person checks the Fram filter site, it says the filter itself has no bypass feature, instead relying on the mechanical bypass attached to the block. A neat stroll down memory lane. I vote for the Melling unit.

 

[marc1]

Here is my $.02 from my BBC days (1970 Chevelle SS454 LS6 and a crate LS7 (Mark IV)):

1 - Orientation of the adapter... from the factory the bypass valve was orientated towards the block. Many people have suggested this shrouds the oil flow into the port that is immediately adjacent and so they flip the adapter around. Personally, on both my engines, the original LS6 and the crate LS7 I stuck with the factory orientation. I have never personally seen any data or testing to show one way is better than the other. I think that would be an interesting experiment and I'd like to see it one day. All my BBC motors lived using the factory orientation but I certainly would be open to trying the other way if there was some data on that.

2 - When I was into racing my cars (and was much younger), I blocked the bypass. You tap the hole and screw in a pipe thread plug. This was recommended to me by my machine shop of that time. The pro for doing this is you never have to worry about that fibre flat disc lifting off the seat exposing the engine to unfiltered oil, albeit not much. The spring tension behind it is so variable from manufacturing differences, brands (Melling vs GM etc.) etc. that you honestly don't really know what the dP valve is for that disc to lift. As you have seen in your travels to buy an adapter, there are various numbers floating around. I've seen 9 to 18. The cons are i) if your filter plugs, no oil will get to the engine. This filter plug was never going to happen to my cars but GM had to do this for the cars that aren't maintained and ii) you also need to be concerned about cold oil and high pressure... without this bypass in place you can burst the oil filter can if you have excessive pressure across the filter pleats. This also was a concern for GM making reliable cars, people using heavy oil in the winter and flooring it cold. My old muscle car engines are always Xw30 or Xw40 (max) engines with reasonable oil pressures and I don't get on them until they are hot so that also was not a concern for me. Burst pressures on oil filters, to me at least, seem way higher than the maximum pressure that could be attained across the pleats with a reasonable oiling system... nevertheless it is possible to pop a weak filter and I have seen popped filters in my lifetime and sometimes a filter gasket blowout. The last configuration I used on my Chevelle was blocked and I didn't worry. Today I'd probably not do this mod as I really like to stick to factory and I advise caution anytime you deviate from the factory system. Just so anyone reading this thread is clear, this is the filter bypass system not the oil pressure relief system, that is a completely different oiling sub-system.

3 - The gasket question... from the factory no gasket was used. I have seen that gasket provided in gasket kits. I have never used it. The theory (various machine shop opinions and mine) being there is risk of gasket debris getting into the engine for essentially no benefit, the mating between the raw adapter and the raw block is excellent.

 

[ZeeOSix]

Here are some pics to illustrate what I mean. If I moved the adapter 180º the oil inflow would be less obstructed by the bulge. Is this how the factory installed it, or has this been altered?

View attachment 307522View attachment 307523View attachment 307524

The "bulge" isn't going to matter to the oil flow - PD oil pump and the budge won't cause any change in flow. Install it like it was originally. Can it actually be installed 180 deg, or are the holes offset slightly to make it install only one way?

 

[ZeeOSix]

Another question: Gasket or no gasket? Some replacements come with gaskets, some without, saying they're not needed.

I'd run the gasket ... why not. If one is included then it must be there for a reason. Was there a gasket when you took it apart? If there's no gasket there actually could be a slight dirty oil leak if the metal-to-metal interface isn't perfect.

 

[ZeeOSix]

... without this bypass in place you can burst the oil filter can if you have excessive pressure across the filter pleats.

I don't think the can would burst because the oil pump still has a pressure regulator in play - and that's what determines the max pressure seen inside the oil filter. The dP across the media is something separate from that. However, if there was no filter bypass valve then the dP across the filter could bet pretty high and damage the filter media (tear and/or collapse it), and the center tube could also collapse ("implode") if it's not very strong.

 

[marc1]

I don't think the can would burst because the oil pump still has a pressure regulator in play - and that's what determines the max pressure seen inside the oil filter. The dP across the media is something separate from that. However, if there was no filter bypass valve then the dP across the filter could bet pretty high and damage the filter media (tear and/or collapse it), and the center tube could also collapse ("implode") if it's not very strong.

Agreed, that is more of a concern than the can itself.

 

[marc1]

Can it actually be installed 180 deg, or are the holes offset slightly to make it install only one way?

There is no offset, you can install it either way. I always went factory orientation for myself.

 

[garageman402]

1 - Orientation of the adapter... from the factory the bypass valve was orientated towards the block. Many people have suggested this shrouds the oil flow into the port that is immediately adjacent and so they flip the adapter around. Personally, on both my engines, the original LS6 and the crate LS7 I stuck with the factory orientation. I have never personally seen any data or testing to show one way is better than the other. I think that would be an interesting experiment and I'd like to see it one day. All my BBC motors lived using the factory orientation but I certainly would be open to trying the other way if there was some data on that.

Thank you, that answers that question, it is that way from the factory. Maybe the bulge creates a flow in a circular motion? I'll stick with that!

2 - When I was into racing my cars (and was much younger), I blocked the bypass. You tap the hole and screw in a pipe thread plug. This was recommended to me by my machine shop of that time. The pro for doing this is you never have to worry about that fibre flat disc lifting off the seat exposing the engine to unfiltered oil, albeit not much. The spring tension behind it is so variable from manufacturing differences, brands (Melling vs GM etc.) etc. that you honestly don't really know what the dP valve is for that disc to lift. As you have seen in your travels to buy an adapter, there are various numbers floating around. I've seen 9 to 18. The cons are i) if your filter plugs, no oil will get to the engine. This filter plug was never going to happen to my cars but GM had to do this for the cars that aren't maintained and ii) you also need to be concerned about cold oil and high pressure... without this bypass in place you can burst the oil filter can if you have excessive pressure across the filter pleats. This also was a concern for GM making reliable cars, people using heavy oil in the winter and flooring it cold. My old muscle car engines are always Xw30 or Xw40 (max) engines with reasonable oil pressures and I don't get on them until they are hot so that also was not a concern for me. Burst pressures on oil filters, to me at least, seem way higher than the maximum pressure that could be attained across the pleats with a reasonable oiling system... nevertheless it is possible to pop a weak filter and I have seen popped filters in my lifetime and sometimes a filter gasket blowout. The last configuration I used on my Chevelle was blocked and I didn't worry. Today I'd probably not do this mod as I really like to stick to factory and I advise caution anytime you deviate from the factory system. Just so anyone reading this thread is clear, this is the filter bypass system not the oil pressure relief system, that is a completely different oiling sub-system.

Did you ever look inside the filter after running it with the bypass blocked? Just wondering if you saw any core collapse? Ya, I've seen the kits offered that do not have the bypass, I would probably never have a problem, but then, stuff happens!! Have you heard of these losing spring pressure over time, or the sealing face hardening & losing sealing ability? My concern is that my (possibly) 54 year old bypass is constantly bypassing. lol. It still seems to have spring pressure, but hard to tell how much. I didn't realize the rabbit hole I was going down with this, but I'm thinking the Chevrolet Performance item with the 17-18 psi opening pressure would be the most reliable. Amazon has a slew of no name $15 items, along with Summit having a couple.

3 - The gasket question... from the factory no gasket was used. I have seen that gasket provided in gasket kits. I have never used it. The theory (various machine shop opinions and mine) being there is risk of gasket debris getting into the engine for essentially no benefit, the mating between the raw adapter and the raw block is excellent.

Funny enough, the Chevrolet Performance item comes with a gasket, but no bolts, they are available separately. I think I'd have to look at the surface of both items to see if it really needs a gasket, but just think if my 54 year old engine had a gasket there, how it would look now. I haven't taken it out yet, but I don't see any evidence of one there.