Engine/Transmission (1994 - 1998) How do you shim the overflow valve?

[ATaylor]

Hi,



I have a 1995 3500 and have replaced the lift pump with a Airdog 150 that has a 40 psi regulator spring. I know that the stock overflow valve is supposed to open at 30 psi. To take advantage of the extra pressure and not have the overflow valve bleeding off 10 psi of pressure all of the time I read that shimming or stretching the overflow valve would help raise the pressure. (I plan on putting in 4k gsk in the near future). I have the overflow valve off the pump and have taken it apart.



How do you shim the overflow valve?



Is shimming the overflow valve better than stretching the overflow valve spring? Or do you need to do both?



Thanks for any help anyone can offer.



Archie Taylor

 

[hsmith]

I've not shimmed, but had to stretch the spring a bit to . 5" Do you need more than 30#?

 

[MLee]

Actual streach should be . 5500 and 30* @ 2000 RPM. Idle should be 18-22*.

Some guys have used a small washer as a shim. Debatable if this is the answer to bring up the PSI of the valve.

 

[WDixon27]

i have stretched mine and the truck likes around 26-28 at idle and 32-34 running but my valve is made up from bits out of mercedes pumps, it had no guts inside when i got the truck so i hit the core pile at the shop and scared up a bearing and spring that fit, sorta hit a sweet spot with that pressure range

 

[The patriot]

General consensus is youre better off shimming than stretching.

That being said, if the spring has lost it's "spring" when the fuel heats up your pressure will drop.

Youre better off buying a new valve IMO.

Theyre cheap enough.

 

[ATaylor]

Where to find overflow shims?

Are there actual shims that are meant for the overflow valve, or do you just find some stainless washers that fit under the spring?



Thanks,



Archie Taylor

 

[hdm48]

I would find an old valve, or some washers (spacers) that are the same dimension as the ones installed. Then use a mightyvac or an air line with regulator to check the pop pressure. That way it will be set before you start it to cut the dial in time.

Just to make sure it will keep the set, I would start with a new valve.

 

[WDixon27]

i did the rough tweaking using the primer pump so i didn't start the truck and end up with 60# or more of pressure potentially hurting something, which is not hard to do when you are playing with the spring, more then once i pegged my fuel pressure gauge with just the primer pump till i dialed it in

 

[ATaylor]

Overflow valve shims

Finding washers that are the same size as those tiny, thin washers inside the overflow valve is proving to be next to impossible.



I was explaining what I was doing to the owner of the local machine shop and he suggested that I machine down the top of the overflow valve, which would therefore compress the spring more.



However, he also said that sometimes compressing a spring does not create more pressure against the ball and seat inside the valve because the spring is going to supply constant pressure until it is completely compressed.



I think I'm going to try machining my old overflow valve down . 050" and see what it does. If I go too far I can always add an additional copper washer under the top bolt head of the overflow valve.



I have made a test block to screw the overflow valve into on one side and a small paint gun air pressure regulator on the other. So I can test where the overflow valve starts to open.

 

[WDixon27]

i haven't touched mine since i tweaked it a couple years ago and the spring is holding the stretch i gave it and is keeping the same pressure

 

[Signal73]

put a spring from a bic pen inside the spring thats already in it. should help with some PSI. Best thing is to make a new return line coming off the P-pump and use an external regulator and junk the stock OFV

 

[ATaylor]

External Regulator VS. the Overflow valve

My original plan was to use an external regulator instead of the overflow valve. I have a Airdog 150 which is internally regulated to 40 psi. The general consensus on this forum was that running a regulated fuel supply (the Airdog) and then adding an external regulator might somehow fight each other.



If the overflow valve holds pressure in the injection pump until say 30 psi, how is that different than running the external regulator? Aren't they doing the same thing? It never really was explained back in the other post, some folks said they would fight each other so I decided to modify the overflow valve instead of trying an external regulator.



If anyone has any thoughts on this, please chime in.



Thanks,

Archie

 

[Signal73]

thats what I figure. I know someone with a fass and they use a regulator. Id put it in the return line with a fuel pressure guage. Aeromotive 13109 is what I use.

 

[WDixon27]

as long as the highest pressure regulator is the last one in the return line it shouldn't matter if there's more then one, but if you do want to run a external why not pull the ball and spring out of the OF valve and store them in the glovebox in a baggy incase you wanted to switch back

 

[hereismylife]

thats what I figure. I know someone with a fass and they use a regulator. Id put it in the return line with a fuel pressure guage. Aeromotive 13109 is what I use.

Did you take out the ofv and put this in the return line after the p pump?

 

[HLEschenko]

I used stainless shim stock; Drilled the correct size hole; cut it with a good shear. Its been in place over a 115K. 22 psi going down the road. Cost time only. Installed shim thickness 0. 065".

 

[hereismylife]

I used stainless shim stock; Drilled the correct size hole; cut it with a good shear. Its been in place over a 115K. 22 psi going down the road. Cost time only. Installed shim thickness 0. 065".

I will check this out. Maybe a good idea



thanks

 

[hereismylife]

I wonder if you take the shim from a old valve and stack it on top of the other how that would work... . ?



Seems like it might go way to high this way... ... .

 

[BGuilty]

i may have my old over flow valve from when i had my pump rebuilt if you want it to play with its yours its out of a 180