I have my engine out on the stand for a refresh and a new set of cam bearings. The current pump is an old-school melling 55 HP, and theyre not kidding about the HP part. It makes close to 100 PSI at ALL times. I think these are also HV pumps as it builds around 50 PSI just cranking. The pressure itself isnt an issue, but the drag from it overloads the front cam bearing, causing the overlay to literally sqeeze out the sides of the bearing. This pump has done this same thing in two different engines.

I want to go down to around 60 PSI to reduce the load and prolong the life of the cam bearing. Which spring is best? I see there are a lot of high pressure springs, but only a few actually list their bypass pressure.

 

hope that link helps, 100psi seems to be alot, only time i saw this occur was when someone was running main tolerances too close, think the crank journals werent shaved properly. dont remember excatly.

http://www.melling.com/Portals/0/SPR...0CORRECTED.pdf

 

Thanks, thats what I was looking for. These pumps came with the GM-GW replacement 350s. They make LOTS of oil pressure. The only drawback is the load on the front cam bearing from the timing chain. In my experience, the stock applications are right on the edge of what the bearing can handle. Add bigger valve springs, and the bearing fails.

Kind of off topic, but the admin. here can reset your password if you want your old account back.

 

if that link helps awesome... the password thing...i dont have my old email account, i know which email its registered to and old post new post/pics to confirm its me...i was gonna send an email but decided not to, mainly cuz everyone i used to know is gone...its weird being being back and only mark is still here...few others too, but it depressed me a little especially after hearing about grumpy

 

Sounds like a defective pump to me. There is NO SPRING capable of supplying that much pressure and absolutely no need in ANY small block for that much pressure. For how cheap they are, buy a new one and move on. Max oil pressure is controlled by the bypass built into the pump. It's a spring-and-bullet kind of affair with oil pressure pushing on the nose of the bullet to overcome spring pressure. If it's jammed shut or the return passage is restricted it can't possibly work right. This is not a part you want to guess/hope/assume works right. Although typically very reliable, if it's bad it's best to buy a new pump than to attempt a fix on a defective one.

 

From what Ive seen, these pumps (it came with my old goodwrench 350) usually peak out at around 80 PSI. My gauge says 80-90 PSI at all times. Its certainly crossed my mind if there is something causing the pump not to bypass oil properly. If it wasnt bypassing at all, wouldnt it basically just continue to build pressure rather than top out at 80-90 or so? Id imagine that at 6000 RPMs the oil filter wouldve taken a hike by now if it wasnt bypassing.

Given the fact that its an HV, Ive been thinking of just downgrading to a standard volume since it puts way too much drag on the timing set. Which are the good ones now? I've been a little leery of using melling since they started messing with the castings. Id rather have a runaway oil pump than one that falls off...

 

I take it the good ones are now the spendy M1055x's?

I was thinking of replacing the spring and trying the pump with the engine on the stand. Wouldnt I pretty much know at that point if it was the pump at fault? Seems if it drops to the lower pressure, its bypassing properly.

 

Dry sump

 

Use the Mr Gasket one; part # 26. Gives around 55-60 hot, cruise, normal weight oil (10W-30 or so) which is what you should have in it anyway.

The oil pump doesn't particularly load the front cam bearing heavily. If you're trashing that, you have something else going on. Too much oil pump takes out the dist gear, LONG BEFORE it bothers anything else.

Let me guess: gear drive? If so, then that's why you're killing front cam bearings. Throw that thing in the trash and get a good chain set. Part # should have 3100 or 3136 in it, depending on whether it's a factory roller or not.

 

No gear drive. Have the stock single roller chain in there.

Damon may be correct about the pump being fubar. On inspection, its a standard melling M55 with a yellow spring in it. Should only make 60 PSI with that spring. It needs to be replaced, anyway, as the cover and pump body are worn and grooved.

 

Ok, I finally figured this out when I went to put on the new standard volume pump today. It struck me that the new pump looked awfully insubstantial compared to the old one that GM gave me way back when with my GMGW 350. That, and the old pump had gears that where about 1.5" long. Hmmm, strange... Oh wait, thats not an M55 like it says, its an M55 high volume.

That explains everyhing. How it can still push 100+ PSI even with a standard 45 lb spring in it, why oil filters always leaked, and why it keeps eating cam bearing after cam bearing... The clearances are really tight on this engine, so the pump moved SO much oil that it just couldnt bypass it fast enough, and the pressure went to the moon. I dont even know what it went to at WOT. The oil pressure gauge would go so high that it would wedge itself in place sometimes.

Man, to think how much agrivation I would have saved if I had known that when I fixed it the first time around...

Anyway, long story short, never ever use a high volume pump in a stock engine.