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Discussion Starter · #1 · (Edited)
The 383 I dynoed with high oil pressure using the 10552 ST oil pump was exactly what I thought was the problem. The bypass valve was to long and not exposing the complete bypass hole. I also have another engine with the same pump same problem.
I don't understand why I have to there home work for them. They told me not to take the pump ap
art it would void the warranty. I said really.
I have used probably 35 of the10552 pumps with zero problems. Now they said the 10552 ST they did change the cover HMMMMM
Here is a link to the dyno run
https://www.facebook.com/cncblocks.northeast/posts/pfbid0CWMCC5tUE7H6txU83MSpjAoU8FzbTU3S2kHjCUGtFtAoZSEQEPaEeG165yXwCig7l

PS
Good customer Jerry Brighthaupt saw my post on FB and took his 10555 ST pump apart and called me and found less the half the bypass hole was exposed. He was just getting ready to put the pump and pan on one his circle track engine. He was going to shorten the valve 3/16 of and inch which will cure his problem.

A big shop near him stopped using those pumps because of high oil pressure.


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Discussion Starter · #4 ·
Excellent. Very useful information. Saves a lot of grief after the fact.
Excellent. Very useful information. Saves a lot of grief after the fact.
I now have two engines with the same problem, Now getting them to pay for oil pan gasket, Oil and oil filer and labor should be fun. Lucky the Dist. gear looks good.
 

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Discussion Starter · #7 ·
hi
WOW
100 psi on the dyno sheet on an engine that sees 6000rpm so,, 60--70psi would be ok and idle 20psi +.

About to assemble
Just checked my 10552st pink spring
Piston travels freely in bore

##### Fully retracted piston covers 20--30% relief hole

Details
It looks like 3/16 inch needs machining from bottom of relief piston so it opens hole up a bit more .
## Does shortening piston actually cure the problem when running .0025 mains clearance
or is it more about hole placement ???
Are people having success doing this mod . Oh yea please state what spring your using .
EG pump comes with 3 springs pink installed ....
I have always used the yellow spring which will put you at around 62 pounds, Yes shorten the valve so the whole bypass hole is exposed.

It's more about having the bypass hole completely exposed, The clearances on my build is .0025 to .0028.
 

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Discussion Starter · #9 · (Edited)
hi
was the engine hot ?? and the spec of oil 10w/40 etc or different ??
idle pressure at what rpm ??
62psi at what rpm ??
When the bypass hole is restricted it really does not matter what oil you use and what the temp is.

On another forum a guy was using a 10553ST and 10/30 Mobil ! oil is running 100 hot

12 dyno runs with 15/40 I have used 35 or so of the 10552 Pumps over the years and changed to the yellow spring and oil pressure has been around 62 PSI

Idle pressure at 850 RPM was right at 35 PSI same as what I have seen over the years.

If you look at the picture of the bypass valve and notice the it doesn't expose the bypass hole you wouldn't asking such a question. Not knowing how a oil pump works is your problem here
 

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Discussion Starter · #10 · (Edited)
I talked to Brian at Mellings he said he was going to look into it.

He seemed dumbfounded. I can’t believe I am the only one that has called. I told him it’s a problem with the 10552 ST , 10553 ST, And the 10555 ST pumps.

A quote from one of my customers who was just getting ready to install his 10555 pump. He shortened the valve 3/16 of an inch to fix his problem
Jerry Brighthaupt
Carl is 100% correct....I have a new 10555st pump and with the bypass spring removed and allow the piston to go all the back less than half of the bypass hole is exposed
 

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Discussion Starter · #11 ·
Now looking at the 10553ST and 10554ST pumps it looks like they are using the old style pin to hold the spring in. Which should not be a problem IMHO unless they are using the same valve,
 

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Discussion Starter · #14 ·
So is the only real solution to shorten the piston? Great info for anyone in the process. I’m surprised more engine builders aren't getting sick of all the time used up redoing pan gaskets.
I think there is more going on with the cover, I have a friend with a 12552ST and a 10555T pumps are have about 65 PSI hot oil. At some point Mellings made a cover change and I believe the problem starts there.

I have posted this on quite a few sites and it seems like its a common problem. One guy has a 10553 pump 10/30 Mobil 1 oil at 3000 RPM he says he is at 100 PSI, Some guys have ruined dist. gears and cam gears.

I talked to Brian yesterday and they still have no answers but still looking into what the problem might be.
 

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Discussion Starter · #16 ·
hi
1/ Concern about over pressurizing
2/ potential issue is piston is closing pressure relief hole by 20-30%

Specification of piston [main circular body ] protrusion into relief hole is .030 inch

Investigate [ measurement from Melling ]
1/ relief piston total length is 1.625 inches
2/ relief spring plug total length .500 inch
spring plug threaded section = .length 370---..380 inch
****If the dimensions are correct the housing has the hole drilled in the wrong position ? TBA.
hi
1/ Concern about over pressurizing
2/ potential issue is piston is closing pressure relief hole by 20-30%

Specification of piston [main circular body ] protrusion into relief hole is .030 inch

Investigate [ measurement from Melling ]
1/ relief piston total length is 1.625 inches
2/ relief spring plug total length .500 inch
spring plug threaded section = .length 370---..380 inch
****If the dimensions are correct the housing has the hole drilled in the wrong position ? TBA.
I don't know if the bypass hole is in the wrong spot or it would have showed up when I primed the engine on the stand same as all the 10552 pumps it was 58 PSI on the drill with the yellow spring. at low idle it on the dyno it was appox. 35 to 38 pound wish has always been normal.

One pull was 106 PSI only ran this engine to 6000 RPM the customer has a 421 I built with the non ST 10552 pump and that ran 64 PSI at 7200 RPM. This engine at 7200 would have been around 125 PSI
 

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Discussion Starter · #20 · (Edited)
hi
I suspect core shift in the casting . I have now checked all my pump factory specs and the location of the hole is the only thing left that can be incorrect . What concerns me is
1 / springs have a very complex design ,ie will shaving the piston work ?
2/ will coil bind [once machined ] occur and not let the piston to fully retract anyway ??

I see you have the same problem with the valve covering up the bypass hole, Even with cutting 3/16 off the valve you should not be into coil bind but close.

I found a 10552 non ST pump it should be here on Tuesday to compare notes against the ST pump.

Remeber the cap on the end is recessed if your figuring out coil bind. The spring sets inside of that.

Put a call into Mellings again no reply.

Had a guy on another site already hurt his Dist. gear I am sure the cam gear is not good unless its the ever wear gear on the cam.
 

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Discussion Starter · #22 ·
OK, so "old wives tale" to much oil pressure will wipe the bearings off and the crank will do the rest?
Some times with a lot of constant high oil pressure it will hurt the Dist. and cam gear. this has already happened to someone on another site.
 

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Discussion Starter · #25 ·
10552ST spec clearances and bolt tensions

CLEARANCES
gear tip to housing .002---.005 inch
gear side to cover plate .004---.008 inch
Gear backlash .076----.772 mm

Tension
Cover plate 4x bolt 80 in/lbs or 9Nm --12Nm
Bolt Pickup 2 bolt 80 in/lbs factory loktite
*****IM Opinion is apply loktite and wire tie all bolts

Dimensions
piston tot length 1.625 inch
piston narrow sections .531 inch

Screw in plug
.500 tot length
gasket face to tip .370--.380 inch
: 11614403, member: 211146"]
Would it not be worth running the titan pumps to eliminate the hassle and have psi adjustability? The new owner is a fantastic guy and offers a great product.
[/QUOTE]

The Titan pumps are nice probably better then the ST pumps right now.
 

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Discussion Starter · #26 ·
10552ST spec clearances and bolt tensions

CLEARANCES
gear tip to housing .002---.005 inch
gear side to cover plate .004---.008 inch
Gear backlash .076----.772 mm

Tension
Cover plate 4x bolt 80 in/lbs or 9Nm --12Nm
Bolt Pickup 2 bolt 80 in/lbs factory loktite
*****IM Opinion is apply loktite and wire tie all bolts

Dimensions
piston tot length 1.625 inch
piston narrow sections .531 inch

Screw in plug
.500 tot length
gasket face to tip .370--.380 inch

I actually found a 10552 non ST pump that will be here in Tuesday to compare against.

Not getting any answers from Mellings right now and they have had a week to review whats going on.

My guess is they shortened the casting where the plug goes in orrrrr they are using the a valve that is to long. If it was shorter it would clear the bypass hole.

This seems to be a bigger problem then I thought I have got alot of emails and calls PM's ETC. There are a lot of ST pumps and running to much oil pressure for some reason.

One guy has a 10553 ST which is stock volume and 10/30 Mobil 1 oil at 3000 RPM he is at 100 PSI.

On one forum one guy hurt is Dist gear and probably the cam gear as well.

I have used probably 35 or so of the 10552 NON ST pumps with the yellow spring always been right at 62 too 64 PSI
 

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Discussion Starter · #29 ·
hi latest is

Screw in plug for pressure relief spring is likely incorrect

Oil relief hole positioning check in casting
1/ cover plate laid machine face down
= hole vertical / height 22.89mm to centre of screw plug/relief hole

2/ cover plate standing on edge , with machined face pointing away from u
oil pickup to the R/H/S
top left centre of mounting bolt
horizontal measure ment to centre of screw plug
= 29.85---30.10mm

Testing and review is being done as we speak .
I should have my non ST10552 in today and see what the difference is between the two I bet the bypass hole is fully exposed on the old pump. We will see.

Or the valve is to long. I had two engine builder that shortened the valve and the pressure was fine after that.
 

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Discussion Starter · #31 ·
hi
The screw in relief spring plug was made longer .
WHY the threads stripped but ,probably the person fitting pump DOH !!!! caused the issue
This resulted in a production change
Then the issues started

NB was the recess depth changed for the spring seat . ?? This whole situation is being looked into .
1-2 approx wks for an outcome .
Still waiting for my 10552 non ST pump to arrive.
 

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Discussion Starter · #32 ·
Well I got my 10552 NON ST pump in to compare against the 10552 ST pump. And I was right on my conclusion. If you look at the first cover off the 10552 there is about .030 of the valve in the bypass hole.
Now look at the new 10552 ST pump cover the bypass valve is covering up appox .135 of the bypass hole which is causing the problem with high oil pressure problems.
Mellings engineers overlooked that the new cover seems to be more narrower then the older cover causing this problem.
The cure is to shorten the valve to clear the bypass hole.
There seems to be a lot of engines running with high oil pressure. Oil filters blown off on the dyno and distributor gears being chewed up.
The cover on the right is the old design and they have changed the new cover quite a bit. Along with a tiny bleed hole for the pilot of the drive gear.
One of my customers had to shorten the valve 3/16 of an inch and oil pressure was fine on a 10555 ST pump.
Some of the earlier ST pumps have the earlier cover and don’t seem to have this problem.
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Discussion Starter · #34 ·
My engine builder caught the ST pump with hi pressure with the drill. He was able to change spring and was good. This was 4+ years ago tho.
That pump probably has the older cover which does not seem to be a problem.
 
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