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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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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 ....
 

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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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hi CNC
yes I do no how an oil pump works
interested in expectations for idle pressure , yes I am running larger clearances .
Oh I am aware that full pressure comes on after idle and if the pump is flowing far to much oil it will find the semi blocked relief hole a restriction and then the engine oil pressure will rise and potentially run away and find its own maximum .
Funny I`ve always seen oil viscosity influence engine oil pressure ,of course until it reaches pressure relief setting .
Oh yea most oem quote at what rpm an engine achieved its max pressure .
 

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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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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.
 

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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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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 ??
 

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OK, so "old wives tale" to much oil pressure will wipe the bearings off and the crank will do the rest?
 

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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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