Oil pump mystery...

[spl310]

I have both R and U oil pumps lying side by side in the garage. I see no reason that they cannot interchange without negative effects. I know that a lot of folks buy the U pumps under the assumption that the U is a bigger motor with more oil requirements (being an OHC model) and therefore it should be better. From what I see, the only difference in the pump designs is that the U has a more easily modified pressure bypass valve setup. The R uses a cotter pin to hold the mess together while the U has a threaded plug.

Add to that, the H oil pump is identical to the R. So, my question is, why could you not use an oil pump from the G, H, or R motors in the U motor? Does anyone have anything solid? It looks like if you wanted to eliminate the possibility of the cotter pin failure, you could thread the port and put a bolt in that style pump and be just as effective. Plus, the G,H,R pumps are available and the U is NLA...

[Daryl Smith]

When I picked up my U20 pump for my stroker, it was under the assumption that it was a higher volume, higher pressure pump.

Clymer manual shows Pressure @ 4kg/cm. sq. for R pump (2000 rpm) and 4.5kg/cm. sq. for U pump (no rpm stated). (from what I can decipher)

Volume on R pump is 22 litres/min @ 2000 rpm, can't find rating for U pump.

From what I have read over the past few months the extra oil (?) would not really be nescessary (R/H/G series) unless you run high rpm for extended periods (racing) even in a stroker.

Unless I could confirm the specs of R/U pumps to be compatible (or modify it to be compatible) I wouldn't risk running an R pump in a U20.

On the plus Side for the U20 pump also, the housing is made of aluminum, and therefore noticeably lighter......

[sgriffin]

I have an "h" pump on my "r" motor. Sam

[spl310]

Well, I have more to add to the mix. I have two U pumps right now. One just arrived (Thanks Mike P!!) that is aluminum. The one that I had here is cast iron. The design is the same on both.

In looking at the specs that I can source, the G/R/H pump actually specifies less play and clearances than the U pump. That seems counterintuitive to me. The pressure ratings for all of the pumps is virtually the same (within 2 or so pounds either way). The rotors are the same size as are the ports, so the volume should be the same.

It looks like they just redesigned the pump to be more easily adjusted with regards to the pressure relief valve. That is ALL that I can see.

With regards to weight, I would prefer the iron pump - more durable!! I am not out for absolute weight reduction - if I were, I would diet more!!

I still am waiting for someone with quantifiable information about their interchangeability...

[S Allen]

Sid,

You bring up an interesting point but I doubt there is in hard evidence to evaluate. I was told by a knowledgeable Datsun mechanic that the U20 oil pump put out more pressure than the R pump. How much I never really found out. 2 lbs is not much. Where did you get that figure from? Even though the pumps look identical I would not use the R pump on a U20. I will give Mike Young a call and pick his brain over this one. Hopefully, we can get some good solid information. This becomes important due to the NLA status of the U20 oil pumps.

Steve

[spl310]

Steve,

I get the info from the Clymer reprints of the OEM manuals, the OEM manuals and the Chiltons manuals. I have the Chilton's here, so I will post a comparison. They don't list the H pump, but they do list the G and the R together. I have seen and H and it looks identical.

Tip clearance - gear or rotor to cover (in.)

G/R .002 - .004
U20 .006 - .009

Gear Backlash (in.)

G/R .010 - .012
U20 .012 - .016

Side clearance - Gear to body (in.)

G/R N/A
U20 .002 - .004

Maximum oil pressure (psi)

G/R 54 - 57
U20 54 - 57

Minimum oil pressure (psi)

G/R 7-10
U20 7-10

The OEM books had some slightly different numbers, but they are not at my fingertips. As you can see, the U20 is more sloppy with regards to tolerances, but the pressures are the same. The G/R pump puts out 22 gallons per hour at about 6psi with 2000 pump RPM with the pressure valve locked if I recall correctly. I didn't see anything regards to the U20's output like that. It was quite interesting to have the aluminum pump and the iron pump in hand. I like the iron better....

[dbrick]

Well, here's another 2 cents..I'm not a mechanical engineer but I saw a Holiday Inn comercial last night on Speed Channel....

1. The different clearence specs might be because of the steel shaft and gears in an aluminum housing have different heat expansion rates than steel parts in an iron housing. The aluminum would expand more, requiring more clearance.

2. Wouldn't the oil pumps pressure be controlled by the relief valve spring
tension? I used to get kits for American cars that came with 3 color coded springs, pick the one that matched the pressure you wanted. Matter of fact, half of one of those springs is in my upper timing chain tensioner and solved the U20 death rattle.

3. Volume would be the product of pump displacment, viscosity and RPM, and to some extent max pressure allowed by relief valve. Same size pump rotors should give same volume at same RPM and pressure. If they are the same size internally, then the higher pressure would provide higher volume.

4. Would a roll pin also work instead of a cotter?

5. A drill, bucket of oil and a stopwatch would be a good test...probably not conclusive, but would be fun to watch.

[S Allen]

Wow, Clymers has a lot more information on oil pumps than I ever thought it would. I have one of those some where Thanks for sharing.

Steve

[dbrick]

The clearance difference looks about right for aluminum vs iron. Are the internal rotors the same size?

[spl310]

The rotors are the same as far as I can tell. (Don't have a micrometer...)

[mikew]

R16/H20 pumps have 23mm gears. U20 pumps have 30mm gears. So the U20 pump flows a higher volume.

Mike

(info thanks to Lou Mondello)

[dbrick]

is that diameter or thickness?

[mikew]

Ahh, good question. Lou specified the gear "length" as 23mm vs 30mm. I assume that means thickness, but I'll confirm.

Mike

[mikew]

confirmed.

diametre is the same for all G/R/H/U pumps.

the gear is taller in the U, so it displaces more oil for each revolution!

Mike

[S Allen]

Hah, Mike, thanks much for the information as to why a U20 oil pump pumps more volume than an R oil pump. I will have to put that in the tech section some where as I am sure it will pop up again. I do know racers do something with the pressure relief valve spring to increase output as well. Anyone have any first hand knowledge on that? Chris Coker-you reading this? Cheers.

Steve