Update on all 7520s

[SPYDERLK]

Brian, I think that similar time at 30% reduced rpm indicates you have some suction leakage. Mine is running again and the loader is doing somewhat better than when I checked it last summer. Im guessing the hoses are sealing better after all the thermal cycling. I had forgotten that full extension on the cylinders is only 22.5". That is 5.5qt for two cylinders. 17gpm should do that in 4.9sec. Mine takes 7. Im planning to clean the suction strainer and replace the filter. If that doesnt bring it down into the 5 sec range Ill have to check into it further. It is not that loader is so slow as to be bothersome at this point, but that the loader should reflect 17gpm delivery by its speed. Otherwise something is wrong.
As for my engine repair, I will post later. What happened is that the cam gear broke. This gear also drives the hydraulic pump. I dont have enuf time right now.
larry

 

[MtnViewRanch]

Larry, I suppose that you are correct about the suction thing, but I will wait for it to bother me before I investigate. See I look at it as the high idle is about what it should be with the self leveler and all, and my "normal" operating rpm is better than normal.

If the lift time should be 4.9 sec, why do you suppose that Mahindra has it at 6.2 sec? That is a 26.5% slower lift rate. With the lift times that Dave got for us last week, what flow rate does that come out to be?

Just wondering, it doesn't really matter other than each owner is happy with there tractor, I know that I am.

 

[DavesTractor]

Brian, I got a Starbucks gift card in the mail from you today. You are my new "favorite customer".

I still think the blue tractor is wrong....but you are otherwise top-notch.

 

[SPYDERLK]

Consider a gear with a helical (angled) tooth profile and with a diameter of about 7". The gear is about 3/4" thick(wide) at the toothface and also at the center hub. The web, connecting between the two areas is about 0.2" thick. There are four 1-1/8" in the web near the hub. The hub is keyed to a shaft and held to that shaft by an interference (thermal shrink) fit.

Subject gear is driven by another gear (drive gear) at about 1200 rpm, and called upon to transmit up to 40hp. Two of these HP are used to drive the shaft fixed to the gear. The remainder are output to a third gear opposite the drive gear. So, for the most part, the subject gear acts as an idler.

So, whats to consider? Well, actually a lotta things - - but sorta brush each of them aside as a distraction until you come to thrust loading. Then dig in, kick back and visualize the situation this gear faces during rotation under load.
Whats this got to do with this thread? This gear is the camshaft gear on the 7520 & 6520. It transfers power from the crankshaft to the main hyd pump, PS pump, alternator, and engine fan as well. Mine broke at 172.4hrs.
larry

 

[SPYDERLK]

oops. Didnt notice that I omitted the word "holes" in the web. This weakens the web, causing it to flex more in response to the thrust reversal that the gear experiences during rotation under load. Unfortunately, the holes are necessary to provide access to bolts that secure the trust washer for the cam.
larry

 

[Blu 82]

All

Checked speed of FEL and here is the average time (out of 3 lifts/drops) at 1500 RPM: up = 7.59 sec (ground to max lift), down = 4.72 sec (max lift down to ground). Manual calls for 9 sec from grnd to max lift and 5.7 sec from max lift to grnd. So it seems my loader is ok w/speed. I changed the 2 hyd filters at 50 hrs and tried to get the strainer out but couldn't. I checked it and it looked good so I didn't keep trying to get it out. After taking cover off of box where strainer is located, I have to refil most of the hyd fluid. I have about 67 hrs on the tractor mostly using it to clear land w/FEL and have used the BH a little. She will pull trees out well and seems stong when pushing over large bushes/small trees. Will addd more later.
Cheers
rob

 

[SPYDERLK]

Quote from Brian: If the lift time should be 4.9 sec, why do you suppose that Mahindra has it at 6.2 sec? That is a 26.5% slower lift rate. With the lift times that Dave got for us last week, what flow rate does that come out to be?

Combined volume of the two lift cylinders is 5.5 qt at 22.5" extension. If pump delivered this much in 6sec [1/10min] it would be delivering 10x5.5 or 55qt per min. This is 13.75gpm. We are looking for 68qt per min- - 17gpm.

I think the 6.2 sec spec is actual test time, and performance does not reach pump spec because of suction leaks and recirculation of entrained air bubbles fron the reservoir - a double whammy. I believe this is a factor to a varied extent in a large majority of the 7520s. I saw someone posted a time of 5.4 sec earlier. I think we should all expect that in a correctly functioning system. The small difference from the 4.9 sec theoretical would be mostly accounted for by internal pump leakage/bypass at the 1000psi the pump has to work against to push fluid that fast in the loader circuit.
A good indication of air in the circuit is a series of jerks when 1st raising the loader after the tractor has been parked overnite and the small bubbles have coalesced. Mine is doing this and I have a 7s lift.
larry

 

[MtnViewRanch]

Larry, by chance does the size of the hydraulic hoses on our loaders put enough restriction on the system that the loader will not function as you believe they should. Again, I am satisfied with mine and I know that it is a little slower than spec. I figured that on mine it was due to the hydraulic self leveling system. My loader is smooth operating and I have not noticed it to have jerky movements what so ever. I have never had any indication of air in, or cavitation of the hydraulic system.

I guess that somebody, (not a dealer) should get a flow meter and check the actual flow at the pump. That way we will all know if our pumps are not to spec, or if it is other possibilities, (air leaks, suction problems, line restriction, whatever).

As for myself, I don't really care, because I'm happy with my 7520, whether it is up to spec or not, it works for me.

 

[SPYDERLK]

Quote from MtnViewRanch: Larry, by chance does the size of the hydraulic hoses on our loaders put enough restriction on the system that the loader will not function as you believe they should.

No. Pls see post 62. More detail later. Iv gotta get up at 4AM tomorrow.
larry

 

[rback33]

I guess that somebody, (not a dealer) should get a flow meter and check the actual flow at the pump. That way we will all know if our pumps are not to spec, or if it is other possibilities, (air leaks, suction problems, line restriction, whatever).

I know this was mentioned before, but this really IS the answer.....