1975 B620 A/C Fan Blade Question

[Phatjimmy]

Hello Ratsun,

I'm new to the forum and the Datsun world.  But I have been lurking for about 6 month now and learned a ton of information on the B620 so far. You guys are an amazing resource of knowledge. So here is my first post!  Be genital ?

 

I was given a 1975 B620 truck from the original owner for some engine work I did on his Ford Ranger.  It only has 73K miles on it.  He's had it sitting in his garage since 2013 so It's in overall great shape but full of rotten fuel. So I have been going through it a piece at a time and making it road worthy again.  But I have run into an issue I was hoping you guys can help me on.  It has the integrated centrifugal fan clutch/water pump combo.  Well of course the fan clutch is locked up tight and unfortunately at a slight angle giving me a nasty wobble.  All the parts houses in my area have (for some reason) the fan clutch/water pump for the A/C equipped model in stock on the shelf.  None can get the centrifugal non-A/C fan clutch.  I think Oreilly's could special order one but it only came with a 90 day warranty and was made in china.  All the A/C ones come with a life time warranty (new and reman). I did check Rockauto and they do list one but I was wanting to upgrade to the thermal fan clutch as it seems more available, life time warranty and more efficient on fuel. So long story short. Do any of you have an A/C fan blade I can buy for the A/C fan clutch? What is interchangeable? Will it fit in the shroud I have for the non A/C fan?  My plan is to keep this truck 100% original as possible. Well, except for this and probably electronic ignition down the road.

 

Thanks,

Jimmy

[datzenmike]

5 hours ago, Phatjimmy said:

  Be genital ?

 

? Yer killin' me here.

 

An AC clutch fan will likely move more air than the non AC one so not more fuel efficient. Better that a locked up one though.

 

 

Blades will not interchange but I did find a larger blades on a smaller clutch fan once, that had four little spacers to allow it. The smaller won't fit over the larger clutch.

 

I think you'll find the AC pump also moves more water.

 

Shallow cavity shorter blades...

 

Deeper cavity, longer blades...

[Phatjimmy]

Thanks for the reply and the pics.  My biggest concern is availability at this point.  Rockauto in the only one who has a centrifugal non-thermal clutch and a crummy warranty with it.  I had read in the forum here somewhere about how these clutches are notorious for leaking the silicone fluid out.  The one on my truck now only has 73k on it and still looks new but it ate a bearing in a bad way.  Being part of the water pump is why I was concerned with the warranty.  I'm no expert on fan clutches but my understanding of thermal vs non-thermal is how they engage.  Non-thermal centrifugal engages at lower RPM and releases at higher RPM. regardless of engine temp.  Thermal is disengaged (30% fan speed in relation to engine RPM) until it sees temperature increase across the spring. It can engage in steps up to 90% fan speed under high heat load.  So in my mind, cursing around town with a non-thermal centrifugal fan clutch I will be engage most of the time. Even in winter months.  But this might be me selling my self on why I want a thermal fan clutch.......

 

Anyway, let me know if anyone had the A/C blades for sale. Also, if it will fit in the current fan shroud I have.  Or if I should just suck up my pride as get the cheapy from Rock.

[datzenmike]

The 'clutch' is always engaged but it's more of a fluid drive mechanism like an automatic transmission's torque converter.

 

 

Fan speed is limited to about  2,500 RPMs regardless of engine speed above this amount on the non AC clutch fan. This is as much air as it can move with the blades.

 

The temp coupled AC fan turns at about 1,650 RPMs but has the ability to increase to 2,150 RPMs when the rad air warms it over a set amount. So yes, I guess the AC one would use less engine power. 

 

 

I've had both on my old 620. The AC one also moves more coolant (see previous pictures) and it seems to me that all 720 Z22 and Z24 engines use them. I have several. Their drawback is high engine loads at low speed. They don't move enough air because of slippage. On the highway, vehicle speed helps push air through the rad. But off road hill climbing or stuck in mud they don't work as well as directly coupled fans. (not a big problem on a car) The other disadvantage is they turn ALL the time including the first 10 minutes during warm up when the coolant is still cold in the rad and out on the highway when enough air passes through the rad anyway. For this, on my 710 car, I cut the clutch off and added electric fans on a thermostat switch. Now the fans only come on if idled long enough at lights or in the summer heat below 30MPH. Most all new cars and light trucks have electric fans for this reason..... and..... quieter.

[]2eDeYe]

Welcome.

Rockauto lists quite a few a/c waterpumps. Not sure which is auto or manual. 

 

https://www.rockauto.com/en/catalog/nissan,1975,620+pickup,2.0l+l4,1210116,cooling+system,water+pump,2208

 

Also the 620 is a PL620, but nobody uses the letters and everyone lists it as just a 620. :)
 

[Phatjimmy]

Thanks for the info.  I went ahead and got non-thermal fan clutch / water pump coming from Rockauto.  Should do the trick.  Happy Halloween!!!

 

Thanks,

Jimmy

[datzenmike]

L16/18.... PL620

L20B........ HL620

[Ben_upde]

10 hours ago, datzenmike said:

L16/18.... PL620

L20B........ HL620

King cab is KHL620

[]2eDeYe]

They are all 620s to me ?

[datzenmike]

I love them all.

[Phatjimmy]

I have the HL620.  A whopping 110 hp (actually not bad for a 2.0L).  I love it too.  My best friend had a B210 back in the early 90's that her delivered pizzas with.  Abused the holy crap out of the car but it ran flawlessly and got about 23 mpg (rough teenager calculation).  Good car.  To bad we were too young and stupid to appreciate it.  Somewhere he had also had found a Honda AZ600 but that's another story.....

 

Since we are off topic I have another question. What are the "do's" and "don'ts" with these trucks and this L20B engine?  Being Datsun tarded I don't want to make fatal mistakes.  I did score a a real shop manual off of ebay to get started. Once I get my water pump from Rockauto, I can run it and get it nice and hot, run the valves and check timing.  It's getting a full tune up since everything on it is from 1975.

[datzenmike]

110 is the old gross HP rating. Car makers came up with novel ways to get higher and higher numbers but the public were always wondering why their cars seemed slower than they should have been. Gross readings are taken directly off the crankshaft without alternator, maybe the water pump, probably no flywheel or any drive train losses and no muffler. A more down to earth number that was adopted is the net or RWHP (rear wheel hp) which is more what everyone 'sees' in the real world. 93 is a more realistic number for parasitic losses in an L20B powered vehicle. You haven't lost 16 hp you were just comparing apples to oranges.

 

Don't unbolt and remove the cam sprocket (if removing the head) unless you know how to block the chain tensioner from popping out. This will save you 4 to 6 hours of needless work.

 

The engine oil back in '75 had a higher ZDDP level that today's oils that are slowly fazing it out. New cars don't need it, but our older cars DO. You can add it with an oil change or look for racing oils that have it or what I do, and run a 'light' diesel oil like Shell Rotella T4. I use it in 15w40 but only drive in the summer. It does come in 10w30 as well. Chevron Delo 400 is also high in ZDDP. All diesel oils are. Diesel oils are very detergent so if your engine is held together with sludge and dirt that seal the rings and prevent oil burning it will dissolve and remove it. I've been running it for 6-7? years.

[Phatjimmy]

Good to know.  Thanks for info.  I just happen to have some diesel equipment and vehicles so I have both T6 and T4 Rotella on the shelf.  Never knew they were phasing out ZDDP.

 

I'm sure I will be back to bother you guys some more as I dig into this truck some more.  I see some electrical issue coming.  I noticed no buzzer when turning the ignition key on and no cluster light or idiot lights.  Probably just bulbs. I just read the LED post on this forum for cluster lights.

[datzenmike]

I urge you to look up the ZDDP controvercy on the internet and decide for yourself. ZDDP is definitely being lowered. It's SUPPOSED to be reverse compatible and the levels in the past were too high to begin with so today's lower levels are fine. Well I'm not taking this chance on my irreplaceable Datsun engine.

 

 

 

[Phatjimmy]

After some reading I can see it's quite the hotly debated subject among the classic car guys (flat tappet crowd, like us).  Makes sense really. The C.A.R.B folks have been trying to get old cars off the road for over a decade now.  Since I own older diesel's and gasser's I guess I need to be up on this kind of stuff.  I have always used straight weight non-detergent oil for break in on rebuilds but even that is getting hard to come by any more.  Well thanks again for the information.

[datzenmike]

Since it's just a matter of walking down the aisle farther for the diesel oil, why not use it?

[Seeker > 620 KC]

If you're still looking for an AC fan I have an original from a 79.

The original Datsun AC fans actually had 8 shorter blades with a little more pitch vs. the 7 longer flatter blade fans.

They are offset about an inch to the front to clear the 3 grove pulley that bolts to the harmonic balancer.

PM me if you want side by side pics of the two fans, measurements, and diagrams from the Datsun AC parts list.