U20 Run Stand Project

[mtngoat]

Well, we've gotten the shop more sorted and organized. Wall 'O Sporting goods still chaos...but ALL of the Datsun stuff along the back wall was removed onto big tables, then sorted and dispositioned. We found a box of U20 parts so that was handy.  Plus numerous oil, air, fuel filters, distributors, distributor caps, a zillion brake pads, manifolds, at least two sets of SU's for L, Z and U...

 

Having done so, we now had enough room for the first steps to the run stand for the mothballed U20 sitting on the floor. First up, drag the hoist up from the barn to the shop. Then, get the L18 long block off the engine stand, and put the U20 on it. My son is pretty thrilled with this progress, and I'm thrilled to see him thrilled!

 

Alternator in hand, we kept trying to figure out where to mount it. Blue 2000 has it on the right side of the engine, which was our default choice because same same. But, no brackets on the mothball engine! Then I realized a bracket on the left side looked perfect and above it was the tension bracket, and sure enough it plugged right in. Reading up, this was a smog pump setup on some engines? I see also people intentionally moved the left side setup to the right side, why is unclear. 

 

Still have to figure out the regulator schematic and make sure that's all wired up right. 

 

Next up, address the carbs, which have had the float bowls screwed with. By me. For some unknown reason, but the parts are all there, including a plastic float mounted to one cover...with the brass floats still in the bowl. Weird. 

 

And...is there a FAQ on turning over an old motor which has been unused for at least 20 years? I'm thinking change the oil. Pull the plugs, put some oil in there and let it soak. Later, turn the crank by hand. Perhaps figure out some way to generate some oil pressure while hand turning? Pull the cover and lube the top end by hand? 

 

Still trying to figure out which of the pile of old starters is the U20 version. Seems me it's possible the patterns are the same and any datsun starter of this era may bolt in. 

 

At some point in the distant future we may try to assess the L18 as well, presumably not too difficult to swap mounting points around a little on the run stand, since it will be 4x4s and big screws. Also thinking it may be worth it to undergo the PITA necessary to haul this thing to town for a steam cleaning. Use hoist to put block in truck. Strap it in. Load stand and hoist. Drive to cleaning place. Unload hoist, jack up engine and install on stand. Steam it and degrease. Reverse order of operations. 

 

The reason for the effort is that this car had a locked up rear end and severe rust problems. The engine still ran fine-ish as I recall when I pulled it. It's simpler to spend a day with wood and a saw to try it out than actually putting it in a car. 

 

Edited November 24, 2025 by mtngoat

[wayno]

The U20 starter is mounted on the left side of the engine like the Nissan SD22/25 series diesel, I am not sure any other starter will fit except possibly a diesel starter.

[datzenmike]

The 71B from a SD 720 can be fitted with some work to the U20, mostly opening up the mounting holes on the bell

 

Roadster bell trimmed off.

 

SD25 front case from '85 720 I gave to Ppeterson at Canby.

 

 

This shows that the starter locations are the same, thus the flywheels are the same diameter and number of teeth as used on the L and Z series engines. I'm guessing that an L or Z starter should work. Worst case the starter may have to be mounted upside down. 

 

Below is an SD front case mounted on a 71C transmission

 

 

That SD25 flywheel got mixed in with about 10 other L and Z wheels and I couldn't tell it apart from them. It was 225mm and that's it. The SD starter was MASSIVE and I brought it to Canby and left in your truck wayno. 

 

 

 

 

[mtngoat]

Interesting idea about cutting the bell free and adding holes!

 

However, as noted in Transmission Palooza, one of the 2 2000 five speeds appears to be fine so we'll bolt that puppy on and see what's what, running it with no load anyway. 

[datzenmike]

I forget why HE cut the bell off. Maybe to weld another transmission onto it, but found out later that the SD might work. I had an SD and didn't need the front case for anything and gave it to him. 

 

My pictures are fitting of an SD diesel 5spd. transmission onto the U20.  

[wayno]

20 hours ago, datzenmike said:

The 71B from a SD 720 can be fitted with some work to the U20, mostly opening up the mounting holes on the bell

 

Roadster bell trimmed off.

 

SD25 front case from '85 720 I gave to Ppeterson at Canby.

 

 

This shows that the starter locations are the same, thus the flywheels are the same diameter and number of teeth as used on the L and Z series engines. I'm guessing that an L or Z starter should work. Worst case the starter may have to be mounted upside down. 

 

Below is an SD front case mounted on a 71C transmission

 

 

That SD25 flywheel got mixed in with about 10 other L and Z wheels and I couldn't tell it apart from them. It was 225mm and that's it. The SD starter was MASSIVE and I brought it to Canby and left in your truck wayno. 

 

 

 

 

 

This is an interesting idea about an L series starter working upside down, but I wonder if it could turn the SD25 engine over, I have issues with my diesel starter solenoids going bad, with the turbo piping being routed right next to the starter even with the heat shield I made it quits working all the time, it clicks but will not turn over, I then put a relay in to operate the starter motor and that worked great for a while, but now the arm that engages the starter to the flywheel has quit moving it full range, sometimes it takes 5 or more tries before it engages the flywheel and then the engine hits and throws the starer gear off the flywheel, I always seem to get it started but it takes several tries sometimes, if the solenoid was pointed down.......................

[datzenmike]

L series might work on an SD but I doubt for long. The solenoid has to connect contacts carrying hundreds of amps. The arcing must be tremendous! If starter was upside down the solenoid would still be horizontal. 

 

The SD starters have a heat shield cover for the solenoid. Part 23341-G7000

 

There is a shim between the solenoid and the starter case. If you were to add another spacer the solenoid moves farther away from the flywheel and this would add more travel to the little arm that moves the the star wheel on the end of the starter. 

 

Perhaps a Maxima LD24 solenoid would handle the power better.

[mtngoat]

Looks to me like the trans is being mated to a R16 in your pic! The valve cover looks wrong for a U20

 

If I recall the rear of the block is identical to the U20...

Edited November 25, 2025 by mtngoat

[wayno]

49 minutes ago, datzenmike said:

L series might work on an SD but I doubt for long. The solenoid has to connect contacts carrying hundreds of amps. The arcing must be tremendous! If starter was upside down the solenoid would still be horizontal. 

 

The SD starters have a heat shield cover for the solenoid. Part 23341-G7000

 

There is a shim between the solenoid and the starter case. If you were to add another spacer the solenoid moves farther away from the flywheel and this would add more travel to the little arm that moves the the star wheel on the end of the starter. 

 

Perhaps a Maxima LD24 solenoid would handle the power better.

 

I meant on the solenoid on the bottom(horizonal) next to the oil pan, I still have that starter you left me at Canby, it is the huge one, it is an all-day job to change out the starter so I keep using them until they die.

 

Still I can put my extra SD25 engine on my stand and try installing an L block starter to see if it would work, maybe a Z block starter will work also as the solenoid it tilted differently, so I have choices.

 

 

[datzenmike]

Z series might be better as they lean slightly to the left, so when mounted on the left side they lean away from the engine. Z series starters on a right leaning L block, press against the dip stick.

 

I remember it being a monster. I pulled that out of an upside down, crushed '85 720 chained on  top of a loaded semi flatbed trailer headed out of the scrap yard for Victoria. Driver said truck was there outside for the night, take what I want, don't care. Transmission looked familiar but starter on wrong side and engine was weird. Thought it was maybe a Mazda or something. I have a larger Maxima starter on my L20B and it's a tight fit near the oil pressure sender and the engine bracket. No way it would fit.

[wayno]

I have a starter off a VG30, I should look at that one closer.

I also have a new looking Z24 starter, it looks bigger and that was why I mentioned it, I never thought about that one.

It is raining too much to deal with it right now and it is still eventually starting the engine, I have not had to push start it yet recently, that is always fun, push starting a diesel engine.

 

[wayno]

I believe I may have got something wrong here, back in 2010 I was building my 521 kingcab stepside box truck with a SD25 diesel that I figured out how to turbocharge, I bought/won this new SD25 engine on ebay and it did not come with a flywheel, I could not find one either, so I had a Z24 flywheel made into a diesel flywheel, but the ring gear had a different tooth count than the diesel flywheel, so I had to take a SD22 flywheel to the shop and have them put the diesel ring gear on the Z24 flywheel, this got me thinking about this thread.

 

The starter of this thread needs to find the U20 starter among the starters he has, that is the only known option he has that is going to work properly for sure.

 

The diesel flywheel has 99 teeth on its ring gear, the Z24 starter has 9 teeth, the L20b has 8 teeth, the SD25 starter has 9 teeth, I do not know how many teeth the Z24 flywheel has, nor do I recall what the L20b tooth count is.

 

This said I did make a Z24 starter work on my work truck with an LZ23(maybe it was an L20b then), as I recall it did not last long.

[datzenmike]

L and Z series flywheels will interchange. I put a Z24 starter on an L series and it started and worked but it bent the dipstick tube to get it in place. Had to get a flexible stick for it. The SD flywheel simply looked the same, nothing obvious.  

[banzai510(hainz)]

dont kow if this helps. Im got a imi202 starter from a place that listed it for roadsters. Its 11tooth. Have not run it. But sold at the 510outlet troy ermish abt 240bucks. Mr bigtanker says they work on L Motors and more as all my starters are 9tooth. I dont know if fit trucks as 510s have more room. As motor is outside compared to selinoid. There was a roadster place said rebuilt japan mitshibishi starters for u20..

[mtngoat]

It might help, anything is good, thanks!

 

Last night we rolled the engine into the warm back room of the shop, and started assessing things more closely. We also dragged out a box we'd found with 4 more carbs in it, all SU 44's. My sharp eyed kid noted that the rear of one pair had a broad rectangular port under the throat in the rear, and that it was actually a set of Z carbs for an L series. Ok, takes that off the table for now. 

 

We pulled the carbs off the U20 and started checking linkage motions and throttle shaft play compared with the 'spare' set now remaining. The throttle shaft slop was *way* worse on the carbs from the box, and pretty damn tight on the ones we took off the motor, so we decided to retain those bodies and scavenge parts from the sloppy shaft pair. Had to move a nozzle and choke actuator from the boxed set, something had hit the U20 in the 20 years it sat on the floor and bent the nozzle and actuator arm. 

 

One weird piece we couldn't figure on the carbs from the engine...they have an odd giant thumbscrew looking thing sticking out of the bottom of the main carb body, next to the nozzle bottoms. The thumbscrew looking thingy is a knob about 3/4" in diameter, and appears to have a locking nut at the bottom of it's shaft where it hits the carb bottom. I have no idea what this, and it's a weird location for any kind of adjustment because it intersects the carb body directly below the float bowl shaft piercing the carb body from side to side. In short, it seems like there's nowhere for the shaft from the knob to go anywhere interesting. 

Edited December 4, 2025 by mtngoat

[datzenmike]

 

Rectangular opening below the throat is for water heating. They will work without it.

 

 

SU identification...

 

https://ztherapy.com/z-car/

 

 

[mtngoat]

We removed the valve cover and plugs, started inspections with bore scope. One exhaust valve was open, that cylinder filled with spider eggs. The others look very good to my eye, clean no scoring etc. A little carbon on piston tops. Plugs look great, no reason to expect I'd clean them or something before mothballing this engine. Valve train looks great, no shavings or baked on crud. We blew out the spiders from #2 from plug hole to exhaust (the open valve). Then some oil in each cylinder and turned it by hand. Very smooth, except the tensioner does *not* like no oil pressure, and a small kink or something builds up and 'ticks' past the edge of the tensioner about every 1/3 turn of the crank. We were very cautious about this and made sure it did NOT skip any teeth while ticking during our slow turns. Did a couple full cycles, left it parked at TDC. The cylinders now look very good on the inside. 

 

Combined with the very tight throttle shafts on these carbs, I'm starting to think we hit a bit of a jackpot..this looks to me like a low miles engine. Pix to follow. 

 

Distributor is a d407-51K 

Edited December 4, 2025 by mtngoat

[mtngoat]

Plugs look great to me. I think this ran good. 

[datzenmike]

Isn't there a 'chain rattle of death' on the Roadster? Type ... Datsun roadster chain rattle of death into google. There's lots of stories about it. 

 

Plugs are a bit dark but this could be it was idled too long. At least not black, sooty or oily wet!

[mtngoat]

This seems like something else. I think zero pressure in the tensioner is not working out. The guides including the tensioner are damn near pristine

[mtngoat]

It got confusing with a lot of borescope pix, but here's what I think is right. Upshot...nothing looks horrible and what's good looks very good to me. This motor has been pulled for at least 25 years. 

[mtngoat]

last but not least, this one is after some oil and a few turns. I can't tell where the dry one was. Had trouble fouling the camera with the after oil and rotation shots. 

Edited December 5, 2025 by mtngoat

[mtngoat]

Frame is blocked out. 

 

[wayno]

Parts are expensive when it comes to U20 blocks, do not throw anything away.

 

As mentioned already, Z therapy can make the carbs like new for a price.

[banzai510(hainz)]

found that starter

https://datsunparts.com/products/datsun-roadster-65-66-67-68-69-70-gear-reduction-starter