Get this pig running!

[Shortbed]

Hello all,

 

From what I have gathered here on Ratsun, this is what I know (or think I know).

 

I have a 77 620 standard cab and bed, In Arizona, suspect truck has been in the state its entire life, altitude is 974'

L20B. Head is spotless. Been taken to a shop for some work i suspect, Block kind of unknown, saw bit of carbon build up on pistons, 130psi compression with one cyl at 120psi.

Emissions delete? no air pump, PCV blocked off, no 3way connection, block breather tube dead ends at adapter off intake manifold.

Stock Hitachi DCH340(-47a) with stock jets (I rebuilt, set up various gaps and float level to FSM) didn't really check flatness but looks flat.

5 speed swap with wires not hooked up,

Matchbox dizzy (Dist. body not bonded to ground), high performance coil (less than 2 Ohm) and resistor, NGK BPR6ES .041 gap, plug wires are 8-9 kOhm, coil lead 6ish kOhm

A/C (york comp and big ol' 12# cast 3 part bracket, R134 retrofit in 2014) not currently in service,

Engine is timed maybe a bit of chain slack?( Cyl 1 TDC with notch on 0 degree, intake lobe at 11 exhaust at 2), distributer is timed? (rotor pointed a few degrees away from post 1)

 

Installed new water pump, oil change Rotella T4 10w-30, silicone head gasket, cap and rotor, ign coil, fuel pump w/filter.

 

2 weeks ago. 

truck was running with different stock hitachi (different variation) with couple of bigger jets (mains and 1 main air bleed), carb rebuild, phenolic spacer was on 180 degrees out, discovered recently the diaphragm for the vacuum break was bad. idle mixture screw was 1/4 off the seat. It would finally idle with a help of carb clean and once warm it was okay. intermittent/ rough idle. would fluctuate 630-750 rpm to  950-1200 rpm. vacuum gauge was steady at 15" but sometimes bounce between 10-15". It appeared to be at 0 degrees on timing couldn't really see straight on. white smoke at the beginning and went away. Water temp was steady 180 degrees top of thermostat housing, block was around 180 degrees as well. 

Drove it around the block a couple of times. wouldn't really accelerate (carb adjusment i thought). ended up dying and not wanting to start after the spin around the block. 

 

Now.

5 pumps and it will start for 2 second and die. can get it going with starting fluid but acceleration does not happen, it slowly dies. sometimes will idle at 300 rpm for a few seconds and die. Kicker, less than 5" vacuum. Even while it was revving high had no vacuum. All connections are blocked off, couldn't really see any loose hoses, openings from the intake manifold. I have spark and when i pull out the spark plugs there wet. Timing was at 10 degrees but could be false for the current condition (suppose to be at 12).

I suspect carb base gaskets, (tried carb clean around the base no real change), carb diaphragms gave out,  intake manifold gasket messed up, timing is also probably off, also going to get the original carb from 2 weeks ago ready for a swap.

 

Sorry for the not so friendly forum write up. Really scratching my head here and could use the power of Ratsun right now.

 

Thanks guys!

 

Here she is!

 

 

 

 

 

[datzenmike]

130 compression is a bit low and indicates normal wear.

 

Get the PCV valve system working. It keeps the engine oil and the insides clean and extends the oil change interval to 5K plus. Before the PCV oil changes were at around 3K and engines lasted with a lot of luck for 100k. The fitting on the valve cover should connect to the air filter housing with a hose. The block vent should connect to the PCV valve screwed into the intake.

 

Get a stock EI coil for a '78 or '79 620 truck. I don't trust alternate after market stuff.

 

If you are at TDC then the rotor WILL point slightly past the #1 plug lead because it is timed to fire 12⁰ before.

 

The vacuum break is not crucial for running and only might be used when the engine is cold, choke is on and you need full power for passing or highway on ramp. Once engine is warm it's just along for the ride.

 

You are near 1,000 foot altitude so if anything the primary jet should be slightly smaller than a carburetor used at sea level. I would expect somewhere in the low 100s.

 

I'm at sea level and 18-22" Hg is normal. 15 " Hg is a bit low for idle, I would expect 17-21 for your altitude. This might indicate a small vacuum leak, ignition timing retarded, Poor idle mixture, tired engine and valve lash too tight. Now some of that can't easily be corrected but some can.

 

1/ Check and set your valve lash 0.010" intakes and 0.012" exhausts on a hot engine. Warm thoroughly, set to TDC #1 compression, set both valves on #1, intake #2 and exhaust #3. Turn engine ONE turn and back to TDC exhaust stroke. Set exhaust #2, intake #3 and both valve #4. This is a very fast way to set the valves without constant bumping the starter, missing and trying again. This can easily do the job before the engine cools down

 

2/ Set your ignition timing to 12⁰ BTDC. Be sure idle mixture and idle speed is set first

 

3/ Check timing chain for stretch which will throw the cam timing off. Remove #1 plug. Set engine to TDC compression on #1 by slowly turning front pulley till the notch on it is on the zero mark on the ignition timing plate. If you over shoot the mark, back up well before TDC and try again. You must hit the zero while turning clockwise. No backing up. Remove valve cover and look through the top hole on the cam sprocket. Use a flash light, there is a small notch on the back of the cam sprocket and just above it on the cam thrust plate is a small horizontal etched line. The notch should be below the line an just slightly to the right, as viewed from the front like this...

 

 

This is an L16/18 so it's factory set on the #1 your L20B should be on the #2. There is a procedure for correcting the stretch.

 

4/ Idle mixture is set by turning the idle speed down as low as possible on a warmed up engine. This will make changes more noticeable. Turn the idle mixture screw in or out till the the idle drops off. If it does, go the other direction trying to find where it idles the smoothest strongest and fastest. If it speeds up, keep going, looking for the fastest smoothest idle. Between the two drop off points is a plateau of perhaps a half turn where nothing changes, set roughly in the middle. It's assumed that your idle has increased, so turn the idle speed screw in to lower it. Keep repeating this in and out adjustment, seeking the fastest smooth idle until you can no longer improve on it and the idle speed is 700-800.

 

NOW CHECK YOUR INTAKE IDLE VACUUM READING.

 

1 hour ago, Shortbed said:

Now.

5 pumps and it will start for 2 second and die. can get it going with starting fluid but acceleration does not happen, it slowly dies. sometimes will idle at 300 rpm for a few seconds and die. Kicker, less than 5" vacuum. Even while it was revving high had no vacuum. All connections are blocked off, couldn't really see any loose hoses, openings from the intake manifold. I have spark and when i pull out the spark plugs there wet. Timing was at 10 degrees but could be false for the current condition (suppose to be at 12).

I suspect carb base gaskets, (tried carb clean around the base no real change), carb diaphragms gave out,  intake manifold gasket messed up, timing is also probably off, also going to get the original carb from 2 weeks ago ready for a swap.

 

 

Get this carburetor gasket sealing fixed first or we will just be running in circles.

 

Block vent hose is off the PCV valve so what is there on the intake? Is it gone? replaced with plug? Was the EGR removed and a cover plate put on??? These are problematic for vacuum leaks. Take a picture of what you have.

[Shortbed]

Thank you for the input. 

 

I'll hunt down PCV and stock coil and get those on asap .

main jets         pri. 99 sec. 160

main air bleed pri. 70 sec. 60

slow                 pri. 48 sec. 100

power valve     43 .

 

I'll try my best to warm up engine and check valve lash, I'll take cold measurements for general idea .

 

Setting both screws might be a battle. Is there a bench set? noticed 7/8 of a turn IN from butterfly fully closed, for idle speed screw, puts the throttle plate mid-way on the keyhole in the bore, basically just cracked open. Or should I just set them both 2/2 and start adjusting (following 4/ verbiage) from there? .

 

Will recheck for TDC, chain stretch procedure if needed. I did see the etch on the thrust plate, but I don't recall anything on the sprocket. Not the best picture hopefully that notch of sprocket isn't to the left...

Also hoping I'm just plain stupid and can't tell I'm at TDC...

 

Got another set of gaskets I'll try for the carb base. 

[Shortbed]

had to resize. block hose terminates to that component and everything is plugged

[Stoffregen Motorsports]

Cleaning up the engine bay by removing all unneccesary devices can take some time. You don't want to use crap hardware that looks out of place either. You can buy new bolts from Overland Metric. They aren't Datsun specific (they are Toyota actually), but they look very similar and use JIS hex sizes, ie - 10mm, 12mm, 14mm, not 11mm, 13mm, 15mm.

 

If you're removing the mainfolds, replace the bolts that hold the exhaust manifold on with studs. The soft aluminum in the cylinder head is know to strip out and you can get more torque on the studs.

[Shortbed]

Was thinking about removing unwanted things also, like that exhaust manifold header tube deal, but didn't want to risk boogering up the threads ect. so ill probably leave the engine bay as is. 

 

Exhaust manifold will be coming off in the future so i can put on new gasket. There's an exhaust leak from where the intake manifold looks like it bolt to the exhaust manifold so if I fix that i might as well replace any gaskets i can. Hopefully it isn't an entire biatch coming off. The stud idea sounds good to me, will make the switch when the time comes.

 

Thanks for the bolting source. Gonna get a cart full! 

[datzenmike]

"main jets         pri. 99 sec. 160" ...... is plenty lean.

 

Cold lash is 0.008" and 0.010" and assumes that it will expand 0.002" on both when hot.

 

If the carburetor was running go from there. Turn the idle speed up to keep running and slowly decrease as you adjust the mixture. Note if you turn too high it will not be on the idle circuit but running partly on the primary and adjustments won't do much. 

 

For TDC front two cam lobes will be up with exhaust at 2 o'clock and intake at 10 o'clock and the number stamped on the front of the cam sprocket will be #2 as in the picture I posted. With it roughly in this position now look on the crankshaft pulley for the ignition timing notch. When that is found, follow my directions turning only clockwise to bring the notch to zero on the timing plate.

 

 

This shows the block vent pipe correctly connected to the PCV valve so that's good!

 

The little brass plug should have a fitting for a vacuum source for the ATC ( air temperature control) on the air filter snorkel. It's a little understood device that prevents carburetor icing in near freezing damp or rainy weather.

 

The air injection manifold and tubes can be removed. You can simply cut them off leaving enough tube to crush with vice grips and roll up to seal. Or with the carburetor off remove them and the long tube that extends down inside near the exhaust valve and put a plug in the hole...

 

 

I didn't know your truck was an automatic!

 

I also see a small dab of white paint on the crankshaft pulley. This might be the ignition timing mark. Owners often put a dab of paint on them so it's easier to find.

 

Just above the top radiator hose is an open hard line. It would normally go to the canister purg and must be either connected or sealed up or you won't have any vacuum advance.

[Shortbed]

Changed mains to 104, 165 respectively . 

Cold lash was a little tight, couldn't warm up engine to check and adjust . 

Sounds like PCV is working then, nice .

It DOES rain in the desert, might have to re-establish .

I'll leave air injection alone for now, don't want to curse at it when it's time to come off, I did the brass plugs .

😮I DIDNT KNOW!!!

Little hard line is plugged, thank you .

 

Currently,

Carb is back on with different set of base gaskets. Hopefully that's fixed .

Still NOT wanting to start, even blasting extra strength starting fluid .

Thinking it might be ignition problem now, had timing light hooked up and would see flashes and then not. Checked all plugs after and no flashes. Checked against 2nd timing light and still no flashes. Gonna have to verify that I have spark. I do remember I had to fix a couple plug wires,  .

For TDC, lobes were 10 and 2 and notch on crank pulley was at the 0 +/- a bit. Second guessed myself and stuck a camera down cyl 1, followed piston up after intake valve closed to the highest point with a tiny bit of extra movement from crank bolt, but not too much where cyl starts going down . That said, the #2 is no where near the etched thrust plate. Maybe its behind the eccentric lobe washer?

 

[datzenmike]

You said...

 

On 1/7/2024 at 12:10 PM, Shortbed said:

Matchbox dizzy (Dist. body not bonded to ground)

 

 

Not sure what you mean but it's essential that the distributor case or body is grounded for it to work. The two mounting bolts should work but nothing like a dedicated ground wire.

 

The 104/165 jets are better.

 

I guess you couldn't find the little notch on the pulley? As long as set accurately to TDC it's good.

 

 

Can't find a better sprocket than the one posted.

 

 

There are only 3 cam dowels so only three choices. Should be on the middle #2 for the L20B engine. Each hole removes about 4⁰ of chain slack. It will run on any of them but best on the correct one and/or with the notch just to the right of that horizontal line.

 

Look for a 2 stamped at about 2 o'clock right up against the timing chain. Should have a large dot stamped there as well.

 

[Shortbed]

Made a temporary ground. 14awg solid wire. No change.

[datzenmike]

It should be wired this way...

 

 

The '77 had points so it had a ballast resistor and that should be removed. Ignore the 1.6 ohm coil. It'll work but it should be 0.75- 1.0 ohms.

 

Check that you have battery on the coil positive terminal.

[Shortbed]

Yeah I don't have that...

Going to clean that mess up tomorrow then. I'll pull up a wiring diagram to reference wire colors.

I added the jumper. Besides that all wiring is how I got it.

[Shortbed]

Success!!!

 

Got timing to 12 degrees. 815 RPM. Speed crew set @ 1-1/8 turns from throttle plate fully closed (to open/ just cracked). Mix screw set @ 2-1/4 off it's seat. 15" Hg.

Very sluggish/ hesitant start. Fingered the throttle linkage to keep squirting gas. 

I'll do a much more detail update from distributor wiring to this point a little later.

I have to check valve lash and then put the A/C bracket back on (draining cooling system, taking fan off, ect.) 

Real test is starting back up here in a few hours AND cold start tomorrow morning (fingers crossed)

 

Thanks Datzenmike for the help, and thanks Ratsun for the plethora of info!

 

Update soon 

[Shortbed]

Starting from advice to see correct wiring of ignition system, 

 

This is what I had wired up.

Made the wiring match the correct diagram, deleted resistor, found that Black White traced (By) and Black Red traced (Br) of right-most branch of harness were the "ON"/"RUN" power. (Mistook y's for w's on initial inspection, found out different after comparing what I had to FSM wiring diagram.) Used the other (Br) from same branch to power choke heater. It was part of the X's which I think were for the condenser.

Left some wires cut and taped off will have to clean up later. That addressed the ignition wiring part of the problem.

 

I did notice I was getting intermittent voltage from (Yw) terminating to thermostat temp sending sensor, which I believe is wired incorrectly, but the thermostat gauge somewhat works so ill figure it out later. (I have a temp gun with me at all times just to verify in not overheating like the gauge says.)

 

Replaced Accel coil for a 79' 620 coil bought at auto parts store. 0.8 Ohm.

Replace spark plug wires for Import Direct set from same store. They were all a bit higher in resistance 3-4 kOhm, but they were new compared to the previous set that had the connectors fall off and re-crimped.

 

Next, didn't know where carb screws were at so upon initial start engine started for 3 sec then died. Tried again same result. Squirt starting fluid and it seemed to run a second longer but died. Squirt a ton of starting fluid and no change. Let some evap off and ran maybe a bit longer. (Maybe its not getting gas). Had throttle cable unhooked so pumped the throttle linkage by hand like 5 pumps. Was wanting to run. Pumped once, ran 3 secs. (Okay, it wants some gas). Pumped 5 times and then kind of kept pumping and watching where the throttle plate wanted to be to keep running. After a couple of minutes of this it was staying on. Quickly grabbed timing gun and moved dist to 12 degrees. Next, started messing with speed screw to see if it would keep engine running. It did but idle was around 1400 RPM. Brought it down to 1100 RPM while looking that the engine didn't die. It stayed so I began messing with mixture screw. Kind of just bounced back and forth and seeing where the engine was bogging down. Left it in the middle and moved on to dropping idle down a bit more. Got idle down to 800 RPM and then back to mixture screw. Tweaked the speed screw to 815-ish RPM and left mixture screw in the middle of where it was bogging down and too far out of idle circuit. Every so often opening the throttle plate by hand to even things out.

 

Rechecked timing and was still at 12 degrees. Then, hooked up vacuum gauge and saw 15" Hg with a little bit of a flutter. Messed with the mixture screw some more to see if it the reading would stay still or higher but no success. Shut off engine and restarted it a minute later and IT DID START. Tried again 5 min later and same result. 

 

Came into the house, quick update, then rushed back outside for valve lash measurement. Adjusted a couple cyl, some where hairy edge of tight, but it'll be okay.

 

Couple hours later after slapping A/C bracket and components back together, she started right up! (my dumbass forgot to make a relief in the bracket for spark plug #1)

 

The following morning (35 degrees or so), SHE STARTED RIGHT UP!  Overjoyed with the result. Fast idle will need some adjustment as it was around 2950-3075-ish RPM and damn near woke up the neighborhood. On the bench for one of the carb set-up measurements (I cant remember which one) I had thought "what's a thou amongst friends", looks like I know which one I forgot about.  

 

Drove it to work and back home. No major issues. Checked temp at the end of each trip, 184-ish degrees top of therm housing, 193-ish around block, non-manifold side. 

 

Things that will need addressing a bit later:

Wiring clean up.

Thermostat to read correctly. (don't know if it's pegged or room to overheat)

Make a makeshift coolant reservoir tank.  

Speedometer to read correctly. (at 50 it shows 30)

Rebuild 5-speed. (fifth pops out might need synchros) 

Adjust steering. (some drift to keep center of road)

 

Again, sorry for the not so friendly forum write-up, but thanks to everyone who has contributed to the forum over the years! Search is a powerful tool.

 

 

 

 

 

 

[Stoffregen Motorsports]