SU Reassembly Step-by-Step [Part 1 Tear Down /Torn n Tattered /Worse for Wear n Tear]

[240260280z]

Lots of photos so it may take me a day or two to get them all up.

Here is a step-by-step procedure for reassembling an SU carb.

Rip it apart and fear not.

I did not take out the throttle valve plate and shaft because of the peening and I am lazy today. (I'll do a step-by-step on modifying an SU in another post in the future where the shaft is filed).

Note: I do not have my rebuild kits yet so pretend there are new gaskets

[240260280z]

Some Pics of the SU Carb body:

Note: I just washed with soapy water, sprayed with carb cleaner, then wire-brushed the outside with a brass wire wheel on a drill

The brass bushing around the shaft wears over time and causes a vacuum leak between the shaft and the bushing. You can put a ring of sealant around the rim of hole (but not touching the bushing or shaft) then place a flat round object (like a dime or aluminum disc or rubber disc) over the raised sealant to seal the shaft. Doing this side will cut your vacuum leak to this carb in half.

The bushing on this side of the shaft will also leak. Some fittings and linkage that will be installed on the shaft will come close to the body so there is not much you can do to seal this one. Maybe put some concentric O-ring up against the body with some silicone spark plug grease as a lubricant and a very paper-thin washer so that when the linkage presses in, the washer and O-rings will squish and the lube will prevent binding when the shaft turns.

The correct fix is to install a new bushing. Here is an idea of what you can do with the right tools:

http://home.comcast.net/~rhodes/Tech_Carb_Bushing_Reaming.pdf

Edited August 7, 2011 by Blue

[240260280z]

This is easy. Just don't loose the weeeeee itty bitty clips.

Needle nose pliers works fine to pull off; and press on the clips.

Here is the lifter rod laying just outside of its home cast in the main body.

Use a Scotchbrite or sand paper to remove the rust then grease the shaft.

Insert the rod into the body.

On the bottom side, install the spring then attach the clip retainer.

Works fine.

Edited August 7, 2011 by Blue

[240260280z]

Here are all the parts in relative order.

Firmly grasp the nozzle sleeve. (No I am not pink! I used colour enhancement and it enhanced me (fingers) too.)

Install the washer on the neck of the sleeve. Some grease is a good thing.

NOTE: The washer is on the wrong side in this picture. It goes under the sleeve.

Slide the Nozzle Sleeve Set Screw onto the sleeve

Install the large washer behind the Nozzle Sleeve Set Screw. Apply grease.

Install the Idle Adjust Spring behind the large washer. Apply grease.

Install (by screwing) the Idle Adjust Nut. Grease between the spring and the nut will make adjustments easy to do.

Here is where it goes at the bottom of the body. Antiseize on the threads is a good idea.

Test fit by hand tightening the Nozzle Sleeve Set Screw

Here it is in place. As you can see it is not automatically centered.

Edited August 7, 2011 by Blue

[240260280z]

The washers are not shown in this.

Edited August 7, 2011 by Blue

[Travel'n Man]

Great write up!

[240260280z]

Reference: Suction Piston

Reference: Piston bottom.

Note the centre groove and the two holes on each side of it as well as the needle hole in the centre.

Note 2: The black insert next to the needle is an inserted stand-off that prevents the piston from sealing against the bridge. This and the centre groove allow air to flow across the bridge when the piston is down

Reference: Piston front with guide groove

Reference: Top of piston.

Note the oil well and two holes on each side of it in the floor.

Insert plastic/nylon washer over oil well and push to bottom

Insert Spring. Ensure it surrounds the washer and is centered.

Reference: Suction Chamber.

Note the passage in the top front. This points away from the motor when installed.

Reference: Inside the suction chamber

Reference: Oil plunger assembly

Oil plunger installed

Edited August 7, 2011 by Blue

[240260280z]

[240260280z]

You can build your own alignment tools here:

http://www.classiczcars.com/forums/showthread.php?43152-Hitachi-SU-Carb-Jet-Alignment-Tool-DIY-for-Datsun-Nissan-240z

Mark I: Aligns the nozzle in the sleeve

Mark II: Aligns the sleeve

Fit alignment pin to piston. (use grease in the hole).

Install piston and chamber.

Here is where the tool aligns the Nozzle Sleeve. Note the sleeve is loose at this point and can move.

Strange photo... note that the 4 (3) rusty screws that hold the chamber are all evenly tensioned to just less than snug (see the lock washers are not compressed). This is how you want the chamber attached for the next step.

To align the chamber, spin it Counter Clock Wise (CCW) to full stop, then spin it CW. Note the limits and try to set the chamber in the middle of these.

Continue to tighten evenly like car wheel lug nuts... opposites.

You can now lift and drop the piston. It should rest flat on the bridge. Here is a photo with no flash showing the piston on the bridge. The only light is from the two hole cut in the piston's bottom (due to the dome removed) and a razor thin gap between the bridge and the piston bottom (due to the inserted stand-off mentioned above). Normally you can see through the grove in the piston bottom but the alignment tool is installed and blocks the light.

Here is how to tighten the Nozzle Sleeve Set Screw. A thin walled 19mm socket with a T handle will work even better.

Note: If you only have a stock needle to align with, install it as well as the nozzle then tighten the Nozzle Sleeve Set Screw slowly. When doing this, hold the carb vertically and move the piston up and down ensuring it hits the bridge and the needle does not bind against the nozzle.

The Nozzle and the alignment tool are same outside diameter.

Here is a shot showing the centered sleeve (left) and the centered sleeve with the nozzle in place.

If you want to double check nozzle alignment you can use this second tool that aligns the nozzle and sleeve at the same time.

Edited August 7, 2011 by Blue

[240260280z]

I wanted to start a needle exchange program but the department of health shut me down.

Edited August 7, 2011 by Blue

[240260280z]

The needle can be placed at nearly any depth in the piston; however, there is only one correct depth.

Lubricate the needle hole and loosely fit the needle in the hole.

You may need to use the side screw to hold the needle if it is too loose.

The needle should be nearly fully out of the hole (Don't worry, we will push it back in).

For greatest accuracy, you can reassemble the suction chamber and secure all 4 (3) screws as mentioned above.

Turn the Idle Adjust Nut all the way up and insert the nozzle.

Drop or, in this photo, press the piston into the nozzle.

The shoulder of the needle will seat tightly against the jet at the correct depth.

Here you can see the shoulder is out of the hole at the correct depth.

Another shot.

Be careful because if the needle is loose, it can drop out or fall back in the hole. Correct tension on the needle is needed to do these steps. As mentioned above, the side screw may be required to loosely hold the needle in place.

When satisfied with the needle's depth, slap some antiseize on the side screw and install.

Lock it up.

If you are wondering if you bent a needle, here is a quick way to check:

Throw the piston and needle in the dome and spin.

You can try to straighten or you can get a new one.

You can also spin it in a drill press for inspection and straightening.

[240260280z]

Below are a drawing and photo showing how to set needle depth in the FSM.

The only difference in this technique is that the needle shoulder is above the bridge by the depth of the stand-off.

When the nozzle is lowered to operating location, this should not make a big difference however, with the NON-FSM method shown above in Part 7, the nozzle top is matched against the needle's shoulder, so any mechanical differences in the sleeve, washers, stand-offs,etc between carbs will be nulled. One turn of the Idle Adjust Nut on both carbs will yield the same nozzle/shoulder gap and effectively "annular fuel orifice size".

Edited August 7, 2011 by Blue