Sigma Astron 2000 water pipe to heater and inlet manifold

[kishogue]

I have a Sigma Astron 2000 engine fitted into a 1971 VW Kombi campervan.
There is a leaking rusty metal water pipe that goes from back of water pump under exhaust manifold and loops around back of engine then has rubber hose takeoffs for heater and inlet manifold to heat incoming air. There is no heater attached and in Australia there is no need to heat incoming air. What happens if I remove the pipe and block off the rear water pump outlet? Will that have secondary effects? Like does the water flow from the inlet manifold into the cyclinder head, or is it an isolated circut? And even if it does flow into the head, will it matter if the flow is blocked? Or have I got it wrong and the flow is *out* of the head into the pipe? Any advice gratefully received.

[geezer101]

Hi kishogue, welcome to S-G. The external water gallery running into the neck of the water pump from the back of the head is purely there to return coolant from the cabin heater. Blocking it off shouldn't have a detrimental effect to the engine. The coolant flows from the thermostat housing on the inlet manifold, through the radiator and back into the block via the water pump. The 'barb' on the inlet manifold between #3 and #4 inlet runners is the point where hot coolant feeds from the head to the cabin heater (once it has passed through the heater core it is pulled back into the water pump). There is a secondary small barb on the side of this main barb - this feeds coolant into the carby for the auto choke assembly. Hope this makes sense. ...and a 4G52 in a Combi? We ALL want to see pics of that!

[kishogue]

Thanks for reply. It makes me wonder if I have a Saturn inlet manifold on the Astron case & head, as the manifold water pipe is from between cylinders 2 & 3, not 3 & 4, and also the autochoke pipe does not go to the manifold but instead straight to the water return rail (it has a t-junction with one stub towards the manifold pipe and the other stub upwards towards the autochoke). There actually doesn't seem to be an obvious place for the heater in & out to connect, unless that's from a separate junction somewhere nearby. Any ideas?
OK, I'll try to get some photos, but it's not a showcase so don't expect anything flash.

[kishogue]

Maybe it is an Astron manifold after all. Have a look on YouTube at "hqdefault.jpg"

I see now that the autochoke connects to the "secondary barb" between cylinders 3 & 4, while the main "barb" feeds water to the heater and the heater outlet connects to the t-junction of the water return rail. I suspect my engine has the "barb" blocked off and has the pipe from the auto choke connected directly to the return water rail instead.

But look at the rear inlet side, where the water rail has a stub with a rubber pipe going along under the inlet manifold. The manual implies it is fed from the inlet manifold between cylinders 2 & 3. What's that for? Is it an essential water return or can that be blocked off without consequences?

[geezer101]

Saturn and Astron engine components aren't cross compatible. The designation code for a Saturn engine is 4G3X (the "X" will identify the engine capacity as being either 1300,1400,1500 or 1600 cc's) They are also a smaller size compared to the Astron engine (4G52=2 litre, or 4G54=2.6 litre) I checked out hqdefault.jpg on youtube but couldn't find anything related to your post. If the auto choke gallery is hooked up to the external water gallery (heater return pipe) I'd say it's set up incorrectly. It should be getting its feed from the inlet manifold between #3 and #4 inlet runners, then returning back into the manifold through the barb at the base of the carby.

[kishogue]

Google "youtube hqdefault.jpg 4g52" and select "4G52 engine from a Mitsubishi Celeste 1977". Yes, you're correct, having looked the autocheck is getting its feed from the inlet manifold between #3 and #4 inlet runners, then returning back into the manifold through the smaller barb at the base of the carby, with the larger barb looped directly to where the heater outlet would normally connect.

About two-thirds through the YouTube clip you can see where the water rail has a stub with a rubber pipe going along under the inlet manifold. Later you can see it connects to the inlet manifold between cylinders 2 & 3. What's that for? Is it a "bypass" pipe to ensure return flow even when the heater is off? Is it an essential water return or can that be blocked off without consequences?

[geezer101]

When the 'tap' (heater control) is closed completely off, it stops any coolant from entering the heater unit. Once the tap is closed any coolant that would've passed into it is forced to continue it's path from the base of the inlet manifold (there's an outlet cast into the manifold and that is where that hose is connected) through that external coolant gallery. My bad, I forgot about that hose feeding into the base of the inlet manifold. This is a pic of the 4G52 inlet manifold and carby (partially assembled). You can just see the cast outlet between #2 and #3 in the lower part of the inlet manifold below the base of the carby - I'd thought about getting a replacement external gallery made up by a plumber out of copper pipe as nearly every one of these pipes end up rusting out on the ends (and it really shouldn't cost that much to get made up out of scrap). They should still be available new, but you wouldn't need that small extension that points up out of the external gallery pipe for the heater unit.

[kishogue]

OK, that's clear now. If it's just a bypass, and if we assume that an inlet manifold doesn't *really* need to be heated (especially in Australia) then it should not make any difference if that whole subcircuit is blocked off. Otherwise your idea of making up a replacement pipe without the heater t-junction seems like a reasonable option. Sigmas bits are extremely hard to get here.

How do you add photos? I clicked on the "Img" button but just get the html header & trailer, no dialog box to select a file.

[geezer101]

You can't delete this connection as it shares the coolant with the auto choke on the carby. They meet via the internal coolant gallery running inside the inlet manifold and into the base of the carby. As for posting up pictures, who do you have as a media storage site? If you're using photobucket you just highlight "get links" on the options icon that appears on the thumb nail images in your albums. Select "Direct" to copy the file location of the image you want to use, then paste it in the image tags. It should then appear as a picture in your post It took me a while to get the hang of it...

[kishogue]

Ah now I understand the image refs, but I don't use web storage, pity.
My autochoke mechanism jammed up on me a few years ago so I tied the linkage off with brass wire, so I have no autochoke anyway.
What I might do is just remove the water rail and join together the two hoses that would normally go to the t-junction. Then there will be no flow, but neither the lack of autochoke nor the lack of manifold heating are of much concern in this climate. Of course I'd have to block off the water pump end too.

[geezer101]

My autochoke mechanism jammed up on me a few years ago so I tied the linkage off with brass wire, so I have no autochoke anyway.

It does come in handy when winter kicks in (unless you're up in the top end of Australia). And getting online media storage is an easy deal to sort out (and all the entry level media storage is free).

[kishogue]

OK, another question, since we've raised topic of auto choke, and also as you posted pic of lovely clean Mikuni carb that seems same as mine, i.e. triangular choke element at right rear of carb above vacuum diaphragm, rather than cylindrical element at centre rear of carb.
The question is he does it work?
That question follows from what my autochoke seems to work. When cold the choke valve is about 5 degrees from horizontal. The element has about 0.25" travel, with about 0.05" slack before it hits the sprun-loaded metal plate that rotates the choke valve. At the top of the element travel the choke valve is about 25 degrees from horizontal, so nowhere near fully open (vertical).
There is a rack and pinion gear on the end of the choke valve shaft, but I can only rotate it a couple of degrees - does that mean it's jammed? What does it do anyway?

[kishogue]

Correction, once the engine is running the element blade moves immediately to the top of its travel, and cannot be moved by hand anymore.
Also with a *lot* of force I *can* rotate the pinion cam lever which rotates the choke valve fully open.
However, as before, if I do nothing the choke valve never gets more than 25-30 degrees from horizontal.
What normally makes the pinion can lever rotate?
(Whatever does it seems not to work on my carb)

[geezer101]

The 'rack and pinion' is the actuator for the choke butterfly. Behind it is a monstrous coil spring - make sure you've had a hearty breakfast before attempting to get it to release the choke while cold (and be warned, it will crush a finger if you get it wedged in there) The wax pellet in the casing with the coolant hoses connected to it works this way: engine warms up and coolant passes through it, the wax in the actuator melts as it's warmed then expands causing the inner rod to push on the choke cam, this then releases the choke. Here is a pic of the 'normal' condition of a Mikuni carby...
^If your carby is covered in this thick dark greasy stuff it more than likely means the wax pellet has failed.

[kishogue]

Where is the 'inner rod' that 'pushes on the choke cam' ?
Is it the 2mm wide flat blade coming horizontally out of the triangular casing at top right of your photo (can't be seen in the photo) ?
If so, how does it 'push on the choke cam' ? On my carb it seems to withdraw in the direction into the housing. OK, maybe that releases the choke cam, but I don't think so since the big spring is holding the choke cam the other way.
Is there anything down inside the carb that is driven by the shaft on which the choke can and big spring are mounted? Or is it just the pivot for the choke cam?

[geezer101]

O.k. I'll see if I can try to make this sound like I know what I'm talking about The assembly with the geared teeth cut into it - behind that is a small brass rod that's pressed into the end of the wax pellet choke unit (2 coolant hose barbs cast into the side of it) It's that small brass rod that exerts the force to load up the 'cam' arm. This twists the plastic gear on the end of the choke butterfly and opens it (the plastic gear is tensioned by a light spring so it will open enough under vacuum at start and not cause the carby to be completely starved of air). There's also a secondary linkage that is connected to the primary throttle butterfly (this lets the choke butterfly open partially while it's cold and under throttle to allow driving during warm up).

[kishogue]

Any chance of a photo that shows the brass rod?
I don't see any sign of it on my carb. On mine the plastic gear is not tensioned, instead the choke butterfly valve is rotated via a metal plate that can only rotate forward of the plastic gear, with a light reverse tension spring (maybe we are saying the same thing?). The thing is that on my carb the wax pellet choke unit with the two coolant barbs does not have a brass rod (that I have seen *yet*) -- instead it has a flat blade right close to the plastic gear. The blade seems to withdraw in towards its housing when cold, and when it does that it pushes the metal plate around towards the choke butterfly valve open direction, maybe by 20 degrees. But no way could it rotate the valve by 90 degrees -- only the plastic gear could do that, but without any obvious brass rod I canna see any way for that to happen.
Like I said, a photo that made the brass rod obvious would be a great help.

[geezer101]

Here's a pic of the resin body Mikuni carb but it shares the same type of auto choke mechanism. The tip of the screwdriver is pointing to the brass actuator rod in the end of the wax pellet unit -
It should not be fully pushed back into the wax pellet unit, about 2-3 mm of the inner shaft should be exposed (as per pic). The head of that actuator shaft is butted up against an adjusting screw on the other side of that 'cam' arm (you can just see the side of the head of that screw with a dab of white paint on it). Hope this is what you were looking for

[kishogue]

OK, many thanks. That's a place that's very hard for me to see into even with an inspection mirror since it's at the rear of the Kombi engine bay with room for the mirror or a small torch but not both. I'll look next week - we're going to be using the Kombi over the next few day.
I wonder what the flat blade coming horizontally out of the top left of the wax pellet housing (travelling 0.1" below plastic gear, sort of halfway between the top water hose spigot and the screw ababove it in your last photo, obscured) - I wonder what the function of that is?

[kishogue]

Correction -- in your first photo.

[geezer101]

O.k. I think I understand what you're referring to. There is a diaphragm cover plate attached to the back face of the auto choke unit - it sort of looks like a radiation warning sign with 3 screws in a triangular pattern holding it in place? Inside of this is the 'auto choke release assist' diaphragm. There's an actuator arm that passes along the body of the auto choke pellet housing and disappears to just under the plastic gear. On the end of it is a 'pickle fork' that moves a small finger that is part of the end of the choke butterfly shaft. it is supposed to help prevent the choke shaft from going from 'completely choked off' to 'fully open' (apparently it was possible that the choke could stick shut longer than necessary during warm up). These assist diaphragms do fail but you don't realise that it has occurred - they split/puncture (the rubber diaphragms go hard from age), then air bypasses through the puncture and into the vacuum galleries in the carby.

[kishogue]

Well explained, thanks. I've never seen any mention of that before.
So, back to the main problem: my auto choke doesn't fully open (butterfly valve vertical) when the engine has warmed up. Maybe the pellet is duff (but there's no black muck about as you mentioned earlier), or maybe the mechanism is worn. I have adjusted the choke screw so the pinion hasn't any slop, so that's not the reason. Any thoughts?

[geezer101]

Maybe you've over adjusted it? It shouldn't snap shut when you tap your finger on the choke butterfly - it should be tensioned so it is just sitting closed at full cold start (engine vacuum should be enough to get the choke to open a few degrees). If you set the choke stop so the alignment marks are pointing at the centre of the plastic gear pinion and the stop on the primary throttle shaft linkage (they are stamped on the choke 'cam' arm), and the choke is shut tight - you need to undo the bracket holding the choke gear pinion in place and gently lift it away from the choke 'cam' arm (just enough so you can rotate the plastic gear a tooth to release tension off the spring) and then refit the bracket back into position. The choke gear only has to turn a tooth and a bit to enter it's fully open position. This must be doing your head in trying to adjust the carby in the engine bay of a van...