Hi everyone - its time for an embarrassing admission; for the last 5 years I have not been able to operate my engine with more than 3/4 throttle
I know, shocking isn't it? All those videos - Nova T33, 2 Novas 2, The Ascent of Little Switzerland, all done on 3/4 throttle. No wonder it looks so slow
Anyway, yesterday I finally got around to doing something about it. As some of you may know, I am using a hydraulic throttle actuator from Chuck Neil Inc. Popular for drag racing, where chassis twist can result in slackening of the accelerator cable, this neat little device uses a tiny master cylinder and pushrod to operate the throttle bar in the engine bay, and a similar slave cylinder under the throttle pedal. The two are connected together by about 8 feet of hydraulic pipe, and use automatic transmission fluid (ATF) as the working medium.
For all of the time the Green Machine has been on the road, the master cylinder support bracket, which is bolted onto the top of the engine through two of the water pump elbow bolts, has been positioned so that the pushrod cannot open the throttles fully. I lived with it, as I rarely use all of the throttle pedal, but there were always occasions where this lack of prod was not only an embarrassment, but could be dangerous as well (overtaking, for example). I also reasoned that, in spite of the system being intended to open the butterflies on a 4 barrel Holley, there ought to be more travel available in the pushrod than I was apparently getting.
So, yesterday I set to work. I removed the master cylinder Hiem joint from the support bracket and then removed the latter as well. I then measured up for a new bracket to reposition the cylinder in a more horizontal orientation, allowing more of the pushrod movement to operate the throttle balance bar. The plate that the bracket sits on had to be carefully reliefed in order to clear the water pump elbow casting. I did this with an angle grinder. I then welded up a suitable support using left-over 3/8" box section. Looks a bit agricultural, but the thinwall tubing (as opposed to the original 4mm steel plate construction) is probably no heavier.
Here it is in place on top of the engine. Note the close fitting around the water pump casting.
Once the new bracket was in place, I offered up the master cylinder Hiem joint and bolted it up in a suitable orientation;
Overhead shot shows the pushrod actuation angle. The picture also shows how filthy the engine got driving through the rain last weekend; I don't know where all this muck came from, maybe the roadworks on the M25...
Incidentally, for part spotters I can state (for the record) that the rubber bellows protecting the pushrod are branded VW!
Alternator back in place and belt tension adjusted.
View from the back, looking forward to the bulkhead.
Overhead view of the reassembled engine. The new master cylinder location has moved the throttle pedal away from the forward bulkhead, and the pedal itself is now in line with the brake and clutch pedals. This is something I will have to get used to, but is no different to driving an unfamiliar car for the first time.
Starting the engine with this new arrangement was a revalation; the original thrust angle may not have allowed full throttle, but was quite progressive. Now, the engine instantly barks with real authority in response to the pedal - I now know that I will get all of my 95 bhp when I ask for it!
However, there was another problem which needed my attention, which was unconnected to the hydraulic system, as it turned out.
For some while now I have been experiencing the throttle sticking in use, particularly if the engine is running at a constant speed for some time. Initially this form of "cruise control" was quite disconcerting, but eventually I learned to blip the throttle briefly and the butterflies would close properly.
I thought this might be due to a wear ridge building up in the master cylinder, as there was a bit of unintentional lateral preload on the cylinder from the hydraulic fluid pipe, which is quite rigid. In repositioning the cylinder, my hope was that the pushrod operating point would move to another position in the cylinder, and the stickiness would be resolved.
Alas, this was not the case - with the engine at idle, gentle pressure on the pedal resulted in the engine note rising and not returning to fully-closed unless the pedal was blipped. I pondered this little problem for a while, with that clarity that only comes with the knowledge that the car would be unusable for the next week unless I found a solution...
The throttle return spring operates on the balance bar bellcrank, but that is the only return spring in the system. It has to force the throttle butterflies closed, and at the same time force the pushrod back into the cylinder, pushing the hydraulic fluid back into the slave cylinder and pushing the pedal out, against the stiction in the pivot mechanism (which was thick with grease). No wonder the throttles wouldn't close completely! What I needed was a throttle pedal return spring, something to overcome the stiction so that the spring in the engine bay stood a fighting chance. The problem was, I didn't have a suitable spring...
Now I apologise if this gets a bit surreal, but I had a flash of inspiration. Why not make a suitable spring? To do this, I needed some sprung steel wire, and a suitable mandrel to form it on. The former came from a dismantled egg-whisk, bought from Woolies before they went bankrupt for the S.K.W.I.D. project. SKWID stands for Submersible Kinetic Water Immersion Device, which unfortunately didn't succeed due to some technical difficulties producing a sound watertight seal without proper machining facilities. But that's another story - back to the egg-whisk. The whisking bit consisted of half a dozen sprung steel wires, formed into a U shape and held together at the top by a tubular handle. Removing the handle provided the wire I needed for my return spring.
An offcut of M10 threaded rod, clamped in the vice provided the mandrel. Then it was a case of having a go...
Whoops! Not a very good first effort, but you've got to start somewhere Now for the Mk2...
Ah, much better. The coil fits around the pivot shaft of the pedal, the big hook goes around the pedal itself, and the little hook slots into a convenient hole in the pedal box flange.
And here it is in place. In oder to engage the little hook, the spring has to be pre-loaded, so the pedal is always trying to pull itself away from the bulkhead. The pedal shaft passes through a steel boss welded to the chassis, and is threaded at the other end. I used a reversed M10 Nyloc nut to locate the shaft while at the same time providing a little bit of endfloat. Also, all the grease is gone - from now on I will be using oil on the pedal shaft!
Now the pedal returns smartly to the closed position, no matter how gently I operate the throttle, and perhaps more importantly, the pedal goes all the way to the floor without the spring becoming coil-bound.
Right - now to put some (cautious) miles on the clock to check out my handiwork!
Lauren