Short block long stroke engine

[ill_will]

I was asked some questions about the camshaft sensor and so thought I'd do a quick update.

The photo a few posts up of a 3D printed prototype used a separate hall sensor and Deutsch Motorsport connector, with magnet mounted inside a nylon rotor arm (ignore the orange rod coming out the side):

I'd gone down this route as I couldn't find a very compact OEM hall sensor, but needing to pin the connector was a hassle and the crimping tools for this connector type are very specialised.

The housing is machined from aluminium, has two Oilite flanged bushes, and the shaft is a shortened aftermarket Lucas one (Powerspark I think?)

Subsequently I found a pretty compact Bosch hall effect sensor and decided this would be cleaner.

The housing diameter works out a little smaller than the first design. The plan is potentially to heat shrink the steel single tooth wheel onto the shaft, cut down as required, although for the prototype I'll probably use a grub screw to get the orientation where it's needed. This connection detail is one area I'm not totally happy with. It needs to take axial thrust load from the gear drive.

Per the powerspark design a nylon thrust washer sits between the toothed wheel and the top bushing.

The shaft has a spiral oil groove and there is a drain back channel in the outside of the housing, per the original distributor design. There is also a small hole to allow any crankcase pressure that makes it's way past the bushes to escape.

[ill_will]

Here is the revised design, 3D printed (at low resolution, for speed, so the quality is quite poor.)

I am hoping to make up the steel toothed wheel and shorten the shaft so I can test it with an oscilloscope before programming up the housing to be machined. Figuring out a machining strategy will be interesting with the side boss, which may need some adjustments to the filleting to avoid long program run time.

[ill_will]

A couple of milestones passed in the last week.

I'm undecided about the easiest way to bed the rings in, and want to do this before trying to get all the injection kit set up and calibrated to avoid glazing the bores.

The plan was to fit the old carbs (function unknown) and a power spark distributor I have, and either stick it on a dyno, or build the car up to the point where it can be driven enough to do some third gear WOT pulls.

I put the engine on a floor stand, fitted the carbs, distributor, exhaust manifold, and set the static timing and set up the plug leads. This was a small faff as I've fitted a plate below the oil filler cap to stop spray leaking out of the cap, and couldn't see the cam lobe positions. One carb off and looking down the inlet it was pretty easy to figure out. I wired up a board with a couple of switches: ignition and starter.

Next, rigged up a fuel line with a hand pump bulb to a jerry can. In my old elan I had one of these fitted permanently in the fuel line in the boot, and used to pump it until you can feel the needle valves close before trying to start the car. Two pumps of the the throttle and it started on the third try or so. But was incredibly loud with no silencer, and it was 9pm and my garage is under someone's flat, so I laid out the centre pipe and silencer and ran it for maybe 30 seconds or so; firing nice and evenly, oil pressure 40 psi on the gauge.

With hindsight I probably should have taken off the fan belt, but hopefully no damage done. But a good point to get to nonetheless.

[ill_will]

The other milestone which has been blocking progress on designing the fuel injection has been not having the actual car anywhere nearby to take measurements from.

I got some quotes on Shiply and arranged to meet a bloke called Alan outside the garage where some of the car has been living since about 2010 or so. Armed with some bits of wood and zip ties everything loose was tied down and we loaded it up, covered it with a tarp and a couple of hours later it was next to the engine, near where I now live.

(Hah, looking at the photos I remembered doing this job was blocking starting the engine in the previous post because the coil was still in the engine bay.)

[ill_will]

I spent the day machining the main body of the cam position sensor housing shown a few posts back (which fits where the distributor normally goes.) It was challenging, with some 5 axis tool paths and tied up features (the main bore for the bearings.) The fixturing strategy I picked for the second operation wasn't great, and I wasted an hour or so figuring out a workaround for two of the five axis toolpaths which were causing the CNC controller to error.

Here is the final result, compares to the original prototype.

[ill_will]

I took a couple of photos of the fuel pump adapter made to weld into the tank, all built up. The clamp ring is finished so all the bits can now be test assembled.

Main aims are avoid fuel starvation; minimal extra gubbins in the boot; in tank pump for reduced noise and to keep it cool, and to use a second hand (but unused) tank obtained a while back. This is a system with a return, so two lines to the fuel rail. Unless the carpet is lifted it will hopefully look reasonably stock.

After a bit of searching and measuring the S1 Elise pump seemed to be about the right depth for the tank. It also has a built in level sensor. It uses quick releases; it seems several sizes are available but these are something like a 9.6mm pipe on the pump and the barb suits an 8mm ID line.

To keep the top of the pump as low as possible relative to the top of the tank the pump is slightly recessed; this was partly to avoid losing space in the boot and partly to preload the pump against the bottom of the tank to reduce rattling. The springs in each of the legs allow it to be compressed a little. The plan is to make some kind of surround out of plywood or similar to go under the boot carpet so any load sits on that rather than the lines or connectors. A second filter will go in the lines somewhere but maybe under the intake manifold rather than in the boot.

[Peter +2]

Looks very impressive.Do keep all up to date with progress.

Regards

Peter

[ill_will]

The plan was to fit the camshaft position sensor detailed above with some "oilite" plain bearings. I hadn't worked with them before and assumed initially that these would require a press fit and then ream.

They are sintered bronze which gives a very open structure and the voids/pores hold oil, a bit like a sponge if you look under a microscope.

Reading the literature however the manufacturer doesn't recommend reaming as this can clog or smear the pores and the recommended process is nerdily fascinating so I thought I'd cover it.

The recommendation is to use a hard polished mandrel to press in the bearings, which has been sized to the final clearance size plus an allowance for spring back. As far as I can tell the assumption is that the pressing process is substantially plastic and the mandrel acts as a form tool.

[ill_will]

Based on their design guide for the loads and speeds I came up with a running clearance target of 0.8 to 1.2 thou. Spring back allowance 0.3 thou. The mandrel bore diameter required was 0.5003" to 0.5007" so reasonably tight. I was making it on a mill as I don't have easy access to a lathe.

There is a feature on mills called cutter compensation where you can offset a path laterally without needing change the CNC program, which makes it easy to make a cut, measure it, and apply a correction delta to the next pass. The key is to do a series of passes taking off an approximately equal amount of material, so the loading conditions and thus deflection of the tool is approximately constant.

I did it in four bites, which gave me a safety net, so:

- first cut to clean up after roughing

- second cut is the first pass with the target finishing material thickness. Cut, then measure and correct the tool offset,

- third cut allows one further chance to measure and correct before doing the final cut, but the measurement showed that I was in the middle of the 0.4" thou target window, so no correction done.

- forth cut gives the finished surface, also in the middle of the target range.