Machining question... cam drive timing cover modification
Posted: Sun Apr 10, 2022 12:14 pm
For the meth monster project, I've got a few changes to make to the engine ancilliaries.
The Repco inlet manifolds are really close to the dizzy mounting hole, so I have to turn the dizzy sideways in order to get the magneto to fit. I've got a McGee angle drive that will do that, though I need to be wary that a lot of weight is then cantilevered off the angle drive. My angle drive (and many like it) had cracked, and I had to have it rewelded. I'll need to make a brace for the magneto back to the sideplate to stop the magneto pendulum cracking the angle drive. Plan at this stage is to use modify a Vertex dizzy timing clamp to do so... should be fairly simple.
The McGee angle drive lets me run a mechanical fuel pump where the dizzy would normally live. Methinks those Repco inlet manifolds are too close to run a Hilborn pump, but the stubby little McGee pump shown above should fit. I rebuilt and had the McGee pump flow tested a few years back, and it failed... still need to sort out the clearances in the McGee pump, so will have to make my own scaled-down flow test rig (flow some kero in/out of a bucket, drive the pump with the drill press, increase the back pressure with some form of needle valve, measure pressure with a gauge, time the flowrate by stopwatch).
If my tinkering on the McGee pump does not work, I will need to run a Hilborn pump (or one of the bigger McGee pumps) off the front of the motor. With the Norman and drysump pump fighting for real estate, it will not be likely to run the fuel pump by belt drive. I suspect it is going to need to be cam driven. Even if I don't use the cam drive for the fuel pump, I have a rather neat tacho drive and cable that runs to a period-correct Jones tacho. It needs cam drive too. So one way or another I am going to need to drive something off the end of the cam.
One of the humpy gentlemen donated an alloy timing cover to me some time back. It's a lot more hefty than the standard pressed-tin timing cover. Plan is to drill and tap some studs into it, and use those studs to either mount the fuel pump or to mount the tacho drive. That part is easy... the tough part is joining the cam to fuel pump/tacho.
I'm aiming to use a tang drive to do the job. These are pretty simple affairs, and only need a slot in the end of the cam to engage with the tang.
The tricky bit is getting the hole in the timing cover in the right spot. According to Kinsler, the pump needs to line up to the cam with less than 15 thou runout. A bit more finicky than my normal angle-grinder-and-BFH shenanigans.
The way I'm thinking of doing it is to use an old reject cam (I have one) and drill and tap the fore end. Make up a pointer (a bolt turned down to a concentric point) and screw it into the cam. I'd then use the engine block with the cam roughly installed and the crank properly installed. Install the timing cover, and centre it onto the crank using the installation tool. From the aft end of the cam gallery (welsh plug removed), tap the cam forwards so that the pointer dents the timing cover. Use that dent as the centre mark for drilling the hole in the timing cover.
Interested to hear if there are easier ways to do the task. Would be interested too if anyone with a lathe would have a crack at tapping the cam end and making up a pointer (happy to pay).
Cheers,
Harv
The Repco inlet manifolds are really close to the dizzy mounting hole, so I have to turn the dizzy sideways in order to get the magneto to fit. I've got a McGee angle drive that will do that, though I need to be wary that a lot of weight is then cantilevered off the angle drive. My angle drive (and many like it) had cracked, and I had to have it rewelded. I'll need to make a brace for the magneto back to the sideplate to stop the magneto pendulum cracking the angle drive. Plan at this stage is to use modify a Vertex dizzy timing clamp to do so... should be fairly simple.
The McGee angle drive lets me run a mechanical fuel pump where the dizzy would normally live. Methinks those Repco inlet manifolds are too close to run a Hilborn pump, but the stubby little McGee pump shown above should fit. I rebuilt and had the McGee pump flow tested a few years back, and it failed... still need to sort out the clearances in the McGee pump, so will have to make my own scaled-down flow test rig (flow some kero in/out of a bucket, drive the pump with the drill press, increase the back pressure with some form of needle valve, measure pressure with a gauge, time the flowrate by stopwatch).
If my tinkering on the McGee pump does not work, I will need to run a Hilborn pump (or one of the bigger McGee pumps) off the front of the motor. With the Norman and drysump pump fighting for real estate, it will not be likely to run the fuel pump by belt drive. I suspect it is going to need to be cam driven. Even if I don't use the cam drive for the fuel pump, I have a rather neat tacho drive and cable that runs to a period-correct Jones tacho. It needs cam drive too. So one way or another I am going to need to drive something off the end of the cam.
One of the humpy gentlemen donated an alloy timing cover to me some time back. It's a lot more hefty than the standard pressed-tin timing cover. Plan is to drill and tap some studs into it, and use those studs to either mount the fuel pump or to mount the tacho drive. That part is easy... the tough part is joining the cam to fuel pump/tacho.
I'm aiming to use a tang drive to do the job. These are pretty simple affairs, and only need a slot in the end of the cam to engage with the tang.
The tricky bit is getting the hole in the timing cover in the right spot. According to Kinsler, the pump needs to line up to the cam with less than 15 thou runout. A bit more finicky than my normal angle-grinder-and-BFH shenanigans.
The way I'm thinking of doing it is to use an old reject cam (I have one) and drill and tap the fore end. Make up a pointer (a bolt turned down to a concentric point) and screw it into the cam. I'd then use the engine block with the cam roughly installed and the crank properly installed. Install the timing cover, and centre it onto the crank using the installation tool. From the aft end of the cam gallery (welsh plug removed), tap the cam forwards so that the pointer dents the timing cover. Use that dent as the centre mark for drilling the hole in the timing cover.
Interested to hear if there are easier ways to do the task. Would be interested too if anyone with a lathe would have a crack at tapping the cam end and making up a pointer (happy to pay).
Cheers,
Harv