Machining question... cam drive timing cover modification

[Harv]

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.

Angle drive assembled with pump and magneto side view.JPG (129.21 KiB) Viewed 1009 times

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.

fuel pump tang drive.jpg (37.19 KiB) Viewed 1009 times

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

[EK283]

Sounds good Harv,

Have you thought about the seal on the timing cover ?

I have a lathe and can tap the cam if it fits into my chuck, can you measure the bearing surface of the cam so I can determine if it will slide into my lathe drive hollow.

Greg

[Harv]

Many thanks

Not sure if this helps:

Grey motor cam bearings.JPG (56.02 KiB) Viewed 995 times

If not, I'll measure up one of the spare lumpsticks when I get home for Easter.

For the seal, I reckon it would be a pain using a lip seal. The Hilborn pumps have an o-ring between the pump and the timing cover, so that would be relatively easy. The McGee pumps don't though. I'm figuring on using a gasket between the McGee pump and timing cover, probably with some Aviation Formagasket goo on it. A little bit of oil splash onto the back of the fuel pump won't hurt (the timing cover is misty, but not oil filled). There is a seal in the pump proper that stops any fuel from leaking from the pump into the timing cover.

Cheers,
Harv

[EK283]

Sorry Harv,

My lathe is only 1.375 in bore size so i can't slide the cam through the chuck.

You could do it in a drill press if the cam has a centre hole drilled in the end of it.

Greg

[Harv]

No problem - thanks for offering though.

I'm not quite game to use my drill press... guaranteed to get it wonky with my fumble fingers

Cheers,
Harv

[FbSTDwagon]

Gday Harv,

Could get really funky and turn up a long shaft to somehow run in the cam bearings, have a Center drill in one end and turn 1/2 inch on the other for a pistol drill.
Install and dowel the timing cover in correct position and bump a Center drill hole straight into position.
Basically a really long spotting drill.

Should be accurate to cam bearing clearance tolerance which is .003 from memory.

Center punching them transferring to a drill press won’t be as accurate as the above suggestion

BTW I have a 2 inch bore on my lathe if it can be of any help to you

[Harv]

Thanks Drew.

I'll do some measurements while I'm home for Easter, and give you a yell.

Cheers,
Harv

[FbSTDwagon]

Essentially make a long drill like these but the length of the motor.
Turn up some brass bush’s which fit in the cam bearing holes, probably best to have cam bearings removed if possible as there would be a chance of damage to them.
Brass bush’s would have a Center reamed hole to match the drill shaft diameter.
Dummy it all up and spot the hole into the timing cover.

I have a grey block here in the shed for sizing and I think I have the material laying around, considering the help you have given me I’d be happy to make it all for you.

[Harv]

Many thanks for the offer.

Looks like a hell of a lot of work for you for something I would only use for 5 minutes. Would it be easier if I sent you a cam, and thread a spike into the end of it?

Cool none the less

Cheers,
Harv

[FbSTDwagon]

Many thanks for the offer.

Looks like a hell of a lot of work for you for something I would only use for 5 minutes. Would it be easier if I sent you a cam, and thread a spike into the end of it?

Cool none the less

Cheers,
Harv

Sure can do that Harv, either way it’s work that needs doing in the lathe.

I’m more thinking how accurate you can drill the hole after you spot the centre punch mark.

If accuracy isn’t an issue sure centre pop it and take it to the drill press.

But for less then .015” accuracy I’d personally would be using a technique that is as accurate as possible.

I can help with either, even got a bung cam here I can drill and tap for you. Would just need to check the bearing journal sizes to ensure they are the same as the what’s in the motor you are using

[Harv]

Thanks mate. I've got two bare blocks on the bench at the minute (one has to go to the FED chassis builder). I'll measure the cam bearings in the other one once I get home this weekend and let you know.

Many thanks for the help - appreciated.

Cheers,
Harv

[Mattbrown138]

I used one of Sonic injection’s finned alloy timing covers and attached a hex drive enderle 80A pump for my hilborn setup on my grey motor. The timing covers never fitted from the “ get-go” so it required lots of die grinding. Needs more work but it should work. I’d need to attach the female hex drive setup on the cam somehow.

I also have a Holden red motor timing cover with a vintage air craft fuel pump attached. Came off a old altered drag car from NSW.

Looking forward to more updates Andrew.