Quote:
Originally Posted by Jacques Reed
Suggest replacing both bushings in it to get accurate timing. Amazing how a little bit of sloppiness there greatly affects the opening and closing points on the jig.
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You're quite right Jacques, a few thou play in the shaft bushings equates to several degrees rotation of the distributor cam, and twice as many degrees at the crankshaft. The points only open 15 thou and it occurs over perhaps 20 degrees rotation of the cam, which is 40 degrees at the crankshaft. That means 2 thou sideways movement of the shaft will introduce a 5 degree timing error on the jig, making it impossible to get consistent readings. And yet 2 thou clearance is perfectly acceptable for bushings, they may have even more when they're new for all I know.
However, a bit of sideplay in the bushings only presents a problem on the jig, not when the motor is actually running. It will be found that even quite sloppy bushes won't cause the timing to deviate, presumably because the flyweight plate acts like a spinning top to stabilize the shaft. I've put some pretty sloppy distributors back in old motors over the years, including flatheads lately, and they don't flick around under the timing light unless there's a fault in the centrifugal mechanism, like sticky flyweights. That's the critical area in a distributor, which is why they use those tiny precision rollers to eliminate friction and wear, and ensure smooth accurate movement.
The problem with static timing is that it doesn't replicate actual running conditions, so you have to expect a few degrees error with the Milesmore, and you won't pick up any faulty mechanism that may exist. It doesn't actually READ ignition timing, it only predicts what it will be, and since it can't take account of normal sideplay in the bushes, or normal wear in the mechanism, including the camshaft keyway, it can easily be 5 degrees off either way. For that reason it's best to err on the advanced side when static timing flatheads, because a few degrees advanced won't be noticed, but a few degrees retarded will lose you quite a few horsepower, and there's very few to spare in a blitz! It can also cause the motor to run hotter, which is enough of a problem already without adding to it!
The reality is that static timing was the best that could be done 70 years ago, but nowadays we have the timing light, which actually READS ignition timing, so we really should try to use it if we can. I'd like to get a discussion going on how to put timing marks on a flathead, so we can adjust the timing accurately, and do it easily in a few minutes, with none of this crazy rigmarole of pulling the dizzy off and fiddling around with a jig.
Recently I put the timing light on my road blitz and found it was running a few degrees retarded, and I was amazed how much better it performed when I corrected it. I've always been led to believe these old low comp motors aren't too fussy about timing, but I've had to revise that belief considerably. I'd be interested to hear what others have found in this regard.
On this occasion I didn't have time to put a degree scale on the motor itself, so I just used a temporary one on the chassis. Ideally you'd want to pull the timing cover off and mount a degree scale of some kind there, or even just a simple pointer with the degree scale marked on the crankshaft pulley. Either way is fine, and both arrangements are used on modern motors. None of that presents any great difficulty, the main challenge in this exercise is finding TDC. It's easy enough when the heads are off, using a dial indicator on the piston top, but we need a method for motors already in service. In this case I used a simple volumetric method, using a cheap home made device, but while it's certainly as accurate as a dial indicator, it's very tricky to use. I'd like to find a mechanical method, because it would greatly simplify the exercise. For example, with the timing cover removed, which needs to be done anyway to mount the degree scale or pointer, we should be able to work off the valve timing marks on the timing gears. That is, if we knew the exact position of the crankshaft when the timing marks are perfectly aligned, we could measure back from there on the crankshaft pulley. Unfortunately I have no idea where to get that information, so I'll probably have to measure it myself one of these days when I come to rebuilding a motor.
I've often wondered if there's anything available in the hot rod scene, but so far I haven't come across anything from Macs or anyone else. What's needed here is an aftermarket timing cover with a degree scale cast into it, and an aftermarket crankshaft pulley with a timing notch. You know, just like you get when you buy these parts for a modern motor! How hard could it be for these guys, given all the other repro stuff they make?
Likewise all the so called flathead experts are completely useless in this area. I've read quite a few of their manuals on how to tune up flatheads, with all sorts of high performance aftermarket gear, but not one of them can tell me how time a flathead PROPERLY! All they tell me is which other so-called expert I should give my crab to be timed on a jig!
Anyway I'm sure we can crack this nut if we put our minds to it, so we can time our flatheads properly like we expect for our car motors. It would also allow us to fit an electronic breaker plate, which at around $100 would be a no brainer. No more fiddling around with points, and you never have to check the timing again, except to prove to yourself what a good investment it was!
