Tue Jun 11, 2013 8:42 pm
I have a '48 that is about to get ignition. I am familiar with the TDC on #1 concept. I have tried to achieve this using Gary Dotson's method posted in the How To section by stopping right between the valve openings on the #4 cylinder. Is this good enough or are there any slightly harder, but more accurate methods? I have a dial indicator to actually find it the traditional way, but I'm not sure that going through the spark plug hole will get you very far on a Cub.
And what about these timing marks? When I got the engine to TDC on #1, I looked at the front of the crank pulley. The divot on the pulley was in about the 12:30 position (looking straight at the crank pulley) and the pin coming out from the front cover is at about 2:30. Does this mean anything? What exactly is the purpose of the divot and the pin? I believe you folks could really help me in this last 15% or so to get this thing running again.
And for those of you keeping score, this '48 had a mag, but is getting an electronic ignition.
In other news, I'm pleased that it looks like the generator belt will be the right length to also work on the alternator. Also, I'm conducting an experiment to see how the valve cover gasket will function as a radiator gasket (on accident
Tue Jun 11, 2013 9:08 pm
Remove #1 plug. Ignition switch off. Place your thumb over hole and rotate engine with hand crank until you feel air pressure. Divot should be approaching pointer. Slowly rotate until divot lines up with pointer. This means #1 is at TDC. Pull the distributor cap and verify that rotor is pointing to #1 tower. Is there one or two divots on your pulley? If two then line up with second divot
Tue Jun 11, 2013 9:10 pm
The TDC mark on your front pulley should indicate when the #1 piston is at TDC with the #1 piston on the compression stroke.
Tue Jun 11, 2013 9:13 pm
Rudi he is no longer using the mag
Tue Jun 11, 2013 9:17 pm
OK. I will try the thumb method. Can I alternatively do this by watching the valves on #1 and quit when the divot lines up with the pointer on the revolution where the valves don't move? I may do it both ways. I have to take the valve cover off and swap the spark plugs for other reasons anyway.
And thanks for the help guys. I've felt pretty good about the restoration so far as things have been mostly mechanical. The last two things ( redoing the carb and getting the ignition installed ) are the things that I'm the most unsure about.
Tue Jun 11, 2013 9:49 pm
I missed that part.
I feel like Eeyore ....
Wed Jun 12, 2013 6:49 am
Dennis, you must have missed something in the procedure. There is only a brief moment when both valve on a given cylinder are moving, as the exhaust is almost fully closed the intake valve is just beginning to open. At this point, your timing mark should have been very close to aligned. Please try it again and see if it comes out differently.
Wed Jun 12, 2013 9:49 am
Desiel D has the best method of checking timing so far from what i've read,look-n at the valves doesn't seem to be the right thing to do to me, one valve lets air/gas in, and one valve lets air out, i take it you allready have no.1 plug out, its easier when you have two people on the job,one can hand turn the crank while one holds thumb over hole (wait a second ain't done yet) the very second you hear air coming out (stop cranking) this may sound hillbilly to you but it has worked for me 15 times,take a 8" length of no.14 romex wire with the plastic coating on it ,take the end and curl it over so it dosen't have a sharp end try not to bugger up the end to much, stick in hole till it stops go-n in- (touch-n piston top)pull back out a couple of inches so it don't get pinched between piston and wall if the plug hole is not directley over piston and at an angle, have assistent crank slow/ watch wire raise until it stops going any farther stop right away, piston should be tdc or btdc or after tdc pull cap check where rotor button is should be on no.1 plug wire or close, or if your installin distributor pull in and out till gear teeth line up to make rotor line up with no.1 plug wire check timing refrence for that model
Wed Jun 12, 2013 10:42 am
DieselDennis wrote:And for those of you keeping score, this '48 had a mag, but is getting an electronic ignition.
Assumption, distributor is not installed in the tractor.
KISS. When the pointer lines up with the TDC mark on the pulley, #1 cylinder is at TDC, either on compression or exhaust stroke. Finger in hole until you feel compression, then line up the TDC mark and pointer.
You next step is to install the distributor and then static time the engine.
My suggestion is to install the distributor with points and get the tractor running before attempting to install an electronic ignition.
Wed Jun 12, 2013 11:43 am
Actually, Gary's method is pretty darn good
With my '47 - Granny, I had mucked up the timing so bad we just couldn't get it right. Compression has a lot to do with that. I have always timed with the thumb on the #1 plug method, but with Granny it wasn't possible.
Troy (my mechanic) and I pulled the valve cover .. freed up the stuck valves and then retimed by watching the valves as they progressed as the crank was turned. Didn't take long to discover #1 TDC. I also used the Spark Plug Illuminators in this thread - How To Understand Firing Order
I also agree with Eugene ... I would suggest you put the mag back into the Cub, retime properly and then convert to the 6v electronic ignition. What that is going to do I am not sure ... as the Mag is more than reliable.
Thu Jun 13, 2013 10:27 pm
Just wanted to let everyone know that I pulled the #1 plug and tried the thumb method. I just couldn't "feel" the pressure though. Guess I couldn't hold it tight enough or press it hard enough. So I just cranked it until the pulley punch mark lined up with the pin and peeked in the spark plug hole. Saw a valve popped up. Rolled the crank pulley another turn until the punch mark and the pin lined up. Peeked in the plug hole again and saw both valves down. That should be it, right?
Fri Jun 14, 2013 4:57 am
Fri Jun 14, 2013 8:38 am
Cubs are "four stroke" engines meaning that the crank shaft rotates twice while the distributor goes through one rotation. Given that the gears connecting these items and the cam shaft are aligned correctly (using the "timing marks" on them, under the front engine cover), these items must be "timed" as a group to the firing of each cylinder's spark. With the gears in correct mesh, the pointer on the left front of the engine case and the two notches on the crank shaft pulley indicate number one (forward) cylinder position.
The engine (crank shaft) turns counter-clockwise looking tractor forward while the distributor rotor turns clockwise looking forward or towards the front. Therefore, the first notch to reach the pointer indicates top dead center (TDC) of the first cylinder piston OR half a turn from TDC. The second notch to reach the pointer indicates sixteen degrees behind these positions.
When cylinder one is at TDC, the distributor rotor will be at or near 2:30 clock position looking forward. If it's at 8:30 position, the crank shaft must be rotated a full turn to set the forward cylinder at TDC. The pointer and first pulley notch are to be used to set the crank shaft positions.
With the crank shaft now set at TDC on cylinder one, the distributor's center shaft clock position can be set at 2:30 with the unit unattached from the engine. Insert the preset distributor into the engine and mark the position of the rotor on the outside bell of the distributor housing. Place the distributor cover on the distributor base and check that the spark contact for cyclinder one is aligned with the rotor marking. If it's not, note how much it's off before removing the distributor from the engine and resetting its rotor shaft/gear.
Under the internal distributor floor there is a pair of cams and springs that change the clock position of the distributor rotor when the engine is running. The springs react centrifugal force of the two cam weights under the distributor floor plate. If this mechanism is gummed-up or binding (from rust?), the weights and springs will not properly advance spark. Before attempted to assemble the distributor to the engine, the advance system should be checked for function. When the weights are "in" (springs relaxed), the rotor is in zero advance position which is correct for making the installation.
The engine can be started after making this set up. A spark timing light can be applied to make fine adjustments to the timing of spark plug one at idle speed (first pulley notch) and sixteen degrees advance can be checked with the engine running at full speed.
Fri Jun 14, 2013 8:59 am
DieselDennis wrote:I pulled the #1 plug and tried the thumb method. I just couldn't "feel" the pressure though.
Before going further. Conduct compression tests on all cylinders. Little or no compression - engine won't run.
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