Valve Timing

Tue Jul 08, 2014 6:53 am

Standard Cub no mag 1954…..While lapping valves I ran into a problem….OK, I have "rock over" on Cylinder # 4, (The Intake closes and the exhaust is starting to open)…Am I correct in assuming this places Cylinder # 1 at TDC ( the timing notches line up)…..If so, my rotor is pointing 180 degrees off ( It is facing about 7 o'clock…The distributor tower is wired with # 1 in that position….Should I pull the distributor and turn the rotor 180 or pull the pulley and check the dots…Someone botched a previous partial rebuild and I'm trying to straighten it out so its kinda like the "Trouble Shooting" contest we had in Boces back in the 60's... :lol: Probably should mention the engine is on a stand with the pistons out etc….Thanks Dave

Re: Valve Timing

Tue Jul 08, 2014 7:24 am

Cylinder #1 and #4 are at TDC when the mark lines up with the pointer. Once cylinder is at the top of the compression stroke, the other cylinder at the top of the exhaust stroke.

Since you have the head off. Rotate engine until both valves are closed on cylinder #1 and TDC mark lines up with the pointer.

You can now reposition the distributor to match the correct spark plug wire location and you can also static time the ignition to the engine. I would correct the distribution/rotor location.

Pulling the pulley and front cover to check the cam shaft and idler gear timing. Not necessary. Mentally think through the valve and piston timing. Rotate the engine, observing #1 cylinder and valve action. At start of compression stroke piston will be at it's lowest position. As the piston starts up both valves will be closed. Valves remain closed for about a 360 degree rotation of the crankshaft. Then the exhaust valve opens. Etc..

Re: Valve Timing

Tue Jul 08, 2014 7:50 am

True to a point but Cylinders 1 and 4 both have their valves closed and the pointer will be on the timing mark in both cases….So I believe that" Rockove'r has to occur on Cylinder 4 to make Cylinder # 1 at TDC….Otherwise it could be 180 degrees off… Which is probably what the PO did...
Eugene wrote:Cylinder #1 and #4 are at TDC when the mark lines up with the pointer. Once cylinder is at the top of the compression stroke, the other cylinder at the top of the exhaust stroke.

Since you have the head off. Rotate engine until both valves are closed on cylinder #1 and TDC mark lines up with the pointer.

You can now reposition the distributor to match the correct spark plug wire location and you can also static time the ignition to the engine. I would correct the distribution/rotor location.

Pulling the pulley and front cover to check the cam shaft and idler gear timing. Not necessary. Mentally think through the valve and piston timing. Rotate the engine, observing #1 cylinder and valve action. At start of compression stroke piston will be at it's lowest position. As the piston starts up both valves will be closed. Valves remain closed for about a 360 degree rotation of the crankshaft. Then the exhaust valve opens. Etc..
.Am I correct in assuming this….

Re: Valve Timing

Tue Jul 08, 2014 7:53 am

Eugene, I think we are both saying the same thing differently….In reference to the exhaust valve on # 4…. and "rock over"…Correct me if I'm wrong…
:lol: Dave

Re: Valve Timing

Tue Jul 08, 2014 10:21 am

pickerandsinger wrote:True to a point but Cylinders 1 and 4 both have their valves closed and the pointer will be on the timing mark in both cases….So I believe that" Rockove'r has to occur on Cylinder 4 to make Cylinder # 1 at TDC….Otherwise it could be 180 degrees off… Which is probably what the PO did....Am I correct in assuming this….
Eugene wrote: Mentally think through the valve and piston timing.
Watch the valve action. Continuing the crankshaft rotation from TDC with both sets of valve closed, the exhaust valve will open on one cylinder and the intake valve will open on the other cylinder.

If you think the camshaft and idler timing is off, go ahead and remove the tractor front end, loosen the oil pan, pull the pulley, remove the front cover and check.

720 degrees crankshaft rotation for a complete combustion cycle. The valve action between #1 and #4 cylinder is 360 degrees different, or one full crankshaft rotation.

This is an edit since I haven't posted it yet. If the tractor ran after you obtained it, the cam shaft and idler gear timing is correct. All you need to do to correct the ignition timing is to remove and reset the distributor.

Re: Valve Timing

Tue Jul 08, 2014 11:09 am

Eugene wrote:rotation from TDC with both sets of valve closed, the exhaust valve will open on one cylinder and the intake valve will open on the other cylinder.
OK, so saying this scenario is Cylinder 1 and Cylinder 4 as we spoke of, the exhaust valve opening on Cylinder 1 would suggest that it is leaving TDC (on the compression then power stroke, and The Intake valve opening on # 4 suggests it is leaving the exhaust stroke correct…( Sorry , if I seem confused but I am :D )So number one would be at TDC and not number 4 correct….Thanks Dave

Re: Valve Timing

Tue Jul 08, 2014 11:36 am

http://electroncastle.com/wp/wp-content ... -cycle.jpg

Re: Valve Timing

Tue Jul 08, 2014 12:17 pm

pickerandsinger wrote:OK, I have "rock over" on Cylinder # 4, (The Intake closes and the exhaust is starting to open)…Thanks Dave

I've never heard that term before...what does that mean?? and how is it possible for the intake to close as the exhaust starts to open???..thats not possible...unless the motor is being turned backwards??

Re: Valve Timing

Tue Jul 08, 2014 12:28 pm

I believe Dave is describing the simultaneous valve action on two different cylinders.

"Rock Over", I'm guessing means to slightly turn the crankshaft so that the piston passes it's TDC position.

Re: Valve Timing

Tue Jul 08, 2014 1:45 pm

Postby Lurker Carl » Fri Feb 13, 2009 12:06 am

Firing order and timing and Top Dead Center are concepts easier to show than explain.

The Cub cylinders are always numbered 1, 2, 3 and 4 from front to rear and those numbers stay the same, just like the valves are numbered 1-8 all in a row. The firing order is when each cylinder takes it's turn to fire, the cylinders keep the same number but do not fire in that same numerical order. The engine would not run smoothly or for long unless the cylinders fire as #1 first, then cylinder #3, then cylinder #4, then cylinder #2 - it's a balance thing that keeps the overall design simple and the crankshaft from self destructing.

The important thing to remember is there are two moments of TDC per piston with four stroke engines, one is when the cylinder fires at the end of the compression stroke/beginning of the power stroke. This is one you need to remember - compression equals power - and both valves are completely closed.

The other TDC is when the exhaust stroke finishes and the intake stroke begins - both valves are slightly open at this time.

This messes up a lot of people for both ignition timing and valve adjustment. Luckily, the head is off and you can easily observe how the pistons and valves operate as you rotate the crankshaft. You'll see why half the valves can be adjusted at TDC compression compression stroke for piston #1 and the other half can be adjusted at TDC compression stroke for piston #4. I'm sure glad someone at IH figured it which valves are closed, otherwise we'd have to rotate the engine through each stroke for each cylinder to be at TDC compression to get the job done.

Take your time and check it twice, it will turn out fine.
"Chance favors the prepared mind."
- Louis Pasteur

"In character, in manners, in style, in all things, the supreme excellence is simplicity."
- Henry Wadsworth Longfellow
User avatar
Lurker Carl
Team Cub Mentor
Team Cub Mentor

Posts: 3939
Joined: Mon Feb 03, 2003 9:54 am
Location: PA, Todd
Zip Code: 16685
Circle of Safety Award
Circle of Safety: Y

Re: Valve Timing

Tue Jul 08, 2014 1:49 pm

Postby cubguy's dad » Fri Feb 13, 2009 6:02 am

Carl is right it is easier to show than to explain. But I will try.

While you have the head off rotate the crank and observe the valves and the timing.

A four stroke engine requires two complete revolutions to fire one cylinder or every other time the piston is at top dead center.

On a four cylinder engine, two cylinders fire every revolution. There are 360 degrees (in a circle) per revolution. That means a cylinder fires every 180 degress or every !/2 turn of the crankshaft.

On a cub engine cylinder # 1 would fire followed by #3 that equals one revolution or 360 degrees or 1 turn of the crankshaft. The next revolution would be cylinder #4 followed by cylinder # 2. In 2 complete revolutions all the cylinders would fire every 180 degress or every 1/2 turn of the crankshaft.

Lets put this together if we are on the first revolution that would fire cylinders 1 and 3 that would mean that cylinders 4 and 2 would be 180 degress apart or behind in the firing sequence.

Look at it this way, put the first half of the firing order over top of the bottom half like this 1 3 /4 2 this illistrates that when # 1 is on tdc compression cylinder #4 180 degrees behind and is on tdc exhaust stroke followed by intake stroke (the exhaust valve will just be closing while the intake valve is just starting to open) I call this valve movement Rockover

Now put his to use, rotate the crank observe valves on cylinder #4 look for ROCKOVER (the exhaust closes as the intake opens) at that moment cylinder # 1 is on TDC compression and the valves are both closed and can now be adjusted on cylinder #1.

Rotate the crank 180 degrees (1/2 turn) the valves on #2 should Rockover and the valves on cylinder #3 can be adjusted at this time.

Rotate the crank another 180 degrees (1/2 turn) look for rockover on cylinder #1then adjust the valves on cylinder # 4

Rotate the crank the last !/2 turn look for Rockover on cylinder #3 then adjust valves on cylinder #2 and you are done.

The nice thing about this method of valve adjustment is that it will work for any four stroke engine. All you have to know is the firing order and the valve adjustment spec. You still only have to turn the crankshaft around one time the same as the other methods. However I like this method because the valves are always adjusted TDC compression stroke with the lifters/valves on the base circle of the camshaft (not close to any lobe).

Work this around with the head off and you will soon understand the fundamental relationship between crank and cam and also the role that ignition timing plays. Once you have this mastered the rest will seem easy.

Mark LaFollette
Last edited by cubguy's dad on Fri Feb 13, 2009 12:12 pm, edited 1 time in total.
Experiance is knowing what NOT to do the next time.......
1937 John Deere A (Big John)
1953 Farmall Cub (LiL Red)
Lots of projects.
cubguy's dad
5+ Years
5+ Years

Posts: 556
Joined: Sun Jan 04, 2009 5:41 pm
Location: MI Onsted
Zip Code: 49265
Tractors Owned: 1938 John Deere A
(owned 38 years)
1953 Cub
(owned 21 Years)
1963 Olds Cutlass
1970 Ford F-350
(Cub Hauler)
Top

Re: Valve Timing

Tue Jul 08, 2014 1:57 pm

Thanks Guys I posted these taken from awhile back….They seemed to explain things that you asked about….It turns out the rotor is 180 degrees off and was given me a fit to adjust the valves…When I realized the problem I went looking for an answer and thanks to everyone I believe I found it…Carl's post made the light bulb go off, but I retrieved valuable information from everyone…Now I just found out the PO broke the bolt off in the front of the crank shaft where you press the pulley on…Aint it fun….Thanks again Dave :D…Oh yeh, Eugene, instead of Intake Compression Power and exhaust, in the old days we called it Suck, Squeeze, Pop and Phooey….Drove our Auto Mechanics teacher nuts…. :bellylaugh:

Re: Valve Timing

Tue Jul 08, 2014 2:10 pm

pickerandsinger wrote:Now I just found out the PO broke the bolt off in the front of the crank shaft where you press the pulley on…Aint it fun….


Just to clarify, there should not be a bolt in the front of the crankshaft UNLESS you are pulling the pulley on. That is a press fit, no bolt required except as a temporary tool. If one is broken off, it might be fairly easy to get out, depending on corrosion present.

Re: Valve Timing

Tue Jul 08, 2014 5:41 pm

Rick Spivey wrote:
pickerandsinger wrote:Now I just found out the PO broke the bolt off in the front of the crank shaft where you press the pulley on…Aint it fun….


Just to clarify, there should not be a bolt in the front of the crankshaft UNLESS you are pulling the pulley on. That is a press fit, no bolt required except as a temporary tool. If one is broken off, it might be fairly easy to get out, depending on corrosion present.
…..OK thanks, I knew it was threaded and for that purpose, I was contemplating taking the crank out and having it machined….I don't know if I need to take the broken bolt out (for the Jack to butt on a threaded bolt) or can I just butt a grade 8 against it and take the pulley off and then attack it, though….I haven't taken a pulley off before and I got a pattern from Ed for the puller…( I just emailed him the same question)….I guess you can take the crank out with the pulley on but I'd just as soon take the pulley off while its on the stand…. thanks for replying…. :thanx: Dave