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Broken camshaft gear (crankshaft timing)

M

Mark Alayne

Member
I posted about my Super M quitting and not starting again. (titled: crankshaft timing) Several of you indicated a camshaft gear issue. Nut backing off, broken gear, or key way problem. After reading my manual I see that the camshaft gear drives the distributor drive gear. My rotor turns "normally" when cranking engine. Does this still indicate I have a broken camshaft gear? I still have a thunk coming from the engine somewhere while doing this. Any more ideas about what is going on? Since it has cooled down here in Kansas I will pull the dist./hyd pump unit once I get it into the barn. I saw a post about feeling looseness on the gear from in there. Thank you in advance.
 
COmbinations of bad things happen when the gear hub breaks. SOmetimes it strips teeth, sometimes it breaks teeth on the other gears (crank and distributor drive. If you really need to be certain of the problem, pull the valve cover and rotate the engine no more than 10 degrees each way with a socket on the front crankshaft nut. if the valve gera hesitates then moves, or does not move, toast it is. There are only a few thousandths backlash in the gears, and the valve train moves with no real slop with the crank. Jim
 
Mark - The distributor will still indeed rotate with the crank with a busted cam gear hub. But the valve and ignition timing may be off. The "thunk" you hear is also consistent with a bad cam gear. (This happened to my Super M. It still ran - but poorly - and it had a deep, ominous knock).

You can determine for sure by removing the hydraulic pump/distributor assembly. Then reach inside the timing gear case and try to wiggle the top of the cam gear. If you can move the gear AT ALL with finger pressure the cam gear hub is broken.

Tip: Before removing the hydraulic pump turn the crankshaft until the distributor rotor is near the #1 nipple and the 1st notch on the fan pulley is at the timing pointer. This simplifies retiming when replacing the hyd pump/distributor.
 
I assume the only way to get to the front crankshaft nut is to remove everything up front including timing gear cover.
 
In another post you said compression on # 1 and none to little on the rest which may indicate a broke camshaft. Does it build oil pressure when cranking. If not the cam is broke after # 1 or the cam gear key or keyways are striped. Gear is still driving the distributor but not the cam.
Unless compression on # one was a fluke I would guess a broke cam. Like Jim said the valve movement or no movement would tell if its broke part way back or the problems to front. For whatever reason if the cam doesn't turn you will have no oil pressure.
 
Well it is inside the front pulley. I have been able to get a 3/4 drive socket on the nut and turn it. you can also remove the starter, and move the ring gear with a modest prybar. Raising one rear tire, using 5th gear, and rotating the tire will also allow engine rotation sufficient to do the job. Jim
 
Correct!

The bolster assembly must be removed to get the front pulley and timing gear cover off. You will need a 2-1/2" socket for the nut on the crank pulley.
 
Bob M My tractor has a Schwartz wide front end. Does removing the bolster assembly include removing the wide front end? If so this will obviously mean finding some way to support the tractor. ???
 
Thank you all. Sounds like tearing it down is certain. I will check for the loose gear first. Also sounds like it would be better to not rotate any more than to find TDC for fear of more damage. Does the bolster unbolt separately? Or do I have to remove the front end. I have a Schwartz wide front end. I can't find any info about removing the bolster. I have had the radiator etc. off to repack before.
 
Do you have oil pressure during cranking or hydraulic pressure? Your cam drives these along with the distributor. If you have compression on No1 cylinder bring it to TDC. Once you feel compression drop a long plastic straw on top of the piston and have a helper slowly crank the engine and you watch the straw rise. When the straw quits rising your No1 piston should be at TDC on the compression stroke. Then look to see where your rotor is pointing. It should be at the No1 plug tower which is about 1 o'clock. Hal
 
I would drop the oil pan and look to see if something is broken when you hear the clunking when cranking the engine. Look at the counter weights on the crankshaft. We had one to break on a military engine and even though it made a lot of noise it kept running. It made enough noise to wake you up. I was on the midnight shift. Hal
 
Didn't see any oil pressure when cranking, that was one of the first things I checked when I started looking into this deal. Haven't checked hydraulic pressure. I also checked the timing first thing. Timing is fine. That has been a problem with this tractor before. It would die, I would reset points and time it and it would fire back up. I will drop the oil pan and valve cover and try everything mentioned here. Does the bolster come off this tractor without taking off the front axle and wheels. I have a Schwartz wide front end. Thanks Mark
 
Mark - If you have access to an engine hoist or front loader, easiest approach is to remove the entire bolster/radiator/wide front as a unit.

Securely chock the rear wheels, then jack the front wheels off the ground. Place some cribbing under the clutch housing (I used criss-crossed 8x8 timbers). Then lower the jack so the tractor is supported on the clutch housing and the front wheels are still off the ground.

Next disconnect the steering shaft and radiator hoses. Then remove the bolts holding the bolster to the side rails. Finally use engine hoist or loader chained to the bolster "wishbone" to lift/slide the bolster assembly ahead and away from the tractor.

You'll now have PLENTY of room to work on the front of the engine!
 
My manual doesn't cover that Schwartz wide front end. You need to make sure you have the tractor well supported. Check the oil and hydraulic pressure. Both are driven off the cam. Hal
 
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