Case 310G Gas Timing Question

Hope someone can help. Last fall, my battery died (Crappy battery that dies if not revving a lot. Common occurance) and my machine quit with a loud backfire. I charged the battery and when I tried to start it, it popped and backfired, but wouldn't fire. I tried purging water, and everything else I could think of, but it was already snowing so I covered it until spring.

Today I went out and drained all the fuel traps and started troubleshooting. I have 90 lbs compression in all 4 cylinders and all 4 plugs fire nicely. I tried to start it and in did just like in the fall. I pulled the distributor cap off and cranked it and saw that everytime it went over TDC, the rotor button was 90 degrees off. I thought maybe someone had played a joke and moved the plug wires. So I pulled all the plugs and made sure each was right. First crank and it started right up, but doesn't take throttle and just idles.

My guess is that it jumped the timing chain, but that doesn't make sense that it had good compression.

Can someone offer any opinions on how I should proceed? How does one check the valve timing, etc? Also, I noticed that the rotor button doesn't just turn, it snaps from one 90 degree position to the next. Is that normal?

Thanks in advance for any and all help.

There is no timing chain. Gear to gear. When it backfired it could have sheared the roll pin on the distributer drive gear. It could still be turning but out of time by somewhere around 90* Pull the dis. check the pin, replace if necessary, and reinstall it on #1.

Are you sure the distributor just didn't get turned?

If it turns out to be the roll pin being
sheared and it does it again, pull the timing
cover and check the cam gear on the cam. Had
one many years that sheared the roll pin often,
finally gave up pulled the cover , key was have
way sheared and gear was loose on cam . New key
and proper torque ,no more trouble .That was
40 years ago and tractor has had an overhaul
since and still runs today.

george

Thanks for the recommendations. So it sounds like the valve timing couldn't have jumped unless it jumped gear teeth? If that happened, it would have had to broken teeth wouldn't it? Then it's unlikely it would ever line up enough to give a full power stroke, let alone actually idle as nicely as it does. So it's likely localized to the distributor?

I'll pull the distributor tonight and check it's gears, etc, and reset the timing. I don't know how the distributor could have gotten turned. It didn't seem loose, but you never know. Hopefully it is as simple as a sheared pin.

This is the gear train for the 148 engine. These are helical gears, there are always 2 teeth in mesh so it takes more than one tooth broken to be out of time.

The crank gear is turning CW so the tooth on the left is coming into mesh it would take 2 broken teeth to change the timing at all. If you have 2 teeth broken there can be enough slipage before the incoming tooth meshs to put it in some way out of time.

There 24 teeth on the crank gear & 48 on the cam gear. The chance of slippage to equal 180* timing change is about like drawing 4 of a kind in poker.

The cam gear is press fit on the shaft with a #6 woodruff key. The nut is torqued 80-90 ft lbs. If the nut backs off or for some reason the gear works on the shaft it will ware the key. #6 is not much of a key, it will shear as George said & the gear can turn 180* and catch.

There are more similar things that can happen here also like the center hub of the cam gear fracturing and catching at some point, etc.

The dist drive gear is helical also so you have a similar situation but less teeth involved since is 1:1 rotation with the cam (geezer memory is 9 teeth for 148 engine?). One tooth broken may put you 180* out, don"t know. Check drive teeth when you pull the dist if you can even if the pin is broken per ACG.

Joe

Excellent info, thanks.

I pulled the distributor tonight. The roll pin is fine and the gear is fine. As best as I could see looking down the distributor shaft hole, there are no broken, worn or chipped teeth on the on the drive side either.

Put it back together with the rotor pointing to #1 when on TDC, started right up and is running fine.

Makes me VERY nervous not finding anything that could account for it being off. Luckily I only use it for yard work and fire wood, etc. So if it decides to do a repeat, it's not like it's my livelihood.

So thank you to everyone who jumped in with recommendations and help. I was all ready to start tearing into the front of the motor to check the timing until you all chimed in.

Thanks again

Rene