Go Bottomonan timing gears
 | Tom Kearns
Join Date: Posts: 1 
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2002-08-19 41397
I'm installing new cam and crank gears on a J.D. 318 w/onan engine. Can anyone tell me which side (left or right) exhaust valve should be open when looking at the engine from gear side, so I won't be 180 degrees off on the cam, or can this be rectified by just switching the spark plug wires from one cyl to the other? Thankyou. Tom.
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2002-08-20 41411
Sorry I can't help with the particular engine. I hope you're in a situation where the engine's orientation can be determined before tear-down. Reversing the plugs might work on a 2-cylinder engine but I wouldn't want to count on it. You probably are aware of things like timing index marks and shaft keys.
I think it's a good idea to have a repair manual before attempting work like this. I've always had manuals myself. However, I may be in a similar position. I have one push mower with a 5hp BS in parts condition. I think my wife hit something and maybe bent the rod on the other 5hp BS mower. Manuals probably would cost more than another junker 5 HP BS so I'll just tear them down blind. Wish my wife would just be happy to get a decent mower, but I guess I have try and get one working engine out of the two—even if the best possible results will be a terminally low compression engine. Junkers are cheaper than new parts too. What can I say—she likes the dang mower.
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| MRETHICS
Join Date: Jul 2003 Posts: 190 Star City, Indiana
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2002-08-20 41420
TomG has given you some pretty good advice, I will add another wrinkle.
If you are replaceing those gears due to failure of the old ones, you may want to consider an overhaul.
Those old Onans tend to fail somewhere in the 1200 hour range( I realize that I just opened the door for a post from anyone who has one of the few odd ones with 2500 hrs and thinks I'm a idiot, but my experience has proven otherwise)and some new internal parts may be in order.
Check those connecting rods!!!!!! ....
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| MRETICS
Join Date: Posts: 1
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2002-08-20 41422
Message to TomG,
My wife also has a phobea about new push mowers, We had an old JD14PZ she had become emotionally attached to. Last fall, she picked up an old corn planter check wire when mowing some weeds in a spot on our farm that had never been mowed before (because I knew how much junk grandad had deposited in that spot).
The crank was bent, we held a service on the back lawn, some friends and neighbors stoped by to pay their respects, a few solomn words were spoken as we placed it to rest in a beautiful spot near the trash cans for pick-up.
I sell these things.....walk behind mowers...and brought a new one home from work the next day. You guessed it....it wasn't the same. She didn't push it five feet in three weeks. She went to a flee market, found the oldest, ugliest, busted up JD 14pz I had ever seen, but it ran. She now pushes it along with a spitefull look on her face.
If I should die in my sleep tonight, I will die a tortured, frustraited, man.
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 | treeman
Join Date: Feb 2002 Posts: 251 Wisconsin
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2002-08-20 41423
On most engines the cam gear is twice the diameter as the crankshaft gear. This is so the cam will rotate half the speed as the crank. If you line up the marks then rotate the crank one revolution, the cam will be 180 degrees off. It's the way they are designed. You should have no problem. ....
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