When I blew the engine on my riding mower the other day, I wasn't ready to buy a new mower, Remembered I had kept my previous mower, a 1980 Murray 36-inch cut, that had been sitting in the storage shed about 15 years. Drug it out, pumped up the tires poured in some gas, jumped it off and was surprised when it fired right up. After servicing (oil change, new filter, sharpened blades, oiled and greased) I set to cutting thinking it would get me through the rest of the season. But then I realized it has a bad vibration whenever the cutting deck is engaged. (Didn't remember this ever being a problem.) I inspected the two jack shaft assemblies and pulleys which seem to be fine. So I tried two new blades which made no difference. Now I'm wondering if the belts could be the problem. Thanks for any thoughts or suggestions.
3/27/25 Update on mower deck vibration problem.
I had hoped to get the vibration problem corrected over winter but it didn't happen so now I'm needing to cut grass again while I shop for a new mower. Following my original post, I noticed there was a lot of "wobble" in the blade belt idler assembly and found the shoulder mounting bolt was badly worn and the mounting hole much enlarged. Thinking that might be causing the vibration I resized the hole and installed a new bolt which stabilized the idler assembly. Still no improvement in the vibration. Next, I removed the recently installed new blades (as someone suggested) and found it runs smoothly without any vibration with the blades removed. Reinstalled the blades and disconnected the drive belt to the second blade but still no improvement in the vibration. Finally I replaced the main blade drive belt (as someone suggested) after which the vibration was practically gone. Thinking I had the problem solved, I proceeded to cut more grass. But here's where it gets a little strange. After about 4-6 hours of cutting the vibration slowly returned so now it's as bad as it ever was. I also noticed some black powdery residue on the mower deck which appears to have come from the new blade belt and there looks to be some abnormal wear on the belt. When the mower is running I also noticed the blade belt idler assembly is not running smoothly but is jumping around quite a bit. Wondering if this could be the source of the vibration or is it just reflecting the vibration caused elsewhere? Also wondering about the spring tension on the idler assemble - is that critical? This one's got me pulling my hair out. Any thought or suggestions based on my new findings? F.Y.I. the mower is a 1980 Murray Model No. 3667 11 hp.
3/27/25 Update on mower deck vibration problem.
I had hoped to get the vibration problem corrected over winter but it didn't happen so now I'm needing to cut grass again while I shop for a new mower. Following my original post, I noticed there was a lot of "wobble" in the blade belt idler assembly and found the shoulder mounting bolt was badly worn and the mounting hole much enlarged. Thinking that might be causing the vibration I resized the hole and installed a new bolt which stabilized the idler assembly. Still no improvement in the vibration. Next, I removed the recently installed new blades (as someone suggested) and found it runs smoothly without any vibration with the blades removed. Reinstalled the blades and disconnected the drive belt to the second blade but still no improvement in the vibration. Finally I replaced the main blade drive belt (as someone suggested) after which the vibration was practically gone. Thinking I had the problem solved, I proceeded to cut more grass. But here's where it gets a little strange. After about 4-6 hours of cutting the vibration slowly returned so now it's as bad as it ever was. I also noticed some black powdery residue on the mower deck which appears to have come from the new blade belt and there looks to be some abnormal wear on the belt. When the mower is running I also noticed the blade belt idler assembly is not running smoothly but is jumping around quite a bit. Wondering if this could be the source of the vibration or is it just reflecting the vibration caused elsewhere? Also wondering about the spring tension on the idler assemble - is that critical? This one's got me pulling my hair out. Any thought or suggestions based on my new findings? F.Y.I. the mower is a 1980 Murray Model No. 3667 11 hp.
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