Are you sure you don't have an extra washer behind the clutch in the drum or maybe the little spacer washer if you are going from a rim to a spur set up?
Is the clutch drum a Poulan drum or an aftermarket drum?
Fossil, you have a very good point, i read the manual and the service bulletin on changing from rim to a spur etc. it says to switch the washers, small black washer goes towards saw and larger washer goes after clutch cover. my question is, do some of the clutch covers have a built in washer? i have several and one looks to have the washer built into it. I did however confirn the 5400.
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