Could i use a 3 Inch oil filter wrench as a ring compressor to put pistons in a 18hp tractor motor?

Although it is not impossible a filter wrench might do the job, to compress the rings you would have to apply pressure to the wrench, which will try to rotate the piston, or the rings you are trying to compress. As well, the entire ring must remain compressed until it has entered at least half- way in the bore. So if your wrench cannot hold it compressed until it enters the bore, which filter wrenches are not generally able to do, forget it.


A proper piston ring compressor is not an expensive item.


A possible alternative is a strip of flat steel, not too heavy in gauge, bent around the piston skirt, then the 2 ends bent out at right angles for a short distance. This can be placed around the rings after entering the piston in the top of the bore, flat against the cylinder block, and a pair of pliers or multigrips used to compress the rings by gripping the 2 bent- out ends of the strip.


Always oil the rings and the compressor well, as you have to tap the piston down while holding the rings compressed.


This is where a proper compressor scores, as it will compress the rings into the grooves without undue force to hold them there. It is of hardened steel construction, and flexible enough to evenly compress the rings.


Don't forget to stagger the ring gaps around the pistons, and the manufacturer may have specific instruction as to how to do it.