New hydraulic piston too large

[fire5096]

I just did a hydraulic lid rebuild on my '73 Ford 3000 and my piston was in terrible shape and scarred up the housing pretty good. I ordered a new 3" piston from farmtractorrepair.com and was super excited to change it. My bush hog would drift down and jump back up while mowing. I tried to put the new piston in after honing out the cylinder. It would not even try to fit. I measured with calipers and it measured 3" but when compared to the original you could feel a difference. I didn't have the calipers at that point to measure the original. I took a chance and changed the o'ring and leather on the original piston and put it all back together. As you would imagine, it still drifts up and down. I am confused why the piston is too large or the cylinder is too small. It is the original cylinder. Has anyone else had one of these after market pistons not fit? Any suggestions on what to do to make the piston fit? Also, I changed the relief valve to see if that was the culprit but didn't fix it so I am positive it is the piston.

 

[SPYDERLK]

I just did a hydraulic lid rebuild on my '73 Ford 3000 and my piston was in terrible shape and scarred up the housing pretty good. I ordered a new 3" piston from farmtractorrepair.com and was super excited to change it. My bush hog would drift down and jump back up while mowing. I tried to put the new piston in after honing out the cylinder. It would not even try to fit. I measured with calipers and it measured 3" but when compared to the original you could feel a difference. I didn't have the calipers at that point to measure the original. I took a chance and changed the o'ring and leather on the original piston and put it all back together. As you would imagine, it still drifts up and down. I am confused why the piston is too large or the cylinder is too small. It is the original cylinder. Has anyone else had one of these after market pistons not fit? Any suggestions on what to do to make the piston fit? Also, I changed the relief valve to see if that was the culprit but didn't fix it so I am positive it is the piston.

Maybe the original is metric; 75 or 76mm?

 

[Harry in Ky]

ANYTHING aftermarket is a crapshoot. I'm surprised that YOU'RE surprised it didn't fit. Try another supplier. Might get one from a different part of China.

 

[TractorTech]

Welcome to TBN!

If you look at the parts book, the oring for the 3000 measures 2.825" (0.215" thickness + 2.61" inside diameter), so it can't be 3". The only place the roughness of the piston would cause problems is around the oring groove. You can clean the old one up and take the sharp edge off of the oring land.
The cylinder on the other hand, cannot have any grooves of significance or you will get drift/leakby.

 

[pmsmechanic]

Could you take the new piston to a machine shop and have it lathed down to the correct size? If you do this make sure you take the cylinder along so that the piston can be matched to it. Also the machine shop can check the cylinder to make sure it's not out of round.