Hydraulic pump blows gasket

Anyone know why it would be blowing the gasket?

thanks

The oil and the fact that these bolts are fine threaded and are a tight fitting bolt because of the fact that it is going into aluminum makes it even more likely to have this liquid lock condition. Blow out the holes with compressed air. Be sure that there is no silicone glue in those bolt holes either.

Zane

The mating surfaces are not flat (check with straightedge).

You are using gasket cement or silicone. Don't.

You are not torqueing the cover bolts enough. The pump uses heavy bolts on this assembly for a reason. Look up the torque specs and use a torque wrench. Be especially careful if you have an aluminum pump body. Torque it down in a diagonal pattern, and in stages, like it was a cylinder head.

The pressure relief valve is set too high, and you are lifting something very, very heavy.

The control valve is not working properly. After the lift arms come up all the way, the pump keeps pumping against the relief valve instead of shutting off. Eventually, the gasket succumbs to the high pressure.

No torque spec is given in the FO-4 manual for these bolts. They are 7/16 - 20 NF capscrews. If we assume grade 2 bolts and an aluminum housing, the table value for torque is 40 ft-lbs.

If it is a cast iron housing, you could assume roughly grade 5 specs for the bolts, and go up as high as 50 ft-lbs.

The above figures are for clean, dry threads. If you use oil or anti-sieze, lower the numbers about 20% -- but you are really on your own here.

The die is a tad expensive, and I've found a permanent marker works just as good, as long as the surface is clean.

Soundguy

Thanks,

Soundguy