I just ran a compression test on my ebay engine. I am at 6,000 ft. elevation. The manual says the pressure should be 3,040 to 2,200 kpa (441 to 319 psi). My air pressure here is only 80 percent of sea level, so I was looking for 353 to 255 psi.

For cylinders 1,2,3,4 I got 300, 305, 295, 295. My gauge only goes to 300 psi, or I would have tried putting oil in the cylinder and retesting.

I tested the glow plugs too, and I had a bad one as I suspected from the smoke.

The compression ratio is 21:1. 21 times my air pressure of 11.8 psi should only be 249 psi here, or only 309 psi at sea level. I don't understand how it would be as high as 441 psi. Can anyone tell me what numbers they have gotten?

Thanks!

I got a diesel compression tester that reads up to 1,000 psi instead of the gas one I used last time that stops at 300. I had to make a fitting to use it:

The fitting is third from the left, next to the glow plug. The other two fittings came with the kit. One had the right threads, the other was the right length. Neither fit.


I got higher readings with the diesel gauge. I tested once then put some oil down the hole to seal the rings. Without oil all cylinders were withing 5 psi of 340 psi. With the oil the numbers went up to 400 psi. The readings were darn consistent cylinder to cylinder.

I am tempted to order this rebuild kit from China. It comes with new pistons and cylinder liners. Anyone know about this kit?

http://cgi.ebay.com/ebaymotors/4D56-4D56...emZ270628732438

I am about to clean,test, and balance the injectors. I got this Mercedes tool and fortunately the injectors fit it.

http://cgi.ebay.com/ebaymotors/Mercedes-...sQ5fAccessories

You have to be aware there are two kinds of pistons and cylinder heads for the 4D56, depending on the vehicle and year.

Turbo and non-turbo pistons are different too.

Also the quality of the piston rings is very important. The cheap ones will last like 6 months before needing replacement, or will never set and the engine will not have proper compression.

Just be sure you order the right ones.