Yanmar 3TN66 rebuild....anyone ever done one?

[Florida Marine]

I have a JD Gator 6 x 4 - and its been losing compression and burning a LOT oil. Now it won't start before the battery runs dead...so its on the dead line.

I need to rebuild it, and am looking for advice, experience etc.

thanks!

Sean

 

[normde2001]

Engines is engines. Obviously you will need to inspect and purchase parts.

 

[284 International]

While this isn't helping you clarify what steps may help you in removing and rebuilding that particular motor, I would look EXTREMELY hard at the intake system on your machine when disassembling and reassembling. I would suspect that there as intake leak downstream of the air filter that caused grit to get sucked into the motor and cause wear in the cylinders to cause that much compression loss. Throwing expensive parts and labor at it without identifying the cause seems wasteful. You should get many thousands of hours out of that engine before it becomes troublesome to start.

Otherwise, as Norm said, the generic process will be the same for all engines. Get everything as clean as you can early on in the process. Have a clean, orderly workspace. I like to use cardboard and trace and label component locations like head bolts etc. Mark the bearing caps and rods with a punch or other permanent method before you take things apart and make sure you can get them back together in the same manner.

Have a decent set of tools. If you don't have any, a 8mm to 27mm sockets in 1/4 to 1/2 inch drive should cover you with a set of box-end wrenches and screwdrivers. Nothing fancy is required, but you may need some unusual pieces in the kit. I keep a few pieces of large wooden dowel for walloping things that are soft but need some encouragement. You will want a quality micrometer. Take pictures and make sketches of what is going where.

Get a solid diagnosis of what is wrong, first. It may very well be that you need new cylinder liners. If you are doing this yourself, it might be easier to pull them with the block still fastened in the vehicle. You will need to remove the cylinder head in order to inspect them.

Get a service manual, or at least the torque specifications for the engine. It may be the same as the 3TN72 with smaller liners, but I don't have any idea. The dealer parts book may help narrow down what you're dealing with.

No matter what, my strong suggestion is to start by figuring out why the motor is losing compression and have a solid plan to fix that before doing anything else. Good luck, let us know how it goes!

 

[bmaverick]

I have a JD Gator 6 x 4 - and its been losing compression and burning a LOT oil. Now it won't start before the battery runs dead...so its on the dead line.

I need to rebuild it, and am looking for advice, experience etc.

thanks!

Sean

Sean,

FYI, the Yanmar 3TN66UJ engine is also found in the JD-330, -415, -655, tractors. Not sure what the UJ designation represents, but the core part of the engine like the block, pistons, rings, liners, etc. should all be the same. Therefore, you can search for parts from several places without spending an arm-n-leg for name brand JD parts.

Have you looked at Hoye and Fredricks? They do have Yanmar cross referenced parts to JD.

As it was mentioned in the other postings, indeed clean the parts as best as possible. My old JD850 had a cracked head and a micro cracked block. One would have never guessed it unless it was super clean. The engine didn't fail because of use, it failed because the diesel mechanic person who worked on it did such a redneck job.