Partial overhaul on Yanmar 3TNE88

[kuboman]

Well, an overhaul is eminent... but I fear there's not going to be anything "partial" about it. Over the weekend I ran a compression test which showed about 300psi on all 3 cylinders. Spec for this engine is 498 +/- 14psi. Leak-down testing revealed that all three cylinders are passing substainial air past the rings and some leakage past the exhaust valve on No. 1 cylinder. So, the tractor has been pulled out of service and is parked in the barn awaiting a tear down.

I talked to my JD dealer to see who they use for machine work and then called that machine shop. He said he has done hundereds of these little Yanmar diesels. He said that it's been his experience that the vast majority of the Yanmar's he's worked on had either broken rings or broken pistons (collapsed ring lands) both of which usually take out cylinder walls. Since the only oversized pistons for this engine are 0.25mm (0.010in), which aint much, he usually has to overbore the block, sleeve the cylinders, and then bore the sleeves back to standard bore.

Assuming that this machinist is correct (I haven't torn the engine down yet), I called up my Yanmar parts distributor and started getting prices on parts... pistions/rings, rod bearings, main bearings, cam bearings, valves, gaskets etc. Again, if the machinist is correct, I'm looking at somewhere around $1,600 for parts and machine work.

My plan is to start by removing the head and pulling the pistons with the engine still in frame to do some inspection and/or measurement. I'll go from there depending on the results of the inspection.

You have to be careful about overboring these little engines as there is not much material between the cylinders. I had a quote on a 3TNA72 and they would not bore it past the .25" over .:confused3:

 

[Mechanos]

You have to be careful about overboring these little engines as there is not much material between the cylinders. I had a quote on a 3TNA72 and they would not bore it past the .25" over .:confused3:

Were they going to install cylinder sleeves? I don't think they make OS pistons any larger than .25mm. If they were not going to sleeve it, then it makes sense that they would not bore past .25mm. With a sleeve installed and rebored to standard size, there would end up being the same amount of metal between the cylinders that you started with.

 

[kuboman]

Were they going to install cylinder sleeves? I don't think they make OS pistons any larger than .25mm. If they were not going to sleeve it, then it makes sense that they would not bore past .25mm. With a sleeve installed and rebored to standard size, there would end up being the same amount of metal between the cylinders that you started with.

The problem is that after the boring process there is not enough material left, installing a liner is not possible if there is not enough block left to hold the liner. Parent bore engines have always had the reputation as throw aways for this reason. Very few have enough material between the cylinders to do a good job of reboring.

 

[Henri88]

Mechanos, just make sure you have that camera ready to go. :thumbsup:

 

[Mechanos]

Mechanos, just make sure you have that camera ready to go. :thumbsup:

I'll do what I can, but with the projected cost of this overhaul I may not be able to afford to charge the batteries in my camera. :laughing:

 

[Mechanos]

Seems like every time I want to get started tearing into the engine, something comes up. Now that the days are so short, it's usually dark by the time I get home from work and the lighting in my barn was virtually non-existant. So, I used the three-day weekend to remedy that problem and put up six 4-bulb, 4-foot flourescent light fixtures with T-8 6500K "Daylight" bulbs. I have six more to put up to finish out lighting the barn, but the six that I did get up fully light the area that I'll be working in to overhaul the engine. After running conduit, pullling wire and installing the fixtures.... that's about eleventy gillion trips up and down the ladder. The barn has a 14' ceiling and I had to do it all from a single extension ladder. My back is killing me and my legs are on fire, but I have light to work in now.

I did move the tractor into the area and began my initial investigation. I started by pulling the exhaust manifold and altenator to get a better look at things. I thought I'd pull the head off and look around on the off-chance that the repair could be done in-frame. Looks like the water pump has to come off in order to pull the head, so I'll have to remove the hood, core support and raditor before I can get the head off. I decided that my back was sore enough and I'd had enough for the day, so that's as for as I got.



BTW... that pic was taken without a flash, inside the barn, with the doors shut. Just to give you an idea of the lighting.

 

[Mechanos]

I pulled up on a jobsite this morning and there was a brand new shiny 4" pump powered by a brand new shiny 3TNV88. Now that's just rubbing it in... :laughing:

The V series replaced the E series but is virtually unchanged in physical dimensions. The V series has a stiffer crank, stiffer rods, tighter tolerances, updated combustion chamber and a distributor type rotary injection pump instead of the inline injection pump the E series used. Swap the intake and exhaust manifolds and a few other bolt on parts and it would bolt straight into my 955. I offered to "return" the pump to the rental company, but rep declined. :laughing:

 

[Mechanos]

I got the engine out and the head off. The cylinder diameters are out of spec... some places exceed the wear limit. The cylinders are also out of round beyond specs. Cylindricity (taper) is well out of spec and is beyond "oversize" specs as well. Looks like if there is any hope for this block, it will need to be sleeved.

 

[tree11]

Just curious, maybe I missed it in a previous post but how many hours is on this engine?

 

[Mechanos]

Just curious, maybe I missed it in a previous post but how many hours is on this engine?

I have no idea. It's not the original engine to the tractor, plus I bought the tractor (with this engine in it) used.