4JH2E teardown report- 8000 hours

[james pask]

Very good report . I did a strip down of a younger VP2020 with 1800 hours out of curiosity , right down to the bare block. I was able to measure the bores and visually inspect all the bearing surfaces which had no obvious signs of degradation. The crank was checked by a local precision engineer and showed no wear at all, it had the journals polished. I rebuilt it with new big end and main shells ,new rings, honed the bores, new gaskets throughout and valve seals, reground the valves and fitted a stainless exhaust mixer elbow, had new tips fitted to the injectors, lift pump, water pump etc, . It starts on the button and runs like a top and burns no oil . I was amazed how little wear had occurred over the last 10 years, I'm hoping for a few more now !.

[jimbunyard]

Do not "move the main bearings around", after 8000 hours they have worn to fit their respective jounals. Babbit bearings do not wear concentrically, for main bearings, the bottom half wears more than the top, for rod bearings the situation is reversed.

The increased wear visible on the rear main is common, seems more pronounced on inline engines, and I generally attribute it to increased loading due to it's proximity to the flywheel.

To not replace them, especially without measuring them, since they should be considered a consumable anyway, is a false economy and probably reckless at best.

The thrust bearings should likewise be measured and replaced.

What is the measurement on the valve seat widths? The seats and valves look fine, probably just need a good lapping. Measure the seats after lapping to tell if they need to be reground.

Don't "move the valves around" either, as they to have likely worn to fit their respective locations...

[markxengineerin]

Jimbunyard- we don't see it the same way. The bearings should only touch metal on metal during startup, before oil pressure is available, as there is otherwise an oil film in there. The thing that's going to make the oil film go to zero (eventually) is excessive clearance. By rotating the bearings, the time before that happens is being extended. It looks to me like the main bearing near the flywheel would be first to go, so rotating a "minimally worn used" one in there is the essentially the same as replacing with new. I saw one report of someone tearing a diesel engine apart after 30K hours on original bearings, never even rotated. They were severely worn, but I don't think there's a penalty for having worn bearings unless they fail catastrophically before something else does. Has anyone heard of a bearing failure on a Yanmar, without extenuating circumstances? It's common on some gasoline engines in cars, but I'm not too familiar with Yanmars, they just seem so overbuilt that I doubt it's a problem.

My comment on driveshaft alignment made no sense- disregard, I forgot there is a transmission between the two.

What is the measurement on the valve seat widths? The seats and valves look fine, probably just need a good lapping. Measure the seats after lapping to tell if they need to be reground.

Without lapping, the seats measured thicker than 0.070", judging by the shiny deposit-free metal, which > the wear limit. They also look a little pitted. I don't see how lapping is going to do anything but make the seats thicker- please explain. It's too late for me to to experiment this time, the shop has instructions to re-grind back to new specs.

Re the theory of not moving things around: Piston rings, lifters, valves, even tires all last longer because they are allowed to rotate, thus spreading out whatever material removal rate there is to more locations. I appreciate the discourse though, I've been wrong before.

[flightlead404]

Originally Posted by markxengineerin

Jimbunyard- we don't see it the same way. The bearings should only touch metal on metal during startup, before oil pressure is available, as there is otherwise an oil film in there. The thing that's going to make the oil film go to zero (eventually) is excessive clearance. By rotating the bearings, the time before that happens is being extended.

I have no experience with diesels of any kind, but have experience with hot-rod Porsche 911/930 engines and Lycoming aircraft engines.

First, I wouldn’t reuse crank bearings period, they are cheap and easy. But, if forced to I absolutely would not move them around. If one is worn, replace them all.

Second, I never want any metal on metal motion. That’s why I use moly build up grease and crank a few times on first start w/o fuel or ignition to build up oil pressure.

Third, comment above about Plastigauge is good. Its what I use and its quick and easy. But, rod bolts (at least in the engine I work on) are a one time use. They stretch at the proper torque. So, if any of the bolts are like that in this engine, first, get new ones, second, use the old ones to check clearance with the Plastigauge.

[markxengineerin]

None of the bolts are torque to yield on this engine, which I much appreciate.

[Kit_L]

Excellent work. Commenting only to see the updates; cheers, KL

[Shaneesprit]

Originally Posted by Timreyn

Nice report. I run many natural gas engines, which are converted diesels, Caterpillar etc. They will run a long long time with little wear. But a head job with new seats and valves is money well spent. We usually do these two or three times as often as overhauling an engine. Ring grooves wear out but sounds like you have this covered. This is what I would expect to see when I get to your hours. I have about 2300 now. Thanks for the info!

G3500s I take it? Probably the best lasting big gas engine there is, G3520C is my all time favourite, although I know service guys like the 3516, for me as long as it’s not a H then I am happy.

Now no one else knows what we are speaking of 😂

[BrightAyes]

Is there a follow on report dealing with the heat exghanger?

[markxengineerin]

I have not finished yet as i want to add a Zinc and re-assemble, but here's a draft

[Statistical]

Surprising there isn't a screw in style pencil zinc in the original design. Would add negligible cost and provide lasting protection with minimal maintenance.

[Normal Saline]

Very interesting post.
I too am responding just to hear the updates.

[BrightAyes]

Mark,
Your draft hx report is excellant & provides much food for thought. It convinces me that when I rebuild my 4JH3-TE, I wiil replace the tube bundle and heat exchanger and find a way to add a zinc.
Keep up the good work.

SV Bright Ayes

[markxengineerin]

This is a generic google photo, but I think my heat exchanger is similar, I remember a few unused M8 tapped holes in the sides. Does the zinc need to touch the coolant in order to work or can it just be bolted to the outside?

If outside is fine, then this is what I have in mind

If it needs to touch the coolant, probably can make something work on one of those blank ports.

[rslifkin]

Originally Posted by markxengineerin

This is a generic google photo, but I think my heat exchanger is similar, I remember a few unused M8 tapped holes in the sides. Does the zinc need to touch the coolant in order to work or can it just be bolted to the outside?

If outside is fine, then this is what I have in mind

If it needs to touch the coolant, probably can make something work on one of those blank ports.

You wouldn't want it to touch the coolant side of the system, but it has to be in the raw water flow. If it's not, it won't do anything.

[markxengineerin]

Ok- so it should touch both the raw water and the heat exchanger metal?
The worst corrosion happening is actually in the coolant area, so that threw me off, not having done any research yet.