Should a 4500 hour engine be rebuilt? 336d

777funk · Jun 12, 2019

I have been getting a recent purchase (my first tractor) back into action and it has for the most part gone very well thanks to the guidance of the experts here on this forum.

This machine reads around 4500 hours. I have no history on the engine, but I know the country club that serviced it did some things Yanmar wouldn't approve of. Surprisingly, it runs well with no smoke. It doesn't fire right up at the first touch of the key, but it doesn't require long cranking either. I doubt the valve clearances are still in spec which would make a difference. I should adjust them. I would also like to check for blow-by next time I run it.

Here are things I'd be concerned about if that amount of hours is without a rebuild in its history:

Valves dropping due to wear
Bearings spinning due to wear
Rings and sleeves being worn (but... no smoke so maybe not)

I also wonder about the oil pump. That's a short list. I could just run it, but I wonder if this list (and maybe more) would be good peace of mind.

California · Jun 12, 2019

One vote here to just run it and ignore the hourmeter.

In that use, it likely was never abused by being run low on water or oil etc. So long as you can get it started and no bad noises, that's just mid-life with no need to repair anything. Checking valve lash is one of the routine maintenance items, and I would re-torque the head bolts at the same time. Also adjust the compression release mechanisms if needed. These are steps to preserve it in good condition, rather than responding to a need to repair.

You might want to put an oil pressure test gauge on it temporarily to verify normal oil pressure (Harbor Freight has an inexpensive test kit) but I would be surprised if that doesn't test ok.

Then just put it in use and enjoy it!

oosik · Jun 13, 2019

If it ain't broke - don't fix it.

radios1 · Jun 13, 2019

your first time rebuilding an engine can be a lot of fun, and a good learning experience!. however, it shouldn't be needed until 10,000 hours if it's a Diesel, you have more than half the life left..

Sawyer Rob · Jun 13, 2019

If it starts/runs well, I wouldn't worry about it too much, but I bet you it will need some engine work before 10,000 hours!!

SR

AWSubie · Jun 13, 2019

oosik said:
If it ain't broke - don't fix it.

rScotty · Jun 13, 2019

Sawyer Rob said:
If it starts/runs well, I wouldn't worry about it too much, but I bet you it will need some engine work before 10,000 hours!!

SR

I agree with that. Those things that 777funk is worried about in the OP aren't usually problems with Yanmars - even with worn ones.

My 336 never did start up at the first touch of the key either. It had to crank over 4 or 5 times or sometimes more. Typical Yanmar. My guess is that the cranking is due to how the injector pump retains its prime, and delivers fuel to the injectors, not related to wear.

Our big JD 310 loader/backhoe is old and has 6500 hours on it - most by an independent contractor. You know it has to have wear on the engine. The radiator has been replaced at one point, and that's got to indicate wear. But even in cold weather it starts so quickly that you sometimes don't hear the starter crank.
rScotty

rScotty · Jun 13, 2019

Another thing. Yes, I would CHECK the valve clearances - but if they are within a couple of thousandths of nominal I wouldn't adjust them. You are unlikely to gain anything useful by adjusting them if they are that close to nominal and always some chance of a problem.
BTW, Some old shop manuals show clearances to 4 decimal places instead of 3. That extra decimal is just an artifact of a poor translation from metric to US measurements. Ignore it by rounding up.
rScotty

777funk · Jun 13, 2019

Good to know and thanks for the feedback. I did a little more reading and it seems the crank main bearings rarely pin (couldn't find a single case). I did read a few threads of valves dropping. But all of this seemed few and far between. I will adjust valves like I used to do on my old Mercedes diesels and keep an eye on oil pressure.