Author Topic: Now I've seen it all....  (Read 478 times)


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Now I've seen it all....
« on: July 02, 2018, 02:08:24 AM »
Hi guys, just wondering if anyone has ever seen this happen.
I just finished repairs on a Yanmar L100 air-cooled diesel. On Thursday  evening she fired right up on my first start attempt; feeling quite proud of myself I did a short video and sent it off so the customer could see the progress.
On Friday I mounted the engine to it's cement mixer and wound up the rope to start her. I yanked the rope and she started right up with quite a bit of smoke and rough running, and that's when I heard my son say "Dad, why is she exhausting through the intake?" Sure enough, that's what she was doing and I put my hand over the muffler and I could feel the vacuum as she inhaled.
Puzzled, I shut her down thinking it might be a fluke, and started her again with the same result. Quite boggled now, I thought maybe she is left-hand rotation, so I wound the rope in the opposite direction and gave her a strong pull. Exact same result except now the engine was running in the opposite direction. I shut her down and left her alone until this morning, all the while trying to figure out if I was actually seeing what I thought I was seeing.
By this morning I had prepared myself for some malady with the camshaft timing, but first of all I turned the engine by hand and felt as it came against something solid. I turned it in the opposite direction and eventually I felt the same hard bump. By observation of the flywheel I concluded that the bump happened every other revolution of the crankshaft which led me to conclude that it was either a problem with the IP, something was caught in the cam gear, or the timing was off.
Choosing easiest first, I removed the Injection Pump, and sure enough the "solid bump" was gone. It was a brand new IP but nevertheless I took it apart and examined it but found nothing wrong.
I then started wondering if the injector could somehow cause these issues, and after a battle I managed to removed it from the engine. At this time I used a piece of wire coat hanger through the injector hole, removed the valve cover, and by observing the valves at overlap with the piston at TDC I was able to determine that the cam timing was correct.
I took the injector apart, removed the needle and sprayed some Carb Cleaner into the nozzle and let it sit for a few minutes while I arranged my Injector Tester.  Not having the correct fitting to hook up the entire injector to the tester, I put the nozzle into an injector that could attach to the tester. At the first few strokes I could tell that the nozzle was not working properly, but I persisted and after a few more attempts I got a satisfactory Pop and Spray Pattern.
I moved on to the body of the injector and discovered that a previous "Diesel Mechanic" had not aligned one of the two alignment pins correctly, and instead of it entering its respective alignment hole, it had caught up on the body of the injector next to the hole and he had tightened the nozzle holder so tight that the pin had actually penetrated the injector body and mushroomed it's head as well! What a mess!
I happened to have a good injector body that was near enough that I could used the "Valve and Seat" from it to replace the damaged seat. I then used my grinder and "sharpened away" the damaged threads in the area where the pin had swelled them.
I then reassembled the injector and reattached it and the IP to the engine, checked that the IP was Popping the injector, and had my son give her a couple of good pulls and off she went.
Has anyone had similar experiences with engines acting this way?


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Re: Now I've seen it all....
« Reply #1 on: July 03, 2018, 07:34:14 AM »
Not me but it sounds as if you had some fun.
Good problem solving.
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