How to / DIY > Engines

Adventures in Engines Part 1

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Willw:
Hi guys, thought I would share my latest head-banging air cooled Yanmar clone experience with you.
A customer of mine who imports goods from China contacted me re: a new cement mixer which wouldn't start, which was part of a batch of 6, and the only offender.
To make it brief I ended up dismantling the entire engine several times, changing the injection system as well but it just wouldn't run.
At my wits end I took the cylinder (crankcase) and piston to the machine shop to have the clearance checked and I was told that the cylinder was bored too large for the piston, which was rocking in the bore and upsetting the piston ring seal. It sounded possible and we even compared the fit to a different cylinder that I brought along.
So I informed the owner and he ordered a new cylinder which arrived with his next shipment.
I swapped the various parts from the original engine to the new crankcase, added a new set of rings and assembled the bottom end no problem... except the crankshaft would not rotate when the fasteners were tightened. Detective work and add approx. .040" of shims between the crankcase and it's cover (which is from the original engine).
Slap all other parts on after that, add oil and fuel (the same fuel still in the tank from before) and off we go. Same results as before... not a blink. What the $%^& now?

Here is where it gets a bit strange; these engines are the first left-hand rotating Yanmar clones that I had ever seen. The flywheel had 2 sets of timing marks; the normal right hand marks which were painted over but visible, and the left hand marks. While rocking the flywheel by hand to squirt more fuel into the cylinder for yet another starting attempt, I happened to notice the timing marks as I listened to the injector fire, and as far as I could tell the injector was firing somewhere between 5* BTDC and 5* ATDC. Aha, I knew that these engines normally run with close to 20* of advance, so off with the pump and remove both shims that were behind it.
Check timing again... looks better now but still not ideal, but what the hell, wind up the rope and let 'er rip... Success at long last. Shut her down and try again...success again.
But now injection timing still not advanced to the spec with no shims under the pump; what does that mean?
The best I can figure is that the camshaft, or at least the fuel pump lobe, is ground retarded, I will investigate this further when I take it all apart again to put the parts back into the original crankcase.
Why put myself through this you ask? Remember that .040" shim? Now the camshaft has at least that much float, possibly more.
So where did I go wrong? Remember these cement mixers are supposed to be test run at the factory, and I assumed that this one was, but obviously that was not the case.
So I checked ring gaps, valve clearances, everything except that one thing, the injection timing.
In the end I will probably have disassembled and reassembled this engine 5 or 6 times, sad, but I've learned my lesson.
The bright side to all this is that this engine is the 2nd of two that I had to fix as a barter, because inside the very next container from China is my very own ZS1130 horizontal diesel which this customer paid for up front. For some reason I find the thought of that strangely motivating ;D.
But aren't I forgetting something? Isn't the cylinder bored too big for the piston?
I have long suspected this to not really be the case, but in the absence of a better theory I went with it.
So I will roll the dice one more time and I will update you in part 2 of "Adventures in Engines" ;D

ajaffa1:
Hi Willw, I am thinking that the camshaft drive gear is one or two teeth out from where it should be. I would recommend comparing the valve timing opening/closing with one of the other engines that do run properly and make adjustments as needed.

Bob

38ac:
Some of those clones are very good engines, some are pure garbage. Around here we call that a "friday afternoon" engine. One that was assembled as everyone was about to go home for the weekend. Unlike the slow speed engines that will run decently with the cam off a tooth it is my experience that a yanmar clone will barely run, if at all unless the cam is properly timed.  it is doubtful that the engine would start and run correctly with the camshaft being off a few teeth but not impossible. Do you have a spec sheet to check the valve timing? if not the valves should be at overlap at every other TDC  or as Bob said, check one that runs right and compare.

ajaffa1:
Hi Butch, I have been inside a lot of cheap Chinese engines recently, I don`t know the Chinese calender but they do appear to have a lot of Fridays each week!

Bob

cobbadog:
Sounds like you have a great sense of humour working out the issues on this engine. You mentioned about it running anti-clockwise and not too many engines will do that either by accident or built that way but 2 examples I can think of now is the early BSA Bantam 2 stroke motor bike when your timing has skipped the smallest amount will kick back and start up and you now have 3 speed reverse bike. Amazing how a 12 year old can go over the handle bars with no effort.
The other engine is the Farm Pumpers built by many different manufacturers both here and the USA. These are cranked anti-clockwise to start and run. Not hard to remember about rotation as the built in crank handle folds away if you try to crank the wrong way.
I know nothing about timing injectors as I have never had to learn this as yet so I'm better off reading and trying to learn but the idea of the cam timing is a possibility.

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