MEP016D Starting Issues - Grrrrrrrr...

[stoneburner]

I've pretty much come to the same conclusion that you did - that the last time i shut it down, it started back up with no problem because it was hot. I've accepted the fact that I will have to tear the engine down, and I am hoping that all of the bearings and internals are still good. I had tried the compressed air trick through the injector port, and got a leak at the bottom of the stroke to where the air was coming up past the pushrods.

I called the machine shop today, and I'm going to have them check the bore, piston, and bearing to see if it's all within spec. If it is, I'll have them rehone the bore ($20) and I'll get a new set of rings and be on my way, If not, i'll have it re-bored to 0.050 over ($50), and pick up a new OE/Yanmar oversized piston and ring set for $32 on ebay. If I end up getting out of this for less than $100 with just a rehone or rebore and new piston/rings, I'll call that a win. If I get out of it for $300 or less, I'll still call that acceptable.

 

[Ray70]

Did you ever get a chance to check for a spun rod bearing? It's pretty simple now that the head is off.
just put it at TDC, go a tad beyond TDC but not enough to begin pulling the piston down, then push on the piston with your hand a see if it moves a little bit.
Or get it at TDC and rock the crank back and forth and listen for a clunk and an abnormal momentary "lack of motion" with the piston.

 

[Ray70]

Although at this point it sounds like you will soon have the piston removed, so you will know shortly if you have a bad bearing.
I'm still not convinced your rings and the cylinder walls are the whole problem.
If it was the grooves I would expect air leakage all the time, not just at the bottom.
Keep us updated on your progress, it's always interesting!

 

[stoneburner]

Thank you, Ray. Before I tear into this thing, I'll definitely give your suggestiona go (at TDC and the slight movement to check for play in the bearing). Do you think this the lack of play is enough to determine that that the bearing is good or bad? I would like to assume that all of the other internals are good if the main bearing is still good? I currently work with a previous (younger) Marine Corps generator mechanic that told me he thought at least my rings were f&$#ed based on the pictures of thrust side(s) of the cylinder being polished and with the light scratching. I'll keep you all posted. The machine shop said they were around 3-months out, so look for an update in June/July!

And, my air/compression test was not totally scientific, so there may have been leakage further up in the cylinder than what I thought I had found. It was a total pain getting the blower attachement to seal in the injector port.

P.S. - sorry for any misspellings or typos. I've started celebrating St. Patrick's day early this year.

 

[Ray70]

If the bearing is BAD you will know right away.
If you don't feel any movement between the rod and crank then the bearing is not the cause of your compression issue, but it can still be worn, just not destroyed!
When the machine shop pulls it apart to hone the cylinder they will be able to visually see if the copper layer is showing through the bearing surface, but either way you should always replace everything while it's apart!

 

[stoneburner]

Checked it, and there is a slight noise at the top and the bottom, but no "thunk" or pause of cylinder movement. It might be something else?

So, I've been looking over the parts catalog and service manual, and doing some thinking, and wondering if anyone can give me some guidance. Here's my potential path forward on this:

I can either take the engine to the machine shop assembled, or take it apart. I am thinking I'll take it apart, take the case to the shop, and have them accurately measure the bore and make the determination of whether it just needs a rehone and new standard rings, or needs to be bored and honed (0.25 mm or 0.50 mm).

In either case, I'll buy the appropriate piston and/or rings.

In all cases, I plan to buy all new bearings (main bearing, rod bearing, piston pin bushing) and all other ball bearings. With 120 hours on the machine, I plan to mic the crank and cam shafts, but more or less assume they are within specification if there is no discoloration.

Does this sound reasonable (I'm assuming I won't see any other damage)? I've read through the overhaul procedures, and I'm not confident I can perform all of the oil clearance and other checks, so I was thinking replacing all of the bearings with new would eliminate the need. And would save a lot on machine shop labor checking everything but accomplish the same thing (since the parts and my labor would be a lot less than the machine shop labor and whatever parts are needed).

The alternative is to just let the machine shop tear it down and perform all of the checks and replace parts as needed. But I'm afraid i'll get into some serious expense. I found a factory new engine for $1200, but this is pushing it for me (though I know it's probably worth it). I am wondering if anyone would have an idea of what a complete machine shop rebuild on a Yanmar L70AE would be? several hundred? A thousand? Their rate is $85/hr. I am thinking I can get all of the parts (all bearings, oversize piston, rings) for $100-$150.

Thanks.