To hone or not to hone old yanmar

[ti325v]

Hello Gentlemen:
I have returned in search of excellent advice...
Just as a check, to be sure all was well, I pulled a rod and piston on my 35 year old 30,000 plus hours Yanmar d-6. 1,800 r.p.m. 100 h.p.
I must say I was surprised and thrilled to see beautiful, unscuffed pistons, perfect valve seats, nice straight valve springs, no scratches on the rod bearing shells, though they are starting to wear though to the copper..
So while I am in here...I want to put in a new set of rings, along with rod bearings...No real need to fiddle with what works well but I would like to keep the old girl running.
I spoke to macboring and could not get a definitive answer to a simple question..to hone or not to hone...
The liners looks good, obviously well polished. Mechanic on my island says do not hone, but what does he know....I have to admit, Sometimes surprisingly a lot, but he cannot read, especailly the japanese service maunal which makes no mention of honing.. this it is completely counter intuitive to me to put in rings and not hone the jug.
If the consensus is yes, I will have to get on a plane to buy a hone, so if you could advise on what grit to do it with that would be helpful.
Thank you !

[kta]

I do not have any diesel experience, so my opinion may be worthless, but... I have rebuilt many gasoline engines from large to small. I always give a light hone to a clean cylinder before fitting new piston rings. Just enough to deglaze the surface and remove any vertical scratches that may be present. For important applications I will use a proper sized ball hone, for lesser important applications I will use a high grit wet/dry sandpaper with oil.

Again - I have no diesel experience.

[model 10]

No question, hone it. If you were so far back in the woods that you could not get new rings or a hone you could use a mild abrasive like Bon Ami in the cylinder to seat the rings but I doubt you are up the Amazon somewhere. It would be a waste of everything to not hone the cylinder. It would use oil, have low compression and probably never get better.

[FLLCatsailor]

hone it... you've already done the hard part...

[T.Treffery]

You should hone it, that is a must every time you pull engine apart and want it to last.

[sabray]

At 30, 000 hours do tell us how you ran the engine, oil used, mntc schedule. We could learn given your 5 times over the time most of us might be concerned.

[dannobee]

What does it say in the service manual? The "hone it every time" meme is old school. If the cylinders still have the crosshatch pattern (and that's a BIG "if" with 30K hours), honing might not be necessary. Inspect and evaluate. IF you hone it too much, I can guarantee you that piston to wall clearance will be out of specs.

We had a bulletin on some GM engines for oil consumption where piston and piston ring replacement was required for a satisfactory repair. Here is what they say, verbatim:


<< "...Follow the SI Piston and Connecting Rod Assemble Procedure to properly install the new piston rings onto the new pistons. Depending on the engine that you are working on, the replacement rings may have different features than the original rings. Due to the great variation between equipment, machine shops, and technicians performing these repairs, we DO NOT recommend honing or deglazing the cylinder walls though. This is just because it is generally unnecessary and can induce unnecessary cylinder wall and/or piston ring damage if it is done incorrectly and/or not cleaned thoroughly. The cylinder walls just need to be cleaned thoroughly with brake cleaner before the new piston and ring sets are installed.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed." >>

To each their own, but honing the cylinders might not be necessary. And I wouldn't recommend honing with anything but a Sunnen CK-10, SV-10 or similar hone run by an experienced machinist, who will carefully measure the amount of material being removed. "Dingleberry" hones or "Bon Ami" have no place in a modern engine.

[ti325v]

Hey guys...thanks so much for your replies...Cylinder walls are polished smooth...
Service manual says nothing about his issue..
to give you some perspective how far up the amazon I am..
This is where we work on it..

[ti325v]

To those who have questions about longevity,,I will post shortly !
Nothing magic !
I am just talking about running the hone up and down the bore 5 times or so as i have done in the past..
P.S. I the engine does not smoke, has good compression, runs well, starts in 2 seconds every time.
Dannobee..The engine is Old Skool, almost as old as me ! perhjaps that was worked then and should still be applied to old machinery ? I asure you there is NO Sunnen hone in the country...dingleberry if I am lucky, but I am happy to import a blade hone..will take two months to get here....I do not live in your world,
You are obviously an auto-tech, and getting advice from somebody with your qualifications is great..but I have to adjust to my reality. See photos above of the best machine shop on the island.
I simply do not know...

[bobconnie]

Use a bead hone and be sure to ck the piston ring groove clearence closely! with that many hours there should be some wear on these!! even if the pistons look good. Be sure theres no ring groove at the top of the cylinders! Im sure you have cked these liners with some mikes, cus a lot of times they can look great and have excessive clearnce and even some taper ! Just sayin if ya want to get the same type of service from your rebild job, be sure to ck things properly, as you might end up with a poorer running engine then ya started with !

[ti325v]

Hello Guy..Not the amazon, in fact I bet you I could get better service there.
I am on a tiny island (Pop 3,500) in the south china sea.

[model 10]

That was then, Now you have a new deal with the piston rings. Forget about runing the hone up and down 5 times thats silly. If you are going to hone , hone it. You are looking for a cross hatch pattern, You hone till you have one. It takes quite a few strokes. Those who argue for using big fancy honing machines are right in a perfect world but for an in boat ovhl it is not practical. A "dingle berry hone" is the minimum thing you can do but it does not straighten out the bore surface, it just puts a scratch on what you already have, a big taper. A hone with stones will do a better job of making a more straight surface but then you end up removing more material. If you want to get technical the manual wil give you the max bore size.

[ti325v]

Hello Bobconnie:
Bore gauge ? Are you serious ? Micrometer ? None here on the island..it fits, if not you hit it with a hammer until it does...Please understand the world I live in is nothing like yours ! I have put a straight edge down the bore and lit it from behind....distortion of the bore is within the limits of what I can determine with a feeler gauge and a "Straight" edge 1or 2 thousands..

[ti325v]

Hello Guy..Thanks for staying with me here...
As before, no inside mic to measure cylinder bore...The manual does give a spec....
If I were to go so far as to need new liners, the engine would have to come out and be sent to by ship to Saigon to be rebuilt, this would of course kill my business as we are talking a three month affair.
I am better of buying a new engine, which I cannot afford...or closing the business. Perhaps just do the rod bearings and leave it alone ? It runs great and we only put 1000 hours a year on it now.
I live in a world of "good enough" I have to know what is "Good enough" and accept that.
Things done here everyday would blow your mind, but they still work...
cracked piston ? Gouge it out weld it up, cut iot down put it back into service for five years..I have seen it !
In a perfect world I would buy a new engine, well maybe not as I love this one, but I have to accept what resources I have and I do have a guy who has been doing "good enough" for about 30 years.. I simply do not have access to the modern world... If cutting the glaze of the cylinders is a bad idea, I will not do it, if that means replacing the rings is a bad idea I will not do it.
My "Good enough" guy says new rings, no hone, as it will oversize the bore..my contention is that we put a light scratch on the bore to seat the rings, and we are doing something positive. Just replacing the rings with new and nothing to seat them is asking for trouble.
What are we taking off a thousandth or so ?

[model 10]

Originally Posted by ti325v

Hey guys...thanks so much for your replies...Cylinder walls are polished smooth...
Service manual says nothing about his issue..
to give you some perspective how far up the amazon I am..
This is where we work on it..

Aside from the dirt it looks OK, nice lathe.. You could make a glaze breaker out of some sand paper and a drill, kind of a flapper wheel hone. It might be better than nothing. You do have new gaskets right?