Bore Honing Without Engine Removal

[model 10]

I remember talking to a missionary pilot/mechanic about top overhauls. They didn't have new parts so they re-used lots of stuff. Pistons, rings and cylinders etc. They would use Bon Ami, but on the work bench. Fit the piston and rings in the cylinder and work it back and forth by hand until it looked good.

[a64pilot]

The Bon-Ami is actually in the P&W R1340 manual. I have seen it.
However that was written back in the 30’s I’d guess, and was maybe a kind of thing you would do in the War years or something. You do things differently then.
I had a friend that was in the Cav in Vietnam, they had an OH-6 come due for phase, Military equal of an Annual. They had never has a LOSH make it to Phase before, didn’t have the parts etc, so they blew it up.

[Kenomac]

I seriously doubt you have “polished bores”. Generator diesels are meant to be run at constant rpms for many thousands of hours, I contacted Perkins regarding our low rpm diesel, and found out that no harm can be done by running it at 800-1200 rpms for days on end. The only issue with a Yanmar running at low rpms is soot build up in the turbo.

When was the last time you cleaned out your turbo? Do you revv it five times every hour like the owners maual recommends? A delivery crew trashed our turbo six years ago, now no problem with smoking going on six years since replacement of the turbo. Have you had a close look at the turbo removed from the engine?

As you know, we have the exact same Yanmar in our 53.

[ccannan]

Originally Posted by Kenomac

Do you revv it five times every hour like the owners maual recommends?

I have a Yanmar 4JH2-HTE and the manual doesn't say to rev the engine 5x/hour. I wonder what has changed.

[Kenomac]

Originally Posted by ccannan

I have a Yanmar 4JH2-HTE and the manual doesn't say to rev the engine 5x/hour. I wonder what has changed.

It does say to revv the engine hourly or run it hard for 5 minutes every hour. Disregard the advice and suffer the consequences if you prefer. I know of three other cruisers who trashed their Yanmar turbos with constant low revvs, one just needed to be cleaned, the other two needed new units. A new turbo costs around $2,000 US in Europe. Your choice.

[Lepke]

In my current boat both generators had badly glazed rings from running long hours at light loads. Perkins and Onan, both 1800 rpm. I had some oil in the exhaust water. I honed the cylinders, put in new rings, and new rear main seals and have near new compression. Solved the oil in the exhaust problem and they start quicker. Looking for a marine Detroit 2-71 and will dump both. Lots of sailboat engines get glazed cylinders from running at speed just for the alternator.

[a64pilot]

Now, both Glazing and Bore Polishing exist, and exhibit the same, but are different.
Bore polishing is just that, most often it occurs in older, seldom used engines. When they sit for extended periods, the cylinder walls form a thin layer of rust, that is cleaned off almost immediately by the rings when run of course, but if repeated enough times, it eventually wears away the cross hatching, and the bores are polished. It is becoming more and more prevalent in the aging, seldom used General Aviation fleet. Bore polishing also happens in gasoline engines.
It can only be fixed by boring, replacing or honing.

Bore Glazing is a film of usually combustion by products and or burnt oil film. Under normal running the temps are high enough to burn these off, it’s a Diesel only phenomena, under lower loading there isn’t enough heat and it accumulates.
Diesel trucks that are idled all night long don’t get glazed most likely cause in the morning they are run under load for extended time driving of course and burns off the film before it hardens, almost no one spends the night in the truck, shuts it down in the morning and goes home.
Bore Glazing can often be cleaned off with a high detergent oil additive and extended hard running, but not always.
Bore Glazing is actually not all that common, it’s often aggravated by poor condition injection system, dirty injectors don’t atomized the fuel well and aggravate the problem.
I suspect that low Cetane fuel also adds to the problem, maybe more than we realize as it doesn’t burn completely or well.

It’s been brought up here on the forum that at least some Yanmar’s require as a min a Cetane rating of 45, while a lot of US Diesel fuel sold is only 40. I’m thinking that may have a lot to do with the “Smoky Yanmar” reputation.
I will I believe start adding a Cetane booster to my fuel and see what happens.

[Kenomac]

My point was... maybe Dockhead should look more at the possibilty of a sooted up turbo needing to be cleaned or replaced rather than bore honing his engine at significant expense.

I’m just suggesting the idea, the choice is his to make.

[a64pilot]

He has spoken of cleaning it, and the price of the Yanmar cleaning fluid before, So I’m thinking it’s not that.
History wise, I believe he has spoken of the engine being smoky almost made him not buy the boat, and had it thoroughly diagnosed, I assume at the sellers expense to determine fault, and none was found.

I think they are to some extent a little like Detroit Diesels, without the leaks. A DD is a nasty engine, that is all there is to it, you can install Walker oil seps etc to help, but it’s just a nasty engine.
No offense intended.

Many if not most Yanmars are smoky engines, this doesn’t seem to affect their longevity, they just don’t seem to combust all of the fuel cleanly.
This has me thinking about Cetane, cause if you look it up, the number 1 result of running lower than optimum Cetane fuel, is a smoky engine.

Could very well be a red herring though.

I assume the newer Yanmars won’t be smoky engines, emissions restrictions will not allow that surely

[RaymondR]

I think they are to some extent a little like Detroit Diesels, without the leaks. A DD is a nasty engine, that is all there is to it, you can install Walker oil seps etc to help, but it’s just a nasty engine.
No offense intended.

If you think the US built DD engines are nasty you are definitely going to have a low opinion of the Russian built ones.

On observing some of these in Egypt I enquired as to why they had 30" extensions on the exhausts and a fenced off area extending about another 30" behind the ends. I was told to keep an eye on them for a while and I would see.

A few minutes later a spectacular fire ball erupted from one of the exhausts hence the extensions and no go zone. Apparently there is a build up of oil inside the engines when they idle which is expelled into the exhaust system when they rev causing the fireball.

[Compass790]

Originally Posted by a64pilot

Now, both Glazing and Bore Polishing exist, and exhibit the same, but are different.
Bore polishing is just that, most often it occurs in older, seldom used engines. When they sit for extended periods, the cylinder walls form a thin layer of rust, that is cleaned off almost immediately by the rings when run of course, but if repeated enough times, it eventually wears away the cross hatching, and the bores are polished. It is becoming more and more prevalent in the aging, seldom used General Aviation fleet. Bore polishing also happens in gasoline engines.
It can only be fixed by boring, replacing or honing.

Bore Glazing is a film of usually combustion by products and or burnt oil film. Under normal running the temps are high enough to burn these off, it’s a Diesel only phenomena, under lower loading there isn’t enough heat and it accumulates.
Diesel trucks that are idled all night long don’t get glazed most likely cause in the morning they are run under load for extended time driving of course and burns off the film before it hardens, almost no one spends the night in the truck, shuts it down in the morning and goes home.
Bore Glazing can often be cleaned off with a high detergent oil additive and extended hard running, but not always.
Bore Glazing is actually not all that common, it’s often aggravated by poor condition injection system, dirty injectors don’t atomized the fuel well and aggravate the problem.
I suspect that low Cetane fuel also adds to the problem, maybe more than we realize as it doesn’t burn completely or well.

It’s been brought up here on the forum that at least some Yanmar’s require as a min a Cetane rating of 45, while a lot of US Diesel fuel sold is only 40. I’m thinking that may have a lot to do with the “Smoky Yanmar” reputation.
I will I believe start adding a Cetane booster to my fuel and see what happens.

Let us know if cetane booster cleans your exhaust up. Our little Yanmar doesnt smoke but its naturally aspirated so i guess it's 23:1 compression ratio would be higher than a turbo

[Compass790]

Originally Posted by skipperpete

Hi Dockhead, I rebuild Yanmars on regular basis and am surprised that so far no mention has been made of replacing the liners, on most of the 4JH series they just slide right out with minimal effort. Best way to do the job in the boat is to remove the gearbox and sit the engine on the flywheel housing then you can easily access both the top and bottom end. Do the front and rear crankshaft oil seals as well as the cylinder head overhaul.

Actually I did in an earlier post

[ccannan]

Originally Posted by Kenomac

It does say to revv the engine hourly or run it hard for 5 minutes every hour. Disregard the advice and suffer the consequences if you prefer. I know of three other cruisers who trashed their Yanmar turbos with constant low revvs, one just needed to be cleaned, the other two needed new units. A new turbo costs around $2,000 US in Europe. Your choice.

Per Yanmar 4JH3-HTE manual

7) When operating the engine at low speed for long periods of time, race the engine once every 2 hours.

Note: Racing the Engine
With the clutch in NEUTRAL, accelerate from the low speed position to the high speed position and repeat this process about 5 times. This is done to clean out carbon from the cylinders and the fuel injection valve. Neglecting to race the engine will result in poor exhaust colour and reduce engine performance.

No mention of turbo.

[Kenomac]

Originally Posted by ccannan

I have a Yanmar 4JH2-HTE and the manual doesn't say to rev the engine 5x/hour. I wonder what has changed.

Originally Posted by ccannan

Per Yanmar 4JH3-HTE manual

7) When operating the engine at low speed for long periods of time, race the engine once every 2 hours.

Note: Racing the Engine
With the clutch in NEUTRAL, accelerate from the low speed position to the high speed position and repeat this process about 5 times. This is done to clean out carbon from the cylinders and the fuel injection valve. Neglecting to race the engine will result in poor exhaust colour and reduce engine performance.

No mention of turbo.

I’m glad to see you eventually found the information in your owners manual. BTW.... where do you think the excess carbon ends up if you don’t revv the engine? Answer: In the turbo. Why the poor exhaust color and loss of performance? Answer: clogged up turbo.

[a64pilot]

It also says low speed, yet doesn’t define low speed.
Then seems to denote low speed as idle when it says move lever from low to high speed position.

My belief is they mean low speed as in idle or above and likely unloaded, although they don’t make that clear.
So what is low speed?