yanmar jh4te burns oil

[Eddie]

It definiely isn't leaking into the bilge and the only time there is noticeable smoke is we i run it after sitting and running the engine to charge batteries for a few days. Even then it will only smoke for about 20 minutes. It starts right up and runs good, max rpm at least 3500 so i don't think i am over propped. Exhaust is on the side of the hull and does collect soot,but not much worse than my last yanmar. I have pup almost 800 hours on the engine,always has burned same amount of oil. I have mentioned it to a couple of mechanics and they haven't been concerned enough to recommend we look into it. Usually run at about 2700 rpm. Thanks

[a64pilot]

Sounds like maybe glazed cylinders, especially if it was babied early in it's life.
Using the Sea Foam in the oil and running it hard may help. Sea Foam may help with the glazing, and running it hard will increase cylinder pressure which will assist in the rings seating.
Won't hurt if I'm wrong and you haven't spent much money.
Does the oil turn black soon after an oil change? Have you checked to see how much blow by there is in the crankcase vent?

[model 10]

[QUOTE=a64pilot;1541421]Sounds like maybe glazed cylinders, especially if it was babied early in it's life.
Using the Sea Foam in the oil and running it hard may help. Sea Foam may help with the glazing,


Pray tell, how might it do that? The only way to remove "glazing" is by mechanically removing it. So if you starve the cylinder walls of oil, the rings might do the job for you but wow!, the price you pay..

[Eddie]

the oil does seem to turn black very quickly.

[ontherocks83]

Would glazed cylinders be evident on a pressurized leak down test or would you need to look with a bore scope? My thinking is if the cylinders are glazed and not sealing if you pressurize each cylinder with compressed air you may hear air leaking out of the dip stick. This is a common test used on small aircraft engines and is quite helpful for finding low compression.

Some examples are if you hear air coming out of the dipstick tube you have bad piston rings. If you have air coming out of the throttle body then you have a bad intake valve and if you hear air out of the exhaust then you have a bad exhaust valve.

The one thing I don't know is if glazed cylinders would leak enough air to show a problem with that test method. Any experience on that one?

[ontherocks83]

Here's an example of the tester I am talking about

http://www.summitracing.com/parts/ot...Fe9r7AodTDYATA

[model 10]

It feels like I've done a million compression tests. Living through all of them without getting wacked on the head with the propeller has been great. 80 psi inside the cylinder and a 6-7' prop ready to turn is pretty dangerous. Using the great big lever of the prop you can get a feel for ring friction but you can't know for sure if the cylinder wall are glazed unless you look at them. If it is a minor problem you can switch back to straight mineral oil and run the engine for another 50 hours and check things again and the rings may seat. This practice is more for breaking in a new engine than resurrecting a dead one.
You can get a feel for worn ring lands in pistons, worn cylinders walls and leaky valves with this type of leak down teter

[a64pilot]

First there is a difference between glazing and bore polishing. Glazing is usually what amounts to a "varnish" build up due to light loads and too cool a cylinder walls. It can be at least partially removed chemically, but admittedly the best way is to dis-assemble and engine and hone the cylinders. I'd certainly give Sea Foam a try, it may well work and the risk and cost are almost negligible.

Bore polishing is exactly what it sounds like, a polished bore, often caused by repeated light rusting that is cleaned off each time the engine is run again, only cure for this is dis-assembly and honing or cylinder replacement or similar.
Of a little interest if you look in the maintenance manual for the Pratt & Whitney R-1340 aircraft there is a procedure where if the engine is using excessive oil to introduce Bon-Ami into the intake while it's running to score the cylinder walls. I wouldn't do this of course, just interesting that it's there.

A differential compression tester will determine both the amount of leakage in a cylinder and tell you where it's going, they have a different orifice in them for big and small engines, we would definitely want the one for a small engine as these things are made for aircraft, and big aircraft engines have pistons the size of coffee cans, the 1340 for example each cylinder is 148 cu in. You have to test the cylinders with the piston at TDC compression stroke though and you need a goodly supply of 80 PSI air.

High oil temps and oil turning black quickly when it's changed are both indicators of excessive piston to cylinder wall blow-by, which of course is what you get from glazed or polished cylinder walls. Of course the crankcase vent will tell you exactly how much blow-by you have.

[model 10]

Originally Posted by a64pilot

You have to test the cylinders with the piston at TDC compression stroke though and you need a goodly supply of 80 PSI air.

If anyone chooses to pursue this , you do not test at TDC. You need to be a few degrees BTDC. At TDC the rings are not loaded correctly and do not seal as well as they can.

[Eddie]

I have run the engine 800 hours with it burning the oil without it apparently worsening, what happens if i do nothing and accept he burn?

[a64pilot]

Originally Posted by Eddie

I have run the engine 800 hours with it burning the oil without it apparently worsening, what happens if i do nothing and accept he burn?

More than likely, accelerated wear of the piston rings IF
the bore is glazed or polished due to the lack of lubrication, the normal crosshatches in a cylinder wall hold oil and provide lubrication and a seal for the combustion gasses. How much accelerated, I don't know, could go for thousands of hours, maybe.
If it's something else, then of course that depends on what it is, turbo seal for example won't get better and will eventually fail. You'll know that when it starts billowing oil smoke and more than likely loses a lot of power

[a64pilot]

Originally Posted by Guy

If anyone chooses to pursue this , you do not test at TDC. You need to be a few degrees BTDC. At TDC the rings are not loaded correctly and do not seal as well as they can.

I've always started at TDC but wiggled the prop around to get the highest reading I could, I also always test a hot engine too as cold ones sometimes test low, especially a Continental , never done a terrestrial engine though, no reason why you couldn't, just never done it. You would have to have some kind of adapter to fit an injector hole.
You would have to have a wrench on the crankshaft, and be real careful I would think to keep from busting some fingers, but with these small pistons maybe there wouldn't be too much force?

[donradcliffe]

Originally Posted by Eddie

I have run the engine 800 hours with it burning the oil without it apparently worsening, what happens if i do nothing and accept he burn?

You will save a hell of a lot of money.

[DeepFrz]

If you have followed any of the other Yanmar threads you may have noticed people saying things like "oh, just another Yanmar that burns oil. Nothing to worry about".

[EasySquezy]

Originally Posted by Eddie

I have had the boat 5 years and put 700 hours on the engine. It runs fine except for burning 3/4 quart every 8 hours. Only notiecable smoke on startup. IWhen i bought the boat ,the engine had 10 hours on it,the boat had mostly been layed up. I don't know how often it was started before i obtained her. I am guessing a stuck ring. Any recommendations on cause of the burn and repair,or better to just live with the consumption? Thanks

I know this is way old. But my Yanmar is doing exact same thing. Did you ever find the problem.