Yanmar 1GM

[tmcclarren]

Hello all,
I have a 1983 CD25D with the original engine. It was rebuilt in 2018 by a Yammer dealer in Oriental NC. It runs great! I know that the WOT on this engine is supposed to be 3600 RPM or so. Is this spec under load or not under load?? The only work I have done, at commisioning this year in March, was to have the primary and secondary filters replaced. WOT now on this engine is 2800 rpms. I am going by the tach on the boat. I have not checked that against a hand help device.
When I had the local diesel tech stop by and run the engine, they said it could be air in the system. So I ran the engine last season and it ran fine but WOT not up to spec. Go figure a 40 year old engine?!?
I have black exhaust residue on the transom but it does not smoke white or black. She starts right up and runs great.

I have had this issue both with the old two blade and still with the new Campbell three blade. She does get to hull speed much quicker with lower r's, and has more control with the three blade.
The diesel folks said it might be worth checking the exhaust elbow and the injector. I am open to suggestions.

Cheers
Thom

[Mbigos]

My family has had this engine in one of our sailboats for over 25 years, which overall has been very good, dependable, venerable motor. However, we have had to replace the exhaust manifold twice due to carbon build up. We used to "baby" the motor by starting it and letting it warm up at low rpm's thinking that we were extending the life of it. The strong recommended remedy for this is to run the motor at high rpms as much as possible. That seems to have worked. It's only one cylinder, and it needs to run at temperature to achieve a near-complete burn. As you know, the 1 gm is a simple diesel motor. Enjoy it at 2,800 rpm or whatever rpm you can get as long as you can. As you allude, you might also check rpm with another device because the engine tachometer may not be accurate. Propellor pitch and diameter are also critical, but your post says that there was no change before and after. If you had air in your system, I think you'd experience stalling and erratic RPM's. I'd suggest that you put $500 a in your engine replacement fund per year for when the time comes. Of course, keep doing annual oil changes, filters, and spray-paint tune ups on any oxidation. Enjoy what you have for as long as you can. Repower when its time if you keep your boat. Fair winds and following seas to you and your crew,

[fmueller]

Can you get to 3600 rpm in neutral ? If yes I'd guess you just have a prop pitch problem because, yes, you should be pitched to be able to get up to redline (or nearly anyway) ... and being grossly over pitched will also cause some smoking and deposits on your transom as well as premature clogging of the exhaust elbow ... in practice many setups are over pitched. And over pitching a little is not necessarily fatal - it allows a clean burning motor to cruise at somewhat lower RPMs - which can be a little more civilized. I re-powered with a Beta 14 in my CD 27 and the Beta Rep in a conversation then said as much. With my current setup I can crank right up to 3600 redline in neutral, but only 3200-3300 in gear. Typically cruise at 2,400 rpm at 4.5 knots if I am motoring, and just 1,800 rpm if motor sailing.

When I get to my slip after a sail I crank my engine in neutral up to about 3000 rpms and let it run for a few minutes there on advice I have heard that this helps clear glazing/carbon from cylinders and exhaust elbow... maybe an old wives tale but I do it.

Also, my Beta tach is not very accurate, or more specifically, it seems to wobble around a bit or need to be "kicked" with an rpm burst to read "correctly" ... and I have no idea if, when it settles down, it is in fact correct.

[tmcclarren]

Thanks so much for your input. I think the first thing I am going to do is take the elbow off and inspect it. A clogged up elbow cold be an engine killer, increase restriction, and starve the engine of air and will lower your RPM's. I'll bet the exhaust residue is due to a clogged up elbow. There are stainless steel mixing elbows for the 1GM for around $150.00. Cheap insurance to just replace it. The question becomes, stainless or cast like the original. The OEM replacement, I have heard, is twice the price of the stainless one.
Keep those thoughts coming!! Anyone here going to the meeting in St Michaels next month??
Cheers

[frankfurder]

I have the same 1983 1gm on my 25d. Used to rev up to 3000 in gear now only 2500 rpm.
Fuel is good to injector, no air in lines and new filters. Starting is difficult unless warm, but I’m careful to close raw water seacock while cranking. Probably needs a valve job.

Replaced exhaust elbow 2022 old one did have a pinhole in the water jacket , not much carbon in the elbow but some in the exhaust head.

I paid for the OEM elbow, couldn’t find stainless version in US?

By the way, what’s the best source for yanmar parts in Texas?

[tmcclarren]

Hello,

I am very happy with Discount Marine Source. I was able to get three studs for the exhaust elbow in no time flat. Nobody else had them. They are OEM Yanmar parts.
The elbow from Exhaustelbow LLC was 1/3 the price of the Yanmar part. All 316 stainless, with the gasket at no charge.
They both in the states.

I am very pleased.

Cheers,
Thom