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**Wotname** · 08-09-2019, 18:27

Quote:

Originally Posted by Jimmy_G

Hi again,
I just looked at #10 and it just said replace the mixing elbow??
Seems to be the wrong post.......

Hmm...OK, maybe a numbering thing, anyway here it is

If it was me, I would do this in neutral.

Quote:

Originally Posted by Scubaseas

You can measure back pressure on the exhaust at the mixing elbow. Shut of raw water, remove hose to mixing valve, install pressure gauge (0 to 5 PSI) on mixing elbow, start engine and rev to 3K or as high as possible for about 5-10 seconds. Do not run longer as you have no water cooling the exhaust. If you get anything more than about 1 to 1.5 psi at wide open throttle your exhaust is clogged. If the previous owner did a lot of idle or off idle charging you probably have exhaust stacking (aka slobbering) which is carbon build up in the exhaust. Like having clogged arteries. This should have come on gradually. If your power loss was sudden you might have an injector issue, injector pump issue or fuel supply issue.

Jimmy_G · 08-09-2019, 19:03

Thanks again Wotname. Sounds like the pressure valve is on the end of the mixing elbow. Presume I'll need to plug the opening where the cooling water comes in. I don't quite get the logic, but can try this if I can locate a pressure valve and presumably fit it onto the open end of the mixing elbow.
Make sense?
JG

**Wotname** · 08-09-2019, 20:17

Quote:

Originally Posted by Jimmy_G

Thanks again Wotname. Sounds like the pressure valve is on the end of the mixing elbow. Presume I'll need to plug the opening where the cooling water comes in. I don't quite get the logic, but can try this if I can locate a pressure valve and presumably fit it onto the open end of the mixing elbow.
Make sense?
JG

This rough drawing might help.

Remove the cooling water from the exhaust pipe and replace with a pressure gauge.

Run the engine with the normal exhaust system attached to the exhaust pipe and measure the pressure in the exhaust system.

Clearly without any cooling water going into the exhaust you can't run it for very long or else things will start melting!

You can let the cooling water run into a bucket or the bilge or wherever you like

Jimmy_G · 08-09-2019, 20:22

Thanks very much.
Nice clear diagram too.
Now to find a pressure gauge....
JG

SailingFan · 08-09-2019, 21:33

Just watching, I have a smaller Yanmar and want to see how you fix this. I really do not look forward to repowering but have an issue as well. I had a broken valve spring, so replaced the springs and both valves, but want to see where this goes... Keep at it!

Compass790 · 09-09-2019, 02:35

Hi sailing fan,
have some info for you. Homer Shannon gave me a SVE8 workshop or service manual which is the earlier version of yr SB8 . I THINK I can fwd it to you. Let me know if you want it. I'm not nuch good On 'puters so maybe Wotname will if I cant.
Gald to hear you still alive. last time I posted to you you had liver cancer which is AFAIK a death sentence.
Jimmy G doesn't know how lucky he is that Wotname posts such detailed instructions for him.
I'd suggest he looks on Aliexpress for pressure gauge for his exhaust elbow
Wish I was there, much easier to diagnose engine problems if you can listen & look
Quite hard to do by owners description tho we try

Jimmy_G · 09-09-2019, 02:45

Hi Compass790,
You are right, I am overwhelmed and grateful for the advice I am getting. Its so incredibly valuable, even the conflicting stuff. It provides excellent context and demonstrates the complexities involved.
I will look on Aliexpress for a pressure gauge. Thanks.
Were you directing the manual to me?? That would be fantastic. But if not, no sweat at all of course.
All the best,
JG

Docaroo · 09-09-2019, 02:59

Hi Jimmy
Have been thru same thing with Y3M x 2
black smoke when hit max revs 2300 one side and 2700 other.
Cleaned air filters with no result (remove and try engine without to see if they are the problem)
Took off the exhaust elbow ;clearly carboned up
Tried to remove crud but one water feed rotted thru so
Replaced elbow with SS replacement
3600 revs both sides
Happy.
Docaroo

**Wotname** · 09-09-2019, 05:18

Quote:

Originally Posted by Jimmy_G

.........
Were you directing the manual to me?? That would be fantastic. But if not, no sweat at all of course.
All the best,
JG

JG, you can download a service manual for the Yanmar GM (and HM) series from the library section on CF.

Shaneesprit · 09-09-2019, 13:33

I will change my statement a little - i wrote it quickly
You cannot be overloaded if your able to achieve good RPM, 2800 is more than enough for this engine,
If your engine overheats due to load you have a cooling problem, if you brought the RPM to very low there maybe a min RPM in the manual and I didn’t have time to read it.
Putting water so cooling the combustion is stupid - there are companies out there that burn off Carbon on running engines, by adding Gases to Increase Combustion Temp.
If your elbow was blocked then so is the rest of the cylinder and the exhaust.

I have spent the past decade or more testing Diesel engines that run over 2500 RPM an yet I have them at full throttle at 1500 RPM they only overheat when the cooling system is wrong.

Polished bores - also fixed by running them hard for hours, it can’t fix everything but when you have the cooling checked and the oil sampled or changed, and the timing chains belts or gears checked then run it hard.
They can spit a bit of carbon on fire out of the exhaust, but mostly it burns off, if the engine really has problems other than Carbon you have to take it apart anyway.
Like my industry boat owners do the same - running the engine on low load either because they have no load or they think it’s better, most manufacturers say not to run more than 30mins at less than half load and should be operated above 70 - 80% not of RPM but if Engine Load

Compass790 · 09-09-2019, 23:21

Quote:

Originally Posted by Jimmy_G

Hi Compass790,
You are right, I am overwhelmed and grateful for the advice I am getting. Its so incredibly valuable, even the conflicting stuff. It provides excellent context and demonstrates the complexities involved.
I will look on Aliexpress for a pressure gauge. Thanks.
Were you directing the manual to me?? That would be fantastic. But if not, no sweat at all of course.
All the best,
JG

I was talking about I had a manual for Sailing fans SB8 but I see Wotname has pointed you in the right direction.
Should post SB8 manual in library I guess

**Wotname** · 10-09-2019, 05:05

Quote:

Originally Posted by Shaneesprit

I will change my statement a little - i wrote it quickly
You cannot be overloaded if your able to achieve good RPM, 2800 is more than enough for this engine,
If your engine overheats due to load you have a cooling problem, if you brought the RPM to very low there maybe a min RPM in the manual and I didn’t have time to read it.
...........

There is no information on this thread that the OP has any cooling problems!

While there is nothing with running at 2800 if correctly propped, not being able to reach 2800 at WOT does indicate 'over propping" assuming a clean bottom and calm water.

The issue with over propping is that any additional load on the system (e.g. fouling, head winds, wave action etc) exacerbates the situation. Some prefer to under prop so that any additional load doesn't overload the engine. There is some more information on this link https://hydrocompinc.com/wp-content/...ts/tex0601.pdf

FWIW, a correctly propped 2GM20 delivers ~9 hp at the shaft at 2800 yet is capable of 16 hp at 3400.

Over propping adds load to the shaft and has the same effect as adding drag to the hull, why would anyone want that?

SailingFan · 17-09-2019, 16:45

Quote:

Originally Posted by Compass790

Hi sailing fan,
have some info for you. Homer Shannon gave me a SVE8 workshop or service manual which is the earlier version of yr SB8 . I THINK I can fwd it to you. Let me know if you want it. I'm not nuch good On 'puters so maybe Wotname will if I cant.
Gald to hear you still alive. last time I posted to you you had liver cancer which is AFAIK a death sentence.
Jimmy G doesn't know how lucky he is that Wotname posts such detailed instructions for him.
I'd suggest he looks on Aliexpress for pressure gauge for his exhaust elbow
Wish I was there, much easier to diagnose engine problems if you can listen & look
Quite hard to do by owners description tho we try

Thanks for remembering me! I have indeed been away a while. Life has taken some dramatic changes and turns. I had that tumor in my right kidney, but only a enlarged liver. The VA cut out half my right kidney and took the tumor with it. They also pulled another out of my neck. No recurrences so far but we keep it praying for no returning issues.

Anyway, I am working full time again, finishing my doctorate as well, and have sadly been unable to get to the boat for some time. She is still there waiting on me, but I have to get things going before the yard master gets nervous! I have the engine somewhat together, but definitely need to get it running. I managed to turn it over before storing it, but I really want to pull it entirely and do a rebuild to be honest. Such a manual could be pivital in that effort!

I do definitely want any information you may have on the engine, because it is rare to get much. There were a few of these SB8's out there, but for some reason there is not as much info now, perhaps too many of them have gone to the salvage yards (or the bottom) by now. The 1970's were a couple weeks ago to be sure! I think they were somewhat underpowered as well, which surely did not help their popularity as much either.

Compass790 · 17-09-2019, 16:59

Quote:

Originally Posted by SailingFan

Thanks for remembering me! I have indeed been away a while. Life has taken some dramatic changes and turns. I had that tumor in my right kidney, but only a enlarged liver. The VA cut out half my right kidney and took the tumor with it. They also pulled another out of my neck. No recurrences so far but we keep it praying for no returning issues.

Anyway, I am working full time again, finishing my doctorate as well, and have sadly been unable to get to the boat for some time. She is still there waiting on me, but I have to get things going before the yard master gets nervous! I have the engine somewhat together, but definitely need to get it running. I managed to turn it over before storing it, but I really want to pull it entirely and do a rebuild to be honest. Such a manual could be pivital in that effort!

I do definitely want any information you may have on the engine, because it is rare to get much. There were a few of these SB8's out there, but for some reason there is not as much info now, perhaps too many of them have gone to the salvage yards (or the bottom) by now. The 1970's were a couple weeks ago to be sure! I think they were somewhat underpowered as well, which surely did not help their popularity as much either.

Good news you up & running. I sent you a PM as i dont know how to attach the file on CF but can do it on email. Will send you manual when I get your email.