SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Low RPMs on Yanmar 2GM20

14K views 17 replies 9 participants last post by  RegisteredUser 
#1 ·
My father and I have a Yanmar 2GM20 diesel on a C&C 29 (1983 or 84?). I calculated the max hull displacement speed around 6.33 kts. This past summer the engine worked great, no problems starting or other major issues. However, we just can’t seem to get that engine up to 3400 or 3600 rpms. It is rated for 3600. The best I can get out of the engine 2000 to 2200, then I see a little bit white smoke from the exhaust and the engine is loud as heck! According to the GPS, at best I did 5.5 kts. I’m planning to ticker with the throttle cable this weekend and see if it needs adjustment. Also planning on changing all the fluids, zincs, filters, etc. since it is close to winter. Any suggestions on how to increase the RPMs?

Here are some other specs for your enjoyment:) : LOA 28’6”, LWL 22’4, BEAM 9’5”, DRAFT 5’3”, DISPLACEMT: 6,700 lbs. I calculated I need 13.4 HP at 3200 rpms for 6kts., unless I misinterpreted the performance curves for the engine.

Thanks!
 
#3 ·
There are many factors to slow you down. Certainly your acvtion plan is aiming some of those and should be conducted carefully. White smoke generally is not bad signal, it would indicate steam out of exhaust due to low engine temperature. Can you get higher revs if your propeler is not engaged ? Have you checked for botton fouling, specially propeller fouling ?
 
#5 ·
Even with a clogged filter you can usually rev the engine to full rpm, but under a load it just pukes out. If the bottom was fouled terribly, or the prop, I would expect to see a lot of black smoke at full throttle but these internet engine discussions are ... let's just say interesting.
 
#6 ·
I'm with jrd, it doesn't sound like a load condition.
Let's start with the basics:
greg, is it hard to start?
when was the last time the injectors were serviced?
When was the last time the valves were adjusted?
What rpms is the engine idling at?
What is the prop size and pitch?
Can you get the engine up to 3600 in neutral? If so, that eliminates the throttle cable.
 
#8 ·
Have you ever been able to hit hull speed or get the engine to 3500-3600 under load?

If yes, then dirty bottom or prop, throttle cable slipped,or perhaps a clogged filter, perhaps the tach is off.

If no, then the prop is likely over sized/pitched for the engine and the prop will need to be addressed.



Check tach with a digital photo tach to confirm accuracy

Check bottom and prop to be sure it is clean

Check throttle linkage

Check engine in neutral and be sure you can get to 3600

Check for fuel starvation. It will generally not be smooth and it will surge at higher RPM. Unless it's surging it may not be a fuel restriction.

Check your speed confirmation. If using STW then make sure your paddle wheel is clean. If using GPS SOG make sure you are not fighting a current.

Check air flow to air intake.



About 7 times out of 10 I find this same exact complaint to be an issue of being over propped..
 
#9 ·
I just read some of the comments from people; let me try to answer some of your questions. By the way thanks for the quick responses!
-This problem has always been around, even after the boat’s hull was just painted and the prop/shaft cleaned. The boat’s performance and handling of course improved but just couldn’t get the higher RPMs.
-I have tried to increase the RPMs while at dock and the engine in neutral, no improvement.
-About a year and a half ago my father hired a diesel mechanic to remove the fuel tank and clean in out. He also added a fuel/water separator filter system before the lift pump. I believed there was some improvement at that time, but even the mechanic commented on how the engine just didn’t get up to the rated RPMs.
-A co-worker suggested it could be the fuel injectors and need to be inspected and even clean. He recommended getting a five-gallon can of fuel and add diesel fuel injector cleaner and run it through the system and look for improvement. But he also suggested using an aerosol fuel injector cleaner, if I didn’t want to bother using the liquid form, any suggestions on that part?
-Before I do anything else, I do plan to change out the fuel filter and of course bleed the lines. Also, disconnect the throttle linkage and see if I can manually push it up to the rated RPMs. I also plan to replace the air filter/screen assembley.
-As for the prop size, I don’t know for sure. It’s a simple two-blade prop, but I will have to look up the diameter and pitch.

Keep the questions coming...given me a lot of ideas!

Thanks again.
 
#10 ·
If the rpm in neutral and in gear under a load are app. the same then I would suspect that you are not getting full throttle either because of a linkage/cable problem or an internal problem in the inj. pump. Obviously the linkage/cable is the place to start checking.
 
#11 ·
Hey I just want to let everyone know who replied earlier that I was able to get the engine up to 3200 rpms this weekend. I disconnected the throttle link and was able manually push the throttle on the side of the engine. The problem I have now is the throttle handle broke inside the pedestal today while doing other work. Metal fatigue on the linkage. :( More money! Anyone know of a good manufacture for single throttle controls, I'll have stop around this week.

Thanks.
 
#13 ·
I know this is an old thread, but I figure I would sum up the current situation. After searching a replacement throttle handle or pedestal throttle/clutch assembly with no luck, I hired a local mechanic/machinist to weld the part back together. The original pedestal manufacturer went out of business back in the 1990’s according Edson marine pedestal who I contacted by e-mail. They of course recommended buying a new pedestal from them, but I did not have $3,000 to $4,000 for that option, an $80.00 welding job worked out best. So this weekend, we are going to put everything back together and get the boat running and hauled out to redo the packing.
As for the engine RPMs, I believe we need to simply adjust the cable to allow for more ‘increase’ throttle or forward movement. Maybe I will look into the prop size, anybody know of a good website to make those calculations?
Have a good weekend!
 
#15 ·
I have a Yanmar 3GMD and am alos working on the problem of not getting to rated speed of 3400 RPM. When I am motoring the boat hits hull speed with the engine rpm of about 3400. If I give more throttle the engine does not go faster and does not seem to make any more noise. Throtle linkage seems ok as at full throtle I hit the full throtle stop. Would this be a prop pitch problem? I cleaned hull and prop before the run. Is the idea to have the prop pitched to hit 3400 rpm at hull speed?
 
#16 ·
I have a Yanmar 3GMD and am alos working on the problem of not getting to rated speed of 3400 RPM. When I am motoring the boat hits hull speed with the engine rpm of about 3400. If I give more throttle the engine does not go faster and does not seem to make any more noise.
FWIW, Diesels have governors to stop an engine from over reving and blowing up. If it has an RPM rating that is higher than 3400, try adjusting the linkage.

A really dirty fuel filter will also slow a diesel down.

HTH!
 
#17 ·
I know this is a very old thread that I started years ago, but I figure I would give an update if anyone runs across it during a search concerning low RPMs or something similar. Well last week we had the mixing elbow replaced by a marine diesel mechanic. I've done it before back in June 2012, it's a back breaking process on our C&C 29 mkII. No room to move around in the engine compartment, figure we pay someone this time. While talking to the mechanic about the mixing elbow, I mention it seemed like we could never get the engine up to the rated RPMs (3400 RPMs Yanmar 2GM20F with 16 HP). He offered to take a RPM reading by using a handheld laser photo tachometer. Well it turns out if the old RPM gauge was showing below 1,000, it was off by at least 50 RPMs. If the old gauge read above 1,000 RPMs it off by approx. 800 to 1,000 in the negative. Needless to say we ordered a new Yanmar RPM gauge and it's going to be installed this week.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top