View Full Version : ShakingClanging when shifting into forward Yanmar 2GM20F

01-03-2009, 12:51 PM
"Hi all --
I have a 2GM20F (16 hp) on a 30' S2 sailboat that has developed a problem over the past year or so. When shifting into forward, I get a clanking noise and a strong shaking of the engine (actually violent might be a better descriptor). It occurs when shifting into forward and not when it's cold, only after it's warmed up. It is smooth through all rpm's in both reverse and neutral. I can usually get rid of the shaking by powering up past 1800 rpm's OR (this might be important) when I add pressure to the shifter lever from the cockpit. I've disconnected the transmission cable and tried manually shifting the transmission. Again, it will shake/make noise unless I put a bit of pressure on the shift mechanism, then it will run smooth again. I've adjusted the cable at the transmission, but no luck on solving the problem.

Of note, I changed the Yanmar mounts last year thinking it might be the mounts and at the same time had a bent strut professionally straightened. Shaft alignment now is very good to excellent.

Thanks in advance for any or all help."

01-10-2009, 11:47 AM
"Hello Rick, your shift cone could be glazed in the forward gear. This will cause slipping. This bronze cone slams into a steel cup and grips into forward. If it slips you have to dismantle and lap in the cone into the cup untill the surface of the cone becoms a satin colour. Assemble and adjust shift linkage ie 1.5" to forward and 1.5" to reverse. Regards, Ron"

01-10-2009, 05:25 PM
"Thanks Ron. I removed the transmission today. Oil was evident on the underside and inside, as well. I plan on taking it in for a rebuild, if needed. The damper plate looked good and springs had no movement, but I guess it's a good idea to go ahead and replace that since the transmission is off. Any thoughts? Thanks again.

01-10-2009, 08:43 PM
"Hi Rick,
The oil leak should be clear, if black it is engine oil and could be the rear seal leaking. (Food for thought). If all the springs are tight and the plates around the springs, and the springs show limited wear. Then the damper is ok."

01-18-2009, 09:31 AM
"Ron -- an update: Transmission seal was leaking and shift cone (as you correctly stated) was glazed. The rebuild in underway and I should have it back by mid-week.

Questions: Much speculation on why this occurred. I have traditionally left the gear in neutral when sailing. I've read to select either reverse or neutral. This is a direct drive with a fixed three blade prop. What are your thoughts on this issue?

Secondly, when I bought the boat, previous owner changed transmission oil to ATF, although it clearly states HD30 weight. I flushed out the ATF in fall and replaced with HD30. Could the ATF aided in the cone and/or seal failure?

Finally, you indicate to adjust cable linkage 1.5 inches forward/reverse. Is that adjustment made at the cable where it is mounted to the engine (it has an adjustment plate there using set screws) or is that adjustment made at the lever end inside of the binnacle?

Thanks again for your assistance!


01-18-2009, 02:24 PM
"Hello Rick.
In the Pacific Northwest (British Columbia) we always use 20W40 in the engine and the gear all year round. I found that the HD30 was to thick in cold weather as the bronze cone has to displace the oil in the cup. ATF worked well in the KM3A gear, the later KM3P states lube oil so stick with that. I do not feel it would harm any thing as both gears have the same shift method. ie cone and cup. The shift detents were different in the early gear. When under way with the engine off, always place the gear in the reverse setting and this will lock the shaft. In neutral the shaft will "free wheel" and glaze the cone. Once all is reinstalled, except the shift cable, shift your gear cable from forward then to reverse. The travel from the neutral position should be 1.5" either way. Some shift levers in the binnacle may have throw adjustments depending on the make. Hope this all helps, regards, Ron"

01-25-2009, 06:43 AM
Ron --
Last update: Rebuilt transmission installed yesterday and ran great. Engine/transmission smooth throughout the RPM range. Thanks again for your help.