Lesson Learned ......

[Dan Hill]

Last weekend I noticed a slightly different vibration coming from my 2gm20f when motoring in. I felt it was most likely fouling on the prop being this late into our northern sailing season. I mentally added it to the todo list for haulout which is coming in 3-4 weeks.

Well...... Bad idea!!

Today while exiting the marina entrance (Allen Treman State Marine Park) into the Cayuga lake inlet, I encountered traffic coming through and had to reverse somewhat hard.

As soon as I throttled up I had a horrible vibration that shook the whole boat including me. Threw it back into neutral and the traffic moved around because they saw I was having issues. Checked below, no water gushing in and motor sounds fine at idle.

Contemplated returning to dock but decided to continue out onto the lake, reverse is a must at my slip and out on the lake I can drift and consider my options. Back into forward and everything sounds fine except that slight different vibration felt before.

Got out onto the lake and gave her a brief stab @ 3000 rpms, all good. OK..... Drift almost to a stop and try reverse again, same as before, loud rattle and vibration. Back into forward and I get a little clunk and then all smooth.

Started thinking the problem through and deducted it was changing due to the different loading on the prop shaft between forward and reverse.

Went below, opened the cover in the rear berth where my cooling water through hull is for a look at the coupler. OMG......!

Found 3 of the 4 flange bolts laying in the engine bilge area along with their nuts and star washers. The last bolt was seconds from falling out, the nut had maybe 3 threads holding it onto that bolt.

Reassembled flange bolts and added checking flanges and loc-tite to winter layup projects, and yes a shaft alignment check.

Fired the motor up and all feels proper in either gear.

So.... Lessons learned, look around more when prepping to shove off. I should have seen those bolts laying in the bilge when I was checking the oil and I should have looked at the coupler when I was opening the through hull valve. And always always investigate any change noticed in noise or vibration from your running gear.

I GOT LUCKY!!

 

[Benny17441]

Yes you did, but make an effort to investigate why it happened. These flange bolts on a 20+ year old boat just do not fall fall off by themselves unless they were recently removed for some work. It is a good practice to replace the removed bolts, nuts and washers with new ones when reconnecting the flange. During the removal process the threads on the old bolts and nuts loose the required tolerances and are prone to loosening by themselves from vibration. Tightening the new bolts to proper torque specs should insure a tight grip. I personally try to stay away from adhesives like Loctite, as that would make a future disassembly that much more difficult. I'm not talking about applications where the adhesive is required.

 

[anchorclanker]

There are several kinds of loctite. Some can be taken apart easily with wrenches, others cannot or are very difficult. Red 271 is real tough and often needs heat to break loose. Red 242 is a bit easier. Blue 242 is quite easy to take apart and is also used as a thread sealant. Very common to see manufacturers spec it, or have them supply new bolts or fasteners with it already applied for high stress components.

I'm curious how often you guys check engine to propshaft alignment. I was reading a motor installation manual (Yanmar) and they talk about checking it every few 100 hours and anytime the boat is hauled out/in. Misalignment could easily account for a sudden loosening of fasteners.

 

[Dan Hill]

The PO had stated he had just installed the new shaft, pss seal system, 3 blade prop, and strut bushing at his last haulout.

I did notice the star washers used were beyond there serviceable limit (flat). These and the original bolts will be remedied this winter layup.

I plan on using the green medium thread strength thread locker which is applied after assembly and is easily disassembled later on.

Thanks for the replies all!

Dan

 

[jtm]

Ask the PO as to any replacement but when you are hauled you might also want to check the condition of the 4 strut bolts in the rear Qberth pocket- for crevice corrosion on the bolt shaft- if you see any rust stains around them - for sure remove and inspect. several years ago I saw such and pulled all four- 3 were subject to varied states of compromise.

 

[Maine Sail]

When you reassemble be sure the flange bolts are fine threaded. I see this mistake often where coarse threads are used as opposed to fine thread. The manufacturers of flanges and engines supply fine threaded bolts or fine threaded tappings in the transmission flange.

I actually prefer a good quality split washers to stars on this application. Nylocs would be okay except for the potential heat the flange can see which could make them next to useless as the nylon gets hot and softens. Properly torqued fine threaded grade 8 or better bolts should not come free if all else is good but I check mine every spring. A little LocTite never hurts and is good piece of mind... If you can get two wrenches on it then red is fine if access is poor then blue might be a better option..