Generator isolation mounts

October 24, 2011, 09:16:10 pm

Greetings,

Among other simultaneous projects, I've been working on converting the fixed mount Onan 6500 generator in my 91 U225 to a slideout system. You only have to take it out once to service it to find the motivation. Needed to reinsulate the bay anyways. Among other things, found the rear spark plug likely to be original (with 2K hours on it). Went through and checked everything, and put in new plugs, wires, and filters. Designed and fabricated a frame, added sound deadening and thermal insulation to the bay, and mounted slides.

Before bolting the gennie to the new frame, I considered that the isolation mounts which support the engine and genset were 20 years old, and had endured heating and cooling countless times. She shook pretty good during starting, and I figured they were about worn out. So a replacement set was ordered (had to wait a month to get the parts).

There are two mounts under the genset, which you can see from the end, and one under the engine near the flywheel which you can't see. The genset mounts use an insert which mounts from underneath where the bolts go in. The engine mount does not. There are thus five pieces in all.

My buddy who's been occasionally lending a hand figured I was wasting my time and money going there - until he saw the old mounts sitting next to the new ones. The old ones were clearly worn out and sagging badly. I've added two pics of the engine mount below. The genset mounts looked the same.

The only simple way to replace these was to stand the gennie on the generator end, and remove the three bolts securing the pan to the mounts. The genset mounts were a snap. The engine mount was not. The steel bolts were torqued into the aluminum block - galvanic corrosion left them frozen in place. The heads snapped right off. Drilled the old bolts out, and as luck would have it, I had a Helicoil repair kit for the 5/16-18 bolts used here. After drilling and tapping, new stainless thread inserts were installed. Anti-seize compound was used on the bolts this time.

Finally ready to go back in, once I sort out a couple of details with wiring and fuel line extensions. Just wanted you to see what a 20 year old worn out mount looked like. Might be something to consider having done next time you have the gennie serviced, if it's near as old as mine.

Steve

Re: Generator isolation mounts

Reply #1 – October 24, 2011, 10:01:58 pm

I'm confident you have considered this but on your final installation make sure you have strongly secured the new mounting platform to the chassis. Even with new vibration isolators, if you allow any movement between the mount and the chassis you will get a lot of noise throughout the coach.

On my 300 the mounting bolts from the slide out frame to the chassis were loose. That caused lots of vibration to transfer into the coach. The factory designed slides are very firmly bolted down so that all movement stays above the vibration isolators.

Re: Generator isolation mounts

Reply #2 – October 25, 2011, 07:10:33 am

Thanks Kent

Appreciate the need for solid mounting. The slides on one side are bolted through frame, using extra thick stainless washers (special order), ss bolts and locknuts. The other side uses a 1/8 thick piece of powdercoated aluminum stock underneath to provide a solid mount (adjacent to frame). We test fitted everything prior to sending the pieces out for powdercoating - solid as a rock. The slides are 22 inch Accuride 9308s (with lock in and lock out), and I used two sets of 9301 mounting brackets to position the slides securely.

The engine is grounded to the pan through a bonding strap, thus whatever the pan is bolted to must provide a ground path (for the starter) I am adding a ground cable from the engine block to the coach frame, not wanting to rely on the ball bearings in the slides to provide a ground path for the starter.

Anxious to see how it turns out. This all started several months ago, and has been an on and off project.

Steve

Re: Generator isolation mounts

Reply #3 – October 25, 2011, 09:18:25 am

It sounds impressive Steve. I'm sure it will work out fine.

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