Creating a Honda GC/GCV Hybrid

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My co-worker had a Generac pressure washer with a Honda GC160 that quit running one day with a pop. I took a look at it, and it backfired through the intake when I pulled the rope. Classic signs of a valve problem. I remove the valve cover and, sure enough, a valve problem. One of the rocker arm pedestals had broken. The machined hole through which the rocker arm retaining pin slides was way off-center, and I think that contributed to fatigue and, ultimately, failure. So I broke (ha!) the news, she declined to want to fix it and said I could have it for parts.

So what do I do with it? Light bulb. I have a spare GCV160 that I bought new back in 2003 on a Sears Craftsman mower. I gave the deck away to a co-worker probably 10 years ago, but I kept the engine. I had that engine on a few different mower decks, but hung onto it all these years. I crated it up when we moved from NC to VA, figuring I might be able to use it one day. That day had come. I was going to make one engine from two.

The GC (horizontal shaft) and GCV (vertical shaft) engine cases are split diagonally through the crank case area. The cylinder side is a common part to both engines. The only thing that differs between the two is the case "cover" as Honda calls it, the case half that goes on the PTO side of the engine. On a mower, it's the case half that's bolted to the mower deck. On something else, like a pressure washer, it's the case half that mounts to the chassis, and that mounts the driven equipment (water pump in this case). I took a good look at both engines to be sure that certain mounting points were common, and they were. Indeed, Partstree.com confirmed the cylinder case is the same part number, so I was good to go.

Here are some pictures of the engines and the process, with captions following.

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This is my GCV cylinder case, after splitting the engine, upside down. The large crankshaft journal is on the flywheel side of the crankshaft. The baffled castings just to the right of that are for the crankcase venting system. Then you have the cylinder and the horizontal pocket through which the timing belt passes just "above" the cylinder (in this picture).

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This is the GC case cover, the "lower" part of the engine that mounts to the pressure washer chassis. That's the PTO crankshaft journal you see. Notice the governor sprocket, which spins counterclockwise in this picture. I think the oil ramp just to the right of it is neat -- it slings oil up into the engine as it runs. I also like the "valley" just above the crankshaft journal, funneling the oil spray that clings on that wall down to lubricate the crankshaft journal. This engine, by the way, still had its original fill of oil I think. I used a good amount of brake cleaner to clean this case cover out. What you see here is about half-way through that process. Black tar was oozing out of all crevices.

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The reciprocating mass. The GCV crank and piston/rod is on the right and the GC crank and piston/rod is on the left. The cranks are obviously different due to their intended application, but the service part numbers for the pistons and connecting rods are the same, meaning they're 100% intechangeable. I used the GCV piston and rod, because this is the piston and ring set that had already mated to the cylinder wall I'm using. My piston was also far cleaner than the GC piston, due to me changing the oil regularly in mine and that NOT happening in the other engine.

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Okay, here we go...assembly! You put everything into the cylinder case, then slide the case cover down on top of it. The engine has two alignment dowels, so it can't get messed up. I worked the piston and rings back into the cylinder bore, torqued the conrod bolts to 9 lb*ft, and installed the timing belt. No tensioners or anything like that...it's just a simple two-sprocket system. The thrust washer is not yet installed, laying against the bottom of the cylinder case.

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This is the case cover, all cleaned up. It's a shame these are "disposable" engines and rarely get opened up. The casting detail is just beautiful inside.

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Detail of the crankshaft area.

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Timing belt interface with the crankshaft. I used the GC's original timing belt, because it has fewer hours. Still, this is a 14 year old timing belt -- looking and working good as new.

I have a picture of the finished product, but I apparently haven't uploaded that to Flickr yet, so I'll link that in a later post. I mounted it to the chassis without the water pump attached, and it lit on the first pull. It runs like an absolute champ. It doesn't even hunt at no load idle, as most of these engines seem to do. After running it off and on for about 30 minutes, I hooked up the water pump and pressure washed my front walk and front steps.

I made a real live engine out of two, using parts that interchange 100%. It was a super fun project, one I'll enjoy using for many years to come.
 
I realize there's not much of a load on the belt in this particular setup, but it is amazing to me how good they still look after years of use being bathed in hot oil. Honda really is a master at this type of stuff.
 
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