DEK 11 rebuild (Honda gx340 clone, I think)

Amateur87 · Jan 23, 2016

Good morning all,
I've been working on bringing a DEK 11hp 270cc engine back to life and have hit a snag. I've been using replacement parts that are for a Honda gx340 clone so far. Carb, gaskets, springs, fuel line for gx340 fit perfectly.
I tried to start the thing a couple days ago and had 0 compression. I found that the piston rings had seized to the piston head so I removed and broke them in the process. I ordered new rings for a Honda gx340 and when they arrived they appear to be way too small. So now I'm confused. Does anyone know if the DEK 11hp is a Honda gx340 clone? Does the Honda gx340 series have different sizes of piston rings/bore diameters?

Any insight is appreciated.

Rivets · Jan 23, 2016

I think your problem may be that the engine is a GX390 clone not 340. If you do some searching, you should be able to find the bore size of the 390 and then compare it to your engine.

Amateur87 · Jan 24, 2016

Thanks Rivets. I think you're right. There appears to be a 6mm difference between the 340 and 390. I ordered new rings, hopefully they'll do the trick.

Amateur87 · Feb 16, 2016

The rings fit, however the cylinder was damaged, so I bought a new block. I'm having trouble getting this sucker to start though. When I pull to start it, it backfires through the carb. It has backfired through the exhaust a couple times, but mostly through the carb.
So, I checked the valves and they seat well and move well, nothing stuck or hanging up. The camshaft/crankshaft timing marks match up. I installed a new plug and coil. I checked the flywheel key, and it is straight and un-damaged.
I'm stumped. On a brighter note, my right should has really beefed up from cranking on this thing.
Any ideas?
Thanks

bertsmobile1 · Feb 17, 2016

Take the plug out and the rocker cover off.
Turn over the engine by hand.
Watch where the valves are with respect to the piston and the ignition coil.
Check the operation of the decompressor .

Amateur87 · Feb 17, 2016

Ok I will. Is it possible to check decompressor without opening the crankcase? When I had the case open, it seemed to be working(smooth movement, spring would retract just fine) I have a compression tester, but haven't been able to get any reading from it(I've assumed no reading is because the engine has the decompressor). Should I be getting any compression reading at all? Also, the compression tester does work, I tested it on lawn mower and got 60psi reading.

Thanks for your help.

bertsmobile1 · Feb 17, 2016

The decompressor will make one of the valves open slightly just before the piston gets to TDC.
If the valve gap is too big it wont happen.
If the valve gap is too small it happens too much.
Place your fingers on the valves while you turn the engine over as the opening is very small and a bit hard to see.

At 60psi the engine will only start if it is spinning very fast.
Low compression readings will result from too small a valve gap and of course, rings not seating properly or people using the wrong compression tester, or using it incorrectly.
To get a reading with accurate numbers the meter must occupy the entire space that the spark plug occupies otherwise you are adding volume to the combustion chamber and will get a false lower reading.

Amateur87 · Feb 20, 2016

I hand turned the crankshaft and watched the operation of the valves and they see to be operating correctly. They appeared to be timed correctly. I did notice the exhaust valve open slightly for decompression,but not at TDC. It looked to me like it was opening slightly when the piston head is almost to the bottom of the stroke. Also, the valve opening is pretty small, maybe a couple of mm wide.

Amateur87 · Feb 20, 2016

I re-gapped the valves and coil to spec and tried compression test again. I got between 30 and 32 psi.

Amateur87 · Feb 20, 2016

Holy crap it just started!

DEK 11 rebuild (Honda gx340 clone, I think)

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