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?
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.
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.
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
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 .
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.
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.
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.
Like a lot of things, compression readings are not as simple as it looks.
On a small engine the compression tester must occupy all of the volume usually taken up by the spark plug .
Thus to get an accurate number you need a variety of ends.
If you are working on a multicylinder engine not so much of a problem as you are generally looking for differences between individual cylinders.
On a single cylinder engine then you are looking at changes over time , using the same tester.
On small capacity cylinders this is even worse as the volume of the spark plug hole can often be greater than the volume of the entire combustion chamber.
If you really only had 32 psi the engine will not fire.
