Fault finding

[Roger B]

I hadn't run my first engine, the 3cc vertical single for some time. When Alex S came to visit I got it off the shelf for a run. It was hard to start, wouldn't rev and just kept stopping (I think Brian R has had similar problems).

I know that the sealing between the liner and the block was a poor design and wondered if I was losing compression there  When I took the head off there were obvious water traces where there shouldn't be 

The bore and piston looked ok although there were some dark areas on the piston ring. When I pushed the liner out half of the water jacket was full of gunge  Was this due to leaking combustion gasses? When put back together the liner was 0.1mm below the block which is obviously a leak point. I gave the liner and block a good clean in the ultrasonic bath ready for the reassembly.

[Roger B]

In the original design the liner was clamped in the cylinder block by the head and head gasket. This was not a good move even though I thought that the expansion coefficients of aluminium and brass were close enough. This time I fixed the top of the liner in place with Loctite and then faced the block and liner together. I punched another head gasket with the original template and reassembled the engine.

The compression was now good, but it still ran badly    Next step the ignition system. The timing was still correct but the spark seemed rather weak. The supply voltage to the Rcexel ignition was still a steady 6V so I decided to go back to the coil system that I used to first get the engine to run. This was much better, not the best as I will have to adjust the timing to compensate for the Rcexel advance curve.

I will now have to decide to keep the 6V system via a 7806 regulator or rebuild the Vellman ignition back to it's original 12V form with a 12V motor bike coil 

I finally took the cover off the Rcexel ignition to see what is inside. Mostly potting compound 

[Kim]

Excellent debugging work, Roger!

It never fails, does it?  When you go to give a demo, things don't work 
I'm sure there's some Peter Principle type thing at work here, you know?

Kim

[AlexS]

Nice work on debugging and rebuilding your first engine.

On my engine I use the same Rcexel ignition with a digital hall sensor electronics. Feeded with 5V from a USB charger. Only thing I had to make from the negative wire from power supply to the engine crankcase. Otherwise I saw when testing with head off no good ignition of the plug.
Currently, the engine is start and go (now fitted with Honda Monkey 9mm carb) and could read the ignition timing by stroboscope. Tested multiple timings. Setting the Static timing (when turning flywheel and hear the ignition or see hall sensor light switch off and than on (ignite)) to 25 degree BTDC, result at low stationary (+-1200 rpm) of 15 degree BTDC ignition timing. And rev up it go to 35 degree (+20 degree advancing) and stays 35 degree when turn up speed (say 4000 rpm).

Nice to see inside of the Rcexel. I saw a supplier that could deliver this kind of ignition kits on request specification (amount of cylinders, timing/advancing).

Maybe this could help!

[Roger B]

I have a couple of displays planned so I thought, based on this previous experience, I should test run the 3cc vertical single. It started off ok and would drive my light bank (12W) fairly steadily. The performance then dropped off quite rapidly until it would no longer power the lights 

After a bit of checking I found a total loss of compression and a hiss from the exhaust when the engine was turned. As it is normally electrically started via the generator I don’t get to feel the compression, but I did turn it by hand to check the valve clearances before starting this test. They were around 0.08 mm, a little tight maybe but should be ok on this engine. I would normally set 0.1mm.

I drained the cooling water and took the head off. The cylinder bore looked ok (for this engine) and blocking the top of the bore gave good compression. Blowing down the exhaust pipe produced bubbles around the valve.

https://youtube.com/shorts/PY2_B0iIkjc?feature=share

<a href="https://www.youtube.com/watch?v=PY2_B0iIkjc" target="_blank">http://www.youtube.com/watch?v=PY2_B0iIkjc</a>

I then removed the exhaust valve, the seating and the valve face had an odd mottled appearance. The seating cleaned up well with the original seat cutting tool, made from an M4 caphead screw in the same way as the valves.

The valve was polished with a fine diamond file but this didn’t remove the mottled finish so I recut the seat in the lathe. I also improved the under head profile of the valve.

Next step lap the valves into the seats, clean it all up, and reassemble.

[cnr6400]

 

[Roger B]

The valves were lapped with 5 micron diamond paste and then cleaned up in the ultrasonic bath. A quick leak check (with breath pressure) seemed ok so I reassembled the engine and tried it again. Back to normal 

<a href="https://www.youtube.com/watch?v=SaH16nAFm3I" target="_blank">http://www.youtube.com/watch?v=SaH16nAFm3I</a>

I’m not quite sure what happened with the exhaust valve       maybe a particle of something got caught on the seat or the clearance closed up