To start with today, I tried wasted spark. This has been suggested before, but I couldn’t find where the setting was until Dennis led me to it. I tried to start, but no joy.
Even ran a few logs, but they didn't look any different to previous ones.
Next, I did a few runs in test mode just to be sure that all coils are firing in the correct sequence. I can easily see when the spark pattern is good from the LEDs I have on the spark relay box.
- Spark box 13c.jpg (30.86 KiB) Viewed 774 times
This video is with the test mode running at 240rpm, so it is easy to follow the firing order 1-6-2-4-3-5.
https://photos.app.goo.gl/v0qMXX59sGtJghgG3
It is also easy to confirm that the coils are actually firing by pulling the coils out of the engine and plugging in a spare spark plug grounded to the engine. So no problems there.
During cranking to start, you can see in this video how the spark pattern becomes random. This is how I have easily been able to identify that the spark timing was being screwed up by something.
https://photos.app.goo.gl/rEIyk7HLaRzjGqq22
Next step was to look into the strange compression pattern on the tooth logs.
Hand cranking the engine as suggested confirmed what the logs have been telling us all along … compression is occurring every 240*, not 120*. That is three compressions per two revs. This implies that two cylinders are firing at once.
When the engine comes up to compression, it is
seriously hard to turn over. = two cylinders on compression?
Knowing something about the internals of these engines, I think you’ll agree Dennis that there is no way a cam can just slip and be out of timing by a whole cycle. Until I enquire further (on PP forum), I just can’t get my head around how the cams could be assembled with two cylinders having compression at the same time. It kinda sounds possible, but I can’t imagine it would run very smoothly.
If I was running wasted spark, I could understand how the engine might run, but it has been using sequential spark from day one, so it is a bit of a mystery that it runs so well.
Anyhow, at this point, I am not going to continue chasing my tail with sensor testing and pot twisting until I confirm that the cam timing is correct. Sh!t, if this is the problem, I can’t even blame someone else because I built the engine! (one of many, I might add)
All along, I have had the gut feeling that sync loss was the result of a problem, not the cause. My theory has always been that the sync loss was due to the erratic cranking speed, and even though it might mean an engine teardown to rectify, I am much happier doing that than learning how to use an oscilloscope.
I will check with the PP forum before going further, but at last it seems there is light at the end of the tunnel.
Thanks Bill and Dennis for steering me in the right direction. I will post more details here later when/if I confirm that cam timing is the problem. I need to figure out the easiest way to check for two cylinders at compression, probably by checking rocker positions.