Hi guys,
I have a strange problem with my engine and need some opinions.
I drove it at Eastern Creek a couple of weeks ago and it ran fine though when I drove into the pit lane after a cool down lap after the third session, it stalled. I then clutched it as I was still rolling and it was spluttering a bit. It had run OK when I was racing. When I went to drive in the 4th session, it wouldn't start. I gave up and winched it onto the trailer.
I checked it yesterday and the plugs were fouled, as I expected. I then put some new hotter plugs in and it still wouldn't start. I was perplexed.
I went through the normal fault finding process and came to the conclusion that the compression in all 4 cylinders was very low - around 75psi
I checked a few things to figure out the cause and found that there was no inlet valve clearance - on any of them. The exhaust valve clearances were however all within tolerance.
I loosened the inlet cam caps until I had the right clearance (for testing purposes only - I didn't run the engine like this) and retested the compression and it was 190psi. This proved that the cam was holding the inlet valves slightly open when they should have been closed.
So my question is this - What caused my inlet valve clearances to change?
The engine had been running fine previously.
I have oversized valves. The only thing that I can think of is that the valve seats have relaxed after a few hundred KMs of hard driving. Any other ideas?
Should I just re-shim and keep driving? Everything else looks fine.