I wonder if there is a way of identifying the spring of perhaps best to change the full set.
SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm
Hi Roger if you check the video no 2 spark plug lead cap is wobbling around have you checked the plugs carefully I have known them to break and leak. What is your oil pressure like, if its low it's possibly an indicator of bearing damage. That's not always the case my engine let go and it was showing 60 psi ! Are you using forged pistons it could be piston breaking up.
That said check all the simple stuff first
Have you got the URL, please, Phil?
Hi Jonathan I'm not that clever but Revilla has posted on it page 2 it looks like it may be a blown spark plug ?
Doh, I'd missed it!
You can do a very rough check of the big ends by dropping a bar down the plug hole and measuring the backlash. If a big end is wrecked there will be a delay between reversing the direction of the crank and the piston crown moving. Obviously this is better with a DTI but you can easily feel it by hand with a screwdriver when they're really bad. It doesn't sound heavy enough or rhythmic enough (to me) to be that though.
I'd also lean towards something light bouncing around in the cam box.
USB endoscope cameras are very cheap now and surprisingly good. I have one I paid less than a tenner for. Very handy for a quick check of the piston crowns through the plug holes.
I replaced all the valve caps and collets on my K series on the advise of Dave Andrews. Some are cast rather than forged and the valves can pull through. Changed all without removing the head using string down the plug hole trick.