Quote:
Originally Posted by kevino
Maybe post on whirlpool automotive it’s a bit quiet on here unless it’s falcon- ranger- Everest
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Very true, will take a look - not signed on there yet.
On this whole MD tensioner thing - the old brain is like a dog with a bone...
It's odd that Alan Howatt simply replaced that broken chain, tensioner etc without knowing what caused the chain to break. In the video with the split sprocket hub and the missing teeth, it's probably the same thing? In that case, you'd think there would have to be gouges or marks in the side of the tensioner to show what happened, if this theory is correct.
ANYWAY, another thought occurred to me.
This is going to depend on lots of things that I don't know about. Citroënbender mentions that there's a ball spring check valve in the oil gallery feeding from the block into the head. That's a good idea, to stop oil draining back from the upper oil passages during shutdown, but what if there are oil passages opening in the head, below the level of the tensioner cylinder? For example, oil passages feeding each cam journal. It looks to me that the cam lobes press downwards onto the rocker arms.
This means the cams are likely to be in a lifted position in their journals during shutdown, pushed upward by open valves. If the journals are worn, or the oil is fed into the lower side of the bearing, then oil could siphon out of the tensioner cylinder. It will be able to do this if there's (still) an oil passage feeding from the tensioner cylinder through the piston and out onto the tensioner foot. This drilling will allow air into the top of the piston & cylinder, allowing the oil to drain out somewhere lower in the head.
So, after standing a while (esp from hot), the tensioner cylinder could be largely full of air. Air, being of much lower viscosity than cold oil, on startup will simply jet out through that opening until the cylinder is completely refilled. No oil pressure will develop inside the cylinder until then. Since the inflow must be restricted, this could take many seconds - based on the time it currently takes for my MC cam chain to quieten down on startup. During that time, the tensioner will only provide spring tension - if the spring is still intact. If it's not, the tensioner won't provide any tension at all.
A Dangerous Time, given the jarring path the chain will follow leaving the driving sprocket. This all seems to be supported by the fact that in one video, the tensioner foot was broken off and the piston out of the cylinder...
So, MY SUGGESTIONS if you have an MD Diesel.
Keep an ear out for cam chain noise on startup.
If you hear it, or, maybe monthly regardless, with the engine Off - of course - look through the top oil filler hole and see if the cam chain is being held upwards under tension by the internal cam chain tensioner spring. If it's not, get a new tensioner fitted ASAP!