Lift the engine rocker cover without specific reason?

[RichardS]

Rocker clearances can also close up if the valve wears faster than the valve gear.
Over-wide clearances can increase stress to the valve as it closes, sometimes related to the head of the valve coming off.
Not aware of either of these things happening on diesels though!

I would have the cover off.

In theory the valve clearances could decrease, I agree, although having spent 50 years checking clearances on pushrod engines I can't ever recall such an occasion. Bucket and shim adjusters are different but I don't think are used in small marine diesels?

I doubt that an overwide clearance is going to over-stress the valve as the opening is getting less and less so the opposite is more likely to be true. In extremis the valve will not open at all and the stress on it will be zero.

Richard

 

[lw395]

In theory the valve clearances could decrease, I agree, although having spent 50 years checking clearances on pushrod engines I can't ever recall such an occasion. Bucket and shim adjusters are different but I don't think are used in small marine diesels?

I doubt that an overwide clearance is going to over-stress the valve as the opening is getting less and less so the opposite is more likely to be true. In extremis the valve will not open at all and the stress on it will be zero.

Richard

Over wide clearances mean the valve is accelerated more sharply as the cam takes up the gap on a steeper part of the curve. At the closing point, the valve hits the seat harder. I think this is more of an issue with people pushing the limits of classic motorbikes, rather than yot diesels TBH. People sometimes increase valve clearance to the point of 'giving it some lash' to shorten the cam duration for more tractability on short circuits. Then they use a lot of RPM.....
Valve seat recession is not unknown, some people point fingers at modern fuel.
Gaps can also close up if the head gasket shrinks over time.
I don't know how critical tappet gaps are on the average yot diesel, but some pushrod motors (e.g. the Guzzi I had) most of the gap disappears at working temperature, so it's important not to have too small a gap.
We've digressed a bit, but I'd be in favour of eyeballing the rocker gear, at worst you see everything is nice and clean and happy, possibly you catch some small problem you weren't expecting like a stray lump of sealant or something out of pace.

OTOH, I have worked a little in the Satellite industry where reliability is obviously important. They have a saying that satellites are reliable because there are no technicians up there fiddling with things.....