Diesel engines (Q2) Overhead cams in small car diesel engines.

Only pushrod wear, camshaft wear etc.

Cam gear on a 4 stroke runs at half crank speed so there is always need for reduction gearing.

Belts are quieter than chains., and chains are quieter than spur gears.

Chevy small block is out of the ark...and you still need to pull a lot apart to change the cam.

I.e there isn't a lot of advantage to any particular layout. Its probably easier to arrange VVT on a twin overhead cam though

Cheapness? So not needing galleries for 2 push rods per cylinder means the block can be smaller and lighter. Easier to assemble, no need to line up push rods with rockers. No need to supply push rods.

Yes there is a cam belt and tensioner but the just bolts on the front.

I would say also easier to design gas flow, with no pushrods to get in the way.

The chevy small block v8 is others have said an old design, but uses a single cam shaft, where as if ohc it would have needed 2...

Dave

When was the last time you wore out a pushrod? OHC engines still have camshafts.

I imagine it’s all just down to manufacturing costs (and possibly weight).

Tim

Very common in these engines around the 160,000 mile mark, and in the USA they do that sort of mileage relatively quickly.,

And other things like VVT. You meed to split exhaust and inlet camshafts to do VVT properly And on a V engine that tends to mean twin DOHC is the answer.

I used to own a Rover 3-Litre which had an odd engine design: Overhead valve inlet, side valve exhaust, all driven by a single camshaft.

I bought it when it had nearly 250,000 on the clock (it had been a minicab mostly used for long journeys and it had 3 drivers working 8 hours each, so the engine never got cold). I used it for commuting between London and Bath. When that was no longer necessary I sold it with 350,000 on the clock. It was still the original engine and apart from routine maintenance I had never needed to do anything to it.

The other possibility is the deliberate re-use of parts fitted to other production models, because that avoids any potential spares shortages after a new product release.

And the development of reliable toothed drive belts?

I know it's swings abnd roundabouts, but I'm not convinced a toothed belt (especially not a wet belt either) will have anywhere as near the longevity of a pushrod or a camshaft, which are lubricated.

In-block gears probably the quietest of the lot though.

Indeed it is. Not half reliable though ;)

Horses for courses? Cheers.