I remember the first time I learnt about cam belts and their failure effects (waiting for a colleague to turn up at a meeting and him ending up being recovered by the AA), I had a read through the manual for my car at the time and was relieved to read it had push rods and a direct drive cam!
cant have a DIRECT drive cam on a 4 stroke... .. 2:1 reduction. Belt gear or chain.
Nothing to do with the pushrods though. Almost all OHV engines (non OHC, non Hemi) have valves with parallel axes, almost parallel to the cylinder axis. Piston impact drives the valve up through the guide, hitting the rockers or pushrods.
OHC engines use OH camshafts to make the valve position more flexible. This gives better gasflow, but it also means that the valve axis is now at an angle to the cylinder. Hitting these valves will bend them, not push them up the guide.
They weren't, even 30 years ago.
Idiosyncratic, tail-heavy, but never rubbish. Compare a Skoda 130 (or a Tat= ra) to a Lada, Polski Fiat, Dacia or (Lenin forbid), a Moskvitch. No-one w= ho followed the RAC Rally laughed at Skodas. Certainly not Tony Pond in one= of Dave Plowman's beloved SD1s.
That is of course true, but you can still have angled valves on a pushrod engine. Simply have a 'bent' rocker
Yes. Not bad cars even then.
Just dull.
Think they sort of arrived at the same time as OHC became the norm on ordinary cars. Before that chain driven OHC could certainly give problems if neglected.
The real pain is that engine makers have made them nearly as difficult to change as a chain - but at a lower mileage. Something which doesn't need lubrication and is at the front of the engine should be an easy job to change.
Perhaps we are talking at crossed purposes...
The cam was adjacent to the crank shaft, and a cog on the end of the latter drove the former. In other words there was no belt or chain required.
No reason why this is the case. Plenty of examples of pushrod engines where the valves ain't in line with the bores.
Just as many SOHC designs had vertical valves. Once you go to DOHC, better valve positioning becomes simpler.
Quite.
And the Skoda was an original design - not some castoff like the rest.
The SD1 is too large for rallies. Generally, the smaller, the better. The Skoda never did much in circuit racing, where the rear engine was a disadvantage.
Just had the one, a 4x4.
Only car I've ever suffered from carb icing on it. Driving fast down a foggy motorway to catch a plane.
so 'gear' then.
Direct drive means in my book 'no reduction ratio'
I knew someone who neglected the chain on a Honda bike - CB72. He let it run very, very slack. It sawed through the oilway that ran up the block, at the front of the chain tunnel; lost pressure to the cam oilers.
He brought it to me because "it's a bit noisy and there isn't much power". I'd never seen round cams before, and concave, scoured rockers!
I bought a Fabia in 05, mainly because for me it was the most comfortable to drive (I'm tall). Brilliant car.
OHC was common a long time ago then fell out of fashion. The '20s Bentley used a triple eccentric drive (I think that's what it was called, basically like a crankshaft operates a con rod at both ends, but three of them so it could only rotate in one direction) - Morris a shaft drive, part of which was the dynamo. Seemed strange that some of these mass car makers then 'progressed' to side valves. ;-)
Rounded cams are quite common on the Rover V8 which has high loads between the cam and tappets. And many oils don't have the correct additives for this - including most modern ones. I looked at one which idled and ran pretty well perfectly - up to about 3000 rpm. But could barely be persuaded to exceed that in any gear.
Cash or trade-in? One is real value, one is not.
MBQ
I have that in the MG. If the top oil seal leaks, oil runs down into the b= rushgear and sets fire to the dynamo.
Sidevalves have better gasflow. After Ricardo invented the "Turbulent Head"= sidevalve design, and while petrol octane was still so low that compressio= n ratios were about 7 at most, the well-designed sidevalve had a lot to rec= ommend it. OHC and hemi combustion chambers don't make sense until engine = speeds have increased such that the flame propagation path length becomes a= limit, and that wasn't until the '60s.
Ford Pinto engine.
The 80's / 90's GM Europe 8 valve (OHC) engine, at least in smaller displacements, was non interference. Probably a few million of them fitted to Astras and Novas over the years.
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