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I guess thats because the push rods are conneted to camshaft which moves the rods and hence the valves operate,how cam you operate the spring operated valve system? And moreover there are springs in the valve tappet settings,so basically they are equal.

WHAAAAT???

Who needs these vids after a first hand session with you?

Ranjith...trust me, I'm still learning!!! And I'm thought someone will help me with the flow. Its been lying here for quite sometime unanswered!!!

Well one thing I remember is that due to the mass of the long pushrods, high rpm operation is difficult. This problem was solved somewhat with the spring valves.

Harley uses pushrods in its engines, maybe the VRod is an exception. I think they use pushrods because their engines remain unchanged from years ago.

The wikipedia page has some advantages:
Overhead valve - Wikipedia, the free encyclopedia

I guess the main advantage will probably be that you can control the valves in a V configurated engine with a single cam.

The spring valve means that each cylinder head would need its own cam.
If you had a V engine then you would need 2 cams.
One in each cylinder head.
But a single cam in the center with pushrods can control all the valves.

That is my point!!! If spring valves are effecient, then why do HD & RE (these are what I can recall now) still use the old push rod technology?

Not necessarily a V config; Old Triumph's had parallel twin & uses push rods.

The old Honda CB650 had a inline 4 with SOHC. Which means multiple cylinders & DOHC are independent.

Hope you meant a single CAMSHAFT mounted with multiple CAMS.

I was about to post "They dont change it because it was being used since ages and they were too lazy for a redesign"

But then I decided to give it a thought... and found this:

2009 Yamaha MT-01

2009 Yamaha MT-01 Features:

Engine:
keeps engine height down for a lower centre of gravity for great handling and ensures more uniform heat dissipation due to absence of a cam chain case.

I need to munch on this more to understand in depth; appreciate if you can elaborate in simple English @Antz.biz.

But, I'm beginning to make out some real difference & pros for push rods. Tks Antz.biz.

Ina push rod engine the camshaft will be placed very low in d crank case. this moves the weight downwards Compared to OHC engine.This saves some space in d cylinder head.Also we can place d rest components more compactly, saving some material mass from d head.this also lowers d engine height.the slots for the push rod can be very thin since they don't need to be adjusted like the cam chain.So nothin like tension adjustin provisions in d cylinder.This reduces the cylinder wall thickness at the slot in push rod engine than d OHC . Reduced thickness and surface area inside slot ensures better heat disipation from cylinder surface and coolant jackets.

Hope u got a vague idea about it.

The thing with pushrod engine is the rod tends to buckle if too long and had to be made thick to prevent it.This increases the valvetrain mass and hence the inertial effects comes in at an early rpm. That is why all the pushrod engines are low reving.
One of the main reason tat HD and RE not upgrading their engines from pushrod engines is that, they are classics and it's their individuality.It is this individuality that a biker expect from these bikes and others respect. Simply
THEY DON'T WANT TO LOSE THEIR MAJORITY CUSTOMERS

Nice points Nithin
Triumph Bonneville?

I meant that you can also do that.
As in an additional feature.

Yeah my bad.
I meant a single camshaft.

I talked to 2 mechancal engineers about this.. they have to say that Push rods are cheaper to implement instead of OHC but suitable for only low revving engines. So, push rods are used wherever the application is in a slow revving engine(RE / Harley / 2009 MT01).

In high revving engines, Push rods are subjected to higher stresses and fatigue whhich can lead to mechanical rear of the push rod leading to mismatched timings.

The reason Harley and RE still use push rods instead of OHC is because high RPMs re not involved, the cost savings in material and cooling outweighs the benefits of OHC. Helps these engines run cooler(as Nithin explained) and hence sustainable with just air cooling.

Some comparisons here... SOHC vs DOHC vs Pushrod Engines: Camshaft Issues

P.S.: The name is antz.bin not antz.biz