Topic Approved

Camshaft Grinding is not a 'modification' process. It is one of the processes by which Cams are generated/cut. The stock cam has no part to play in this process hence the modification tag is incorrect. However if you are referring to the jargon as an extension to 'modification done to the design' of a camshaft then it is agreeable in this context. There is a thin line distinguishing the two, hope it is clarified.

The terms Lift, Duration are basic data used while generating 'a' cam.

'Lift' gives us the value of the lift (or gap) obtained by the valve when the cam is at its maximum height, this value is derived from the 'Stroke' off a cam.

'Duration' gives us the value of the time for which the valve is held open. This time duration is expressed in degrees.

Where as the 'Over Lap' is a data the value of which simply defines the relative positions of two cam lobes on a cam shaft (conventionally its between the exhaust and intake, and is expressed in degrees) In conventional camshafts there is a slight degree(3~5degree) of over lap between the exhaust valve and intake valve cams. In simple terms it means that the exhaust valve remains open for for a brief duration, while the intake valve is opening, and closes a few degrees thereafter. This helps the flow of gases from the intake manifold to blow out the remaining (expanded) exhaust from the cylinder. This phenomena is referred to as 'Scavenging' of the engine

When Performance gains are in order these values are tweaked to produce better gas flow (quantity as well as flow) and better scavenge the engine. Like all 'performance' improvements these too come at a price. But first details of how it affects performance.

Higher lift provides a bigger opening for the port to (E* same incase of exhaust ports the exhaust gases flow from cyl thru port to exhaust is improved via the larger opening) dump the incoming air and fuel mixture to. If the port geometry is designed in synch with this higher lift cam then further reduction in restriction to the flow of gases is obtainable. Depending on the engine (block+piston+head+cam duration) the piston crown will need or not need alterations.

Higher duration means that the valve will remain open even after the stroke has finished and the next stroke has started. This is benefiting in high rpm engines as the momentum of flowing gases cause more charge(air and fuel) to be rammed in thru the intake ports, higher Duration in exhaust cams will add to overlap and the intake stroke pulls more charge into the cylinder which displaces the exhaust gases out of the exhaust port.

Cons-

Higher Overlap cams or Hotter cams in street speak, will change the engine characteristic from being good road mannered to peaky and ill mannered, i.e rough idle , oh and yes the idle will be higher.

Higher Duration cams also add peakiness to the engine and the engine tends to idle roughly (depending on the duration)

(an extreme example would be the 2.4l v8s in formula cars, those idle at 6k. cams are not the entire reason for it, but one of the reasons)

Higher lift cams will demand alterations in piston crown design, valve spring design, rocker arm design, camshaft bearing design, timing chain train. (mild->extreme) ofcourse most aftermarket manufacturers could cut corners here, as far as they are concerned if the stresses fall within permissible limits then things are 'ok'.

To assume this post to cover all the bases would be incorrect. hence i would recommend that you read up more on Cams, how the cam lobes are generated and the different processes used to cut and treat them. and further study into valvetrains, valve geometry, the likes. (some pointers if you are interested in knowing more about performance tuning )

PS: as to how the process of cam grinding is carried out, make a search on youtube, "cam grinding lathe jig" it is admirable how much effort people are putting into making such videos.

Cheers

Edit (E*) : it should have been 'same', typed 'vice versa' wrongly, grammatical structure of that sentence was wrong. +some words which i ate.

Camshaft is a round rotating part, but with a hilly/ lifted up area (cam lobe) on its circle boundary. A camshaft is connected to crankshaft's movement and thus it opens and closes valves with a certain lift & timing only.

The valve lift, duration & overlap according to this cam lobe's start to end length, slope and height. Cam lobes specifications changed = valve action changed.

So, any modification/ grinding that changes the cam lobe's shape (see the figure below), will definitely affect these factors, and ultimately the characteristics of the engine as a whole.

Camshafts can be of various types like Single overhead, double overhead, etc.

This is a typical camshaft. When it rotates, it moves the tappet which in turn moves the rocker arm and ultimately the valve:



And this further explains the camshaft lobe:



All around the world, major changes to engine tuning are done, keeping camshafts in mind. For example, one of the changes from 2004 R1 to the FZ1 was definitely a camshaft change. Even Duke 200 and P200 have different camshaft setups, among other changes.

But what is your question exactly? Do you want to grind your bike's cam or you're just asking for info?

sorry for the noob question

how can we change the cams to high lift ones ?

^^^ you will have to make/ source a new one. As mentioned above by Saerius a whole load of factors will need to be considered before you can use a hotter cam.

God, just thinking about all this gives me a headache and makes me long for the good old 2 stroke days. How uncomplicated they were ....

^ ^
thanks

I remember, someone from Xbhp did tell me to use a longer duration lift (mind you, that's different from high lift) camshaft originally from Pulsar 220, in my Pulsar 180 UG3. It would've costed about Rs. 500 and given some boost to the top end. But I never tried it. Will try after Joel's bigbore though, if he agrees to the setup.

Actually, camshafts are very potent. The valves are in their hands. They can make or mar an engine.


Can any of those guys who tried this setup (P220 cam into P180) share a small bit of their experience? How did this cam change affect the engine?

Pls help understand the difference.

But he only rebores the cylinder; he doesn't make anything with camshafts or will you get this done from two different sources?

Thanks MG for the approval.

Not true... he does do camshafts...

Saerius's post explains the difference... its actually a very nice write up...

Thanks Saerius, Samarth 619, abhimanyu31 for sharing your valuable comments.

Will read well enough on these and post more meaningful questions

Yes, he does and I do have one of them installed in my FZ.

Thanks Saerius ! This makes it much easier to understand now.
So, what is better for an engine:
- High lift with changes (or replacement) to head, rocker arms and piston (crown) with presumably smooth idle OR
- increased duration (overlapping) but a rough idle

Let's leave the financial aspects aside for a while.

1. Fictionally, at a particular rpm:

A longer duration lift might open for 650 miliseconds and 0.6 cms.
And, A high lift cam might open for 500 miliseconds, but for 0.8 cms.

Difference is because, Opening Valves can be lifted higher or for longer. Precisely, The difference is "length vs Time".

2. There is no relation between Joel's Bigbore and the new P220 camshaft (it will be obviously from Bajaj) I'm planning. These are unrelated events.

Its just that while installing the Big bore, the engine will be open and the mechanic will be working on it, so I'll plonk a new cam in too...! I'll have to take Joel's advice because I'm unsure how the new cam will react to the Bigbore, etc.

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Would like to add another self clicked diagram to this thread. Please watch this for a precise working of the camshaft: