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Reground cam's bad idea ?????
monck - 4/11/11 at 12:45 PM

Straight to it is having a cam reground a bad idea ?

There must be downsides, else everyone would just have there cams reground and not buy the likes of kent , piper


I have never heard anything bad but i guess someone might change that .

I just thought i cant really afford to buy kent or similar after everything else i have done ... My only thought was they will wear quicker but given my car does not do that many miles does it matter ?

If the negatives are not to bad it must be a locost way ???


Cheers

ReMan - 4/11/11 at 12:49 PM

Presume you mean reground to a differnt state of tune, not just to repair worn?

r1_pete - 4/11/11 at 12:50 PM

I understand Kent do, or used to re-grind cams to their profile, either way all cams are ground from blanks in the 1st place.

In reality its no different to having a crank reground.

Autosri - 4/11/11 at 01:00 PM

The only problem I see with reground cams different metals joined together

The way I understand it is the grind the tops of the lobs to give a longer duration but then they have to replace the metal on the opposite side plus a little more for added lift I think the added metal is weld so you have two different metals how would they react to heat and stress

britishtrident - 4/11/11 at 01:00 PM

Main problem is with a reground cam the base circle radius is reduced, wild high lift profiles this could cause sometimes problems and made setting the valve clearances a right royal pain in the ass on engines with shim adjusted tappets.

britishtrident - 4/11/11 at 01:28 PM

To explain cam re-grinding a bit they increase the lift and duration by grinding more metal off of the base circle of the cam --- think of it as increasing the height of a mountain by lowering sea level.

I once saw a full house cam in a race 100e Ford 1172cc side valve engine in which the base circle had so much metal removed the back of the cam lobe was flush with diameter of the cam shaft.

Metal spraying is used to build up material on the cam but it is a relatively expensive process and is mainly restricted to producing race cams for engines that don't have suitable blanks available.

monck - 4/11/11 at 03:23 PM

Sorry for not stating that , yes i do mean i want a sportier cam not that my mine is worn

I don't even want a race cam just fast road

ReMan - 4/11/11 at 03:51 PM

Presumably a "standard" cam can only be ground to a limited different lift and duration? and to achieve bigger changes , particularling in duration or timing would need a different cast/grind in the first place?

MikeRJ - 4/11/11 at 04:36 PM

quote:
Originally posted by ReMan
Presumably a "standard" cam can only be ground to a limited different lift and duration? and to achieve bigger changes , particularling in duration or timing would need a different cast/grind in the first place?


Yes, there's only so much material you can remove, since the new profile has to fit within the original one. For higher lift/longer duration than can be fitted into the standard profile, you need to grid a cam from a new blank.

One of the problems with removing metal from the base circle is that this has to be made up for by valve clearance adjustment. Obviously there is a limit as to how much adjustment you can use and on some finger follower designs e.g. Pinto, this can have a significant impact on the cam lift and timing.

The regrinding process can also break through the hardening on the cam, so appropriate heat treatment is important in this case or you will suffer chocolate cam syndrome.

[Edited on 4/11/11 by MikeRJ]

mark chandler - 4/11/11 at 05:40 PM

Its more suited to push rod type system where the adjustement does not carry a weight penalty.

Where you adjust clearance with shims such as an OHC pushing on shim buckets on top of the valves as you grind the base of the lobe you have to increase the size/weight of the shim which is bad.

Regards Mark

laptoprob - 4/11/11 at 07:09 PM

I have had some Autosprint reground cams in my Redtop all year running 11.2mm of lift and 302 duration.

Started life as 180 bhp and with some high comp pistons and porting its happily singing at 230 bhp with no known issues.

Thats as far as the cams can go before you need to use a blank so if your only considering a fast road cam then your going to be well in.

monck - 4/11/11 at 07:51 PM

Laptoprob - Cheers for that can you remember a rough price ?? I may aswell post them there if you recommended them

laptoprob - 8/11/11 at 08:00 AM

The regrind was done here AUTOSPRINT.