Re-profiled cam sweet spot

Hi guys can i find the sweet spot in a re-profiled cam thas as no Specification Sheet??

Sure you can. You just need to get degreeing wheel, dial gauge and take measurements of valve movement. After that you can make little plot plan in Excel to visualise cam profile vs piston movement..

I'm very wary of "reground" camshafts, ESPECIALLY of unknown origin or spec'.

There are WAY too many uinknowns - such a...

the accuracy of the grinds -are they the same for each lobe, lift, duration, timing, consistent arcs, etc?

the hardness/treatment of the reground lobes - they initially have surface treatments for hardness and durability and that is ground off, leaving the base cast iron (unless special steel application, eg, roller followers), which has poor wear resistance.

the base circle may be too small for the followers to tolerate - especially hydraulics - which means the preload/clearance required may not be achievable, which brings up

is the camshaft a hydraulic design or mechanical grind - they are different - and if the latter, what clearance are you supposed to set them to, anyway?

lobes are normally ground with a VERY slight taper, in order to offset the thrust line and rotate the followers to minimise wear, of they're the round, free rotating type. Obviously, directly acted on rocker arm variants are different.

other reasons that don't immediately come to mind

OH, the obvious one is not knowing if there will be issues with valve to piston clearance - some engine run very close, others are 100% non-interference. While checking - you can use the thumb method if you can't, or prefer to avoid, use a plasticine, DTI, or other method.

The easiest option, especially if 'off the shelf' verniers are unavailable and offset bushings/keyways are going to be required, is to simply fit using all the OEM marks, etc. After checking - see above - of course!

If it is a single camshaft, with inlet and exhaust lobes, a base setting may be with equal lift on exhaust and intake at TDC, sometimes called "straight up" timing, then you can advance and retard a couple of degrees to see what works best for your application.

If it is only intake, or exhaust, you can start at the OEM timing for it, and see how that works, and try advancing a couple of degrees either way to see what works best.

All that said, my best advice is to keep it by the bedroom door, so you can use the camshaft to bonk burglars on the head!