Cutting down my threaded P2`s and impact headset

I haven`t done this for years!

I want to fit the P2`s from my old Lavadome into my explosif.

They are the original forks from the lavadome with impact headset (1992)
I want to fit them to my explosif which is a later model with 1995 impact headset.

The lavadome had a headtube exactly 150mm,
The explosif is later and has a headtube of exactly 130mm

The forks have a 180mm steerer.

Did the stack height of the impact change between 1992 and 1995? (I no longer have the 1992 impact to measure)

I was intending to cut exactly 20mm off the steerer if the impact stack height didn`t change. This would leave me with only 15mm of thread on the P2`s. Is this enough for an impact or will i have to try and find somewhere which can still cut threads?


Thanks

I will probably be corrected by the deeper knowledge here but here's what I think from looking out for my 92 Explosif:

The 180mm steerer is a match for the 150mm headtube plus 30mm stack of the Impact headset. The 30mm of thread works.

The 130mm headtube thus requires a 160mm headtube with some 30mm of thread. I don't think cutting 20mm of threaded steerer off the P2 and leaving 10mm of thread will be enough.

But there's more: The move from 150mm headtube to 130mm headtube (for the same size frame) coincided with changing the Axle to Crown on the P2's from 39cm to 41cm. This is referred to as suspension corrected geometry as it allowed to fit both P2's and suspension forks to the same frames.

From what you are saying your plan is to fit 92 P2's that are not suspension corrected (short 39cm) into a nice Explosif frame that is of the "corrected" geometry. The '95 Explosif was fitted with (or requires) the longer (41cm) forks by design. So is this really what you want?

Enjoy!!

(edit: small corrections on A-C after Anthony's response)

My 96 Explosif with an 11cm head tube has a steerer of 142mm, implying you need to cut yours to 162mm, so much the same as the earlier design.

I haven't got an Impact at the moment, so not sure whether 15-17mm would be enough thread, but might be tight.

I'm sure you know all about it, but just in case not the 92 fork is 39cm a-c and the 95 frame is dsigned for a 41cm a-c fork (hence shorter head tube), so strictly speaking you shouldn't fit the 92 fork anyway, unless you like very sharp handling and a low front end. I think 39cm P2s are rarer than 41s, so you should be able to sell your 39 and buy a 41 without it costing you anything, and hopefully find a size 19 P2 from 94 or later which would solve both problems.

Apologies for not making myself clear!

My explosif frame is a 1993, it has the grooved downtube and fade paint but I had it resprayed in 2001 white (yes I know!). I am pretty sure despite it having a shorter headtube than the lavadome had that it is non suspension corrected still.

I "upgraded" it to a pair of Pace RC35`s and changed it to aheadset years ago. I am now changing it back to p2`s of the correct length for the 93 which I beleive is still 39cm and have bought an impact off a 1995 Kona.

Do many bike shops still have the gear for cutting threads?