ShopTalk Forums | Aircooled VW Tech & Restoration Help

Good day,

A friend of mine ask me to post a question he has regarding the FK-97 cam. I didn't understand what he wanted to say but I believe it was that he has street eliminator heads with 44x37 valves and a fk-89 cam. He wants to change to fk-97 and wants to know if there will be "binding" of some sort.

Thanks,

He's most likely concerned about the possibility of "coil bind" due to the increased valve lift. The FK-97 has 6½% more lift than the FK-89 (.040" more with 1.4:1 rockers) which could be too much for his current valvespring setup.
If the motor's still together with the FK-89 he can simply measure the gaps between spring coils at max lift, adding them up to estimate how far he'll be from coil bind with the bigger cam. Typically if the outers are OK the inners will be also, but it's best to check both. At the least, he should remove the springs for one valve and make accurate measurements if there's any doubt.
http://www.hotrod.com/how-to/engine/150 ... e-is-safe/

Another point of concern is the height of the valve guides - they may need to be trimmed down to ensure that the retainer and/or keepers don't make contact at full lift.

I seem to recall "un-massaged" Street Eliminators being good for ~.550" lift. He's already past that with the FK-89 and 1.4 or 1.5 rockers (.582"/.624") but the FK-97 will make .622"/.665" so he's justified in approaching this cam change with caution.

Presumably he has sufficient valve-to-piston clearance too. Note that it's not just valve lift which affects that, duration and valve timing also make a difference (even switching to a different cam with the same lift can change that clearance).

Marc,

Thank you very much. I think that's the answer he was looking for.