Os 46 vx-m / .46 size head clearance

Jeremy Bodley · Aug 10, 2024

Hi All. I have an os 46vxm. Wondering what others have run the head clearance as?

Engine has two shims, manual suggests remove one for sub 40% nitro and keep the two for above 40%.

Clearance with the two shims is about .025”. Removing both drops it to about .017”. Even with two removed seems on the higher side. Just wanted some feedback here. Running 10-25% nitro

Jeff Lutz · Aug 10, 2024

Jeremy Bodley said:
Hi All. I have an os 46vxm. Wondering what others have run the head clearance as?

Engine has two shims, manual suggests remove one for sub 40% nitro and keep the two for above 40%.

Clearance with the two shims is about .025”. Removing both drops it to about .017”. Even with two removed seems on the higher side. Just wanted some feedback here. Running 10-25% nitro

Yes that’s high. Especially considering how large the bowl is on the old OS .46. I’d machine it to .008” head clearance myself.

Jeremy Bodley · Aug 10, 2024

Jeff Lutz said:
Yes that’s high. Especially considering how large the bowl is on the old OS .46. I’d machine it to .008” head clearance myself.

Hi Jeff. Yeah even with two shims out it seems quite a lot @ .017” . I’ll give it a run without the shims today. Thought i’d check here encase some suggested otherwise and they needed that clearance??Just seemed alot.

My os 21xm outboards without the factory head shim have minimal clearance, and go great