Helicoils found in base to bolt down block - what do?

[namtip]

Hello all, new member here.

Last week I 'acquired' a CB650Z café racer project which was in need of some TLC. I have dived straight in and have removed and stripped the engine down. Worryingly I've found what appear to be helicoils in the engine base used for screwing in the 12 bolts that secure the cylinder head and block . I'd say on early inspection about 4 or 5 of them are helicoiled. My question is this - can I have these holes bored out to a larger diameter and re-tapped? Obviously I'd have to find correct size bolts, and may have to enlarge the holes in the block and head. I'm just not sure how much metal I have to play with down there

Maybe someone out there has already done this? Any advice would be appreciated. I'll be starting a strip-down/rebuild thread soon...

Many thanks,

Colin.

[jcasey007]

yes I have heli-coils in over half of my cylinder head long bolts, done properly they are fine. at least half of the treaded holes are blind so when I did mine I drilled out through the bottom so I have more meat to helical into.

I would not recommend trying to go to the next size up.

check the heli-coils and if look good don't mess with them

[namtip]

That's reassuring to hear! They seem solid enough. On with the rebuild then...!

Thanks again.

[cb650]

Helicoils are actually stronger than regular threads.