Ovalled engine mount holes in block

[Sheds Moderator]

Because a threaded insert needs more meat to screw into. A helicoil is only marginally bigger than the original hole so if the casting is a bit thin it will still (usually) work. Helicoils are good enough, they are very quick and easy to fit. I've heard they are stronger than the original thread, how true this is I don't know. Inserts are excellent, but they are more laborious and as stated above need more meat.

[anthonym]

I recall reading (on the manufacturer's site) that Helicoils et al facilitate the interface between the hard metal of the bolt thread (say steel) and soft materials such as magnesium and aluminium, providing a sound marriage where the steel cannot damage the aluminium, for example where there is repeated insertion and removal or simply greater confidence in the ability of the hard steel thread to grip without ripping out or damaging the soft metal. In this way we can have strong steel bolts holding engine mounts to soft ally block with an appropriate interface in the form of a Helicoil or presumably an even stronger thread insert.

 

Would you say it is true to say that all helicoil types are thread inserts but not all thread inserts are helicoil types?

 

Seems to me Roger can go for a helicoil solution and have later space for a thread insert if needed? His oval holes seem now to be an opportunity to upgrade his engine mounting fasteners. Having said that, if in say another accident, one had to choose which piece will break (be sacrificed), would having the interface between bolt and ally block made of the toughest stuff, be the optimum solution? Oddly that leads back to an M12 (say) and no helicoil.

 

[Roger Ford]

And also because an M10 Wurth Time Sert kit is over £100 whereas a Helicoil-style kit is a tenner.

 

Edit: DON'T buy from that second link! It's M10x1.0, an ultra-fine thread I didn't even know existed. £20 seems a more normal price for M10x1.5.

 

Yes, it's wet sump with Apollo.

 

Edited by - Roger Ford on 11 Nov 2011 08:36:47

[anthonym]

grief! That's a huge difference.

I found that the Apollo swaged fittings together with the alternator after removing the first two primaries made tightening (and therefore "spanner checking") the mount bolt (i.e. one of them) impossible to get any real purchase upon. The modern mount is also in itelf (having "wings") more difficult to access and if not cap heads then I dread to think.

 

Remove all these bits or engine out then not such an issue.

[Sheds Moderator]

Quoting anthonym: 

Would you say it is true to say that all helicoil types are thread inserts but not all thread inserts are helicoil types?

Yes

Seems to me Roger can go for a helicoil solution and have later space for a thread insert if needed? His oval holes seem now to be an opportunity to upgrade his engine mounting fasteners. Having said that, if in say another accident, one had to choose which piece will break (be sacrificed), would having the interface between bolt and ally block made of the toughest stuff, be the optimum solution? Oddly that leads back to an M12 (say) and no helicoil.

Yes he can. As for engineering some kind of sacrificial fastening, this is WAY beyond the scope of this discussion. In any case, why would you especially want to? Accidents are by definition impossible to predict and I would say that the engine mountings are the least of your worries if you are going to bin it. At the end of the day the brief is to provide a fastening that is strong enough. The original M8 (say) into ally is OK. So is a helicoil insert, so is another machined insert. Stronger isn't automatically better, strong enough is good enough. There are better things to worry about, any car is a set of compromises, the lash up that is a Caterham 7 especially so. Sacrificial engine mounts do not advance the breed.