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[razzo]

Restoring the Volvo 2.5 5 pot engine in a Focus but have found threads for the offside engine mount to be damaged. To far gone to restore with an m12 x 1.75 tap so will need to be helicoiled, block is Ali so any tips for getting this right first time as it is still in the car & is it worth changing fixing from bolt to stud, head size is 15mm, length is about 50mm & should be torqued to 115nm

Ta

[Nick W]

You only get one chance of drilling out the hole so that it is where it needs to be, perpendicular to the surface, doesn't break into the rest of the block and the correct size. The existing hole will make that trickier than drilling a new one.


Then you have to do the same thing with the tap.


I would be making a simple jig to align the drill bit and to stop it wandering.

[razzo]

Thanks Nick, was thinking about a jig but wondered if it’s worth changing thread size to m12x1.25 as that needs a 10.8 mm drill but m12 x1.75 needs a 10.2 mm & changing fixing to stud so may get away with just rethreading rather than drilling?

[Nick W]

Thanks Nick, was thinking about a jig but wondered if it’s worth changing thread size to m12x1.25 as that needs a 10.8 mm drill but m12 x1.75 needs a 10.2 mm & changing fixing to stud so may get away with just rethreading rather than drilling?

A tapped thread needs to be in a correctly sized and round hole. If you're being really critical, you would drill and ream before tapping. Trying to retap coarse to fine starts with neither of those things, so is going to end in tears. And is one of the reasons why Helicoils(and other similar repairs) are readily available.

[biggriffin]

1st question? Will they be keeping the car forever? If no,, then use the coarse bolt with a slot cut in, and some epoxy glue,, whack it in job done.  If it's a long term keeper then do as Nickw has advised.

[Nick W]

1st question? Will they be keeping the car forever? If no,, then use the coarse bolt with a slot cut in, and some epoxy glue,, whack it in job done.  If it's a long term keeper then do as Nickw has advised.

I would buy one of the Loctite products that is designed for that sort of 'repair' rather than epoxy.


Using a fixed stud instead of a bolt is worth considering, but will you then be able to assemble the mount?

[razzo]

Have managed to get hold of an old engine mount & thinking of cutting it down to use as a jig, with the idea of bolting into one hole & drilling then tapping & helicoiling the other hole, when done swap fixing over to sort original. Helicoil drill belt is a very snug fit in old mount so any other pit falls I need to be aware of?