Stripped engine mount bosses

[jolotter]

I'm preparing a 1.6td 1990 engine for my vanagon.  The front mount, under the IP is located differently from the jetta mount.  As a result, after 17 years the bosses have rusted so much that the threads just crumble at the sight of a bolt.  Is the correct procedure to simply drill and tap it to the next size?

[Kudagra]

Helicoils

[jolotter]

I've never installed a helicoil.  Is it something I can do at home?  
Is there any reason why tapping it one size bigger would be an unwise choice?  The bosses seem to have enough metal to support a bigger bolt and the holes in the mount have some play in them...

[55mpg06]

Helicoils are very nice and easy to use at home and are really valuble when needed.  I have never used ones all that large but one guy just posted that he used one for a striped head bolt with apparent sucess. They look somthing like a stiff thickish stainless steel spring with one end having a tab across the opening to give the install tool somthing to grab on to. You drill out the the hole and tap it to the size instructed and then tread in the helicoils. They work well but the initial kit (tools) are fairly espensive though. here is the company link and here is a how to article

With that in mind they are normaly used when the diameter of the hole of the piece that is getting bolted on cannot change. (hope that made alittle sense  :? ) Since for a heliocoil you would have to make the hole bigger and tap it anyway, I guess just using a bigger bolt depends on if you think there will be enough meat on the part you are bolting to compinsate for the metal lost in drilling it out.

[tylernt]

I see no problem with using bigger bolts. Since you have to drill and retap to use a helicoil anyway, I can't see how it would make any difference, strengthwise. I suppose the helicoil might add a little bit of strength, but not much (since it's not welded in).

[jolotter]

Thanks all for the advice.  I'm going to tap the bosses to the next size, even though I curse people who replace a bolt or screw in a set with another type.  $120 for a helicoil kit (is that right?) seems like a lot, especially when I have the drill and tap already.
Looking at the helicoil kit, it looks like it'd be pretty easy to make a tool to turn the helicoil in out of a piece of rod with a slot cut in one end and some flats filed on the other to grip it with the handle from my tapping tool.  The other parts, the tap and drill are already in my shop, and the special punch to snap off the tang for the insert tool sounds like a thin punch with the end ground to the correct shape.  Has anyone done this?

[jolotter]

Andrew, do you mean the tap is a custom size/pitch not available in the Metric or SAE range?  So I need to buy only the tap and insert.

[mk2diesel]

just drill and tap one size up .... helicoils are only used when you have to bring things back into "spec" or put steel bolts in to alum housings  or plastic parts .... save your money ......