I need to re-tap a few holes on my LG4, does anyone have the bolt sizes for the following 2 items. I need to know what size/type of tap I need

1. Timing Cover bolt holes(one bolt broke off in the block)
2. Crankshaft to crank pulley bolt(threads are stripped on the inside of the crank)

Also, any tips on tapping since I'm new to it? I know to use cutting oil and back off the tap occasionally, but anything else I should know?

Thanks.

-Matt

 

1. ¼"-20 (std thread)
2. 7/16"-20 (fine thread)

But before you go thinking that's all you need to know:

1. Before you can tap the hole, you have to get the old bolt out.... try grinding or filing it flat, center punch it VERY CAREFULLY in the EXACT CENTER like maybe use a magnifying glass so you can see it as well as possible so that you don't punch it off center, then drill it with a small bit like a 1/16" and then successively larger ones. The thing to watch out for, is that the bolt is far harder than the block. Imagine trying to drill a piece of wood out of a stick of butter: that's pretty much the situation you're in. One slip of the drill bit off the bolt and into the cast iron, and it's done for; you'll never get it to re-center again. You only get one chance, so do your best to be certain that it's all centered. And in case I maybe forgot to mention this: it's critical that the hole you drill in the bolt be ABSOLUTELY CENTERED.

2. Tapping won't work. A tap is a cutting tool; it takes a hole that's the size of the narrow part of the bolt threads, which is too small for the bolt to slide into, and cuts threads into it. Once the threads are stripped, there's nothing there to tap, no metal to cut threads out of. You need a Heli-Coil kit in that size.

 

Thanks for the reply.

I'll start looking for the heli-coil kits. Are they available in local parts / hardware stores or is this something I'm better off looking for on the internet somewhere?

-Matt

 

Very easy to find in parts stores.

What it does, is to literally install a whole brand-new thread. You drill the hole out to some slightly larger size (the kit tells you what bit to use, sometimes it comes in the kit); then you tap the hole with the tap supplied in the kit; then you screw the thread insert into the hole. You end up with the same size hole as before, that takes the original hardware just like it did; except now you have hardened stainlees steel threads, instead of cast-iron or aluminum or whatever the original material was. They're often used as an "upgrade" to threaded holes in castings (especially aluminum heads), in addition to merely a "repair" for damaged holes.

 

Thanks again. I'll be off to the parts store after work...