Engine mount arm question 84 300 SD

[dannyF]

I managed to get the engine mount arm removed - will give details later, was a bit challenging for me, but do-able.

Anyway, my question is that when I drilled out the screw that supports the engine mount into the arm, I had inadvertently drilled into the screw hole such that a portion of the hole was drilled into. That is, there are threads for about 1/2 of each turn. I already knew this and it was the reason I removed the engine mount arm. However, surprisingly, now that I removed the old screw remnants, my new allen head screw seems to fit fine! So, can I go with this, or, must I now assume that the old system is compromised and that I need to drill all the way through and get a longer bolt supported by nuts at the end? My temptation is not to drill into the engine mount arm and to use the old system, but I will drill it out if safety is compromised.

[bbboomer]

If you have removed part of the threads on one side of the hole you must not try to use as is. The bolt will screw in but will not hold for long.

[dannym]

You have some options:

-Make a bigger hole and use a Helical Coil, http://www.acehardware.com/search/index.jsp?kwCatId=&kw=thread%20repair&origkw=thread%20repair&sr=1

-Coat the bolt with Epoxy and screw it in. You will always have to remove the arm.

I wouldn't bolt through the arm.

[dannyF]

Thank you both. I will research the helical coil. Is another option to get a longer bolt, drill through and use nuts on the far side?

[fdanielson]

I replied on your other thread where you said a quarter of the thread was damaged. If it's closer to half the thread even I wouldn't chance it.

Helicoils rock. The kit and drill bit will set you back around $30.00 and if even if you use it only once that's cheaper than going to a machine shop or spending a couple of hours of your own time modifying the arm for some sort of through bolt setup. If you're a cheapskate like me you could sell the kit on eBay afterwards and recoup half your money. Or you could list it in the tool rental section of this site for the next person that mangles the threads while changing an engine mount.

[charmalu]

DANNYF, since you live in Monterey, why don`t you go to the Moss Landing PNP and remove an arm off that 81 SD that is back in the first
row in the back left corner where the Euro cars are?
It was there on Saturday.

Charlie

[Diesel911]

Originally Posted by charmalu

DANNYF, since you live in Monterey, why don`t you go to the Moss Landing PNP and remove an arm off that 81 SD that is back in the first
row in the back left corner where the Euro cars are?
It was there on Saturday.

Charlie

This is the best advice. Helicoils are good but you have to have a way to drill the larger hole for the Helicoil exactly where you want it. If there is already a crooked/off center hole the larger drill will try to follow that hole.
Also the drill all the way through the arm would work. But again it is better to have a straight hole than an angled one.

[dannyF]

Thanks, Charlie, for that idea. I will consider it, although I am about to go out of town for a week and if removing that arm is anything like removing the one I just took out..... (plus I don't feel that comfortable getting under those cars at the P&P...).

However, one other thought...

On an 84 SD this MM arm bolt hole does go all the way through - at the top is a 17 mm hex head bolt (also an M10 1.5) that holds down the battery cable. The threads are workable all the way through (even though they are half gone...). If I found a long enough M10, I could thread it all the way through, put the battery cable bracket onto it, and tighten on the top with a lock nut or 2. Would nuts on the end provide the insurance I need for the security of this bolt? Only issue is that the long M10 allen head bolts have a large piece that is not threaded and the threaded part isn't quite long enough to screw through the entire arm segment, so I may need to use another type of M10 1.5 bolt.