Apparently I Fugged up... Fixed it..? Thanks for ideas.

[shady]

So a while back I swapped an LS into my burb.
(BASS BURB)

I had the engine on my stand, and had bought bolts just for that purpose.
I took the engine out to upgrade some things and got out my labeled bag of LS to stand bolts.....
And the don't fit. Won't thread in

The bolts that came out of the 6.5 dizzle that had been in the truck, were normal 3/8 and were in a bag labeled 'transmission'.
I grabbed those, not thinking, and they started threading in. Ran them down with the impact and torqued them.

Now. They held fine, none were loose. All was good.

But the threads now want the 3/8 back, which is a smaller diameter.
Not a huge deal since they worked before in the truck.
Stick em back in and run it right...?

But, if I put 3/8 in on the stand.....
Compromised threads, and slammer diameter than the hole wants.
I'm afraid they're going to rip out and drop the engine.

Can't re thread to stock, because that'll just make em even weaker.

All I can think, is build stands to hold at the motor mounts so that the bolts don't hold all the weight of the engine on the stand.
Them run the 3/8 again.

Or, make a steel plate for the back of the engine to mount the mag drill to.
Use a drill stop to set depth, re-drill, and tap to 7/16"

Either way....

 

[Babaganoosh]

I’m confused, why can’t you just get longer 3/8 bolts and use them on the stand sense that’s what you had in it before? Or did they cross thread in and your afraid they won’t go back in?

Cross thread is free lock tite!

 

[shady]

The 3/8 is smaller diameter than the Metric bolts it originally was drilled and tapped for.

With an engine in the vehicle, the mounts hold most all the weight, trans mount holds the rest, very little stress is PULLING on the threads.
They're just clamping the trans and block together.

On the stand, all the weight of the engine is trying to pull the top bolts threads out due to the leverage.
Normally the right bolt and threads would hold this just fine. The 3/8 is not only smaller diameter, but the wrong thread so now the threads are damaged.

I'm afraid the top ones will pull out, break the lower tabs off, and possibly my feet or legs in the process.

 

[shady]

Silver one is the correct one

 

[shady]

I just looked some more and I found little slivers of thread from the holes, and 2 of the 3/8 still have thread slivers from the block in them.

At this point it actually looks like I don't have any choice but to re drill and tap.

I have a plate big enough to make a place for the mag drill. Then drill em one at a time, and I know they'll be accurately placed and straight.

Tapping I'll just have to be careful getting them started.
The holes in the trans are more than big enough for the slightly larger bolts.

I'll take pics and post the process here I guess.
Even though I'm sure nobody else will be stupid enough to do this and have to try it lol.

 

[Babaganoosh]

Ohhh I see, I would redrill and tap to make sure.

 

[Truckman4life]

Just hand drill and helicoil back to the oem metric size. Just make sure to mark your bit with tape for depth and just be cautious going in straight. It will follow the hole that's already there for the most part unless you really fubar it. If there's lots of meat and you don't like helicoils you can do a thread-sert or whatever name they call the threaded inserts.

 

[shady]

Looks like 7/16 is the way to go.
Drill size for it is .37"
Next up would be 11mm which has a drill size equivalent of .374"
So either one should be ok, but I'd rather keep the hole smaller to keep the most wall I can.

 

[nvrenuf]

I got nuthin except - Ouch!

 

[shady]

Just hand drill and helicoil back to the oem metric size. Just make sure to mark your bit with tape for depth and just be cautious going in straight. It will follow the hole that's already there for the most part unless you really fubar it. If there's lots of meat and you don't like helicoils you can do a thread-sert or whatever name they call the threaded inserts.

I'd rather upsize than helicoil.

If I do the 7/16 it looks like all I'd be removing is the cut threads. So yeah it should guide its self fairly well and be doable by hand.

 

[kennyw]

The best fix is to use a Keensert if there is enough material. That will keep the original thread pitch but you tap it a size larger based on the insert and the insert brings it back down to the correct size to avoid problems with the transmission side holes.

 

[shady]

Not worried about keeping the stock size threads.
Holes in the trans side are 1/2" or bigger.
Plenty of room for a size up bolt.

 

[Blue85]

A 10-1.5mm bolt is basically a 3.15/8"x16.9, pretty close to 3/8-16, which makes this a rather common mistake. It takes a few turns before the threads get tight. You could keep the same thread pitch and tap it to 12-1.5mm, which is still smaller than 1/2", assuming you could follow the old thread. I guess once you drill to 10.5mm, the old thread pitch doesn't matter anymore and what you'd need is an 11mm bolt .

By the time you go up much in size you're risking needing to upsise the bellhousing holes because of tolerance and what-not.

Pics for amount of material reference?

 

[shady]

I'll get some tomorrow. On my way to work in a bit.

 

[mrk5]

I would run a tap in them for the correct metric size then put a bolt in them and see if the threads will hold to torque to spec.

 

[shady]

......
I hadn't thought of that...

 

[Blue85]

I would run a tap in them for the correct metric size then put a bolt in them and see if the threads will hold to torque to spec.

This is certainly worth trying. You would think some of the metric major diameter would be outside of where the 3/8 would hit. Did you run all of the bolts all of the way in?

 

[kennyw]

... you'd need is an 11mm bolt

7/16=.4375" which is close enough to .4331" = 11mm.

Not worried about keeping the stock size threads.
Holes in the trans side are 1/2" or bigger.
Plenty of room for a size up bolt.

The holes in the transmission were sized for 3/8" bolts and the tolerances that they could hold with machining both sides of the interface back in the day (1950s). 7/16" bolts may still fit, but no guarantee you will not need to enlarge a hole or two on the transmission in the process. What you don't want to do is enlarge the clearance hole on the transmission. So a 3/8-16 or M10 x 1.5 Keensert will be the best solution with the least amount of risk.

 

[shady]

The holes in the transmission are pretty big. More than big enough for 7/16.
As long as I don't touch the alignment pins or holes for them, it would be ok even if I did have to clearance them. But I don't think I'll have to.
I haven't measured them but the transmission side holes could easily be 1/2-9/16.
Look that big anyway.

Threading to the next size up saves the most amount of original wall material I can. I'd rather save wall thickness than worry about staying the same size bolt.
Any insert will require drilling and tapping bigger than 7/16.

I got a pic of the block quick on my way to work. Forgot to measure and take the ones of the trans side.

These are the thinnest.

 

[obijuank5]

A keensert it timesert is an easy fix. No need to compromise and never trust something in the back of your mind.