Engine block repair question

[Ian]

I need to repair what used to be a threaded bolt hole in my S14 block.  Twenty years ago, a P-car mechanic looked in at the top of the transmission and told me the bolt was loose.  So, as a dutiful newby, I tightened it.  And it snapped.  Now, all these years later I pulled the engine to swap transmissions, and I decided it was time to fix this.  Unfortunately, about 10 years ago the broken bolt gained a broken easy-out, so it became a bit more difficult.  I managed to drill out the bolt and extractor, but now have an 11mm wide hole for an M8 bolt.

 Thoughts on filling the hole?  

 

I know its possible to weld cast iron and so could probably fill the hole, but the engine is assembled and I'd like to avoid putting that much heat into the block.  

 

Perhaps tap the hole and thread in a large bolt, which I could then cut flush?  Then I could drill and tap that bolt for the M8 bolt.

 

 

[Son of Marty]

I'd check the various thread inserts (heli coil ETC) to see if you can find one that might bridge that gap, other wise your bolt idea might work if you stake the filler bolt so it can't back out. 

[tzei]

I’d go with the bolt idea.

[irdave]

It's worked just fine without any clamping force at that point for how many years?

 

I'd be inclined to wait until it was going to the machine shop for one of John's 2.7 cranks and deal with it then...

Edited December 16, 2020 by irdave

[Ian]

5 minutes ago, irdave said:

It's worked just fine without any clamping force at that point for how many years?

 

I'd be inclined to wait until it was going to the machine shop for one of John's 2.7 cranks and deal with it then...

A fair point, and that's been my strategy up till now.  However, as much as I lust after John's 2.7 conversion, unless I win the lotto I don't see that in the cards in the near future.  However, I'm bolting up one of Camperman's adapter plates for a Mazda rx8 6-speed transmission, and want to make sure the adapter is solidly attached to the block. 

[MOESPEED2002]

Ian,

 

From what I can see, I'd be nervous about taping for a bolt or heli-coil. There just doesn't look like enough "meat" in the 7-8 o'clock area. I believe that would just crack from any amount of stress. Cutting threads there will make that thinner.

 

Since you are using an adapter plate, Is it possible to stud it instead and pin the stud? So you can use a nut.

 

At any event, you may not need anything there. Isn't there some 12 bolts holding the trans in place using a bottom adapter that cover the pan. The oem E30 flywheel cover clears the VAC pan, no?

 

Moe

[Ian]

2 hours ago, MOESPEED2002 said:

Ian,

 

From what I can see, I'd be nervous about taping for a bolt or heli-coil. There just doesn't look like enough "meat" in the 7-8 o'clock area. I believe that would just crack from any amount of stress. 

A fair point.  Although what I was thinking was tapping and then threading a large bolt, and holding it in place with red loctite.  So to my mind the first bolt would be structural.  Then I'd drill the loctited bolt and tap it for the M8 that holds the adapter plate to the block.

[Einspritz]

Search Timesert brand big-sert on amazon. Maybe #5812 will take up enough room. Otherwise I would weld it shut and re drill. Consider Muggy Weld for cast iron to do that in lieu of a proper weld. If all else fails - JB Weld........ Or peanut butter ?

That's all I got.

[jimk]

It also looks like it got drilled out of place.  Use a template to drill the larger bolt if that is you end result.  A timesert in that hole may not line up with the plate/transmission that you intend to use.

[MOESPEED2002]

Scenario. If you were able to tap that area to accept a bolt to loctite in. To then cut flush with a grinder to a point that the affixed bolt would potentially be heated to a point to risk the properties of red loctite. Then redrill the bolt to the proper size to then heat again, (though less). Would risk the potential of turning the said cut off bolt further tighter when installing the "correct" bolt, stressing the thin side of the block.

 

Im nervous for you Ian. I would look into the properties of cast iron and how they could easily crack or start to fracture in very thin areas such as this example. The simple vibrations of a part that are simply just loctite in place could cause more damage than the risk of doing nothing at all. Cast Iron, although tough is not malleable and brittle too, that is my concern. That thin area won't bend, it may crack or break, and the microscopic fractures after that you wont know till its too late. Remember the other side of that face is the cooling jacket or an oil jacket. How thick that is, is the million dollar question.

 

This may go beyond my engineering abilities an I maybe over thinking it from a picture. Unless you can truly secure a "fill" bolt. Find an old school welder that can pre and post heat cast iron correctly and control the nature of the welding process in such a part. That would be unfortunately your best repair or let it be.

 

Hope my point makes sense.

 

Moe

Edited December 17, 2020 by MOESPEED2002

[Einspritz]

Consider that a bolt will probably be a different hardness (Grade 8.8, 10, 12) than the cast iron and more difficult to drill accurately. And add in the fact that now the hole is oval and / or off center so in order to drill anything you might have to make a jig to hold your drill bit (and tap) in the exact spot and orientation. or maybe your adapter plate can become the basis for that.

 

This is a challenge in that trying to drill a bolt off center just gets weird as you may drill into the threads.

 

I hate to admit, but there are YouTube videos that address drilling bolts through the center of the threads (and removing broken taps and bolts, but you are past that point). Perhaps seek those out for an alternative.

 

 

[tech71]

S14 block?

20 years it's been like that in a running car? with no discernible problems?

Definitely  leave it alone!  

No telling what's going to happen if you start drilling, welding, inserting.

Doubtful any stop gap repair there would hold much torque and what are you going to do when your S14 block cracks from the attempt? 

Thats a repair best deferred until the block is stripped down for overhaul

 

If it aint broke, dont fix it!

Edited December 17, 2020 by tech71

[man_mark_7]

What about completely grinding away that portion of the block, then making a template to weld in a suitably tapped piece of replacement material? The replacement material could be nearly any shape that gives it good purchase. You might even be able to get away with welding in a nut of the right size/material. Good luck!

[Einspritz]

This might work. 12mm OD.

https://www.clipsandfasteners.com/Metric-Thread-Repair-Inserts-M8-1-25-p/a12390.htm

[JerryC]

Hmm.... that hole looks too big and close to the edge. What about adding a pin as suggested earlier, or two, and a pair of M6 bolts threaded into the good part of the web? Spread the load away from the weakened area. Just thinkin'...