Repairing stripped threads in 90+ year old aluminum engine castings

[Oregon Desert model 45]

I was installing the oil pan on my 1924 6 cyl engine and discovered some tapped holes in the aluminum crank case casting have been stripped out. These are adjacent to the main bearing end seals. I can put a nut over the bolt tail at the forward location, but the flywheel blocks access to do this at the rear location.  Locations are marked with red arrows in the photo below.

Should I just omit the bolt at the stripped out rear locations and put a nut over the next adjacent bolt to prevent it from pulling out ?

Should I try to install a helicoil threaded insert ? has anyone else installed an insert in an aluminum casting this old ?

 

 

Kevin
BCA # 47712

 

 

[ply33]

Don't know about doing it in a casting that old, but when I worked in a aerospace factory in the 1970s all threaded holes in aluminum castings had steel inserts installed in them. I suspect that a properly installed insert (helicoil or other brand/style) will be stronger than original.

[Larry Schramm]

Here is what GM now recommends for repairing stripped out threads in aluminum blocks like for head bolts.

 

http://www.timesert.com/

[Restorer32]

We've used Helicoils to repair many aluminum parts. A bit expensive since you have to buy the tool for each size.

[DonMicheletti]

You can get away with just leaving the bolts out of some locations (I think the front is OK for sure). However some holes are tapped through to the inside of the crankcase. Those will leak like heck if you leave them out.

To test you can poke a rod into the screw hole and see if it either bottoms out, goes through to the inner crankcase or comes out to the outside of the crankcase.

With so many bolts there is no danger of anything falling apart. Leaving the 2 bolts out at opposite ends of the pan is no big deal.

 

Obviously, Helicoiling the crank case is the right way to go, but you'd have to be carefull to get things straight and square.

[my31buick]

does aluminum and steel together cause some kind of corrosive reaction? if so, would it be an idea to use corrosion inhibitor on this project when putting in the helicoil?

[Bob Engle]

If this were my car, I would use the GM recommended repair.  Larger diameter threads in the aluminum gives better strength.  Drilling for helicoils is best done in a mill or drill press so there is no wobble when drilling. A loose hole will mean a loose helicoil.  Corrosion will be less of an issue with the full insert.

 

Bob Engle

[Larry Schramm]

With the amount of oil in the area, corrosion should not be a problem.  I think the helicoils are made of stainless steel.

[Barney Eaton]

I often use inserts when rebuilding headlight motors for Buick Reattas.   The only problem I have seen is cracking the part if the tap drill is too small.....there is very little aluminum around the holes I need to repair.   If the tap drill is too small, then the pressure of tapping for the insert can crack or break thru the small amount of material. 

This should not be an issue on an hefty part like your engine block.

 

On the dissimilar materials.......the original bolts were steel in aluminum.....right?

Edited September 8, 2016 by Barney Eaton (see edit history)

[JV Puleo]

As a general rule, threading aluminum castings is a poor idea although it is frequently done. High end cars and industrial equipment nearly always used some sort of insert, especially if the bolt is expected to be removed and replaced frequently. For instance, Rolls Royce used bronze inserts in their aluminum heads and through bolts to hold oil pans on. Aluminum is actually very abrasive, especially aluminum oxide (effectively aluminum rust) so it is fairly common to see steel bolts broken off in aluminum castings. I have several in my 1910 Mitchell and repairing them will be a chore. All will get bronze or steel inserts. That said... I think the best solution in your case is a steel insert. The problem is that the larger hole cannot be drilled freehand. It is simply impossible to do that straight enough, without any wobble. As your engine is assembled, I would suggest making some sort of bolt-on fixture to center and guide the drill... a "super drill bushing" of sorts. If you made an identical fixture with a larger hole you could use it to guide the tap so that everything would be in perfect alignment. Does the hole go through or, can it? This would be far easier to work with although you will have to pack underneath it with something like an oil soaked rag to catch the chips from the drilling and tapping. You don't want them floating around in the engine.

 

Go to the McMaster Carr on-line catalog and search for "threaded inserts"... there are several types available. I prefer the threaded steel inserts when there is metal enough around the hole but have used heli-coils where I had to deal with a tight fit. To hold on an oil pan – not a high stress application – either will work. I'd also use one of the never-seeze solid lubricants on all the bolts that are threaded into aluminum. If used properly, this eliminates many of the problems with steel bolts sticking in aluminum castings.

[Restorer32]

Helicoils are stainless steel.

[26-25Buick]

An to answer the corrosion question. It is true aluminium is anodic to steel or in other words will corrode to protect the steel and corrode even faster to protect stainless steel. There are however a few things working in your favour here that means it's less of an issue. For corrosion to occur you need a conductive electrolyte e.g. Water, which if the part is wet with oil that's not going to happen. The second thing that helps here is what is called anode to cathode ratio. If you can't avoid dissimilar metals being connected the best way to have this ratio is with a large anode and a small cathode as you have lots of metal trying to protect just small pieces, which is the case here also. So I think whichever you choose its not going to be an issue unless you go really left field and find an insert that corrodes to protect the aluminium.

[Guest Staley]

Timesert. I use them at my auto shop and they are absolutely fantastic. 

[JerryVan]

I would definitely use Heli-Coils here. Should be no problems at all.

[Brian_Heil]

Heli-coil and done.  It's an oil pan, not a spaceship, you will be fine.  Do your best not to drill through to the sump area if possible, but if you do, put sealant on the coil and the bolt.

 

Don't omit this location.  The reason these holes stripped is these are the most important fasteners on the pan since they are next to the cap and the 'long' distance over the cap that needs to maintain clamp load to maintain a seal to stop leaks and someone has been reefing on them before to stop a leak and stripped the threads for you.

 

Make sure your bolt is long enough but not so long it bottoms out in the hole and has 2 time the diameter of bolt for thread engagement depth/distance and mind your torque.

 

Your engine has an 'oil loss system' for the lube you put in the rocker shafts so your engine will be covered in oil soon enough.

 

 

[Oregon Desert model 45]

Thanks for the advice.

I disassembled the pan, oil system, and flywheel to gain access to install helicoils. Fortunately, the stripped out holes don't penetrate into the crank case. I can make a drill guide by drilling the helicoil tap drill diameter thru a small block of steel using the drill press to ensure perpendicularity. This block can then be centered and clamped over each stripped hole, and allow use of a portable drill motor to drill a perfectly straight hole thru the aluminum housing flange.  I also ordered a helicoil kit which should arrive sometime in the next week.

Kevin

 

[Brian_Heil]

And I need to make a correction. 

 

This is a 1924 so you have (first year 6 cylinder) pressurized oil to the rocker arms and return drains and not an oil loss system for these.  All the more reason to fix this and keep the engine exterior dry.

[superbuick]

I have used Heli-coil and Timeserts in my shop repairing engine parts for over 35 years. The Timesert is the best way to repair hands down. It is the same size as the Heli-coil but is a one piece insert unlike the 'coil'. Timesert is swedged in place during installation and has never moved or come loose during future servicing. The heli coil will work OK for this application. I consider the timesert as a permanent repair.

[Oregon Desert model 45]

Project update: 12 helicoils installed and all stripped or imperfect tapped holes in the aluminum casting are fixed!

Using a freshly sharpened tap drill and tap from the helicoil kit, both drill & tap operations went very smoothly.  I used the pictured drill guide and another similar guide made from a block of wood to start the tap straight into the holes.

thanks for all the advice.

Kevin

 

 

[MrEarl]

Kevin, is this the last picture you took of this project of do you perhaps have a picture of one of the actual helicoils being inserted or installed. or of the oil pan back on?

[Oregon Desert model 45]

I took one more photo of tapping for the helicoil using a wood block for a guide, then the next photos are of the motor getting installed into the chassis- sort of a fast forward. Installing the helicoil itself was pretty quick.

Kevin

 

[dibarlaw]

Kevin :

 Thanks for the progress photos. I will also be getting a rough engine with the 1925-45. The blocking of the engine will be helpful for me for when storing it.

[sligermachine]

On 9/7/2016 at 5:23 AM, Restorer32 said:

A bit expensive since you have to buy the tool for each size.

Not if u figure how much to replace a old part to your favorite car you're restoring .the big cutting tool company that I buy all my end mills from  lends them for free if u buy the insert from them  cost like $ 2.20 for a 1/2-13 tpi  helicoil insert just find out who all the big machine shops use in town .I bet they do the same better than buying helicoil taps of each size .I would buy the tap only thats all you  need make the rest with a bench grinder in under 1 minute -Kyle 

[sligermachine]

looks great nice work