Well, crap -> Damaged/stripped threads on gearbox fluid port - 3.2 Mondial

Retap with tap with grease on it to catch metal filings

Are you sure there isn't a helicoil in there .. hard to tell from.photos

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A tap will work,but a better option might be a metric re-threding tool. These tools are designed to deal with the problem you have. Also, follow the advice in Reply 1 to use grease to catch any chips.

 

Happens all the time, there should already be a thread insert in there. 14x1.5 helicoil kit is what you need.

 

Only my opinion, if you could remove the first 4-5 treads with a reamer or a drill and grease to catch up all the shaving and them you have the remaining (good) treads to deal with, to know if you have a helicoil use a magnet, hope you succeed in with the repairs.

 

Hello,

Since the initial threads on the bolt hole appear to be knackered a bit, a tap with a tapered end on it might be your best bet. The taper allows the tap to make its entry with a better chance of being straight.

Chasers typically feature a straight end that makes an off-centred entry likely - unless the initial threads are in relatively decent shape. Since your initial threads are compromised, the chaser would have difficulty entering properly as you found out.

Likewise, bottom taps may not be the best because the square shoulders will increase the difficulty of entering the damaged threads on the bolt hole properly. Therefore, a tap with a tapered end (left in photo) may be your best bet. Best wishes for a successful outcome…

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Having dealt with this, you might just try threading the new long plug as the thread chaser. I was concerned that the tap with its taper would potentially damage deeper in threads if I crossed. The new plug if crossed would strip the first few threads, which is not too bad as they may need to be reamed out anyways, and the plug may do the reaming. And of course, you might just find the new plug catches. It is nerve racking, as there is some resistance before you know for sure if you are crossed or not.

The good news is the hole is very deep and has lots of threads.

 

Not sure if anyone has ever replaced the plug with this,

https://www.pegasusautoracing.com/productdetails.asp?RecID=9592

With the matching female piece, this would eliminate the need to bolt and rebolt the plug. Would simplfy the gear oil level check process considerably.

If you really badly strip the hole, which I really don't think you will, I would Permatex epoxy the quick drain item noted in the hole, and that would probably solve things worst case.

 

If you've got a plug with longer threads, I wouldn't be shy about carefully "Dremeling" away the damaged area (like making a counterbore down to the good threads) as long as you keep the debris from going in the hole -- just a thought...

 

Are you sure you used the right plug ? It looks like the beginning few threads are different then the lower fine ones.

 

One more suggestion: Since you already have a thread chaser, you could grind a taper on the end to make it easier to start.

 

I've repaired many threads in aluminum. About the only viable option is using a Time-sert or TIG welding the aluminum and re-machining the threads. Here's the M22 insert kit:

https://www.amazon.com/TIME-SERT-Metric-Kit-Part-2215C/dp/B003VW6B9I

If you check the Time-sert website, they have a 15mm and 20mm depth insert you can buy also (e.g. part # 22155):

http://www.timesert.com/html/mtrcsert.html

Assuming you have access, you can usually drill and re-thread for the insert by hand using a tap handle or wrench. Use grease on the cutting tools to help catch the chips. Clean the new threads with Berryman B12 and then use 7649 primer on the aluminum and install the insert using 271 red loctite. You can also install the insert using JB Weld, which is the method I use a lot of the time. If you've never done this sort of repair before, I'd suggest doing a few test runs on something like an M12 or M10 insert into a few holes in some scrap aluminum plate, just to get the hang of things. I would not learn as you go using your Ferrari gearbox.

JB welding in that part from Pegasus Racing would probably also do the trick.

Any other approach to repairing this is just wishful thinking.

Ray

 

Only problem is this required the engine out to do. There is not enough clearance to the hole to do this in situ, a frame rail, etc. being in the way.

The casing hole is threaded probably about three times deeper than the factory plug thread depth. So especially if only a few starter threads are sheared, a much longer threaded plug which is available is a viable solution, assuming you can get it to catch beyond the damaged thread.

Keep in mind this plug is at the top level of the gear oil, and there would be no pressure in the casing in operation, and you could probably put a wine bottle cork from a good Italian Chianti and it would keep the gear oil splash from leaking. So a bit of bodging here is appropriate given the engine out and gold standard time sert alternative, which would indeed be the better than stock repair.

 

Cork it is

Ray

 

I would also need a longer fill plug of the same thread size. Does anyone have a source?

 

Dorman part # 090-055

Has an 18mm thread reach compared with the stock plug at 10mm. It has a 19mm bolt style head, rather than the recessed allen key type of the stock plug,




Bel Metric has a 14mm reach plug that has the same recessed allen head as stock. https://www.belmetric.com/m22-22mm-plugs-c-11_90_986/dp22x15ahclz-metric-drain-plug-zinc-p-9700.html

 

You can try Amazon, eBay or McMaster.com

Ray