Helicoil problem - Ferrari Life
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post #1 of 3 Old 01-29-2008, 11:32 AM Thread Starter
Saint Bastage's Avatar
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Location: Essex Connecticut
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Helicoil problem

My Major is nearly complete and I was just made aware of a problem that scares the crap out of me. I'd like your opinions please.

It seems that some previous owner or mechanic crossthreaded or otherwise screwed up the threads for the transmission dip stick. They repaired that problem by installing a Helicoil. My mechanic had some difficulty removing the dip stick because the helicoil had broken and was spinning in the hole. As I understand the story now, the helicoil apparently cracked a thread at approximately the same depth as the dip stick plug "max reach" meaning that some portion of the coil remains in the hole and (hopefully) the remaining piece was removed, intact. The dip stick plug cannot reach those threads and was therefore replaced with a longer bolt to seal the box.

Here's the fear...how can I verify that no smaller portion of the threaded helicoil has fallen in to the gearbox. I know I have to replace the 3rd gear synchro soon, but if there is a chance that a piece of coil is in that box, the car should not move, period. Just that little piece can change the job from a $5000 gearbox rebuild to a $25,000 gearbox replacement.

Are helicoils made of ferrous materials? Will the magnetic drain plug hold any possible piece away from the gears (assuming if gets captured)? Is oil flow dramatic in those boxes?

Next question...once the gearbox is disassembled (for the synchro job), what is the "proper" way to fix these threads? It seems to me that installing a small metallic insert is just stupid.


Previous owner of 348ts SS #64, Now Ferrariless
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post #2 of 3 Old 01-29-2008, 03:54 PM
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Hi Lane,
I had some helicoils in my toolbox and I checked and they are ferrous, a magnet does capture them. So that answers that question.

I'm not familiar with the 348, but I've never seen a manual gearbox with a dipstick; they usually have a fill/level plug, I'm guessing that is what you mean. I can't imagine the oil flow would be too dramatic in the box but at high RPMs I am guessing it would slosh around pretty good, maybe enough to overcome the magnet. I think my 308 tranny has a pan that can be removed, maybe your tranny also has a pan that can be taken off to clean out any junk in the case?

As for the "proper" fix, there is nothing wrong with using a helicoil, I've used them for years on cars and motorcycles fixing everything from oil drain plugs to spark plug threads. When you put in a helicoil because the original aluminum threads stripped out, the new helicoil setup is actually stronger than the original threads because with the larger hole needed to put in the helicoil the load is spread out over a larger area. Personally, I'd rather put in a helicoil than drill and tap for a larger bolt or plug.

Capt. Pete
'79 308 GTS, '82 Jeep CJ7 Jamboree
"Time is what prevents everything from happening all at once."
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post #3 of 3 Old 01-29-2008, 06:37 PM Thread Starter
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Sketch 1...part number 16...resembles a standard 1/4 pipe plug with a angled sheet metal dip stick on the end.

gear box pan does not access the under side of the hole. (sketch 2) It means I cannot drill and tap the hole without removing the case and all internals. It also means I should have reasonable access for cleaning out.

Helicoils still scare me. small metallic parts should never be placed near a lubrication system opening.
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