Bellhousing Blues

Guy Marshall · Dec 28, 2018

Hi all,

Reinstalling a rebuilt BN6 side change gearbox I discovered the PO had replaced the slave cylindar mounting bolts with 20mm M10 metric bolts which have now stripped out.

There seems to be plenty of space to re-tap with longer (1½"?) 3/8" unf bolts but has anyone had any experience/recommendations?

steveg · Dec 28, 2018

20mm seems short (roughly 3/4"). Maybe there are still good threads in the hole. You can make a chasing tap out of a 3/8-24 bolt. This one's 1-1/4" long:

Otherwise you might be able to loctite studs in the holes, or install helicoils.

Bob_Spidell · Dec 28, 2018

I put helicoils in mine (stock size). These seem to strip out pretty easily. I did run for years with some of the 'thread repair in a tube' stuff: https://www.amazon.com/Stripped-Thr...7?s=automotive&ie=UTF8&qid=1546009896&sr=1-17

Guy Marshall · Dec 29, 2018

Score 1 for the good guys!

A thread clean, then two longer 1[SUP]3/8[/SUP]" screws to replace the metric ones that had been forced in and a little loctite and the slave cylinder is working.

I'll get some helicoils too...

Thanks all!

Randy Forbes · Jan 1, 2019

Do it once. Do it right.

Every Healey I get the opportunity to, I put Heli-Coil/Re-Coil inserts into the slave mounting holes. I once had the slave cylinder fall completely off my car in Lafayette, Louisiana (a LOT easier to deal with than the time I had a clutch hose burst on an MGB in San Francisco).

Patrick67BJ8 · Jan 4, 2019

Randy Forbes said:
Do it once. Do it right.

Every Healey I get the opportunity to, I put Heli-Coil/Re-Coil inserts into the slave mounting holes. I once had the slave cylinder fall completely off my car in Lafayette, Louisiana (a LOT easier to deal with than the time I had a clutch hose burst on an MGB in San Francisco).

My bellhousing for my Toyota trans only has one bolt to attach the slave cylinder to it. There’s a stud for the other mounting point. Simplies removal and replacement.

steveg · Jan 4, 2019

Interesting there are multiple cases of stripping these holes in aluminum. Guess there are few aluminum bolt threads on a Healey. The only other ones I can think of offhand are on the steering idler.

Are folks using "cast iron" torque on these aluminum threads and stripping them out? Or are the slave cyl bolts at such an awkward angle as to promote cross-threading?

Enquiring minds...

Dandare · Jan 4, 2019

I think that a fine thread into aluminium was kind of frowned upon in engineering circles and even BMC/BL changed to UNC later.

Could it be worsened with the ageing of the ali.

Danny

steveg · Jan 4, 2019

Dandare said:
I think that a fine thread into aluminium was kind of frowned upon in engineering circles and even BMC/BL changed to UNC later.

Could it be worsened with the ageing of the ali.

Danny

Interesting. Sounds logical. I believe the Smitty bellhousing uses coarse threads for the slave attachment.

Addendum: So the optimum setup would be to tap the holes for a coarse helicoil.

Dandare · Jan 4, 2019

Nothing wrong with the insert being fine and you can still use your original bolts if they're good.

Danny

Keoke · Jan 4, 2019

steveg said:
Interesting there are multiple cases of stripping these holes in aluminum. Guess there are few aluminum bolt threads on a Healey. The only other ones I can think of offhand are on the steering idler.

Are folks using "cast iron" torque on these aluminum threads and stripping them out? Or are the slave cyl bolts at such an awkward angle as to promote cross-threading?

Enquiring minds...

Must be I never had any problem like these. //

Bob_Spidell · Jan 4, 2019

Maybe dissimilar metals corrosion contributes? IIRC, mine stripped really easily, and I'm not THAT ham-fisted. That, or trying to get the slave off and on in situ, with all the hassle that entails. I never use split lockwashers on aluminum, BTW; the washers dig into the soft metal and release tension on the bolts. I use Grade 8 flatwashers under the bolts, with blue threadlocker.

Guy Marshall · Jan 5, 2019

@steveg - mine had a pair of bastard 25mm M10 metric thread bolts forced in which is why they stripped. Happily the M10s were very short so I could clean up and extend the thread and replace with 1 3/4 3/8 UNF bolts which is now "better than new". For what thats worth!

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Bellhousing Blues

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