Heli coil from the factory?

fiatfan · Feb 16, 2023

I´m going to run a belt drive and dry clutch in my -73 850 and I´m a bit worried that it might be some oil seeping through past the three small bolts that hold the inner TC to the crankcase. There is Helicoils in the three holes in the crankcase, are they fitted from the factory? I´m not sure how to stop the oil from coming past the threads, since there´s no gasket or anything on the bolts, would an O-ring help? But then there´s the locking tab..... Has anyone running a dry clutch had this specific problem?

Peter R · Feb 16, 2023

I have been running a dry clutch and belt drive for years and never had any problem with oil seeping past the threads.
There are no helicoils in the bolt holes of my bike, so I suppose that the Helicoils are a mod or repair done by a previous owner.

L.A.B. · Feb 16, 2023

fiatfan said:
There is Helicoils in the three holes in the crankcase, are they fitted from the factory?

There's evidence that helicoils were fitted there at least to some cases at the factory.
https://www.accessnorton.com/NortonCommando/primary-to-crankcase.19693/

Helicoils were certainly fitted at the 850 cylinder base stud, through bolt and oil pump locations.

MichaelD · Feb 16, 2023

How about some PTFE plumbers tape to seal the threads?

Nortoniggy · Feb 16, 2023

My 72 version has helicoils from the factory in those positions. I use a bit of silicon sealant on the threads as I have a belt drive. I don't use the tab washers and have never had a problem with them coming loose.

robs ss · Feb 16, 2023

If unsure I would try Loctite 577 - low strength thread sealant.
I use it on fuel taps.

concours · Feb 16, 2023

MichaelD said:
How about some PTFE plumbers tape to seal the threads?

fiatfan said:
I´m going to run a belt drive and dry clutch in my -73 850 and I´m a bit worried that it might be some oil seeping through past the three small bolts that hold the inner TC to the crankcase. There is Helicoils in the three holes in the crankcase, are they fitted from the factory? I´m not sure how to stop the oil from coming past the threads, since there´s no gasket or anything on the bolts, would an O-ring help? But then there´s the locking tab..... Has anyone running a dry clutch had this specific problem?

My '74 850 has the helicoils, which I believe were factory installed. I believe that because all three are perfectly executed. I've seen (done) hundreds of helicoil REPAIRS, and seen THOUSANDS of factory installed examples.

Jdub · Feb 16, 2023

Those helicoils might allow you to torque beyond the ~65 inch/lbs recommendation, but I would stick to it regardless. You want to pull each 1/4 coarse bolt, clean it and the case threads (Q-tip) thoroughly, then apply some non-drying gasket sealant (Wellseal; Threebond 1104) very sparingly to the underside of the tabbed washer and the underside of the bolt head as well. Finally, a touch of purple or blue Loctite to the thread (cleaned of any sealant when you pushed the bolt through the tabbed washer) and torque it up.

concours · Feb 16, 2023

Jdub said:
Those helicoils might allow you to torque beyond the ~65 inch/lbs recommendation, but I would stick to it regardless. You want to pull each 1/4 coarse bolt, clean it and the case threads (Q-tip) thoroughly, then apply some non-drying gasket sealant (Wellseal; Threebond 1104) very sparingly to the underside of the tabbed washer and the underside of the bolt head as well. Finally, a touch of purple or blue Loctite to the thread (cleaned of any sealant when you pushed the bolt through the tabbed washer) and torque it up.

Good advice.

concours · Feb 16, 2023

I would add, the gasket cooks down, (large surface area, resists initial compression from three 1/4" bolts) and then the joint becomes loose.

JMWO

texasSlick · Feb 16, 2023

Blue loctite or loctite #545 thread sealer should do the job.
Any of the anaerobic thread lockers can function as a thread sealer. Avoid the high strength types in this application.

One other caveat....... if you are going to run ATF in the primary, you might consider seaing the threads with Pematex 81880 gasket sealer. ATF degrades many types of sealers, and 81880 is specially formulated for ATF

Slick

ashman · Feb 16, 2023

Seal the threads and you won't have any problems at all.

mean gene · Feb 17, 2023

Little late but my 69 750 has Heli coils from factory! I use grey gasket maker to seal them.

fiatfan · Feb 23, 2023

Jdub said:
Those helicoils might allow you to torque beyond the ~65 inch/lbs recommendation, but I would stick to it regardless. You want to pull each 1/4 coarse bolt, clean it and the case threads (Q-tip) thoroughly, then apply some non-drying gasket sealant (Wellseal; Threebond 1104) very sparingly to the underside of the tabbed washer and the underside of the bolt head as well. Finally, a touch of purple or blue Loctite to the thread (cleaned of any sealant when you pushed the bolt through the tabbed washer) and torque it up.

That´s more or less exactly what I ended up with.

fiatfan · Feb 23, 2023

texasSlick said:
Blue loctite or loctite #545 thread sealer should do the job.
Any of the anaerobic thread lockers can function as a thread sealer. Avoid the high strength types in this application.

One other caveat....... if you are going to run ATF in the primary, you might consider seaing the threads with Pematex 81880 gasket sealer. ATF degrades many types of sealers, and 81880 is specially formulated for ATF

Slick

It´ll be a dry clutch, no oil.

Heli coil from the factory?

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