Stripped threads/Inner primary cover to CC

[dirtymartini]

I was starting to put my inner primary cover back on and found one of the three bolts holding the inner primary cover to the crankcase would not tighten up. My question is this; if I try to put in a thread insert it would mean drilling the hole a little bigger for the insert. These are through holes into the crankcase and I'm worried I would push some metal chips into the crankcase....any thoughts or suggestions?

 

[pete.v]

I would pressurize the case in some manner if only a few pounds, maybe through an adjacent thread or the oil drain plug or the like. Use grease on the bit to collect and the pressure to maintain an exhaust through the flutes of the drill and the tap.

Helicoil is ok in a pinch but thread inserts really do the job. These are readily available at the hardware store. Seat them with JB weld and never look back. Make sure they are nice and flush.

I did a crankcase swap out and did many threads including these and the oil drain. Many people do all the thread in the cases.

Good luck.

 

[dirtymartini]

Thanks, I like the idea of some low pressure into the crankcase. I'm going to go look for inserts now.

 

[swooshdave]

I did a Helicoil.

 

[pete.v]

I see you have this issue with either the 69 or the 75. If this is the case, you have that nice big sump plug and strainer to collect what may linger after precautions applied. This is a bonus as the 72 units do not have this luxury.

 

[dirtymartini]

I see you have this issue with either the 69 or the 75. If this is the case, you have that nice big sump plug and strainer to collect what may linger after precautions applied. This is a bonus as the 72 units do not have this luxury.

Yes, this is the '69. I + on the day!

 

[DogT]

One of mine was stripped out by the PO. He just put a 3/8-16 in it. I replaced all the bolts with studs, red locktite nuts and blue locktite on the nuts. The auto store has 1" 3/8-16 x 3/8-24 studs and 5/16-18x 5/16-24 studs and nuts. I didn't even use washers. You'll have to grind down the bottom one to clear the chain. A hobot mod.

Lots of grease and slow on the tap, pressure and clean it out early. You should be good. Might as well put some silicone on the inner cover to cc gasket, I had to re-do mine to keep it from leaking. And make sure the washer on the inner case center stud does not allow the inner case to bend when installing.

Dave
69S

 

[dirtymartini]

One of mine was stripped out by the PO. He just put a 3/8-16 in it. I replaced all the bolts with studs, red locktite nuts and blue locktite on the nuts. The auto store has 1" 3/8-16 x 3/8-24 studs and 5/16-18x 5/16-24 studs and nuts. I didn't even use washers. You'll have to grind down the bottom one to clear the chain. A hobot mod.

Lots of grease and slow on the tap, pressure and clean it out early. You should be good. Might as well put some silicone on the inner cover to cc gasket, I had to re-do mine to keep it from leaking. And make sure the washer on the inner case center stud does not allow the inner case to bend when installing.

Dave
69S

Well I couldn't find any kind of inserts in my area and I didn't feel like going into town so I ordered some inserts from my local NAPA store, they will have them tomorrow AM.
I like the idea of studs and nuts...I'll see if they have those.

Of course I was in the middle of putting the inner primary on when I found out the one hole was stripped by the PO I am assuming. I remember that bolt wasn't tight when I removed it. I already had silicone sealant on the CC side of the gasket but was able to pull the primary off and the gasket stayed on the CC. I wiped off the silicone on the primary side...It should be okay. The funny thing is when I ordered the gasket I got two so I would have a spare and wouldn't you know one of them was broken when I got it!

 

[swooshdave]

I believe the original bolts are 1/4-20

 

[DogT]

Yes, the originals were 1/4-20, so if you just go up in size it would be a 5/16-18 in the cc and a 5/16-24 nut for oversize and the standard one would be 1/4-20x1/4-28. I didn't use any helicoils or timeserts, but 2 of my holes are still 1/4". If you do it, you may want to look into jam nuts for the outside, then you may not have to grind anything down except the stud at the bottom. Make sure the cc holes are clean with acetone and a .22 bronze brush for the red locktite, I even put a bit of silicone under the nuts to help with leakage. Last time I had it apart it was good.

Dave
69S

 

[dirtymartini]

I don't know what happened to mine during it's lifetime but all mine are 5/16-24

 

[DogT]

You don't want a 5/16-24 or even a 1/4-26 thread in the aluminum. The coarse threads are better from what I have read in AL, the UNF are fine as nuts. If I were you, I'd do a helicoil or timesert to get back to the coarse thread in the cc, or maybe someone has a better idea? I'd ask J Comstock to see what he has to say, if he'll help, I understand he's kinda busy with family things now. Or you might call Leo Geoff at Memphis Motor Werks, or windy here on the forum.

It's real easy to strip those threads, they're pretty thin to start with and I'm real careful tightening them. I don't think they are that structural, but they do keep things from leaking.

Dave
69S

 

[pete.v]

I don't know what happened to mine during it's lifetime but all mine are 5/16-24

If that what you have, that just fine. All you need is the size insert that will have the 5/16-24 internal thread.

That being said, you could revert back to 1/4-20 with differant external thread available. You can get these at the hardware store.
http://www.reidsupply.com/products/fast ... l-inserts/