Will the agony ever end? (aka stripped crank threads)

josh912 · 02-19-2002, 07:09 PM

I am so increadibly happy that my engine surived this incredable misshap. The cluch got a little distrorted, and the tranny spine got a little dinged, but everything made it through. I got everything replaced for free as it was caused by a failed gland nut. I even got the new dowel pins free! Anyway, I got everything put back together, but the gland nut wouldn't screw in. When the gland nut failed, it backed out until it hit the clutch. Then it spun and stripped the threads. There still is thread, so all hope is not lost. However, I need to retap the threads on the crank. My question is, how? BTW, Grainger doesn't even carry a tap that big!

Also to clear this up, the engine was NOT overreved and I didn't miss a gear. A few people believed that to be the case. I will say however, Harry Pellow had never heard of a gland nut failing in the way mine did!

Kiwi912 · 02-20-2002, 09:12 AM

Good to hear you're nearing getting back on the road!
Out of interest who supplied/manufactured the gland nut?

How did it actually fail, did it just come loose or did it break as well?

I'm getting close to a rebuild so I'd love to know who's gland nut I should use, especially if they repair failures for free!!!!

josh912 · 02-20-2002, 06:57 PM

To be honest with you I don't know the name of the company. I got it through my local parts supplier, and they contacted the company.

As for the crank threads, HELP!!!!!!!!!!!!!!!!!!!!!!!!! Nothing is working! Any suggestions are definately appriciated. Everything else is perfect, except for the crank threads. I want to see the car on the road, and not on a dolly or flatbed!

craign · craign's Garage

Can you get Helicoils that big??

I found that the previous owner on my 69, who had the engine rebuilt, had them put in the spark plug wells, no idea why unless one got damaged during a plug removal/install.

Craig

josh912 · 02-20-2002, 08:32 PM

Thanks craign. Now the question is: a) do they make helicoils that big, b) can they withstand 400 ft/lbs, and c) can I take that much out of the crank. Very good idea, worth persuiting.

I'm going to call Harry Pellow, again, and call Walt at Competition Engineering. The first 3 threads (toward the flywheel) are gone and the next few are severely damaged. I can get a tap for $175, but I'm not sure if it will work, and $175 for something that might not work, I don't think so. I hope I can find something and not have to crack the case, but it isn't looking good. The fact that half of the threads are bad is not good, and if a helicoil doesn't work, well....

josh912 · 02-21-2002, 10:04 AM

Well, helicoils are out of the picture. First off, it doesn't appear that they make a 26-28mm one, second, they won't withstand 400 ft lbs torque, and third, I still have to spend $200 on a tap. Oh well. Keep the ideas coming.

Green 912 · 02-21-2002, 01:32 PM

1 Best way to fix. Have the threads recut on a lathe by a good machinist.

2. Using an old but not damaged G nut... Grind 4 groves just like a tap and then use it to chase the existing threads. Be careful to set it up so the threads are chased and not cross threaded. Use oil.

3. Use a dremel and a small grinding wheel to grind the damaged portion of the threads away. You can cut the crushed/deformed part out in a mater of minutes. Blast the threaded socket out with Brake Klean first so the wheel won’t clog up. Mask the rest of the crank off with plastic and REALY clean everything after.

3A. If you have the time you can clean up the threads surprisingly well with a dremel by using the thin cutoff wheel and carefully following the existing threads. Start by grinding the cutoff wheel down on some brick to make it small enough to fit inside the end of the crank and also have some extra room to see and work. Take your time, remove small amounts and you will be surprised how easy and good the work will be considering the “shade tree” nature of the fix.

Shasta Design (530) 238-2198 sells a very good SCAT G nut for $50. It will take more than the crank can and has an excellent pilot bearing. The torque you can set will only be limited by the crank you are using.

Green 912 · 01:53 PM

Now that I see your latest post and know that half the threads are bad (Ouch!)you might start to think about a crank. The high torque needed hold the flywheel is important and a nut puling out of the crank can trash the flywheel and the end of the crank. (Unfortunately as you now well know) There isn’t a huge amount of metal to work with to tap in a coil before you get close to the pin holes.
Cranks are not too hard to find. I have 2 and know of 2 more that are already reground and ready to install. Good luck with the fix and you might just find a way to do it without splitting the case.

What the hell... Try cleaning up/ gringing off the first 3 very bad threads up with the Dremel, chase the somewhat damaged threads and then torque up the flywheel. The worst you can end up with is what you now have, a bunged up crank, and it might work.

Use a New SCAT nut!

cgarr · cgarr's Garage

After reading all what can happen you guys are getting me worried now. I am putting my flywheel back on this weekend, everything is in good shape on mine but to prevent future problems do they ever use locktite on this nut or is that a no no?

Let me know your ideas for those of us who have not yet had a problem and dont want one.

Thanks

Craig

cbbest · 02-21-2002, 07:00 PM

Couple of thoughts...

You might want to crack open one of your text's and check to see if you have enough thread left to carry the load. Can't exactly remember the math here, but its a function of diameter, pitch, material, etc.

How did your flyweel make out? Mine was pretty much wobbled out and would need to be cut for larger pins. Any slop in this fit I would think would take the pins out again in no time. Also - look for burs. Won't take much to get oil to leak past the soft metal gasket there.

Just curious. Have any of the VW guru's done anything interesting here? seems like such a weak link in these cars...

Cb

josh912 · 02-22-2002, 10:05 AM

First off, the gland nut failed. It was a good type and it just flat out failed. I used locktite ad torqued it to 400 ft lbs. Done this many times and this was the first problem. So craig, don;t wory too much. Just use red loctite, use a good gland nut, and torque it to 400 ft lbs. You shouldn't have any problems.

Next, I am really worried about the number of threads left. I goot really lucky, and a gland nut faiure can take out the entire engine as well as the tranny, so I really don't want to take my chances by just screwing it on as is, which it won't anyway.

As far as the flywheel goes, it shiered of so quickly that it came out fine. I cleaned it up and it looks perfect. I debated about putting another one on, but this was the best one available.

I've been checking around and I can't find any fix, even among the VW gurus. Mainly because they just use a new crank. Cheap, easy, rebuild kit costs only a few bucks, crank a few more, 1 day, and your back on the road. Not the case with the 912.

All I know, is that if Walt at Competition Engineering can fix it, well then, I need a new crank. I'm probably going to bring it up to him pretty soon (1 hour away from Bakersfield), so only time will tell.

Any other ideas?