911 Clutch Bell Screw Broke Off In Crankshaft 911

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tbill
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Post by tbill » Wed Dec 03, 2003 7:47 pm

you should be able to skip the brass bushing and use some shims outta the ofna kit, then use one of the small black shims in the kit to put betwen the end screw and pilot shaft. i went in circles grinding down the brass shims, took forever, and they never came out flat, so i used the method described above.

i just hope you get bashing again, *censored* of a road 'we have been down' on this deal, can't wait to see the final result :)
savage #1 lrp z28, savage #2 mach .26, savage #3 wasp .26, savage #4 mach .26, savage X, Hellfire, GS storm,
2 nitro M/T's with a few mods, mini-T, 'magic wheels' Snap-On truck, xmod evo [firebird], LST2

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Post by iCow » Wed Dec 03, 2003 7:56 pm

yeah i know... my wife actually asked me why i haven't been running my truck with the new engine. I didn't have the balz to tell her what happened to a brand new engine, so i just said i've been busy with other stuff.

That's a good idea about using just shims instead of the bushing i'll try that later tonight too. i know the bushing is just to hold the CB in place so shims should do the job just as well. I'll take pics of all the solutions just for reference, but i'll just do the essential pics on the final write up.

thanks again for all the help. i really miss the track.

oh and to throw another wrench in the works , i'm considering adding a 4 wheel steering setup to the ol' SS. I'll have to relocate the header tank though, so we'll see. maybe that will be my springtime project.
[url=http://www.iconicarts.com/savss/racer/]My Racer Project - Codename: Little Boy[/url]

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Post by iCow » Wed Dec 03, 2003 11:43 pm

ok folks here we go...

How To Repair A WASP .26 Crankshaft With A Broken End Screw

From time to time things happen in the world of RC maintenance. I had the unfortunate experience of my clutch bell end screw head breaking off and leaving the shaft stuck in the crankshaft. Also this was a brand new WASP with only 5 tanks through it... barely broken in. I have to caveat this procedure with the following statement... try all other means available to remove the offending screw before performing this repair. Other folks have been successful in removing the screw by drilling it out, etc. I myself tried a lot of methods, but in the end I just had a screwed up crankshaft on a brand new engine. Now could i have just bought a new crankshaft? Sure, $80 and you have to wait for it to come in, plus you have to dismantle more of the engine. Eventually I will replace the crankshaft with a new one, most likely when it is time to service/rebuild the engine. Until then this $10 US repair will get you back on the track in a few hours.

This repair is NOT for the faint of heart and is meant specifically for SG crankshafts. Do this at your own risk. Neither I nor Savage-Central are responsible for any further damage to your engine. Also the number of shims and measurements, etc in this tutorial are for my particular WASP and clutch setup. You will need to do your own dry fittings and measurements for your particular engine/clutch configuration, but this will get you in the ball park.

NOTE: You will be dealing with fine metal grindings here. Do your self a favor and plug your carb intake and the exhaust port. Make sure the glow plug is in as well. The last thing you want after this is metal grindings in your cylinder.

Parts Needed:
1 Dremmel Tool w/ Cutting Wheel
1 OFNA Clutch Shim Kit (Part# 10099)
1 XTM Clutch Nut Pilot Adapter (Part# 233220)

Procedure:

Step One: Gathering The Parts
This is how I started off. You can see the end of the crankshaft with the screw broken off and the attempted drillout.

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Here are the parts bags...

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Get all the parts and the Dremmel tool ready. For my particular needs I pulled the shims seen below from the OFNA kit. Your shims may vary, but try my setup first. I have an eNVy 3 shoe flywheel.

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Before we go further here's a quick comparison of the different pilot adapters and the stock clutch nut. On the left is the stock nut, center is the XTM nut and for comparison only is the OFNA nut (right). You can clearly see there is a big difference in length and shoe spring groove position. FYI the OFNA nut is way too long for this repair, trust me I've tried it. Traxxas makes a pilot nut adapter as well, but I didn't have one to compare.

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Here's another comparison of lengths after I made my crank cut... it's not exact, but close enough for you to see the importance of the shim kit.

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Step Two: Shim Check
You will need to double check your nut shimming before you proceed. As you can see below that I need probably two of the brass shims between the flywheel and the clutch nut. These will also be needed for the pilot adapter since the spring groove is in the same position on both nuts.

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Step Three: Cutting The Crankshaft
Ok here comes the scary part. Remove everything from the crankshaft. Flywheel, collet, everything. Take the stock clutch nut and screw it on the crankshaft all the way until it bottoms out and can't be turned any further. You only need to hand turn it. The exposed threads all the way to the end of the shaft is what you will be cutting off.

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Using the top of the nut as a guide, CAREFULLY begin cutting the shaft using the Dremmel tool. Be sure to stay straight. The nut will help. Also take your time here, there's no rush. Cut from only one side as well. This will help avoid burrs on the end of the shaft.

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After you have made the cut you can use the Dremmel to grind off any imperfections. basically just make it flat and even with the top of the nut. DO NOT GRIND THE NUT!

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After you get everything cleaned up remove the clutch nut. As it backs off the shaft it will straighten out any thread problems. Voila! A trimmed crankshaft ready for reassembly with the new parts.

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Do a dry test fitting of the pilot adapter on the length of threads on the shaft. The adapter should not bottom out brfor reaching the end of the threads. If it does, then you may need to trim some more off the shaft.

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Step Four: Reassembly
You've made it through the roughest part. Now it's just like a regular clutch assembly except you have a stubby crankshaft. Let's get to it. Start by putting on the collet. I didn't shim my collet. I tried it and it pushed the clutch bell a little too far forward into the spur gear for my liking. No shims made a better fit.

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Add the flywheel and two brass shims. NOTE: Shimming will vary depending on your flywheel. This is where you really need to do some dry fittings to get the proper shimming for your flywheel and clutch bell.

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Screw on the pilot adapter and tighten as you would the stock nut. Remember the flywheel should not spin on the collet.

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Add your shoes and springs (yes my springs are missing in the pics).

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Add the STOCK clutch bell shim that came with the truck (if you are using a stock bell).

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Slide on the bell. Notice there's not much shaft left. We need to address that.

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Because the shaft end is about 1/8th shorter than the stock crankshaft the stock brass bushing that goes on the end of the shaft will not work here. If you try to use it, the end screw will torque down into it, pressing against the bell bearings and binding the bell. This is critical to avoid. The end screw should pretty much end up flat against the shaft end. The bushing and end screw are just there to keep everything on the shaft so we can substitute a few shims for the bushing.

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From the shims we pulled from the OFNA kit, locate the small THIN silver shim and place it on the shaft.

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Then add the two larger silver shims. You can see clearly how the shims end even with the shaft end. This is what you want to see on your engine at this point. If your bushing happens to fit, great then you are set, otherwise, experiment with the shims to get things even.

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Use the small BLACK shim and the small hex bolt and screw them into the shaft. Tighten, torque and lock tite as needed. WARNING: Be careful with the lock tite, it's the reason I ended up here in the first place. :) This keeps everything in place and adds just a tad of front to rear play in the bell. A minute amount of play is a good thing. The hex bolt is better than the stock phillips screw anyway.

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There you have it! All fixed! Before you go further, you may want to do a quick blast of Nitro cleaner or air over the engine to get any metal flakes and grindings off it. Put the motor back in, mesh and crank it up. This should make the motor just like new. Others have done this repair before and report no problems. I have to thank all the SC members that contributed info, part numbers, and instructions on making this repair. I'd have a $180 paper weight if it weren't for you guys.

Hope this helps you out.
[url=http://www.iconicarts.com/savss/racer/]My Racer Project - Codename: Little Boy[/url]

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Post by iCow » Fri Dec 05, 2003 2:07 pm

EXCELSIOR! I cranked up the WASP this morning. I took a sick day... i really am sick. But the WASP was calling... fix me... fiiiiiiiiiiiiiix me.

So I did. Got her all tightened up and put on the ignitor and 3 pulls later... BAM... cranked right up. I gotta do some retuning but all in all she sounds good. I can't wait to get out on the track again. The new shoes seem to be grabbing well too. i did have to sand a bit off them to allow the bell to spin freely, but i think she's gonna be a screamer.

As for the bushing replacement... the small shim is so thin it clears the clip slot but has just enough thickness to keep the two larger shims off the bushing. I tried moving them around, but then ended up binding on the bearing. it won't bind up.

After all this i think the PS is going. It feels like it's slipping and it's making a sqeeking noise. It's always something ain't it. Anyone know the part number for the nut i need to allow a non-Orion PS to work with the WASP? I want to get the best PS I can as well. Any thoughts on that?

Thanks guys... I'll treat her tender for the next few tanks until I'm sure she will hold together, but so far it seems pretty tight. Good fix.

Muey Bueno
[url=http://www.iconicarts.com/savss/racer/]My Racer Project - Codename: Little Boy[/url]

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Post by Nomercy » Fri Dec 05, 2003 5:13 pm

WOW iCOW!!!! this thread is awsome. i just broke my screw off last night. i was hopping i could drill it out but wound up cracking the end of the shaft, dont know how but i did. any way id just like to say thank you and thanx to all those who helped you along the way, now i can fix mine. it just snowed here today and i was hopping to get in some time with the snow but i guess there is always the rest of winter. thanx again
I havent slept since I woke up and found my whole life was a lie
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