915 case - another crack question

[profblue]

For my rebuild, I finally took a gamble on a locally advertised 915/02 box. After cleaning for what seemed an eternity (still not finished), I found this crack:

During cleaning, I have kept the oil inside, and have seen that it does leak from this bolt as well. I can't say for sure that this is from the crack or from the seal though.

Based on my reading, this is "only" the bolt blocking in the spring & detent, so therefore my assumption is that the crack was caused by over-torquing the bolt (my read of the manual says 15-18Nm). As professional welders for magnesium in my area are like gold dust, my current approach would be:
- cleanup, and slightly burr the crack open, to prevent further spread
- apply JB weld with keeping a bolt inside (to keep from leaking inside)
- use heat gun to heat casing to have JB weld properly fully go into crack
- when rebuilding, use additional Loctite?

Question:
- should this be a "high stress area" or would the approach above work - or should I find a new housing?
- any other suggestions (except welding)?

[kevingross]

This can be repaired by welding. I recommend you tear down the case, clean it well, and send it to California Motorsports. They've done this repair for me. I attribute the damage to overtightening the bolt.

[profblue]

thanks, Kevin. I am based in Belgium, so shipping costs will kill me there . Am looking into local welding specialists as well, but haven't yet found one with any Porsche experience or magnesium yet...

[Discseven]

Originally Posted by profblue

...professional welders for magnesium in my area are like gold dust...

Know the feeling. Not concerning the same issue but regardless... can relate on "gold dust" sensation when certain specialized capabilities are needed.

No question professional attention is called for---someone with proven credentials. In the pure absence of this capability, am going to run through alternative idea and we'll see how hammered I get. Am open for a good lashing---RonO... if you read, here's open door:

Looks like black "filler" has been applied to bolt. Makes sense given whomever accomplished this realizing crack made stock bolt not fit so good. First move, would remove bolt and check case threads---are they still there? What condition? Assuming theads are in tact, and given NO MAG WELDER IN SIGHT, I'd think about closing crack with a heavy duty clamp. Any debris/filler within crack is surgically removed first. Would be very careful about this so only air is within crack before clamp arrives. What filler's in threads can be chased out... no problem... but I.D. needs to be returned to original dimension beforehand. Risky to close crack... yeah... This is totally NOT the way to correct this but is a possibility. Will end break off under clamping making matters go from bad to worse? Yeah, is possible. Being a risk taker... would like to say I'd go for clamping it but... thinking this through as I write, concern meter now reads in RED. Been down enough paths to know: don't go when RED. I'd definitely change course. My reasoning here, am not sure but don't believe mag has doable back & forth flexibility (like aluminum does for example.) Even with crack closed and clamp remaining installed, vibration could terminate mag's bond along back & forth "fault line." Nothing appealing to this. Conclusion = while focusing on other details of rebuild, I'd be dedicated to finding the ONE local person that can make a professional repair. He/she is out there---just got to dig & dig until found. (Or I'd learn to mag weld.) ...My 2 euros Pblue.

...OK, let me have it for even thinking... "clamp it."

Note - I do NOT support using a clamp here.

[MBAtarga]

That crack was probably caused by over-torquing as you suggest. If no experienced welder is available, I'd clean up the area and apply JB Weld into the crack and reinstall the bolt with the minimal torque spec. Then monitor it during regular maintenance/oil changes.

[911pcars]

Rebuilding the transaxle just to repair that threaded boss seems like over-reacting. I'd try less expensive alternatives first.

If 2-part epoxy applied, I wouldn't use the drain/filler plug to back it up while curing. If the bolt is also epoxied in place, you'll have another issue to content with. To prevent the epoxy from affecting the threaded plug while curing, coat the threads with grease. To ensure the plug doesn't leak in service, apply a coat of Loctite PST thread sealer to the plug threads. Works best if contact parts are clean and dry.

Sherwood

[florio]

Hi, I would be very surprised if you cannot find a shop that will weld that for you close to where you live. With Spa not far and all the little racing garages that are near it, our german friends in the fourons region, and the gearhead dutch up north, you should find a shop that will weld it without taking the case apart assuming that you can remove the detent pin without things getting lost inside. Just imagine having to pull the engine if that leaks again. I'd put it in my trunk, and drive to a couple of shops that do work on engine heads. If they won't help you, they can point you to someone that can.

good luck,

Dario

[john walker's workshop]

Poeple tend to tighten that very short bolt too much and strip the case threads. The fix is a 10mm timesert. That may work and do the sealing as well. Timeserts use a finishing tool that's run through it to finish rolling in the last few threads, which obviously expand the insert to lock it in place. If the expanding threads are below the crack, it should work.

[profblue]

thanks guys, great to tap into sooo much knowledge here, appreciated. First item I wanted to seek input on was if welding is indeed the way to go - I do have agree that for the total piece of mind, it is probably the best route.

Have made inquiries to several welding shops today awaiting their response. Guess they're not to keen to take a risk for a tiny job on such a part, but let's see.

I agree this item here is not worth a full rebuild. I like your suggestions, should I not find a welder. However, I am inclined to actually go for a full rebuild: I have very little history of the box, apparently acquired as part of a bigger parts lot. The oil drain was clean - too clean in my view, so suspect to have been changed very recently. Next to that leaking bolt, I have a leaking shift rod seal, but more importantly - it's stuck!!! Not sure in which gear - as the pin hole in the input shaft is perfectly vertically aligned, can I assume either 3/4th gear? (Input shaft and flanges do turn with effort). the shaft only has little play pulling fwd/bck...