Crankcase Crack

[radicalfil]

I have just noticed a crack the the crankcase just below the case stud on the bottom of my motor. It is the 2nd case bolt from the rear. I rebuilt this motor a while ago, but it has only about 7,500-10,000 miles on it. Is it possible to repair/weld this crack while the motor is in the car without causing damage to any of the internals? What might be an worthy alternative to welding it? What will be the most likely scenario if I do nothing?

1972 911T 2.4L MFI Targa
Phil D

P.S. Posted this same Q in the technical forum by mistake. You engine builders should be able to help me.

[Eagledriver]

Phil,

Sorry to hear about your case crack. I can't picture where the crack is from your description. A picture would help for others to give advise. I have a 2.7 RS replica engine that was originally build on a 72 case. My case also cracked. The crack was in an area under one of the head studs. I ran the engine this way for about a year. It's a race car so it had high temps and high RPM all the time. I patched the crack with a small piece of aluminum and some JB weld. This worked for about a year and then it started to leak around the patch. I finally rebuilt the engine with a later case last winter.

I would say if you think the crack is not in a critical area you could clean the area and patch it like I did. This may work for a year or more for a street driven car. Eventually I think you'll need to take the engine apart to repair or replace the case.

-Andy

[radicalfil]

It is right on the casting on the stud side. I don't have my camera here with me, but I'll try toshoot a foto in time and post it if I can figure that out.

BTW how thick was the piece of alum. that you used in your patched. It might work as my car is for cruising only, no racing except for that on ramp to the fwy.

Phil

[Eagledriver]

The crack was on a flat surface of the case and was about 1/2 inch long. I used a piece of 1/8 inch thick aluminum that I cut into a square about 1/2 inch per side. I'd like to have made the patch bigger but there was no more room in the area the patch had to fit.

-Andy

[radicalfil]

I think with the other advise I have gotten I am going to use the JB Weld fix and I'll try and find some real and strong metal to bridge the crack. In addition I'll probably dril the end of the crack as well as route out a bit of the crack to form a channel as JB Weld all items together.

Phil

[911pcars]

You'll have more success if the crack is clean and oil-free before filling with JB Weld. This might be difficult on the bottom of the engine where gravity is working against you. It's worth a try before disassembling the case.

Sherwood

[David]

If you can rough up the area around the crack with a coarse sanding disk, the JB will stick better. I've used JB weld on many motorcycle case cracks with 100% success.

[radicalfil]

OK Clean & rough it up before I use JB Weld.
Phil

[Manipou]

Hi, I have a 2.7 Euro carrera engine and I have found a crack in the area behind the flywheel through to the area around piston No.3. Is this weldable? Is Magnesium weldable? It has previous been repaired with JB weld but looks to have cracked again actually through the JB weld. What are my options. Obvioulsy I do not want to loose the carrera engine number and changing crankcase will probably mean a non carrera engine number (which is currently 6650145) and the will greatly de-value the car. As the engine number is on the other side of the crankcase, could I find a 2.7 crankcase and only use the side that is cracked, therefore keeping the side with the engine number? Any ideas would be a great help. Thanks

[adomakin]

ive had good results using jb weld. i have always cut the crack with a thin cutting disk along the length of the crack, then drilled the ends. that allows you to puddle the jb into the groove left from the disk. cleanliness is the real prob though. try using some trike free solvent in a can-you want to use something that evaporates quickly. you may want to try using jb quick-it set in like 5 mins- may be a better choice if you have the problem of oil seeping out.

[magic930]

Case cracks can be fixed with HTS-2000 aluminum brazing rods.
http://newtechnologyproducts.net/index.htm
1lb of rods costs $80. It will require an Oxy/Acetyline torch for that thickness. I bought a lb of these rods and would be willing to sell some of them, PM if interested.

[Eagledriver]

I think your idea of using a fresh case on that half will give the best results. You'll need to have a shop align bore the "new" case and make sure everything fits together. The worry would be the main bearing alignment and the intermediate shaft bearing alignment.

-Andy

[BReyes]

I would be careful with any drilling (don't go in too far), as to not introduce any metal debris into the engine (even a minimal amount) which could cause a serious problem, and make plans -if intending on keeping the car- on replacing the case, should it not hold or at the next tear down.

Good Luck.

Regards,

[Determined]

Gentlemen,

I have a similiar dilema with my 3.2L Carrera case, I'm considering replacing the damaged half of my case. My question is, "after line boring the mating cases does this change my bearing configuration?" I currently have a standard crank since the case was never line bored before. Thanks for your time and input.

Best Regards,

Alex

[Eagledriver]

Alex,

This is a very good question. But first why do you want to only replace half of the case? You car doesn't look like a numbers matching car so what is the benefit? You'll find that whatever machine work you do to the case will probably cost more than buying a good used case.

There are 2 line bore methods that are commonly used. One is to over bore the mains. This is the cheaper method and a good one. The drawback is that you have to buy oversize bearings and about 500 dollars for the set. The other way is too shave the case halves along the center to make the bores undersize and then line bore to original size. This way is more expensive and harder to do.

Don't forget that if you replace half of the case you'd probably need to line bore the intermediate shaft bearings as well. I don't know if you can even get oversize bearings for these.

-Andy

[Determined]

Thank you very much Andy for your feedback, I have some thinking to do. I would really like to find an complete case in standard.

Best Regards,

alex

[mb911]

mag is weldable but a bit tricky. For temp stuff jb weld is fine but I would personanly weld it