Head bolts Pulling threads from block

[apolnicki]

Our shop is familiar with how to handle head bolt threads pulling out of an aluminum blocks.

BUT... I have a problem with a boxster blown head gasket job.

While I was beginning the assembly process, I noticed one of the head bolts (bottom rear-driver side) would not thread in smoothly by hand. I pulled out the bolt, re-lubed the threads and tried to insert the bolt again. I loosed and snugged the bolt a few times, until I felt I could get a reasonable initial torque.

While I was making my first round of 60deg rotations, the bottom rear bolt spun. I stopped after about a full rotation, pulled it out and found two turns of threads remaining on the bolt. I doubled checked the original bolts pulled from the motor, and they indicated no problem, no threads.

Our shop does a bit of maintenance and service work on air and water cooled Porsches, however this is our first water-cooled head job, and we have no idea what might be the best solution.

Do I need to go deep and split the block to fix the threads?
Should I fix all of the threads?
I am looking at this job as a learning experience, How bad will it be to split and reassemble the block? I have already read through the process on Alldata, I am not excited.

[Lapkritis]

Originally Posted by apolnicki

While I was making my first round of 60deg rotations, the bottom rear bolt spun. I stopped after about a full rotation, pulled it out and found two turns of threads remaining on the bolt. I doubled checked the original bolts pulled from the motor, and they indicated no problem, no threads.

Do you mean the threads stripped in the case or the bolt stripped or both?

If nothing has stripped and I've misunderstood, then I would recommend thread chasing and clearing the holes (again, even if you have already done so) with a close visual inspection. Brake cleaner and compressed air as the final step. I've seen assemblies where blind holes build pressure when liquid thread sealants are applied which prevent the fastener from hand-threading. A hydraulic blockage could feasibly cause threads to strip.

In these cases with blind holes, I apply the thread sealant sparingly to the threads near the bottom of the hole rather than the hardware. If you have air/fluid trapped in the hole you can sometimes hear it leak/burble out.

If you have stripped the hole then I would repair the single hole with your choice of aftermarket solution. The trouble hand-threading in indicates damage to the threads even if the old fastener appears clean. It may be the aluminum was corroded. TimeCert or CaseSaver would be my recommendation on aluminum engine cases for thread repair - helicoil only on lower stress joints such as intake/exhaust studs in aluminum or cast iron blocks where expansion forces are much lower.

[Eagledriver]

That's boing to be a B***H to fix. I haven't taken the heads off a Boxster but I bet the holes are deep and blind. I would suppose an insert would work but you'd have to make sure it can go deep enough for the job. Since it's a Boxster and there are thousands of them out there, I would consider getting another engine from a wreck and rebuild it.

-Andy

[RedCoupe]

apolnicki got a knowledgeable reply over on the Boxster-Cayman forum. Reading that sure makes me glad that I only mess around with an air-cooled Porsche!