3.8 spigot o-rings breached case

Peteinjp · 04-16-2020, 09:46 PM

Hi all,

First time 911 engine rebuild here and have been using this forum extensively but yet to post. I have an issue with machine work that was done on my 964 case. As you know cylinders 3 and 4 have a total of 3 blind holes where no through-bolts are used. 2 are right behind the flywheel on #3 and 1 is nearest the pulley end of the case on the bottom. I have found that the machining for the spigot o-rings has breached these holes.

As you’ll see in the pictures if I were to remove the thin parts of metal that remain I’ll be left with at least a 1cm gap in the o-ring groove. Obviously this will not work and its almost impossible spot to weld so the only way I can think to deal with it is to leave the thin metal as is plug this hole with a custom plug. Alternatively I could fill the hole with some type three-bond and then plug it with epoxy on top of that.

Have you seen this before?
Any thoughts as to how to deal with it?

I had planned on having the shop do the rebuild but based on the fact that they did not follow the specs that were provided to me (via Colin at 9m)I’ve taken the project on myself which is why it’s going so slowly. Had I known what I know now..... etc etc.

The o-ring does protrude into the cylinder ever so slightly (roughly 0-.25mm) and initial test for of the piston seemed good.

On to the pics:

Pete

racing97 · 04-17-2020, 06:31 AM

Typically one would make a undersized plug out of Aluminum to take up room in the hole making sure it is under the deck height on the case then JB weld or PC7 the plug into the case. Check both sides of the case in this area to make sure the other side of the case does not have the same issue.
You can still do this just sand after or smooth the JB before it hardens.

regards

Peteinjp · 04-17-2020, 08:24 PM

How would I return the o ring groove to the proper shape in that case? It’s hard to get in there.

Thanks,

Pete

racing97 · 04-18-2020, 05:35 PM

JB weld will sand easier than the Al you can find something the same size as the oring and while it is still workable shape it a bit.
You should probably know that nothing done by the machine shop that did the job for you buyt they should of plugged the holes first they just did not know.
regards

stownsen914 · 04-19-2020, 05:36 AM

Looking at that last pic, honestly it seems kind of obvious that putting an O ring groove at that spot was going to breach the smaller oil passage hole.

Peteinjp · 04-19-2020, 05:53 PM

Yeah- one of the machine shops I contacted about repairing this said they have seen this several times- which was a bit of a relief actually because that means that its not necessarily true that the shop that did the work cut the groove too deep. Apparently these blind holes should be bored out a bit and fit with a plug before machining.

I think I could get it too work- probably with epoxy but I’m inclined to let the shop that did the work take responsibility for fixing it correctly.

Pete

Peteinjp · 05-21-2020, 07:52 AM

Just to follow up- The shop that did the work has agreed to fix the case as I requested. I asked to have the holes plugged with aluminum and have the grooves re-machined. The spec for the grooves was .5mm deeper what I have requested however I test fitted the cylinders with the seal and it felt right- taking just some light taps to slide into place. This problem seems to occur regularly. What I did notice is that it seems only the early 3.6 cases have these holes. The factory mush have recognized that this was a problem when they started to bore out cases for 3.8 builds.

For future reference the proper way to deal with these cases is to plug the 3 holes before machining.

Pete