mrmoots

I assembled my case a few months ago now and was thumbing through the Porsche manual today for something else. I came across an important note that some how I had completely missed when putting the case together.

The note says not to push the “O” rings fully onto the through bolts like this…….



But to assemble like this……



Now I have done photo 1!

Have just pulled out a through bolt and played around with the “O” ring on it. Even if it is inserted as photo 2, when it comes out it looks like photo 1.

So what’s the big deal? The only conclusion I can draw is that as you insert the through bolt with the “O” ring in photo 2 it is more likely to catch and tear on the case shoulder. My “O” rings were lubricated with a small bit of RTV silicone before installation.

Do I risk it, or pull each bolt one by one and change the "O" rings.

springer3

As long as the o-rings did not get cut or pinched, they are fine. Assembling with some silicone grease is a good way to make sure the o-ring can slip around the corners, and then twist to get to its correct alignment.

The case sealant is a back-up to the o-ring seal. As long as you were thorough with that, you should be OK even if you have one or two pinched o-rings. I think you will do more harm than good if you remove bolts after the case is assembled. The case will distort with one bolt removed. Perhaps you can get one back in harmlessly, but if you walk around the complete circle, I have a hard time believing you would not risk shearing the now-cured case sealant.

mrmoots

Ok, I have just come in after removing three through bolts one at a time and replacing the "O" rings with new in the correct fashion described by Porsche.

None of the "O" rings I have removed have any sign of splits or tears to them. I think you are right, I am going to leave well enough alone.

Thank you

dboyle

Damn you O rings...

I had my engine rebuild earlier this summer, complete bottom end. Everything comes together and runs great.

Few weeks into driving it around (trying to get like 500 miles before getting back on the track) and it is leaking oil, can't see where but talk to the mechanic. He thinks it is the oil return, remembers that it was a bit odd on my engine (it is supercharged so kinda an oddity).

So bring it in and damnit if it wasn't one of the O rings coming apart.

Good news? He took care of me, had to drop the engine to do so the poor guy. Funnier news? As he put it 'I had a moment where I was a woman and read the manual' and put them in as porsche described (not sliding all the way). He had never done that, has done tons and tons of rebuilds sliding it all the way down the bolt, and picked my engine to try it the 'proper' way.

Needless to say he will be going back to the 'improper' way

You will immediately know if the ring gives way, certainly isn't worth replacing it IMHO if it isn't leaking. Mine cost me a few days on the track which was a bummer, but engine doesn't leak now, and I have > 0% compression on cylinder #6!

-Dave

Geoffrey

The case sealant is NOT a backup to the case thrubolt O-rings. There is pressurized oil that runs in the thrubolt hole and the O-rings keeps it from leaking. If they are cut, they will leak, and you'll need to pull the cylinders off to get to them.

wilson234

I just completed my 89 964 rebuild, engine runs great but leaking significant oil from cylinder area. I suspect it to be the case bolts as I took one out at a time and replaced with green Viton seals. I'm in the process of dropping the engine again and was planning to start all over again, as I did not follow porsche guideline on install. But it appears others have slid the orings all the way on the bolt with no issues. PLEASE chime in if anyone made this mistake, had an oil leak, reinstalled o rings according to porsche recommendations and oil leak was resolved. I don't know if I can take another disappointment like this. I took the engine as far as removing the cylinders but didn't split the case. I had a broken head stud. My biggest question is whether the idea behind porsches install instructions is to have the oring sit on the smaller diameter section of the bolt and ideally have oil pressure push the seal to the start of the tapering to the larger diameter area. I cannot remember if the metal washer essentially bottoms out on the case. If it does I can see why you wouldn't want the oring to sit on the larger diameter section as it would get smashed as you tighten the bolts. If you read the instructions there's a tool 9511 that I can't seem to find for sale anywhere that allows you to slip on the orings as well as when you install the oring on the nut side, it pushes the oring I imagine past the large diameter section of the thread end onto the smaller diameter of the bolt. Anyone have this tool and can measure the distance the tool pushing the oring onto the end of the bolt? This would confirm my theory that the oring is designed to sit on the smaller diameter area of the bolt, as the nut side oring wouldn't move like the one on the bolt head side. Help!! Please!

FeralComprehension

FWIW there has been significant discussion in the PP Engine Rebuilding area on this topic. IIRC, there are some experienced builders who recommend putting a small chamfer into the case hole where the throughbolts go in.

Additionally, (again, IIRC) there were some 964s with mis-machined cases and there's a TSB indicating that these should receive TWO seals at that joint. Here's that TSB: http://www.pcarworkshop.com/images/f...0791geolab.pdf which I found at this site which we should ALL bookmark:

http://www.pcarworkshop.com/index.ph...C_Parts_Guides

Michael D'Silva

I'm asking a question regarding 964 case through bolts, since I have taken some measurements and do not understand what I am seeing.

Firstly, here is a pic of my o ring from a Wrightwood Racing kit, on my through bolt. Does it look 'thinner' than the one at the beginning of this post?

Secondly, I measured the depth of the recess in the case, that the o ring and the insert part of the washer, protrude into. On the case, it is approx 6.25mm but varies up to 6.4 on some of the orifices, perhaps I am not holding my vernier perfectly each time. However, when I compare the hole that has to be filled, with the thickness of the washer 'core' and the o ring, the hole is too deep for the o ring to be in any form of compression. If the o ring is not compressed, then how is anything sealing?

I'm curious if anyone has measured the depth of this recess on their 964 case before.

Also, no, my case number does not fall into the parameters of the ones needed 2 o rings on the 1 side. When I disassembled the case, it only had 1 o ring on each side.

gotmypony

Hello,

I’m checking in to see if you ended up installing the o rings dry with no leaking issues.
I rebuilt a 91’ and installed the o rings without ever measuring the depth. I installed them dry per recommendations and the motor never leaked.
I’m currently on my 2nd engine rebuild and it is an 89’ block however it’s not in scope with the Porsche bulletin serial numbers that had an issue. I measured and got same results as you. Did you ever find out if that is the standard depth and the o-ring stretches to fill the gap to the chamfer?
Thanks!

No_snivelling

Interesting problem.

Can you get a hold of a depth micrometer to measure with higher accuracy? The squeeze (if any) on the thickness of an o-ring might be as little as 5-10% of the thickness.
Why did I say "if any"? Well it is possible that Porsche did not intend for any squeeze on thickness, and they only wanted a squeeze on the ID and OD of the o-ring. As long as the ID and OD have an initial seal, then oil pressure will try to flatten the o-ring making the ID and OD seal even tighter. Just a semi-educated guess on my part.

Luxter

Correct, the O-ring seals on OD and ID only.
The reason Porsche wants you to locate O-ring on smaller diameter portion of through bolt is that the O-ring needs to clear the OD of the block FIRST (get into the opening in block first) before it gets literally pressed against the OD of the block with conical portion and subsequently the larger diameter of the through bolt.
Cheers,
L

Luxter

Yes, you can remove one through bolt at a time without splitting the case or breaking Loctite 574 bond and reinstall O-rings following the P manual. Assuming it's not too late.
Cheers,
Luxter

Michael D'Silva

hi
my build went fine. No leaks whatsover.
Use lots of molykote on the o ring.
Only push it up on the narrow section of the bolt.. not like I have shown it in the photos (that was for a different purpose).
The o rings as others have said, seals on its inner perimeter (against the bolt) and the other perimeter (against the case). Yes, that is why you only slide the ring up the narrow section of the bolt. When you push it into the case, the o ring will clear the case and there is no chance of nicking or shaving the o ring. As the bolt pushes through, the o ring is pushed up onto the wider section and forms the seal. Thats why you need to use lube on the bolt/ o ring.