Separating Nikasil cylinder and piston - ok?

[Cevan]

I’m in the middle of disassembling my 1986 3.2 engine to finally address the numerous oil leaks I have and oil consumption (qt/400 miles). I’ve got the heads off and it’s apparent the exhaust guides need replacing. Will also replace the lower Dilivar head studs. Given the mileage (168,000) and unknown rebuild history, probably splitting the case too.

The cylinders are Mahle and best I can tell, they are Nikasil. 11 fins and slightly magnetic. I’ve read a bunch of threads here and it appears it’s fine to separate the pistons from the cylinders and if everything is good, they can be reassembled as they were taken apart. I would like to at least visually inspect the components for broken rings, worn skirts, damaged ring lands, and clean the buildup of carbon on the tops of the pistons. Couple of photos below.

Any downside to doing this?

[Jeff Alton]

You are in there anyways, do it proper. Remove, inspect and measure all components, including your pistons and cylinders.

Cheers

[PeteKz]

Sure inspect and measure the pistons and cylinders. No need to split the case unless you have further reason to do so, such as, the case was leaking, you found some metal bits inside the case, timing chains stretched, etc.

[safe]

The idea that you should not separate piston and cylinders seems stupid/"wife tale" to me.

Remove, inspect, re ring if needed.

[Cevan]

Am I able to just put new rings in and run it? I thought that was a no no.

With 168,000 miles on the engine I figure it’s prudent to inspect the crank et al.

[safe]

Yes. There is probably a thread here describing "deglazing", I used scotchbrite to clean the cylinders after checking that they were in spec. This is for Nicasil, to be clear.
Checking/changing bearings after that many miles is in order. Exhaust guides in the heads are probably worn out to.

[Black 993]

I would split the case. I've never seen a 911 engine at that kind of mileage that couldn't use layshaft bearings. The additional labor in splitting the case once you have p/c's off is a pittance compared to the peace of mind you gain.

[dtxscott]

It makes sense to pull the Ps&Cs apart to measure and measure. If you think they are OK and will go back together, just mark them so you know which piston and cylinder are matched and their respective location on the engine.

At 86k miles, my Alusil Kolbenschmidt Ps&Cs were 40% worn so I went back together with them. The valve guides were a whole 'nuther story. I also pulled the Dilivar studs and replaced with steel.

One pro-tip is to clean the threads on the case THOROUGHLY before you re-install.

[Cevan]

Thanks for the responses. I will check with the place that is going to do my heads and see if they will measure them to see if they are within spec. I don't own the required bore gauge. If so, I guess I'll have to determine if I will use as is and re-ring, hone or replate ($2400 quote by Millennium).

[brighton911]

I second Black 993's comment re case splitting and layshaft bearings. Clean those cylinder bores with scotch pads (do a search). Carefully clean the pistons including ring lands. Measure them including ring lands and pin bore too for wear. With the rings in the bore, you can check the end gap to determine how worn they are and replace if necessary. You only want to do the job once.

[Cevan]

I split the case and all the bearings (main, rods) are date coded 10 85. Evidence it’s never been opened up I guess.

I have both case halves stripped but for the main oil line adapter. Any advice on removing this? Can I use an impact? Looks like it’s on with 89 ft lbs. There’s a seal under it I’d like to replace.

[Dpmulvan]

Originally Posted by Cevan

I split the case and all the bearings (main, rods) are date coded 10 85. Evidence it’s never been opened up I guess.

I have both case halves stripped but for the main oil line adapter. Any advice on removing this? Can I use an impact? Looks like it’s on with 89 ft lbs. There’s a seal under it I’d like to replace.

I’ve seen cracked cases from not being careful, a little heat just to be safe and If your using a 1/2 pneumatic might want to turn it down a few notches or do it by hand

[PeteKz]

The one on the lower left front of the case that the crossover metal oil line connects to? Leave it alone. Unless it's leaking, I see no reason to remove it.

What condition are the main and rod bearing shells? My guess is they show very little wear. I'll go against other recommendations and say that if they measure within limits, reuse them. I'll go further: If the mains are good, do not even remove the rods, otherwise, you be buying new rod bolts, and you'll think, "if I have the rods off, I might as well take those to a machine shop for checking, etc. And I might as well have the crank checked..." Then your job snowballs, and instead of refreshing the heads, as you started out to do, you will find yourself doing a $12,000 rebuild to new, and it will take months, instead of weeks. The bottom end of these engines is very robust and easily goes over 300,000 miles from the factory (including the lower shaft bearings, even if they look worn). The pistons and cylinders easily go that distance too. By going further, you may cause problems that you demonstrably don't already have.

If you choose to replace bearings, get the Clevite bearings. From what I've read in other places, as of a couple years ago when I built mine, some bearing sets are poorly made. Using Clevite, my main and rod bearings were all right about 002" clearance. But check with someone who builds lots of engines to see what are the best bearings now.

What condition is the oil pump? That's important too. Especially the scavenge side.

Now, carefully, back away from your worktable...

[Cevan]

I'm not sure I follow Pete. Getting the crank and rods magnafluxed and having the rods rebushed isn't that expensive. APR rod bolts are $250. And it's too late. Everything is apart.

[PeteKz]

Well, I guess you just really wanted to take it apart! Now you get bragging rights for doing a complete rebuild.

As long as you’re in there, you might as well twin-plug it.

[LukasM]

The rod bolts are a known weakness of the 3.2 that has an otherwise very stout bottom end, and while most hold up, some do not. And that is not an annoying failure like a broken head stud, we are usually talking full destruction with a hole in the case and bent crank is going to cost you $10k+ on top of an already ridiculously expensive rebuild....

I think you are doing the right thing by taking everything apart, measuring it, replacing what is worn and going with ARP rod bolts and steel head studs. You will sleep better and if you document it well, will get much more than that cost back in resale value.

One more thing - depending on the condition of your exhaust studs - these usually look terrible on cars that see any salt at all - I would upgrade these to (corrosion resistant) titanium. One of the more painful moments of 911 ownership is "just wanting to swap the exhaust" and having a rusted solid studs snap off in the head. Stomski even makes a special tool for that removal but I'd much rather not have to use it....