The Heartbreak of Alusil?

[dkirk]

When recently performing a teardown on my 3.2 L engine for a top-end overhaul, I was anticipating seeing Mahle cylinders and pistons. Upon removing the cylinder baffles my heart sank…I saw the KS logo (Kolben-Schmidt) on the cylinder castings. But after removing the heads, I was amazed at the nice appearing bore finish. All cylinders were of the same coloration (light gray) with cross-hatch still visible uniformly around each bore. Cylinders were removed as all head studs were replaced. The piston skirts looked equally as pristine, with only light polishing of the iron plating in the skirt thrust areas.

Piston rings were of Goetz brand (as engraved on the upper sealing surface) and all rings were chrome plated. With cylinders removed and rings accessible, I decided to measure end gap of a top compression ring. Locating and squaring up the ring in the bore location shown in the Bentley manual, I was amazed to find the end gap to be .016 in. The book indicates a new installation tolerance of .008 to .016 in, with a max wear limit of .031 in. This is remarkable – here is an air-cooled engine with 110,000 miles on it with ring end gap clearance still in the new installed tolerance band!

The cylinders and rings are going to be refitted without any reconditioning as there is absolutely no need for it. Which brings me to my question – why have Alusil cylinders gotten a bad rap? Both Nikasil and Alusil resist wear by the same function – silicon particles standing proud of the aluminum substrate, thus forming a hard working surface. I realize the hypereutectic alloy of Alusil (18 – 22% Si) possibly has a lower thermal conductivity than the Mahle material, but this would be relatively insignificant for the heat load dissipated by the cylinder. And I’ve read on this forum where Alusil can be reconditioned to seat new piston rings successfully. And I’ve also read that if all else fails, the Alusil can be plated with Nikasil to run the unplated Mahle pistons.

My German friend told me that all 3.2 engines made from ’87 through ’89 were fitted with Mahle cylinders and pistons for the European market whereas the US market got the Kolben-Schmidt’s.

Would anyone know why Alusil is considered to be inferior?

[Flat6pac]

The bore of the cylinder shows too much wear.
On the other side I open for customers with a top end and a reseal 3 units in the last year of alucil and the compression numbers with a hot engine come in above 160# per cyl.
Giving the man an option of running what he has been running or spending $4K+ for a set of new Mahle has consistantly lost out.
Good luck,
Bruce

[Steve@Rennsport]

Dave,

The issue of Alusils is all about pistons. These silicon-aluminum bores required iron-plated pistons which are not always easy to find and JE or CP may be offering this now.

We've had good luck boring them oversize and then having them Nikasil plated back to standard so any 2618 piston can be used with the correct (not chrome-plated) ring package.

Those pistons are not going to last 100K like the originals, however this represents an inexpensive alternative. If you need 100+K durability, your best choice will be a new set of Mahle's.

[Eagledriver]

I use Alusil on my race motor. I've also found them to be extreemly durable. My machinist thinks that Alusil got a bad rap because it started on the 2.7. He says people think "Alusil is a pile because the 2.7 is a pile".

-Andy

[cgarr]

Yes the 2.7 is a piece of crap. You got any for sale?

[dkirk]

Thanks guys,

Appreciate all the viewpoints. Judging from the appearance of the cylinder bores, pistons, and ring end gap clearance, plus the fact that this is a street engine, I'm confident that another 100K miles are easily attainable from this engine.

[aquazulu2]

Hello Folks, Given the information in this post I am hoping to jumpstart a response to a few questions.

I am very close to removing my cylinder and pistons and reading a PP bulletin; it recommend NOT separating Alisul pistons and slieve, that one should access the wrist pin and remove them as a unit. Can someone say why this process for Alisul, or is this a standard practice for all if you plan to reuse them.

Also, can I assume that my 1986 911 Carrera would had been fitted with Alisul heads and pistons from the factory..

Is it fair to expect that replacing worn piston rings on Alisul pistons is not a fix for wear.

Thanks for any help.

[Eagledriver]

If you think your pistons, cylinders, and rings are in good shape, you can leave them in place while you do the rest of the rebuild. I started out with that plan on a rebuild I did years ago and then decided I had to measure the rings and ring grooves. There is nothing stopping you from taking the pistons out and measuring everything. Just make sure to not mix up any of the parts, I would even take notes on where the end gaps were so they can be installed in the same orientation.

I bet you will find that the original piston rings are less " worn out" than brand new Goetz rings. I would do this the same for Alusil or Nickasil.

-Andy

[RedCoupe]

There is nothing stopping you from taking the pistons out and measuring everything. Just make sure to not mix up any of the parts, I would even take notes on where the end gaps were so they can be installed in the same orientation.

This is good advice. I know that ring gaps move around, but you want everything to take the same "set" as it was originally. I once tore down an engine that had only a few thousand miles since a total rebuild to have it balanced and replace the fasteners with higher quality ones. (I bought the car with the work already done and the PO gave me all the receipts, etc.) Although I was very careful to put the pistons and rings back in their respective locations, and I used a proper ring expanding tool when I installed the rings, the car always used more oil after I reassembled it than before I did the work. A leak down test confirmed that the rings weren't sealing perfectly, so I always assumed that I should have done something differently (like be more careful with the ring gap locations). I have been since told that I should have roughened the cylinders a bit, but at the time I remember thinking that there was no need to touch the bores as everything was going back in the original locations. Obviously, you don't want to touch your Alusil bores, but I sure would follow Andy's advice about reinstalling the ring gaps the way they came out of the cylinders.

[Mitch1]

While not an expert, I did consult several old school, factory trained pros. Their advice was to check pistons and cylinders. If the piston ring grooves and cylinders check out. Just clean cylinders really good and re-ring with Porsche p/n: 930.103.986.01. There will be a sticker shock. These rings are 3 times the cost of the Goetze rings. But, according to Howard Freeman and Ed Mayo, they are the way to go with Alusil.

Another route to go is have the cylinders plated with nikasil via US Chrome or like facility. They'll want you to send your pistons so they can over bore and plate to spec. Cost about 1200.00.

Forgot to add. Ollie's re - conditions alusil cylinders using the Sunnen procedure. Cost is 45.00 to 50 a cylinder I think. Those guys are really great and super old school. Give George or Ike a call.

[brighton911]

My 86 had Nikasils, got lucky on that one, maybe you will too.

Dave

[aquazulu2]

Thanks for the response folks. I understand now that if you know your unit to be ok that one should try to keep the pistons and sleeves together to avoid changing their break-in wear pattern.

I am going in to replace two broken head bolts, and while I am in there
plan to replace the valve guides. Your point to maintaining the gap location is understood and appreciated, I could not have asked for a more comprehensive response than I received from you guys...

Still trying to break free the first head stud, after spending three days on the exhaust studs, I will suffice to say that I now have to purchase the special drill guide and a new set of exhaust studs..

Thanks again for the help, it is really appreciated.

John.

[aquazulu2]

Originally Posted by brighton911

My 86 had Nikasils, got lucky on that one, maybe you will too.

Dave

I hope so..

I did some more searching and found Wayne,s write up on the technique of removing the pistons and sleeve as a unit.

About removing the barrel nuts on the head studs, do you just point the torch down the head stud chamber, or is there a specific point to aim for. I did a test on one of the broken studs, held the broken section in a vice grip and heated the barrel nut for a minute with propane, and it screwed off with no effort. I have been using MAP gas on the barrel nut in the head, heated it up for over three minutes and it will not budge. Can you say if I can use MAP gas down that chamber for an extended period without the heat causing any damage..

As a possible solution I am getting ready to use an impact gun on a low setting and gradually increase force to try to turn them off , comment..

John..

[Eagledriver]

I sprayed penetrating oil on mine and let it soak overnight. Then just broke them loose. Some were very stubborn but eventually they broke lose. You should be replacing all the bottom studs, so if one breaks you don't really care that much (unless it breaks at the case). I think an impact gun is a good idea.

-Andy

[dkirk]

Hard to believe that I did that engine top-end 3 years ago. Last summer I put a little over 5000 miles on my 911 using Mobil 1, 15W-50 oil. Total quantity of makeup oil added was exactly 2 quarts, indicating consumption is a little less than 1/2 quart per 1000 miles. According to what I've heard, this is about as good as it gets for a 911 engine.

The cylinder head reconditioning with new valves, guides, and stem seals really eliminated the high oil consumption that was experienced prior to the top-end overhaul. Obviously the Alusil cylinders and piston rings are still sealing and functioning properly. At 127,000 total miles on the car, I feel confident that it will run for many more miles without any major intervention being required.

[aquazulu2]

Originally Posted by dkirk

Hard to believe that I did that engine top-end 3 years ago. Last summer I put a little over 5000 miles on my 911 using Mobil 1, 15W-50 oil. Total quantity of makeup oil added was exactly 2 quarts, indicating consumption is a little less than 1/2 quart per 1000 miles. According to what I've heard, this is about as good as it gets for a 911 engine.

The cylinder head reconditioning with new valves, guides, and stem seals really eliminated the high oil consumption that was experienced prior to the top-end overhaul. Obviously the Alusil cylinders and piston rings are still sealing and functioning properly. At 127,000 total miles on the car, I feel confident that it will run for many more miles without any major intervention being required.

Dave, Thanks for allowing me to use your history to point to problem and get some solutions. Good to hear that your 911 is still working well with the factory originals. The same gentlemen with the Valve Lash adjusting tool correct?..

I too would like to keep the original units. How much disruption to their set-up in order to change the valve-guides and seals I am still investigating, but it seem I will have to separate the piston and sleeve in order to change the valve guides.
If needed, the heads up on marking the orientation of the rings is helpful.

With help from folks who have blazed these trail before us, a lot of costly mistakes are avoided, and new ways to work learned..

I have just been practicing on one head bolt nut removal, I still have to back-up to Camshaft Timing chain and Camshaft removing. Have to purchase PP tool 9191..

Thank again folks for the help.

John

[aquazulu2]

Originally Posted by Eagledriver

I sprayed penetrating oil on mine and let it soak overnight. Then just broke them loose. Some were very stubborn but eventually they broke lose. You should be replacing all the bottom studs, so if one breaks you don't really care that much (unless it breaks at the case). I think an impact gun is a good idea.

-Andy

Andy, I had the bolts soaking in PB blaster close to a week now, after my difficulties with the exhaust bolts I expect I am a little hesitant as to how much force I place on them. I plan the use the jarring effect of the impact hammer tomorrow.. I will do all my experimenting on the lower row, since they are the units that will need replacing.

Thanks for the points, they are really appreciated.

John

[dkirk]

John,

I'm the lash tool guy. When I performed my top-end overhaul, all cylinders were removed from the case but pistons were left on the rods. Had to do this as all 16 hold-down studs were replaced just for piece-of-mind. Here is the link to that rebuild post:

3.2 Top End Overhaul – A Success Story

The pistons were protected during head stud replacement by wrapping in shop cloths with rubber bands holding cloths in place. All rings were left on the pistons except the one top compression ring that was used to measure end gap clearance. Upon assembly, I staggered the top and second compression ring gaps by 180 degrees - oil ring gap location is about 90 degrees from second ring gap.

Remember that in normal engine operation the rings do rotate (very slowly) in their grooves - this is desirable. The gaps never maintain their 180 degree placement as rings rotate at different rates...gaps will align and mis-align several times over many millions of cycles. With all components in proper specification, this action will not cause an engine to burn oil nor have low compression readings. Care and cleanliness in the reassembly goes a long way to having a reliable engine that doesn't burn oil.

I've worked on lots of engines in my day, but the 911 engine was truly the jewel-in-the-crown. Take your time on the rebuild, follow the shop manual, and enjoy every aspect of working on this beautiful machinery.