tresamore

Long story kinda short. 87S4, Engines out due to a bad main bearing. The motor looks like its been running hot for a long time. PO couldn't figure it out (2nd hand info from dealer, he got it as a trade). I changed the rear t-stat seal (thanks to "rennhelp") solved the hot running. Was doing MM, rack and pan gasket & saw the bad main. So I'm going to check and repair anything necessary and regasket the whole shabang. Figured I'll re-ring while its all apart. I've read a few too many "broken ring/destroyed block" threads lately, and seeing as its been a hot runner for so long I figured I'll change them. The bores have a few light scratches, nothing major. Pistons are still in the cylinders, I don't want to take them out until I know whats up. I'm reading a few threads mentioning ring changes, but none w/ solid details about honing or anything else. I found the following thread from last year <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=14;t=001113#000000" target="_blank">Rennlist honing</a>. I just want to know what the proper procedure is. I've built a few motors in my time, but this ones got me a little apprehensive . My previous experience tells me that the rings need a honed surface to set up the proper seating or they'll never seal properly. I'm looking for solid answers on this one please, I DON'T want to spend alot of time and money to see a smoker when I'm done. Thanks once again <img border="0" alt="[byebye]" title="" src="graemlins/wave.gif" /> .

Erik - Denmark

Tresamore,
Regarding the honing, see the Shop Manual pages 13-27 to 13-30, here you have all the needed info.

You need a good ring spanner for installing the pistons without damaging the rings - See page 13-3
Good luck with your project
<img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />

tresamore

Thanks again Erik,
I didn't even think it would be covered in the manual, so I didn't look <img border="0" alt="[sleep]" title="" src="graemlins/sleep.gif" /> .
Randy

Mike LaBranche

The boring process described in the manuals is very extensive and should probably be left to resizing the bore. Depending on the miles, your bores should be just fine. Don't be tempted to run one of those 'beaded-bore-cleanup' tools on the end of a drill. It will tear up the delicate layer of silicone on the surface of the bore. It's too bad you don't have a recent compression/leak down test to determine if your rings are really tired. And... if you pull the pistons and see the skirts shiny/scuffed, you're looking at replacing or recoating them which is big bucks. I'd either run the engine the way it is (with fresh main/rod bearings) or at most, uncap the rod, push the piston up, re-ring it, oil it, push it back in. Use fresh rod nuts.

Just be careful before you decide to bore it and gather all the facts available here in the archives. Many, many discussions about this issue.

tresamore

Thanks Mike,
The miles are 106K, The motor ran fine. I have no comp/leakdown data. I just figured while the motor is completely apart, I 'd change the rings. How does putting new rings on an unhoned surface work? How do the rings seat? I have NO intention of boring this out. I just want to freshen everything up while I'm in there.
Thanks,
Randy

Erik - Denmark

Tresamore and Mike,
Correct Mike, but what Treasamore properly need that only the last process where the grinder blade are replaced by felt blade and wetted with Sunnen Silicium mixture.
I have not done it myself, but have seen it done on my cylinders 1,2,3,5,6,7 when Tailacker Stuttgart bored my cylinders 4 and 8 and installed new piston rings on the remaining pistons
PS: Tailacker is the company in Germany doing renovating of engine blocks for the Porsche factory
PSII: But I also agree with Mike don't change the rings if not needed - I just overhauled my engine (140.000 Km - 88.000 Miles) but I did not remove the pistons, and the engine is running wonderful <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

tresamore

The more I read the less I want to change the rings. I just don't feel very good that they've been running hot for a long time. Maybe I'm just chicken $h!#, but who can blame me. I still don't know the answer to changing them w/o honing the cylinders. Can new rings seal in an already ring seated cylinder?

Mike LaBranche

Maybe you're just running lean.

I'm sure Marc at Devek and others can comment on applying the last stages of honing to get the silicone out... I've not done it.

New rings will not seal to a an already run bore as _well_ as a fresh bore anymore than a tranny synchro will improve with fresh fluid. It will slow degradation... and fresh rings should seal better than 100k rings. You probably don't have any problems with a 100k block/piston/ring engine. I'd just do the main/rod bearings, valve seals, valve seats if they're tired or 'soggy' and button it up. Run it another 100k _then_ think about boring/stroking...

Erik - Denmark

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by tresamore:
<strong>:.........The motor looks like its been running hot for a long time. .....The bores have a few light scratches, nothing major. Pistons are still in the cylinders, I don't want to take them out until I know whats up. .</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Tresamore,
I understand your confusion, my advise will be:
- If you have longitudinal scratches that's most properly due to broken piston rings
- Remove the worst looking piston and check - Most properly #4 and #8 (The hottest)
- If the rings are broken, change all the rings and check the ring lanes carefully!
- Get the cylinders lightly honed and silizium-treated if you can find an expert in your area, if not, just change the rings
- Remember to get/use a good (narrow) ring spanner when installing the pistons, and take care - The rings are d... thin!
Good luck!

Erik - Denmark

Tresamore,
I just found an interesting article, 20 pages long, about alu- blocks, unfortunately that's in French, but Ok, then we can 'repeat what we learned in the school' - That will be good for us!
See: <a href="http://www.msi-motor-service.com/download/broschueren/alu_fr.pdf" target="_blank">http://www.msi-motor-service.com/download/broschueren/alu_fr.pdf</a>
I hope this can help you <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

tresamore

Thanks Erik and Mike,
I would say the scratches look like normal wear and tear. The PO didn't maintain the car very well so I'm sure its from some debris working its way into the induction system through a bad filter and or vac leaks. I pressure washed all the gunk off everything last night. I going to do an inspection of everything tonight and see where I'm at. Erik thanks for the link! I'll see what I can do about a translation. Once again, I appreciate the help you've both given me on this.
Randy

Abby Normal

read this....

<a href="http://waw.wardsauto.com/ar/auto_boring_trutheverybodys_ideas/" target="_blank">http://waw.wardsauto.com/ar/auto_boring_trutheverybodys_ideas/</a>

tresamore

I found this thread on the Pelican Parts forum. It was written by Wayne. It relates to 911's and mentions Nikasil and Alusil. Knowing they're Alusil, I'm going to leave the pistons in the bores and reassemble my motor and drive it! Abby, thanks, that was a good read. I might be a Metallurgist after this is done! Thanks guys! <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />
Pelican:
"Nikasil vs Alusil Cylinders - In 1973 Porsche introduced a new type of cylinder used on the 911 2.7 Carrera RS. Engineered by German manufacturer Mahle, Nikasil cylinders are manufactured out of a dense, aluminum alloy that is centrifugally cast in a mold. The cylinder bore is then electroplated with a very thin layer of nickel-silicon carbide. Originally designed and used on the venerable 1971 917, these cylinders provide several unique advantages over the older-style ones. The primary advantage is that the micro-thin layer is extremely durable, and allows for thinner cylinder wall thickness. As a result, the piston bores can be enlarged without changing the original cylinder head stud bolt pattern. In addition, the reduced friction along the cylinder walls combined with the surface properties of the nickel-silicon coating creates a tighter seal between the piston rings and cylinder wall. The result is a slight increase in overall horsepower, due to the increased efficiency. These Nikasil cylinders are the most durable of any of the production cylinders and are highly sought after for engine rebuilds. These cylinders can be retrofitted to the earlier cars, however, you will need to install the updated piston squirters in your early case (1970 and earlier) if it doesn’t already have them. The piston squirters lower the piston crown temperatures so that you can run the close clearances used by Nikasil or Alusil pistons and cylinders. It’s also important to note that Mahle makes replacement Nikasil pistons and cylinders for 2.2 liter and 2.4 liter engines.

In 1974, Porsche introduced the Alusil cylinders, manufactured by Kolbenschmidt. The Alusil cylinders were primarily used as a less-expensive alternative to the Nikasil cylinders. These cylinders are manufactured out of a special 390 eutectic aluminum silicon alloy, and are used with a special iron-plated, ferrocoat piston. Like the Nikasil cylinders, they have a special coating on inside bore. This coating is electrically etched to leave a microscopic layer of silicon particles exposed on the cylinder wall. The iron-plated piston and the silicon cylinder walls operated together to create a durable combination. In addition, the Alusil cylinders have the same thin-wall construction of the Nikasil cylinders, meaning that they too can maintain the same head-stud spacing pattern.
So what are the main differences between all of the available pistons and cylinders? The early biral cylinders can be honed and reused just like other cast-iron cylinders on non-Porsche cars (Figure 3-17). Starting in 1974, Porsche mixed and matched the Alusil and Nikasil sets, so it’s really the luck of the draw as to which set you have in your car. For the most part, Porsche used mostly Alusil in the 2.7L and 3.0L engines because of the reduced cost of production. The Alusil cylinders, unfortunately, cannot be honed. The honing process destroys the etched layer, and renders them useless. In fact, a general rule of thumb is that the Alusil cylinders are a one-time-use product, and should not be used again if the engine is rebuilt.

Alusil cylinders cannot be reliably re-ringed. This indeed is a common misconception in some Porsche circles. There are no replacement rings available that are specifically designed for the Alusil cylinders. Of course, throwing out your current pistons and cylinders leads to the large expense of new ones, so a lot of people reuse them anyway. In some cases, the new set of rings seat fine, and they indeed can be reused successfully. However, you cannot hone these cylinders, nor predict whether the rings will indeed seat properly. The correct action to take is to purchase new pistons and cylinders, otherwise you may be tearing down your engine again in less than a mere 1000 miles. These Alusil cylinders typically have a ‘KS’ Kolbenschmidt logo cast into their base, although for a time, Mahle also made Alusil cylinders. The coating on the Alusil cylinders is non-magnetic, so you should be able to tell the difference between Alusil and Nikasil cylinders with a simple refrigerator magnet. The Nikasil coating will be ever so slightly magnetic when you place a magnet next to it.

If you are tearing apart your engine for reasons other than worn out rings or valve guides, then you might opt to reuse your Alusil cylinders. This would be the case, for example, if you were tearing down your engine to replace broken or pulled head studs on an low-mileage engine. If this is the case, I would recommend that you take your pistons and cylinders off of the engine, put them high up on a shelf, and don’t touch them until you are ready to reassemble. Don’t pull the pistons out of the cylinders and don’t dislodge or disturb the rings. Of course, you are taking a risk here that you will have worn rings in the near future. However, if your engine is a 3.0L, with 100K on the odometer, then there is a good chance that you can get 100,000 additional miles or more out of your set of rings, cylinders and pistons. I don’t necessarily recommend playing the odds like this, but if you’re rebuilding a good running engine with excellent leak-down numbers for the purpose of replacing head studs or some other non-wear problem, then it might be a good bet.

The Nikasil cylinders can be honed and reused. They typically have a ‘MAHLE’ stamp on the lower side of the cylinder. The nickel-carbide surface needs to be lightly honed with a special silica impregnated tool, or what is commonly known as a grape or flex hone. The surface properties are too hard for normal tool steel honing machines. You should only have an expert familiar with the Nikasil cylinders perform the honing process".

Fastest928

After building 390 based egines and working with one of the Reynolds developers of the 390 some years ago, I disagree with the usage of new rings on old bores. And from exp have found that I can seat a ring in a bore in about 2 minutes by hand and they will have a less than 1.5 - 2% leakdown prior to running. If the bore is sized correctly and not worn.

Advice - use new rings.

Marc
DEVEK

tresamore

Thanks for the input Marc. I'm leaning towards putting it back together as it sits. I'm glad I left the pistons in the holes when I did my disassembly. From what I've been able to find and read, at 106k I should have plenty of life left in this one. Plus it sits in the winter months and shares the summer driving with another toy. Hell, I don't even drive them in the rain. I only took it out to replace the main bearings and re gasket it all. At first, I figured I'd be a good boy and go nuts on the motor. Well now I am nuts! <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> Now that I'm back on earth and have looked at my checkbook balance. I'm going to freshen up the bearings and gaskets. Besides, I'm going to need all my extra cash to feed this thing premium fuel this summer <img border="0" alt="[cherrsagai]" title="" src="graemlins/drink.gif" /> <img border="0" alt="[crying]" title="" src="graemlins/crying.gif" /> . Thanks