993 Engine Rebuild Questions

[aneckas]

Both a friend and I have spent the prerequisite hours searching the manuals and forums but cannot find answer for the following questions. Any insight would be greatly appreciated (and where the information can be found!).

I have fairly extensive engine rebuild experience (mostly Audis). Much to my surprise, the Benltley manuals seem to be more informative than the factory Porsche manuals.

Which way do the connecting rods get oriented? I understand that they will opposite from right bank to left but cannot find any reference to which way to start. If I use my Audi manuals as a guide, it looks like I should orient the tabs recesses downward on all cylinders. Can anyone tell me if this is correct?

What is the piston ring end gap tolerance? I have seen the DIY that states to check the manual but, again, I (and a friend) could not find where it was called out. I am in the "rule of thumb" range of 0.004 (inch) for every 1 inch of bore diameter.

Lastly (at least for tonight), is there end gap orientation for assembly? One of the diagram on 13-18 of Vol 1 General Engine shows an exploded view with the compression rings oriented 180 degrees away from each other (on either side of the wrist pin) and the oil ring 90 degrees from that (aligned along a piston skirt, intake side). Another diagram on 13-23 shows the ring gaps stacked almost on top of each other.

Any help / experience would be greatly appreciated.

[e3photo]

I have an engine I am presently taking apart for a winter build project, so I am curious as to the answers.


Cheers,
Emerald

[Mike J]

The book "How to rebuild and modify Porsche 911 Engines 1964-1989" is usefull, since the engines are very similar to the 993 engines.

The orientation of the con rods does not matter, they are symmetrical. You can align all the tabs if you want if you want to be anal, but then which side of the engine are you aligning too? :-)

You should continue to use the shop manuals, and a 993 specification booklet, it has a lot of these measurements.

The ring gap orientation in a way does not matter, the rings will end up rotating anyways. I like to orient the top two compression rings 180 degress from each other, not lined up with the wrist pin, then the oil ring is oriented so the gap is facing the top of the piston, hopefully 180 degrees again, so it minimized the amount of oil leaving past the piston when the engine is shut off.

The piston ring gap should be specified with the new rings if you have bought them, but the general rule for earlier 911 engines is around +0.15 to 0.45mm. My notes indicate that the 993 engine has a ring gap of 0.075 - 0.107mm, and 0.20 is worn out, which is tighter than the older engines. Do not take this as gospel, you are responsible for your own determination of what to measure, and how!

BTW, check out my web site www.pcarworkshop.com, I have my engine rebuilding thread there...you should know all of what I am showing, but you never know! :-)

You should also visit www.pelicanparts.com, and go onto the engine rebuilding forum...much more technical than here, and there are lots of guys who have rebuilt 964 and 993 engines.

Best of luck!

Cheers,

Mike

[Stealth 993]

I'd listen to Mike, he rebuilt his own engine, & I was going to recommend this site, he just beat me to it.

[aneckas]

Thanks Mike for the response and for your site. I have been using your web site since before the engine came out; all the great hi-res pictures have been very helpful.

Thanks also for pointing me toward the other forums, I will check them out.

FWIIW, Audi is fairly serious about rod orientation. On the engines I have rebuilt (of inline five cylinder variety) the tabs end up on the outside of the circle that the crank forms as the piston is traveling toward (the center) of the crank (post combustion). If I follow that philosophy, viewing from the pulley side of the engine, the right bank would have the tabs on the bottom, the left bank would have the tabs on top.

But then, I am more than likely over thinking it. I have never been accused of that. . .

Again, thanks for the quick response.
Alex

[aneckas]

Found another mystery. . .

One of my piston oil squirters (#4) appears to be higher than the rest. It also seems to have a _slightly_ smaller hole than the other five.

Links to pics:
http://home.comcast.net/~aneckas/temp/IMG_2365.JPG
http://home.comcast.net/~aneckas/temp/IMG_2367.JPG
http://home.comcast.net/~aneckas/temp/IMG_2368.JPG

How worried should I be??

Alex

[Mike J]

Ok, here is a shot from my engine:

http://www.pcarworkshop.com/index.ph...205_-_0017.JPG

Yours looks normal, although you are right, one is slightly higher.

Did you flush out the squirters, i.e. got them to squirt cleaner/solvent?

Cheers,

Mike

[aneckas]

Thanks for the quick response Mike, you must have sensed my unease.

The first thing that Reiner and I did after I noticed the discrepancy was to check your site. Five of my squirters look just like your picture. But #4. . . . not so much.

I didn’t crack the case. So no, I didn’t flush out the squirters. They are as I found them.

Alex

[Tango635]

I'm guessing those squirters are just an orifice nozzle that is pressed in? I overthink stuff too so i'd be a little worried. Does the nozzle move at all? You might want to post on Pelican or ask Steve Wierner at Rennsport.com.

[aneckas]

Thanks, I think I have it figured out.

The nozzle looked different than the other five. I decided to measure the depth of recess. It was 0.077 vs. 0.580 for the others. It took a wide punch and was able to push it down fairly easily. Something was clearly wrong, it needed to be removed.

I wasn’t able to drill it out. The head only spun under the drill bit. I was able to work a variety of picks on it and eventually get to the top out. Under that found and removed a small spring. I was then able to run a tap down into the oil squirters housing and pull that out. Inside the housing I found a ball.

It appears that the piston squirter came apart. There was some sort of failure and the “top” (jet) separated from the housing went missing.

This picture shows all the remaining parts:

http://home.comcast.net/~aneckas/tem...2379_crop1.jpg

(Quarter added for perspective.)

Thanks again to those that passed on advice.

Alex

[NineMeister]

From memory I think the ring gap figures are new 0.2mm with an upper wear limit of 0.8mm. Going back to my days of 3.2 Carrera engine rebuilds (which wore out rings for fun) we toleranced to a 0.6mm gap with a new ring in a used cylinder.

Keep in mind that we saw 3.2 engines coming apart with ring gaps measured in mm - some had even worn the top ring to a point - and they were still running fine when they drove in. The 993 engine has a much improved ring life incomparison, so if you are just looking to freshen up your motor and the bores are good, a simple deglaze with fine scotchbrite used in the honing directions of the bore and a new set of rings will usually be fine as long and expect to see a gap between 0.4-0.7mm.

[Bill Verburg]

As you've found the squirter is consists of a caged spring & ball arrangement.

factory says to drill 5mm to a depth of ~2mm to remove, heat surrounding area, clean w/ a 5 or 6mm finishing tap#3

use Loctitie 640 or 270 to bond in place, ball points toward bearing saddle, oversize are available(964.101.020.50), the originals were also peened every 120* which should also be done for replacements

[NineMeister]

Oh, as mentioned, gap orientation of 180-180-90 works fine, place the top ring gap at the bottom, second ring gap at the top and oil gaps at the sides of the bore.

[ReinerFink]

Alex -- I found this:

http://www.pcarworkshop.com/images/a...0097geolab.pdf

(MikeJ: I now owe you at least a case of whatever beverage you like best!)

This jives with your 33.5 mm measurement (since this is cylinder #4). I'll get one of the long spray jets comming your way, and we can tackle it when you are nice and rested from vacation, and have forgotten where everything goes :-)

-reiner

[aneckas]