Nicholbry

Maybe I'm not looking in the right place in my WSM. I find a page or two regarding the pistons and rings, but can't locate the answers to these specific questions so I'm just going to ask.

Re: '87-'88 short block to be used in my '90 S4

I have located (but not taken delivery yet) a replacement short block for my '90 S4. It is an '87-'88 (not certain just yet) with approximately 90Kmi. It will come with a set of new piston rings and rod nuts by the dealer to insure good compression when I am through. Although I've done some reading elsewhere on the subject of pistons and rings, I've not answered a few fundamental questions. Can you guys help?

1. When installing piston rings and test fitting them in the cylinders before fitting them onto the pistons, what is the factory tolerance of end gap for this early S4 engine?

2. How far down the cylinder is the best location to make this measurement? Should it be made in multiple locals within the cylinder?

3. Is it really necessary to use the special tool for removing/installing the rings since most of the videos I've seen on the subject simply show the mechanic feeding one end into the piston groove by hand and working it around rather efficiently?

4. If a special tool (spanner) is necessary, where might I find one reasonably as this will be a one time event for me (I hope)?

5. If I understand correctly, all the ring end gaps should not line up and be worked around the piston in such a manner that the end gaps oppose each other. However, is it necessary that the gaps be located in a specific place on the pistons or can it be somewhat arbitrary?

6. When I remove the pistons I will try to clean them up as best I can. Any recommendations on the best chemical or process for cleaning them? Will it be necessary to disassemble the piston from the rod to do this? I'm a little concerned about doing that as I don't know how the rod and piston are married.

7. I realize oil is not desired in the upper portion of the cylinders where combustion takes place. Therefore, how should I go about lubricating the pistons for reassembly? Should I oil them up good and just wipe out the excess after assembly from the upper cylinder walls or am I worrying needlessly about this as I'm just not sure how vital this is?

8. Is there a safe and effective process that you can do at home to lightly hone the cylinders, or at least clean them up a bit for a freshened surface to mate the rings to? I understand some have used the Silicon solution (AN-30 or something like that) with a felt pad, a drill, and special attachment. I'm assuming this would be a very brief activity, but unsure if this is recommended and for how long a duration to hone each cylinder. Someone suggested using sand paper instead (just joking).....seriously though.

9. Please include any additional tips or information that you feel would be useful with this project.

Thank you for helping; you guys are great.

928Shane

Nicholas,
Can't help with everything,I am sure you'll get more info from others. Heres my 2 cents.
#2-Measurement should be taken at the smallest point in the bore.Generally this will be closer to the bottom(2/3 way down) . If you have access to a bore gauge you can determine wher the narrowest place is.Extremely important is to make sure the ring is positioned evenly in the bore ,If it is tilted you will not get correct reading.Once the ring is in the bore you can use a piston slid into the bore upside down to staighten it out(most be a flat top ,or at least have a flat land around the top).
#3 Not neccassary but if you haven't put rings on before it may be worth the investment(you could always sell when done,or rent or borrow-check local auto parts stores for rental)It is not hard to break a ring and the are quite sharp. It would be a good idea to practice either with the old rings and pistons or with any ring and piston to get a feel for it(breaking a ring on a sunday sucks and some places only have them in sets).
#4 answer in #3
#5 I have always clocked my rings by using thirds(this is how i have done it and if anyone has a better way I am all ears)On the oil ring which generaly are a three peice set-up i put the top and bottom rings at least an inch off center of the middle ring and have the middle ring so the gap is facing the outside of the block. If you are standing at the side of the block looking down at it this would be 6 o'clock,then the top and middle rings would go at 10 and 2 .
#6 You will want to make sure to clean out the ring lands on the piston ,again you can pruchace a ring land scraper or you can use a peice of piston ring by preaking an old ring and using it.Be careful not to gouge the ring lands,just clean out the carbon and residue. yoe should not have to remove the pistons from the rods. Keep everything in order . I would use a regular parts cleaner to clean the pistons. make sure the tops are free of carbon build up also.
Thats about all I got,I have never been inside a porsche engine so I can't help on the other specifics. Just remember you can't be too clean when assembling any engine. Good luck.

BC

Berryman's for the piston cleaning. I let them soak.

I suppose if you wanted to do the cylinder re-lap at home you could, but I have no idea how. Possibly try and find a place that is used to alusil Mercedes blocks.

#7 differs for whom you speak to, but I have always oiled the pistons and rings to make sure nothing sticks on startup.

Nicholbry

This is "good stuff" guys, thanks many times over. Does anybody have the factory tolerance +/- for the end gap clearances of the piston rings?

mark kibort

dont touch the bores if they look good with no scratches.
ring gap is aroud .0017, but ill check that for you. probably just fine if you are using stock rings (measure a little below the top of the cylinders (about 1" down)
lube up pistons by dipping them in oil . I usually, use a mix ot oil and assembly lub and spread all over the cylinder walls. any residual oil will be blown out when it first starts up.
rings gaps are 120degrees off set. I would have someone else install them, if you havent done them before. You dont want to crack any of them, or not properly set up the oil ring

scratch the cylinder number on the top of the piston. dont forget the arrow pointing toward the front of the engine.

There you go, you are all set

mk

BC

PLEASE don't use assembly lube in the oil when you coat the pistons and rings.

mark kibort

why not? the redline assembly lube is pretty thin.

Mk

BC

I don't mean for you Mark. You are going to think and do exactly as you already do, and nobody will every change your mind even on the most simple issues, no matter how logical and factual the offending argument is.

I was speaking to the OP Nicholbry - please do not use Assembly lube on your piston rings.

Nicholbry

Thanks guys for the input. It would be great if you find the time to get the end gap clearance range. I tried looking again this morning on the CD WSM, but no prize. I'm sure it's here somewhere, but can't find it.

I'm curious, is it common to have to adjust the end gap on factory piston rings or are they good straight out of the box usually? I'm talking Porsche parts here, not after market and not for race applications (normally aspirated). Remember, we're talking about an engine with 90K mi. or so.

If adjustment has to be made, what is the tool called that lightly grinds down the end gap? I've seen it in use, but don't know what it's called when looking for one to purchase.

Has anybody had success doing the honing with the aforementioned equipment?

These replies are awesome! Thanks for the no-nonsense, direct answers.

mark kibort

Hey, what do you mean!?

Give me two things that i do that is against logic or fact. (even on a simple issue)

I live by logic and fact. why do you think my cars have run as well as they do? Luck??

what i asked was a simple question. I was told by an engine builder that dipping the pistons in oil, and then a light coating of assembly lube on the sides is ok and a mixture of oil in the bores. Hey, when i started i had no idea how to build up an engine. I learned by guys that were sucessful in doing them. Guys like Greg brown had some great "logic" on doing things that i didnt do before. Devek had some cool ways of doing things, as well as many other "nobodies". The list has given me TONS of ways of doing things. However, its funny, when i mention of the successes of the ways I do things, i get illogical arguments from many, including you with your "dont use asembly lube on the rings". If there is a reason not to, then lets hear it. if it is logical not to, then i probably wouldnt do it.

well?

mk

mark kibort

the bores are not like chevy where you want the hashing marks that hold the oil, the 928 bores can be perfectly fine if they are smooth and a mat looking finish. The rings are often fine, right out of the box, if there is not an overbore involved.


mk

Vilhuer

See CD1 Tech spec books on Jim Morehouse extra document CD's if you have them. Should be in there. In case you don't have these CD's get them ASAP.

On my case 968 rings were little on loose side already but not over the limit yet. None needed any adjustment at all.

Cylinder walls must be absolutely smooth without any honing marks at all. Grayer non shining color the better.

BC

Its common sense when you understand what needs to happen with piston rings and their operation against the cylinder walls.

But I promised I would play through on this, and give the proper advice without getting into it with you. I have failed:

From Lawnmower engines.....
http://www.oilstick.com/chute/joe/paper1.html

To "Real Engines"
http://www.nabble.com/Assembly-lube-t3717431.html

Now before I continue can everybody please apply some actual common sense here just incase you actually believed mark. Most assembly lube is an anti-friction and moly-based (nearly) grease. Piston rings are a wear-in item that need to seat properly against the cylinder wall. When they do not seat properly, you do not get proper ring seal, and your performance suffers.


Anyway, from total seal:
http://www.racetep.com/totalsealframe.html

"A light coat of oil"

http://www.gmhightechperformance.com.../rod_prep.html
http://www.mustangandfords.com/techa...hetic_oil.html


Are we done?

mark kibort

Thanks for the post. Really, as I am no expert in the area. I just used what logic i have and taken the advice from engine builders, and those that have built 928s.

And no, we are not done. (and you were making comments of my bedside manners in our last discussion??? gezzz)

I think for your response to have the correct information, you would need to adjust some things for our 928 engines which have quite different characteristics.

1. Redline assembly lube doesnt have moly.
2. our 928 bores couldnt be MORE different than Chevy or iron bore engines, for which that information was in reference to.
3. There is not the charateristic "seating" that the rings go through like on a chevy block for example.
4. Honing (cross hatch honing in the traditional sense) with a 928 bore, for example, will destroy itself before it even starts. Honing is using to catch small volumes of oil for ring lubrication. the rings seat and wear this area down to fit. 928s do not break in this way.

By the way, i used the mix of assembly lube (redline) and oil on the cylinders and on the pistons skirts. I was avoiding the ring area, basically like your 1st reference from the lawn mower guide

mk

Vilhuer

Ring do break in on 928 engines too. I think they will wear in very fast compared to more normal setup. Using stuff that prevent fast wear in might be very bad idea.

IIRR factory says to use normal motor oil on practically everywhere on engine rebuild. For some reason they didn't see the need to use special assembly fluids.