Correct ring end gap

[natman]

Hello,
I'm currently rebuilding the top end on my 79 911Sc with 9.5 Forged JE Pistons with original German rings. I'm coming up with an end gap of .011 (with reconditioned cylinders) which is on the high end of the Porsche specs. JE recommends a gap of around .004 per one inch of bore which comes out to .015 with there rings.
The guys at EBS Racing say go with the Porsche specs. I guess I'm worried if the gap is to small at .011 and if they close up, I'll be doing another top end. On the other hand, I don't want to lose compression by increasing the gap more than required.
I'm running the stock CIS injection with the Web Camshaft 20-21 grind.
If you have any comments on this subject, please let me know.
Steve

[cnavarro]

Ignore the specs on the JE insert. You don't want to know how much grief those specs have caused over the years. Ideally, if using a Goetze ring (factory), then you should run the factory recommended ring gaps. In some cases, the rings out of the box have a larger gap than the Porsche spec, so there's nothing you can do, but when they are nice and tight (or even better file-to-fit), you can run them as the factory intended.

If you want to convince yourself about the ring gap, put the cylinders in the freezer and then pop in the ring. You'll see that even cold, you'll probably have .005-.006" ring end gap. Likewise, when hot, you can drive a bus through the ring gap (not really, but you get the picture).

Even more confusing, some rings actually expand more than the Goetze rings so we've found that different ring materials sometimes can run tighter or looser ring gaps than the OE rings. At the end of the day, you can be secure with EBS's recommendation.

[kenikh]

OK, here's a really DUMB question...how come no one has oversize rings for remachined piston grooves? I seem to recall Detroit iron does this effectively. It sure would make life a lot easier going a few thou over on freshened ring lands...

[Eagledriver]

I have oversized rings on my engine. Had to order them through EBS. They had them made custom by Total Seal.

-Andy

[natman]

Charles,
Thanks for the info on the end gaps. Coming from someone that makes the "Nickies" means quite a bit.
JE was saying that there pistons (or at least the set that I have) has less silicone in the aluminum which makes it a little less stable then factory. Thats there reasoning for the slightly larger gap.
Another question for you if you don't mind. With new cams the break-in recommendation is to run the engine no less than 2000RPM for twenty minutes. With the reconditioned cylinders (Nikasil) they recommend an idle condition for the first 15 minutes. I don't think the cams will break-in correctly at such a low RPM.
Any comments?
Thanks again,
Steve Natale

[cnavarro]

You won't have any problem with breaking-in the reconditioned cylinders if you do the prescribed cam break-in process. I've never heard anyone recommend letting the engine idle for the first 15 minutes. Yes, cam break-in is important, but as soon as you get that done, you want to get a good load on the motor to get the rings to seat up and you don't want an overly rich condition or no load that would lead to glazing over of the cylinders/rings resulting in poor ring seal. Your best window to break in the rings properly is in the first 45 minutes.

Good results with seating of the rings also relies heavily in how well everything is cleaned and prepped - I recommend after a precursury cleaning, that denatured alcohol and chemwipes are used to wipe down the bores until the chemwipes come out as clean as they went in. You'd be suprised what will come off of what is considered a 'clean' cylinder with the above process. The nikasil dust/honing oil mix is very pervasive and is some very nasty stuff. Then a good oiling of the bores and rings will ensure you don't have excess scuffing and streaking of the bores that can occur with rings and nikasil.

[mca]

Charles,

I just got my parts back from EBS - JE 9.5 pistons and they honed the cylinders b/c they said they were in spec.

However, my cylinder ring grooves are nasty nasty nasty. I am using break cleaner and a plastic spatula to clean them out (as well as gasket remover) but it isn't as effective as I had hoped. Do you have any suggestions for me?

Also, how could the cylinders be determined to be in spec if the grooves are all crudded up? Just curious.

Thanks,
Craig

[cnavarro]

Craig,

That would be a question to ask EBS how they determined they were in spec. To be honest, I've only had a very few sets of pistons and cylinders come back for eval and the pistons usually look like new and are easy enough to measure without much, if any, cleaning. And usually, if it's something like a recondition job - say a set of 4-cam piston and cylinders, I ask the customer to check everything first before sending to me.

If anyone has any suggestions on cleaning the pistons, don't be shy. I have a can of the old non-epa friendly parts cleaner in the gallon can with a basket in it that has to be a million years old. Just leave in overnight and the parts come out easy to clean with nothing more than a toothbrush.

[mca]

The pistons are brand new ... they are perfectly clean.

The ring on top of the cylinder is the problem area. I assume that I can leave these soaking overnight as well?

[cnavarro]

Oh, I didn't realize you were talking about the CE/sealing ring/gasket groove on the top of the cylinder. I thought you were referring to the ring lands on the pistons. I've never had to do what you're doing. I would venture to say that there's no real easy way to clean those. Lots of patience is all I can offer to you. You have the right idea to use something plastic as to not scratch or damage the cylinder. Maybe someone with more experience re-using Mahle cylinders can chime in.

[BoxxerSix]

DYI trick for those doing their own rebuilds.......to aid in cleaning ring grooves on pistons or fire rings in cylinder tops go pick up some permatex gasket remover spray. Comes in a blue can. Soak any carbon deposits for a few minutes, then flush with brake clean. Repeat if necessary.

The gasket remover spray has some effect on carbon, but does a neat job at really softening the hard stuff up.

WARNING....this stuff will cause a painful sting if even a pinsize drop hits your skin so wear long sleeves and goggles!!!!!!!!!!!! It's not going to leave any permanent burn on your skin but it sure as hell hurts. But if you get it in your eyes is can do damage so just take precautions where needed.

[DSPTurtle]

I had good luck using a bottle of techron poured into a dish with a toothbrush. Then followed up with carb cleaner and a little brake cleaner for good measure.
As for the portion of the cylinder at the top where the rings do not come all the way up... I used a green scrubbie, simple green, dish soap, elbow grease, brake cleaner, more elbow grease and another green scrubbie. Took awhile but once you get it started it tends to come off much more quickly.

[ChrisBennet]

Whatever you do, be sure to CC your motor. The last 2 sets of "9.5:1" JE pistons I recieved from EBS CC'd out to 10.5:1. When you go away from stock, you need to check everything. EBS is great but they don't/can't check everything JE sends them.
-Chris

[notmytarga]

Would it be a mistake to use glass beads to blast the piston ring lands and cylinders? - except the nikasil surface of course.

Also - is it recommended to do ring gap checks in each ring/cylinder combination? or can you use one ring to check each cylinder? Are the rings going to vary at all. Obviously it is best to check each mating set to optimize.

What 'system' do you piston/cylinder gurus use to run through all the preassembly checks -

Match piston/cylinder bore - clearance
check piston ring side gap
check cylinder - ring gap

What am I missing? I'm struggling with confidently moving forward with reusing my pistons and cylinders. Should I polish my domes like I did my wheels?

[ChrisBennet]

Originally Posted by notmytarga

Would it be a mistake to use glass beads to blast the piston ring lands and cylinders? - except the nikasil surface of course.

I wouldn't want glass beads anywhere near my motor.
I clean the ring lands out a piece of old ring.
I scrub the carbon off with a wire wheel. I see no benefit and getting them super clean.
I scrub the cylinder surface (Nikasil) with some soapy water and red (?) scotch brite pad and then clean them in my parts washer which has something in it (lanolin) that leaves a light coating.
Check the ring/grove clearance on every piston. The grooves tend to get pounded out.

-Chris

[shbop]

Would it be a mistake to use glass beads to blast the piston ring lands and cylinders? - except the nikasil surface of course.

I recently set-up a cabinet for soda blasting. Worked well on the ring lands, and rinsed off completely with warm soapy water.