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Nux Nux is offline
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Re-ring or not on top-end rebuild?

I'm getting ready for re-assembly of my 3.2SS top-end rebuild due to several head-to-cylinder leaks.

The heads are currently at the machine shop for new guides, valves etc. I'll be changing lower Dilavar to steel. Cylinders (Nikasil) are all looking good and I will not be honing those.

Now, pistons: There are no broken rings. Piston side clearance to cylinder is within spec, and top compression ring is within wear limit (0.40 - max is 0.8). Oil ring is also within wear limit.



What do you guys normally do?
Old 03-01-2018, 01:00 AM
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IMUO, (in my unprofessional opinion), if you have removed the rings from the pistons, you may as well go with new rings. Reason being your old rings will have to re-seat any way....

How many miles on the old rings?

FWIW, I have reused rings in the past with good luck , however those were not with Nicasil cylinders.
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Last edited by Trackrash; 03-01-2018 at 08:58 AM..
Old 03-01-2018, 08:55 AM
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The rings are back on the pistons (same as before).

No idea on the miles. Previous owner said 10.000 miles after rebuild. But I kinda doubt that.....
Old 03-01-2018, 09:24 AM
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It’s the ring lands on the aluminum pistons themselves that also wear and cause of loss in compression. As long as the steel ring end gap is in spec you’re ok to reuse in my book.
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Old 03-01-2018, 09:45 AM
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My concern is that there may not be enough roughness in the cylinders to allow the rings to re-seat. You may want to use Scotch Bright on the cylinders to allow the rings some bite.

Then again you might be ok just as is. Then again, worse case, those rings don't re-seat?

I should have mentioned in my previous post that when I re-used rings successfully, I had freshly honed the cylinders.
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Old 03-01-2018, 04:38 PM
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I would reuse the rings. In my experience, new rings have end gaps as big or bigger than used.

-Andy
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Old 03-01-2018, 07:44 PM
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Complete your measurement picture by checking ring land to ring clearance as per Porsche service manual.
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Old 03-01-2018, 07:54 PM
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Originally Posted by manbridge 74 View Post
Complete your measurement picture by checking ring land to ring clearance as per Porsche service manual.
I did, and they are within spec. I will re-use then. Thank you for your help once again.
Old 03-01-2018, 08:08 PM
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Be careful here. Rings wear too. Along with checking the lands for wear, don't forget to check the rings as well.

The ring faces shown wear. Best way to describe is, new they will have a sort of matt finish across the face and as they wear the finish will become more shiny. You car track the wear rate by engine time and how much of the ring face appears shiny. Different ring faces show this slightly different depending if the ring has a tapered face or barrel face.

End gaps typically change with age as well as the rings will generally loose their tension over time.

My advice is to fit new rings every time. A lot of the so called poor seating often is due to other issues not understood. These liners want to have a finished RA between 6 & 8 and can be less. More will accelerate the ring wear and cause just the issue you are afraid of. Best is to have the cylinders measured for size, the pistons measured and the clearances calculated and if everything is in spec, then lastly have the liner surfaces checked for its roughness.

If its lower than RA4, then you still have options, surface preparation, ring face material, ring tension, use of a napier 2nd etc.

Once you commit to re using used rings be prepared to commit to pulling the engine down again too if they don't seal. I think its easier to do it right the first time.
Old 03-01-2018, 08:58 PM
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Originally Posted by Neil Harvey View Post
Be careful here. Rings wear too. Along with checking the lands for wear, don't forget to check the rings as well.

The ring faces shown wear. Best way to describe is, new they will have a sort of matt finish across the face and as they wear the finish will become more shiny. You car track the wear rate by engine time and how much of the ring face appears shiny. Different ring faces show this slightly different depending if the ring has a tapered face or barrel face.

End gaps typically change with age as well as the rings will generally loose their tension over time.

My advice is to fit new rings every time. A lot of the so called poor seating often is due to other issues not understood. These liners want to have a finished RA between 6 & 8 and can be less. More will accelerate the ring wear and cause just the issue you are afraid of. Best is to have the cylinders measured for size, the pistons measured and the clearances calculated and if everything is in spec, then lastly have the liner surfaces checked for its roughness.

If its lower than RA4, then you still have options, surface preparation, ring face material, ring tension, use of a napier 2nd etc.

Once you commit to re using used rings be prepared to commit to pulling the engine down again too if they don't seal. I think its easier to do it right the first time.
I perfectly understand that. And I greatly appreciate your input. I have measured my rings, and everything is within spec according to Waynes book.

What I do not undertand perfectly is the term "re-seating of the rings". If I understand correctly, the "seating the the rings" is the ability of the rings to align 100% with the cylinder walls. So, I presume that these rings are already seated - und thus 100% aligned?

If the rings are within wear limit and I use the same rings on the same cylinders and pistons, do they then re-seat if they were 100% aligned before?

Why do we have a wear limit for rings, if they are not to be re-used?

And if I use new rings, should I then hone my Nikasil cylinders as well?

I'll admit the engine rebuilding knowledge is quite a jungle for me. Lots of different opinions on everything. I'm scientifically founded, so I really like an evidence based approach. However, I rarely find someone posting real evidence and hard facts. The easy way is always to buy new. But if it doesn't make a difference, then I would rather spend my money elsewhere. It's always cost-benefit in this world.
Old 03-01-2018, 10:37 PM
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There is so much myth and mis use of words in the engine building world.

I have not read Wayne's engine building book but years ago he did send me one. I think I re grifted it.

Taking nothing away from his opinions etc, but proper engine building cannot be done by reading a book.

I have several sayings I tell my folks each and every day. One is, "there are only two types of people in this business; those that see it wrong and can fix it and those that do not see it at all".

My over used one is, "Nothing will humble a man more than an engine or an angry wife".

There is no such thing as re seating rings. Rings do not need seating period!!!!!! This is one of the many mis understood "things" in engine building. What you are actually doing is removing the microscopic high spots off the cylinder walls after honing. The cross hatching will have high and low spots. You are lowering the high spots making the "valley's" not so deep. If you are removing ring face material, the cross hatching was far to course, using the wrong ring material and in more trouble. Remember with Nikasil, no chrome.

This is why washing the honed cylinders is so critical. You are removing all of the trash buried deep in the valleys of the cross hatch. It gets stuck in these valleys and embedded with the honing pressure, only to dislodge with the rings passing over it. There goes the "ring seating". Not really, but this trash gets embedded in the ring face, in the bearings etc, and causes all sorts of other issues.

This is typically done at 45 or less and is there to "hold" oil helping to lubricate the rings against the cylinder walls. Today, we have honing machines that can control the honing procedures way tighter than in years past, as most honing machines are now computer controlled. Cross hatch angles have changed, RA finishes have become a lot lower, ring faces and materials have changed as has oil viscosities.

To put this into perspective, we are now at surface finishes well below what was always considered, required.

To answer your question, you will not have to "re seat" the rings or re hone the cylinders as the high spots should have been removed already, if there were any in the first place. This is the reason to have the surface finished measured. It takes seconds to do each cylinder and any machine shop should have a profilometer.

If the ring faces show some wear but still some area where they have not worn, you have to make the determination to fit new or go with used. As long as the tension is still where it is required, end gaps are good, fitting new or reusing used should not be an issue. What's the difference? What's the gain? Fitting new is always the better option. You have more ring life.

If you do fit new rings use a Napier style 2nd ring.

Last edited by Neil Harvey; 03-02-2018 at 10:41 AM..
Old 03-02-2018, 10:36 AM
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I perfectly understand that. And I greatly appreciate your input. I have measured my rings, and everything is within spec according to Waynes book.

What I do not undertand perfectly is the term "re-seating of the rings". If I understand correctly, the "seating the the rings" is the ability of the rings to align 100% with the cylinder walls. So, I presume that these rings are already seated - und thus 100% aligned?

If the rings are within wear limit and I use the same rings on the same cylinders and pistons, do they then re-seat if they were 100% aligned before?

Why do we have a wear limit for rings, if they are not to be re-used?

And if I use new rings, should I then hone my Nikasil cylinders as well?

I'll admit the engine rebuilding knowledge is quite a jungle for me. Lots of different opinions on everything. I'm scientifically founded, so I really like an evidence based approach. However, I rarely find someone posting real evidence and hard facts. The easy way is always to buy new. But if it doesn't make a difference, then I would rather spend my money elsewhere. It's always cost-benefit in this world.
OK, since we are getting into the details. Sorry if "re-seating" isn't the official technical term.
As mentioned the roughness (RA) of the cylinder walls is one concern. A freshly honed cylinder will have relatively sharp ridges if viewed microscopicley. As the rings seat in the tops of those ridges will wear some and be somewhat flat at the top. The valleys will still be there to retain oil. The flat tops of the ridges will not continue wearing at the same rate once the seating or break in is complete. Some material will also be removed from the rings in this break in or seating, what ever you want to call it, process.
Now if the walls of the cylinders is very rough the rings will have more material removed in the seating process than one would like. If the cylinders are too smooth perhaps the rings will never wear enough to match perfectly with the cylinder walls.
There is one more variable the OP faces. He removed the rings from the pistons and cylinders.
Lets say that the rings had conformed to a certain position in a certain cylinder when it was first broken in. That particular cylinder was in spec but perhaps now it is not perfectly cylindrical. The ring that was in that cylinder took on the shape in that particular cylinder. If that ring was not moved, no problem. However can you be certain that all of those rings will perfectly match the cylinder walls in their new positions. Will they eventually wear in and perform adequately?
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Last edited by Trackrash; 03-06-2018 at 10:27 AM.. Reason: spellling
Old 03-02-2018, 11:18 AM
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ahhh see, now you make sense! I'm getting properly educated - love it!

Although we are still calculating the probability of the rings to match the cylinder walls - if the rings are re-installed in the same position as before. I find it unlikely, that the rings are not moving at all during many many engine cycles. But then again, I'm just guessing.

It does make sense to measure the cylinder surface, and act accordingly.

How often do you see a rebuild that need to be re-done because of rings not seating?
Old 03-02-2018, 12:28 PM
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This is all true.

The part you want to wear, is the ring.

As for the ring position, I guess that is true but the differences there are so small that gas pressure and ring tension hopefully over come this.

These engines suffer terrible "blow by" and crank case pressures by out of round, taper, high acceptable tolerance spec's on cylinder "roundness and taper".

These are not easy parts to manufacture and honing the nikasil is extremely difficult, holding concentricity etc on thin wall aluminum cylinders. Add in the factor that they are air cooled, you have all sorts of issues heading your way.

Also included, are the clearances these engines require if the pistons are made from 2618 or 4032. This is why Porsche have historically used wide faced rings, I think.

All points brought up here are valid.

I believe the builder has to decide what he feels more comfortable with. We have the luxury of knowledge, experience of past failure and success to draw upon.

What I would do, would be to fit new rings and go with the extended life. Just make sure you choose the right ring face material, back clearances etc and end gap. There is a common gap calculation to establish the "correct" end gap, but here too you need to select what your use is etc. These are the small things that make a huge difference. Go slow and gap the rings carefully. Once it's removed you cannot put the material back on. Continually check the end gaps for their "alignment". Once you have the gap you want, always check the rings by gently pushing the two ends together. If they do not butt evenly, get another ring and start again. Trust me, this is critical.

The devil is in the details.
Old 03-02-2018, 12:29 PM
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Rings do move. This is why today due to the very tight emissions laws, you see pins in the ring grooves stopping rings from moving and creating a path for oil to enter the combustion chambers.
Old 03-02-2018, 12:31 PM
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Did you figure-out why you were having so much trouble sealing the head/cylinders?
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Old 03-02-2018, 04:39 PM
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Did you figure-out why you were having so much trouble sealing the head/cylinders?
I'm not sure, but some of the head studs were only torqued hand tight(or at least it felt like that). Everything else seems to be fine. Also, I don't know why the previous builder chose Dilavar lower studs.

Last edited by Nux; 03-02-2018 at 11:24 PM..
Old 03-02-2018, 10:06 PM
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Quote:
Originally Posted by Neil Harvey View Post

These engines suffer terrible "blow by" and crank case pressures by out of round, taper, high acceptable tolerance spec's on cylinder "roundness and taper".
This was actually an argument used by a 911 engine builder in LA to use iron cylinders rather than aluminum
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Old 03-03-2018, 04:15 AM
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Originally Posted by lvporschepilot View Post
This was actually an argument used by a 911 engine builder in LA to use iron cylinders rather than aluminum
Whatever builder argued for iron cylinders over aluminum/nikasil doesn't know his stuff.

And it's great to have Neil on here. He's a wealth of knowledge and his responses are spot on.
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Old 03-05-2018, 08:19 PM
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The rings move. A LOT. I posted on here (maybe 930 forum) the ring gap positions after about 1-2 hrs running. For some reason I had to tear the engine down again. I think I was trying to cure an intermittent smoke issue, and changing parts out til it went away. The ring gaps were totally random. Altho I still feel compelled to line them up properly, I doubt it makes any difference.
As for honing, when I do a tear down and re-ring I always scotchbrite the cylinder - we are trying to remove glaze? Unless someone tells me this is not necessary either. I'm happy to take short cuts if they are proven to work (Neil?).
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Old 03-05-2018, 08:35 PM
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