Searching for reasons of Nikasil scoring and ring fretting - PHOTOS
 

Hey all, in my investigation of minor blowby and oil leaks (RMS leaked enough to kill clutch), I'm bummed to find a lot of scoring on my cylinders (3 of 6) and coinciding ring fretting on my 3.4 (3.2 based).

Reason for teardown was to fix all the leaks I endured the 1st time I freshened it up (used Yamabond 5 on the case - big mistake!). This was when I discovered all of this damage. Did not have any of this the 1st time I tore it down.

Engine is turbocharged at 1.4 max using 93 octane (7.5:1 CR), IC keeps temps manifold air temps no more than 10-15* over ambient.

I posed a question a long time ago about using TotalSeal conventional rings in Nikasil cylinders (98mm Mahle's) and my concerns. Thread: http://forums.pelicanparts.com/911-engine-rebuilding-forum/852347-long-term-effects-total-seal-conventional-rings-3-2-nikasil-cylinders.html

Was thinking this is detonation based, but started wondering if there is something I am overlooking??? :eek::confused:

The main and rod bearings are near flawless, and do not show signs of detonation that I've seen in the past on other motors. All rings were intact, no breakage, but I do see witness marks/rings nearing TDC, indicating to me at least, there was possible detonation.

I checked the ring gaps I remember, and they were right on from TotalSeal. Not sure if I mixed NA gap specs with boosted? Doubt I'd make that mistake, but don't see any notes on what I actually checked them at.

With that said, who does the most economical replating?

Take a lookey:

http://forums.pelicanparts.com/uploa...1487953289.jpg
http://forums.pelicanparts.com/uploa...1487953289.jpg
http://forums.pelicanparts.com/uploa...1487953289.jpg

I assume you gapped and deburred the rings for 3.4 build, was the gap tight or loose with the feeler?

Can't tell but how was the condition of the oil scrapper ring, mine were all clogged with debris on tear down. Not sure how mine were properly lubricating.

I checked the gaps, and they were in spec. Not sure what the exact gap was off the top of my head.

Oil control rings look fine. No junk in them.

I have a set of Total Seal rings sitting in the box ready to go in my cylinders once heads are done. I am very interested in what the cause of this turns out to be.
David

Probably detonation, but wasn't 100%.

Fretting on the rings is what raised my eyebrows! http://forums.pelicanparts.com/support/smileys/puke.gifhttp://forums.pelicanparts.com/suppo...leys/loki5.gif

Did you measure the width of the ring groove in the piston and the tickness of the ring?

Did you measure the ring tension on the oil control ring?

It would be interesting to know if you have the numbers

I haven't measured them, but they float nicely in the lands.

The rings in the cylinder top I have seen on high milage NA engines.

Oh really? They weren't there 4 years ago when I tore it down the 1st time.

They'll don't catch your nail and cannot be felt. Just simply witness marks.

Apologies to the OP for interruption --- chris_seven, I've been trying to contact you via PM but haven't heard back, could you pm me when you're able? Thanks, back to regular programming.

On the jugs, it is the vertical scoring you are concerned about? Can I assume that what we see in the photo is, indeed, a score (can feel with the finger nail)? Isn't that likely due to either some defect in the end of the top ring for that cylinder, or foreign objects which got in there?

US Chrome in Wisconsin had a pretty good turn around when I had them replate cylinders.

Yes what I've noticed is more like a wave at the top, than a grove or ridge like you would see on a iron cylinder.
I figure that this is from the rocking action the piston does (acting on the rings) as it stops at TDC. I also could see an undersized piston accelerating this issue.

That said I wouldn't expect this in 4 years, more like 150-200K miles, at least on a NA engine.

You can really only feel surface roughness nearing TDC. The rest is more cosmetic appearing only.

You know the pricing per cylinder from them?

The pistons are fairly snug in the bores at TDC.

How do I know that? I tried to put the pistons from the top of the bore instead the bottom.

Needless to say, it was impossible.

:)

I had US Chrome Nikasil a set of Alusils five or more years ago. Way cheaper than good used on the market, but best to check current prices. EBS offers this service also (doubtless through a 3d party).

If you can't feel those two prominent vertical stripes, one wide, the other narrow, what's to worry about? Isn't the top of a cylinder, above the top of the top ring, always a bit narrower than the rest of the cylinder? On V8s shops used a ring ridge remover tool to get rid of the build up of combustion products there, but we don't have to put pistons in from the top. I'd wonder why the stripes are discolored for sure, though How could that happen, especially if top ring gaps are normal and not huge.

Or can you feel those stripes at the top, and less farther down? I think anything you can feel in the ring swept part of a cylinder is cause for concern.

Yeah Walt, unfortunately, the majority of scoring damage is near TDC where the ring rides. If it were near BDC, I'd probably ignore it.

But I know it'll leak slightly being where combustion pressures peak.

My guess at this point, is light flaking of the pistons from running lean is causing this?

The side of the piston in the picture shown is exhibiting this.

None of my plugs were damaged, so I know it never got too out of hand.

The Carrera intakes flows very disproportionately, resulting in a big swing in AFR's between cylinders.

Going to fatten her up and reduce boost and timing.