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1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

Breaking this out from the concurrent "Cylinder Head Removal" thread which is getting unwieldy

Damage to cylinder #2 wall. Zooming in to the photo, it looks like lots of superimposed little impact marks rather than a scratch.

forumosauploads-12829.kxcdn.com/original/3X/1/c/1c...g

My best guess was broken end of a piston ring dancing around, but I have now taken the piston out and so far can't see anything wrong with it or the rings.

I'll clean it up, check the ring gaps, and maybe smooth off the ends a bit, though I can't see any burrs.

Havn't decided whether to hone the cylinder yet. Probably not.

I suppose this damage could have been from a hard object that has since departed

Alternatively, could it be detonation or pre-ignition forcing impact of the ring ends onto the cylinder wall?

(The top ring gap was probably roughly in the right orientation on removal)

When I first got the car it seemed to have some pre-ignition on idle and had some run-on after switch off, both of which went away after a water decoke.

Edited by edlithgow on 30/04/2023 at 01:45

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - craig-pd130

Strange marks, aren't they? I think it's unlikely to be detonation, as the marks go all the way down the bore to BTDC. And if there was an object in the cylinder like a bit of spark plug ceramic, that would usually mark the piston crown and head too before being ejected.

I've seen the damage from sharp ends of piston rings, they make a continuous gouge or scar, not a series of little individual marks like that.

My 10 pence is that the marks are the leftover signs of corrosion in the cylinder: perhaps the car had been standing unused for some time before you bought it, maybe with one or more spark plugs out, and a little rust had formed on the liner. The rust got scraped away when the engine was next started but leaving the corrosion pitting behind.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - bathtub tom

I hope you clear those waterways. I wonder if the damage could be due to lack of circulation?

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

I hope you clear those waterways. I wonder if the damage could be due to lack of circulation?

Well, assuming the liner isn't actually breached, which it doesn't appear to be, that would seem to require pre-ignition due to hotspots caused by local failure in the cooling. Seems a bit unlikely

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

I think that (if anything) I had pre-ignition rather than detonation, since it (and the overrun) went away with a water decoke, which is perhaps less likely with detonation'

My very tentative speculative model was pre-ignition, perhaps initiated by glowing piston ring ends or a bit of glowing coke in the ring gap region "pinging" the ring open (briefly, so you don't get a continuous scratch) causing the ring ends to clout the cylinder wall..

I assume pre-ignition could happen close to BDC on the down or up stroke, though on the downstroke you might wonder why it didn't happen earlier, and in either case you might expect it to break the engine in short order.

Corrosion is a better explanation and likely involved, since some of the marks are rusty, but a lot of them arent, and they do look to me like impacts

So I dunno, and perhaps never will. Was hoping someone might have seen similar marks before, and go "Ah yes, thats ......My Bentley Le Mans used to do that all the time"

The other question is do I need to try and hone them out?

Edited by edlithgow on 30/04/2023 at 10:32

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - Adampr

Possibly not helpful, but I note that the marks seem deeper and narrower at the top, shallower and wider at the bottom. That suggests that whatever it is, it wasn't a physical object as that would be consistent all the way down. Secondly, it was happening at the top and gradually dissipating on the way down.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

Yes, I suppose that top down pattern could be consistent with either pre-ignition or corrosion. but I'm favoring the corrosion explanation now

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - Adampr

Yeah, I'd say there's water getting in and sitting in that valve recess next to the mark. Eventually, it's spilling out of the recess and sitting against the cylinder wall. A tiny little bit is dribbling down or possibly getting rubbed along the cylinder wall when starting.

I would get the cylinder honed and check the head/valve above it.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow
Was hoping to avoid honing, mostly because I don’t want grit in my engine, which I think will be hard to avoid (plus I have no power where the car is so will need to get/make a battery drill and a hone.)

Did have a wheelbrace er...somewhere, but that might be too wimpy

Edited by edlithgow on 30/04/2023 at 12:02

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - skidpan

What you are proposing to do is a waste of time. If its damaged it needs either a proper hone or better still a re-bore both carried out at specialist workshops. DIY will not work, the kit you can buy is simply not up to the job and without practice you would never get a correct finish.

Normally after a hone (unless its just a glaze buster) new rings are needed, old ones rarely bed in correctly and high oil consumption and low power are pretty much guaranteed.

Adding any swarf/grit to the engine would simply cause more issues now or later.

I have built quite a few engines but I have always had the engineering work carried out by a trusted workshop and supplied back to me cleaned and ready to assemble. Even then they got part of the job wrong once but at least they put it right with no argument, at least I spotted it before assembly.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

Well, I suppose if high oil consumption and low power are pretty much guaranteed I might as well leave it, at least for now,

Though neither would bother me a great deal in themselves (I have plenty of oil), poorer fuel consumption would be annoying, and it might be harder to pass the emissions test.

Odd that it hasn't been using much oil even with that cylinder wall damage, though I suppose it could be recent.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

I am puzzled however, as to how, if you’ve always had this work done by trusted workshops (and even they, by your own account,, can’t always be trusted) you can be certain that a home hand hone can”t work. The rednecks at Uncle Tony”s Garage seem to think it does.

www.youtube.com/watch?v=X3Crh_URvrk

Certainly they will have skill that I don’t, but I do have a surplus motorcycle engine I could practice on, or, less elaborately, some steel tubing of about the right diameter.

I can probably get new rings and may be able to buy or make a hone.

But probably not worth the risks and effort involved at present.

Edited by edlithgow on 01/05/2023 at 22:56

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - Bolt
Was hoping to avoid honing, mostly because I don’t want grit in my engine, which I think will be hard to avoid (plus I have no power where the car is so will need to get/make a battery drill and a hone.) Did have a wheelbrace er...somewhere, but that might be too wimpy

As skidpan said, waste of time and old rings won`t work and expect them to be more brittle if moving on or off the pistons, and honing may not work if the damage is worse than it looks, without measuring properly you wont know, the photo is deceptive

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - paul 1963

Ed, you won't hone that out my friend, it'll need a rebore.

I'm not being rude but why don't you just give up on the old girl? I really can't see you getting that all back together and running.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? s - edlithgow
Well, I would take that as a challenge, except that I suspect you may be right. We’ll see

Red neck rule of thumb rebore required limit is does it catch a thumbnail. It passes that test

I suppose rednecks might be nail biters (mine are too oily dirty to bite at present) but they have a fairly low stress existence.

Apart from being shot at quite a lot.

And of course zombie anxieties.

Edited by edlithgow on 01/05/2023 at 08:29

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

Rings came off ok. Apparently one isn’t supposed to “spiral” them off, I think because the sharp edges can chew up the piston lands, but I found by slipping short sections of drinking straw over the free end, and adding more as I went along, they rolled around ok

Whether it was necessary I dunno, but it seemed to help

Whether it’ll work going back on remains to be seen.

I'm still a bit puzzled as to the origin of this damage though. Zoomed in, the bright metal looks like recent impact damage to me, with the corrosion around the edges as secondary. I suppose the engine operating could have cleaned corrosion pits out, and that is the best explanation available, but I'm surprised it was that thorough.

Better picture, allowing more zoom

photos.google.com/album/AF1QipOlqdXkrhwsGpCYnW0jeb...T

Edited by edlithgow on 02/05/2023 at 00:19

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

Ah Google Photos.

Now you see them, now you dont

alternative link, not involving dysfunctional mega-corporation, AFAIK

forumosauploads-12829.kxcdn.com/optimized/3X/2/3/2...g

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow
Now thinking this might be spalling damage from cavitation in the water jacket, like what you get on the inside of tank armor from a non-penetrating round impact or explosion.

images.app.goo.gl/2MyRtRdW2BwW7prp6

Plenty of discussion of cylinder liner cavitation (mostly in the context of heavy duty diesels) out there, for example

www.constructionequipment.com/equipment-maintenanc...s

But I have not seen any mention of corresponding spalling inside the cylinder, so that’s just my speculation.

If that IS the cause, it might have been promoted by my practice of boiling the coolant to clear air pockets. Might have to figure out a vacuum fill method instead, a hassle I could do without.

Probably worth trying a different coolant (I use Shell last fill) and maybe changing the rad cap.

Can’t think of anything else
1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - Sprice

Seriously, life's too short, give up on this POS, there must be more fruitful things to be doing.

Edited by Sprice on 20/05/2023 at 07:29

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow
IIRC that’s been said before, but it is of course bound to happen eventually.

Be a bit daft to give up now, though, before I know the outcome of the spark plug repair. (Epoxy applied about 20 minutes ago)

If I gave up on this POS, I might have to get a newer, and thus likely to be Sier POS which would likely PMO more

Re the cavitation / spalling damage, I’m not proposing to do anything about it currently, which might be defeatist enough for a good consuming seal of approval. Just thought it a bit interesting, since I hadn’t seen it described.

Sort of thing you might see discussed in a technical car forum, if you could find one
1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - Oli rag

The cylinder walls look very shiny on the first photo. Don’t suppose there’s some kind of bore coating on these engines which is wearing off?

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

The cylinder walls look very shiny on the first photo. Don’t suppose there’s some kind of bore coating on these engines which is wearing off?

Dunno. I imagine they could be described as “glazed” but I havnt the experience to say, having only had the head off one engine before, and that a very long time ago. Not seen any mention of it in the manual. There doesn’t seem to be any description of cylinder liner replacement procedure either, so maybe it’s considered a specialist machine shop job. There’s a Charade G10 restoration site that I seem to have lost access to that might know. I’ll try and get back on there. I have seen the inside of tanks hit by HESH rounds and they do look quite like bigger versions of individual instances of that cylinder wall damage but I haven’t seen this discussed in the context of cavitation. If that is whats going on there will be matching pits on the inside and it seems likely to cause a hole in the wall eventually.

Edited by edlithgow on 21/05/2023 at 04:30

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow
Or could it be spalling due to thermal shock, from water droplets hitting the cylinder wall?

IIve done water decokes a few times, using a plant sprayer, and for a while I rigged an IV line to suck water in at relatively high revs using the negative pressure generated inside the air cleaner. It seems rather more linear than I would expect, but I dont really know.

This cylinder seemed to have less carbon than the others, consistent with it having got more water

In future (if there is one) ill maybe restrict water decokes to using steam rather than liquid water.
1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - bathtub tom
In future (if there is one) ill maybe restrict water decokes to using steam rather than liquid water.

With the pressure drop in the carb venturi and the cooling effect of petrol evaporation, would it be likely the steam will quickly turn to water?

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow
In future (if there is one) ill maybe restrict water decokes to using steam rather than liquid water.

With the pressure drop in the carb venturi and the cooling effect of petrol evaporation, would it be likely the steam will quickly turn to water?

Could be, though I'd guess starting from vapour the droplets are likely to be smaller and thus perhaps less damaging.

I've wondered if one of those unltrasonic (?) atomiser gizmos sold for misting essential oils aromatherapy stylee would work. IIRC they were pretty cheap.

Not a current issue though. The gear is currently all manually decoked so even if it runs again it'll be a while before it needs doing.

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - edlithgow

Though I'd think the " pressure drop in the carb venturi" would tend to keep it in the vapour phase rather than cause it to condense out

1986 Daihatsu Skywing - Cylinder Wall Pre-Ignition Damage? - bathtub tom

Though I'd think the " pressure drop in the carb venturi" would tend to keep it in the vapour phase rather than cause it to condense out

Thinking about it, I reckon you're right. Physics 'O' level was a long time ago.