General engine question - scored bore
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  1. #1
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    Default General engine question - scored bore

    Hi guys,

    I hope this is OK in this section, not being a Frenchy.

    I was in the midst of changing a head gasket for a poor student on her 2001 Toyota Camry. It'd done 382,000km, had a full service history, ran really well, but started pressurising the cooling system. Three cylinders had 195psi, and one, 168psi. So off came the head.

    Three of the bores had negligible bore wear (no ridge at all and original cross hatching hone marks) but the low cylinder had moderate vertical scoring on the bore.

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    The owner has abandoned the car as not worthwhile, and has already moved on to another car.

    Question for my knowledge base: is it possible the coolant cleaned the bore of oil in the bad cylinder and then the ring snapped due to 'mild seizure'? The car was blowing quite a bit of steam out the exhaust on startup for a couple of weeks before we decided to strip it.

    I'm aware it could have been just age and miles, but the car had a distinct point at which it started running lumpily and pressurising the coolant quite distinctly, after the coolant had been being mildly pressurised for a month or two, which makes us think it was the head gasket that blew first and let coolant into the cylinder, then the ring snapped. (I'm also aware it might not be a ring that's the cause).

    I'm just trying to get my head around what happened for interest's sake.

    Cheers

    Stuey


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  2. #2
    1000+ Posts robmac's Avatar
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    I'd post the question on a Toyota Forum, they may be more aware and even flag your experience as a known problem.

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    1000+ Posts PeterT's Avatar
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    168 is not bad. You certainly have created a transfer port (2 stroke style) however. You'll never know if the ring is snapped without removing that piston. Given you've gone that far, it's only a few more bolts to remove the sump and withdraw the rod/piston assembly.

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    Do you know for a fact that coolant went into the cylinder with the score marks? How? I am just exploring the possibility the two events were not connected (maybe coolant went into another cylinder and the other cylinder had some other problem). I guess the piston in that cylinder would be a bit cleaner/would show some sort of signs it had been in contact with coolant, I am just not sure what these signs would be. The valves? spark plug? and exhaust manifold might show telltale signs, I guess. And of course, there might be clear signs on the gasket itself/block/head to show where things failed.
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    Your guess sounds OK & would be evidenced by piston crown, valves & spark plug being cleaner than all the rest.
    Possibly the marks are just scuffing from lube breakdown.
    Depending on the car's condition it would be a worth removing & cleaning up the piston, fit new rings on that pot & refit after deglazing. That car 6 mo regn in reasonably good shape should bring up to about $2K+

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    They all have this broken ring problem
    https://www.toyotanation.com/threads...rings.1640872/

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    They all have this broken ring problem
    https://www.toyotanation.com/threads...rings.1640872/

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    Quote Originally Posted by driven View Post
    They all have this broken ring problem
    https://www.toyotanation.com/threads...rings.1640872/
    The above is for engines used in USA.

    Australian vehicles use the 2.0 , 2.2 or 3.0 liter V6 engines. And seem pretty vice free based on my ownership.

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    Yeah, it's a 2.2. I forgot to say, the offending cylinder has a pristinely cleaned piston crown with some minor chip marks at the squish points from some sort of hard debris and the plug was corroded, with the others mint. The other crowns were blackened with carbon as expected (the engine's never been apart; one former owner who was a friend of the family). Also, the bore looked glazed on this one pot.

    Peter, this car is not so easy to access the sump; we'd already thought about that. There's a flat cross member in the way; but yeah we might have a look if we have time before we have to move it.

    I'd already thought 168 psi wasn't bad which convinced me it was just the gasket (and to take on the job, since the cams have to come out so it's not that simple). The car only cost a few hundred, so it was always touch and go whether to spend money. Toyota quote nominal min pressure of 175. If it was just a suspected ring we might have had a crack, but the scoring was too much to correct (although I do have a bore hone, I think the scores were too deep).

    The car's elsewhere, but I'll take some pics sometime this week and post them just for interest's sake.
    Last edited by Stuey; 28th August 2019 at 09:24 PM.


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    All engines:
    What proof is there of piston ring breakage?
    'Pictures' of actual cylinder 'wear' condition helps knowledgeable people assist.
    Piston ring breakage is usually the top ring/s on the engine & will be evidenced by piston damage!
    Doesn't always need piston removal in identifying although often does.
    Ring breakage cause is, regularly, over advanced ignition timing.

    I often buy cheap cars like this, Astras & Korean cars , fit timing belts, brake discs pads etc. & fix to roadworthy to assist income, since assets test was lowered stopping my service pension supplement.
    Last edited by Artificer; 28th August 2019 at 09:19 PM.

  11. #11
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    Yeah, I'm not looking for proof or a firm diagnosis as I'm aware the piston needs to be removed for that. I'm just throwing it out there that it might have been from the bore being steam cleaned and then catching the ring and it breaking. That was my rough guess when I saw it. I Googled this, though, and didn't find any instances of this happening on any car....I just wondered if anyone had heard of this happening.

    Incidentally, the scoring is concentrated on the thrust axis of the bore, worse on one side as you might expect.

    I did wonder if it could be hard carbon off the crown that caused it, but I don't think there was enough to cause this, judging by the others which had a fairly thin coating.

    By the way, there is no damage to the top edge of the piston (as if bits of ring have escaped).


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    COL
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    Hi Stuey

    My take on this is that there is probably nothing wrong with the rings, the lower compression reading is bought about by the fact there is more volume in the combustion area because of the damaged head gasket.

    The scoring could of been made by either carbon or maybe bits of head gasket.

    If the car is worth repairing I would get the head checked to make sure that it is straight, not cracked or gone soft. Get it skimmed. Get new head gasket and re-assemble to manufacturer specs.
    Regards Col

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    Col, what about the scoring though? I'd assume there would have to be some blow-by down the scores.


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    Quote Originally Posted by Stuey View Post
    Col, what about the scoring though? I'd assume there would have to be some blow-by down the scores.
    How bad is it?

    Maybe put up a pic of the cylinder wall showing the scoring
    Regards Col

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    Subject to the pictures and based on the new info provided I would take a shot in the dark and say the scoring is caused by the piston touching the cylinder wall. This is mainly supported by the fact the scoring is on the thrust side and the cleanliness of the various parts, which supports the guess that this is the cylinder invaded by coolant. This has washed the oil out and then it is not a stretch to assume cylinder to wall contact. I would support this idea even if it turns out there is a broken ring as well. Which means the cylinder wall scoring might not be the worst part, but the piston scoring, because that is bound to be verschnickered as well. My guess is the piston being softer will be in much worse shape than the cylinder wall. Which means there is little chance of reviving the engine without some cost. Which to me is motivation enough to just drain the oil and take and angle grinder to the sump to create a big enough opening to remove the conrod bolts and take only that piston out just for the heck of it.

    Possible scenario now looks like this: headgasket failure - coolant invasion - cylinder washed of oil/lubrication ceased - piston contact to cylinder wall - scoring/possible ring failure. Lesson about what it means to keep going with a blown headgasket.

    Either way, good conversation starter for the coffee table.
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  16. #16
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    The scoring is just perceptible with your nail scouring around the bore.

    Yeah Schlitz, that's what I thought. I like discussing engine stuff. I think you're right BTW.

    TBH, we didn't figure the gasket was buggered until it was too late - the rad also had a mild leak (pressure?), so it confused us because we thought that was the problem with the slight coolant loss. Then the owner turned up one night with it idling rough and obviously pressurising the cooling system, whereas before it wasn't clear. This is one of those Toyotas with an overflow tank rather than an expansion tank. The rad has a normal pressure cap, with a pipe into a non-pressurised plastic tank.

    We even bought a new rad, but luckily got a refund.

    Interesting geared cam arrangement on these...one driven pulley, and second cam is driven by a gear with auto backlash adjustment.

    I'll take some pics this weekend.

    Thanks guys.


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  17. #17
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    Hyundai Accent (one of them) uses the same cam driving setup. I guess it's pretty popular.

    Well, if the scoring is barely perceptible, you might be able to resurrect the engine. It may be scored from crap coming off the cylinder walls/piston top/combustion chamber. That would mean there is a chance the piston may be okay. Now you've really got to get that piston out or nobody here will have a restful night again.

    That said, machinists say that if you can feel it with your fingernail it is in the tenths of millimeters ballpark, maybe one or one and change, up to two tenths (if you can't feel it, but you see something, it is in the hundredths). From my experience, they are on the money. That's quite a fair bit for a cylinder wall.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

  18. #18
    1000+ Posts robmac's Avatar
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    You can purchase a bare 2.2 engine complete from a DIY wrecker for less than $200 (in Victoria)

    I'd assume prices are similar in other States.

    So you don't need to purchase too many new parts before another engine becomes a practical option.

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