: Piston detonation evidence - 1998 Northstar



daveyhouse
01-04-13, 10:16 PM
Okay so I picked up another motor and transmission back in in July for my son for a $142.00 and they pulled it. I thought that was good deal, since now he has a spare tranny.
Any been slowly dissembling it since then. It is now all gutted and was cleaning the pistons with extremely hard and heavy carbon buildup on them, when I discovered number 1 piston on right bank looks like it has pits in it.
Which I am guessing is from detonation.


My question should the piston be replaced?
http://i100.photobucket.com/albums/m6/daveyhouse/IMAG0021_zpsb9981b83.jpg

http://i100.photobucket.com/albums/m6/daveyhouse/IMAG0024_zpsaf46bad3.jpg

http://i100.photobucket.com/albums/m6/daveyhouse/IMAG0029_zps252e009f.jpg

http://i100.photobucket.com/albums/m6/daveyhouse/IMAG0036_zpsf38b6729.jpg

Thanks in advance for any input,
Dave

98eldo32v
01-05-13, 04:07 AM
In my opinion,

If you're asking, then it won't be right unless you do.

Yes, it has some pitting on it from detenation. I'd personally try wet sanding the pit marks down a bit.

If you replace the piston, you either have to get a stock size piston and make sure the bore is fine for replacement of the piston.

You have the piston marked from the bore it came from so it should go back nicely into that bore. The pitting doesn't seem that severe to warrant replacing it.

Just my 2 cents.....

Submariner409
01-05-13, 10:59 AM
As above - smooth the pits and use the piston. Clean all the grooves with the proper used ring broken and used as a (careful) scraper.

daveyhouse
01-05-13, 07:10 PM
Okay wet sanding it is. I found some pits on other pistons as well but not as bad.

Thank you for your input guys, it is greatly appreciated,

Dave

98eldo32v
01-05-13, 07:41 PM
Good luck with it........

daveyhouse
01-05-13, 07:45 PM
Thanks,
I need all the luck I can get.

Ranger
01-05-13, 09:18 PM
:histeric:

OK, Sub, you've probably forgotten more than I know about this. That minor pitting doesn't look like anything of any concern to me. What's it gonna hurt if it is not wet sanded? It's gonna be covered with carbon shortly anyway.

Submariner409
01-05-13, 09:22 PM
The engine builder in me says "Make it look pretty" even though I would be the only person to know........

daveyhouse
01-05-13, 09:22 PM
I do plan on wet sanding, BUT do tell, what is it gonna hurt! I am no pro obviously or I would not be asking.

Submariner409
01-05-13, 09:28 PM
I do plan on wet sanding, BUT do tell, what is it gonna hurt! I am no pro obviously or I would not be asking.

Leaving the miniscule roughness alone would hurt absolutely nothing. You seemed concerned, so I replied with what I would do.

........... and if you DO sand/wet sand it, be very sure to wash the piston thoroughly in gasoline. One granule of grit in one of those piston ring grooves could make a real mess of a cylinder wall.

When you bang in the pistons, use copious amounts of engine oil on the rings and entire piston. Use the proper tapered ring compressor sleeve.

daveyhouse
01-05-13, 09:35 PM
Ok, so it is cosmetic only? Sounds good I will do it anyway. He spent enough money on this build already. I am sure it will be no buttermore job, but my son is spending all the money he can on this, so I will try to do this right.

----------

I have a ratcheting ring compressor do you not think this would work?

Submariner409
01-05-13, 09:39 PM
Sure it will work - but the tapered sleeves make the job laughably simple.

daveyhouse
01-05-13, 09:40 PM
Just my luck, nothing is simple, LOL

Ranger
01-05-13, 09:50 PM
Ahh, cosmetic only. Now I don't feel so dumb for asking.

daveyhouse
01-05-13, 09:55 PM
Oh yeah I got this, lol

dkozloski
01-06-13, 12:29 AM
The marks are from corrosion. A piston from an engine in detonation looks like a mouse has been gnawing on the top edges. The pits are of no concern. I'd be more worried about upsetting the static balance by removing even more metal. Leave the piston top alone.

daveyhouse
01-06-13, 10:05 AM
I didn't even think about balance. I already have one vehicle with a terrible vibration at certain rpm's, I'm sure he don't won't his motor doing the same.

Submariner409
01-06-13, 11:16 AM
Koz is absolutely correct - and the British even have a term for piston damage due to detonation: "The mice have been at it !"

SC2150
01-06-13, 01:07 PM
That is signs of detonation, and with the carbon buildup you described also a sign of oil ingestion from the intake air charge which causes detonation in itself as oil does not burn clean like gasoline and one more thing, if you leave it rough like that you will have "hot spots" as it affects both the burn pattern and the quench area.

Do not resue that piston w/out dressing the top...but even taking it down far enough to eliminate them will increase the CC's of the stroke/chamber slightly.

vincentm
01-06-13, 01:22 PM
If it is in the budget, id replace them all

daveyhouse
01-06-13, 04:23 PM
I would have to say they are not within his budget.

He has been slowly buying parts a little at time depending on his paycheck. He is still saving to buy re-manufactured heads yet. He is only making $9.00 hr with less than 40 hrs a week. He is driving my full size van which is only getting about 8 mpg in town if he is lucky, so feeding that beast is putting a dent in his wallet also.

I think I will lightly wet-sand the pitted areas. After all, the pistons are not perfectly smooth because they also have numbers etched into the top along with the directional arrow. Unless somebody has a couple used pistons they want sell :eyebrow:

Submariner409
01-07-13, 12:23 PM
daveyhouse, Use the piston(s) as-is. The slight erosion is inconsequential and IS NOT due to "oil ingestion" from the PCV system. The slight erosion WILL NOT cause "hot spots" or preignition. Several thousandths of an inch of carbon buildup is a perfectly normal consequence of burning a hydrocarbon fuel - gasoline - along with trace amounts of lube oil from cylinder wall lubrication. In 1,000 miles of driving the rebuilt engine the slight erosion will disappear - the carbon bugaboo.

Hot spots caused by that slight erosion ??? Too bad the fairly sharp edges in the fly-cut valve head reliefs all were left out of this revelation.

"Increase the combustion chamber cc volume" - It takes quite a bit of metal removal - visible metal removal - to change combustion chamber volume - in this instance, a slight polish job will remove practically NO piston metal.

SC2150
01-07-13, 03:51 PM
daveyhouse, Use the piston(s) as-is. The slight erosion is inconsequential and IS NOT due to "oil ingestion" from the PCV system. The slight erosion WILL NOT cause "hot spots" or preignition. Several thousandths of an inch of carbon buildup is a perfectly normal consequence of burning a hydrocarbon fuel - gasoline - along with trace amounts of lube oil from cylinder wall lubrication. In 1,000 miles of driving the rebuilt engine the slight erosion will disappear - the carbon bugaboo.

Hot spots caused by that slight erosion ??? Too bad the fairly sharp edges in the fly-cut valve head reliefs all were left out of this revelation.

"Increase the combustion chamber cc volume" - It takes quite a bit of metal removal - visible metal removal - to change combustion chamber volume - in this instance, a slight polish job will remove practically NO piston metal.

The respect I have had for your usual correct posts is disapearing....what world of engine building do you live on? You are correct on a "polish job" not removing enogh...but that piston would need to be resurfaced (turned on a lathe) to get down enough to eliminate them. Those erosin marks are no smooth valve releifs, but jagged errosin and it will only get worse with time.

How many engines have you built in your lifetime? I do them steadily and have for over 38 years....and the invitation to vist the facility in person to see is still open. Misguiding someone on something like this helps no one.

Submariner409
01-07-13, 05:17 PM
daveyhouse, Use this link to a Federal Mogul PDF for some idea of what detonation damage looks like and the origins of the phrase used by me and dkoz (Post #16 - and the man is an airframe and powerplant mechanic). A few more minutes spent with Google will turn up more on detonation and preignition. Don't take my word for it - do your own study.

http://www.mlcmotorfactors.co.uk/Trouble%20Tracers/PistonTT.pdf

SC2150
01-07-13, 06:06 PM
Point made....2 engines and that says enough.

More good links:
http://www.enginebuildermag.com/Article/77966/uncovering_the_causes_of_burned_or_scuffed_pistons .aspx

http://www.contactmagazine.com/Issue54/EngineBasics.html

And this I like the best...read the causes of detonation:
PISTON DAMAGE DUE TO COMBUSTION DISTURBANCES


Normal combustion of the air-fuel mixture takes place in the cylinder with a precisely predetermined sequence of events. It is initiated slightly before top dead center by a spark at the sparking plug. The flame spreads out from the plug in a circle and travels through the combustion chamber with steadily increasing speed from 5 - 30 m/sec. The combustion chamber pressure thus rises steeply, reaching its maximum level briefly after top dead center. The rate of pressure rise per degree crank angle should not exceed 3 - 5 bar to ensure long life of the power unit components. However, normal combustion can be disturbed by the most varied effects, of which the following three, which are quite different from each other, are the most important: 1. Pre-ignition: causes thermal overload of the piston.
2. Detonation (knocking): causes erosion-like material removal and mechanical overload of the piston.
3. Fuel flooding: causes wear with consequential oil consumption and piston scuffing.
1. PRE-IGNITION
In the case of pre-ignition, combustion is initiated before the spark by a glowing area in the combustion chamber. Possible sources of pre-ignition are the valves (usually the exhaust valve), the sparking plug, the gasket, deposits on these parts, and the surfaces surrounding the combustion chamber. The pre-ignited flame them operates with uncontrolled timing on the components causing a sharp rise in piston crown temperature. Continued pre-ignition causes the piston material to reach melting point after only a few seconds. In engines with substantially hemi-spherical combustion chambers this results in holes through the piston crown, which usually occur on an extension of the sparking plug axis.

On engines with larger squish areas, scorching and melting of the top land occurs at the most highly loaded zone adjacent to the squish surfaces. Melting often continues down to the oil ring and onwards towards the engine interior.

CAUSES OF PRE-IGNITION
-- Sparking plug with incorrect heat range.

-- Damaged, leaking valves or too little valve clearance.

-- Glowing deposits on the piston crown, cylinder head, valves or sparking plugs.

-- Soft carbon formed in the combustion chambers of high performance engines with extended city driving.

-- Unsuitable fuel.

-- Diesel fuel in petrol.

-- Oil in the combustion chamber due to leakage past the piston rings or valve guides. -- High engine or high inlet temperature.

Pre-ignition can also be caused by the severe heating of individual combustion chamber components due to detonation, which always leads to high surface temperatures.

2. DETONATION
In the case of detonation, combustion is initiated by the sparking plug spark. The flame front generates pressure waves as it spreads out from the sparking plug, thereby cauisng critical reactions in the unburned mixture. This results in self-ignition simultaneously in many areas of the remaining mixture, giving a 10 - 15 fold increase in the flame speed. The rate of pressure rise per degree crank angle and the peak pressure then become substantially increased. High frequency presure oscillations then occur during the firing stroke.

In addition the surfaces surrounding the combustion chamber are overheated. When combustion chamber walls are burned clean of deposits, it is a sure sign that detonation has occured.

Light, interrupted detonation can be withstood by most engines over a long period without damage. More severe, maintained detonation results in erosion-like removal of piston material from the top land and piston crown. The cylinder head and head gasket can also be damaged in a similar way. Components in the combustion chamber (e.g. the sparking plug) can then be so severely heated up that pre-ignition and the associated severe thermal overload and melting of the piston occur.

Heavy, sustained detonation results in land and skirt fractures within short periods. These are not usually accompanied by melting or scuffing.

CAUSES OF DETONATION
-- Use of a fuel with insufficient detonation resistance (too low octane).

-- Diesel fuel in petrol.

-- Oil in the combustion chamber due to leakage past the piston rings or valve guides diminishes the detonation resistance of the fuel.

-- All engine related factors which cause high temperatures at the end of combustion also lead to detonation. These are:

-- High compression ratio, possibly due to deposits on the piston crown and cylinder head or to excessive grinding of the cylinder block and head surfaces.

-- Ignition timing too advanced.

-- Inlet temperature too high due to insufficient underbonnett ventilation or high exhaust back pressure. Failure to switch the inlet air flap to summer operation or a defective automatic inlet temperature control system also result in a significant increase in the inlet air temperature.

FUEL FLOODING
Fuel flooding can be caused by a too rich mixture, loss of compression pressure or combustion irregularities which lead to incomplete combustion. The lubrication of piston, piston ring and cylinder bearing surfaces becomes increasingly ineffective. Mixed friction with wear, oil consumption and scuffing are the consequences.

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The pictures he posted show this:

Detonation causes three types of failure:
1.Mechanical damage (broken ring lands)
2.Abrasion (pitting of the piston crown)
3.Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)


I do this for a living, I am NOT a backyard do it yourselfer (even though there are tons that actuall do have enough knowledge to recognize this).

This is what I do for a living and my qualifications speak for themselves.

:thumbsup:

daveyhouse
01-07-13, 06:48 PM
I would like to thank everybody for their input and help on this. That was quite a bit of reading in those links.

I have decided to wet-sand the affected pistons to dress them up a little.

I imagine the previous owner probably ran the motor quite hot. Again this motor came out of a 96 Eldorado with unknown mileage. We just got the crank back today from the machine shop, we had it polished.

Now I guess I should start a build thread. I am no master mechanic and could use all the tips this great site and members provides.

daveyhouse
01-07-13, 10:03 PM
couple hours later

http://i100.photobucket.com/albums/m6/daveyhouse/caddy/IMAG0044_zps891cf205.jpg

Couple more hours with black fingers

http://i100.photobucket.com/albums/m6/daveyhouse/caddy/IMAG0043_zps11ed8000.jpg

How about buffing the piston tops when I am done, any benefit?

98eldo32v
01-08-13, 02:22 AM
What grit sandpaper did you use?

I'd wet sand it to 800/1000 and be done with it.

320 then 400, then 600, then 800/1000. Wash the piston thoroughly and that's it.

Looks like you've removed most of the issues, you won't get it all but nothing is perfect. .

Good luck.

Submariner409
01-08-13, 09:29 AM
Not necessary to buff the tops, but again, before the heads go on it looks trick and would make a nice file picture..............

Just for grins and kicks, here are some of the possibilities for a Northstar - BUT many are NOT workable in the FWD configuration - the modifier - CHRFAB - does some gorgeous engines for sand rails and kit cars.................. this article merely explains some of the Northstar technical points.

http://www.hotrod.com/pitstop/hrdp_1006_northstar_cadillac_engine_buildup_questi on/viewall.html

SC2150 asked how many engines I have built. I have no idea - a lot - been doing engines of various types, makes, models since my first MG OHV 1250cc overhaul in 1954. Worked part-time as an engine mechanic at 3 foreign car shops in DC during high school. Did a flathead V-12 Lincoln Zephyr in the late 50's, along with a bunch of B-Block flatheads. Even throughout my Navy career I still built engines as a hobby - and Navy bases seem to have great automobile hobby shops where sailors can work and store stuff while at sea. In '83 I started on the Ford 302 series in the Mustang "GT" Fox body cars. Among other engines, my marine business builds Olds 455 engines from slow-speed workhorse to tweaky screamer (although - you twist a 455 over 5500 for a while, it comes apart). Anyway, I enjoy the challenges and the friendships - as SC2150 knows, as an engine builder you become acquainted with every gearhead and machinist in a wide radius of your work. Right now, I'm in the middle of doing a '65 Pontiac 389 for a guy in the Kent Island Cruisers - he's restoring a '65 LeMans sedan as a sleeper. I will probably never touch a later Cadillac engine than 2003 - no desire to start over, and arthritis is slowly eroding my ability to do fine assembly work. One thing I can take pride in is that over the years none - not one - of my engine rebuilds has been a "come back".

EDIT at 1255: 1968, Naples, Italy. Apartment parking lot. My '65 Chevelle Malibu SS 327/350 developed a bad head gasket - coolant leaking into #2 cylinder. Did a decarbonising and top overhaul in the open with essentially NO proper tools or parts. The top of the piston looked exactly like dkoz' "mouse bites" analogy. Rolled it to TDC, packed the edge of the crown with grease and rotary wire brushed the edges of the hundred or so pits smooth. Cranked the piston down an inch and cleaned the bore. I blew that engine at the strip in Willimantic, CT in 1972.

daveyhouse
01-08-13, 10:08 AM
I was using 1200.
The only other grit I could find in my hoarding mess was 150 LOL, I think I have a file smoother than that.
Wish I had lower grits, that would save me a lot of work and finger swapping.

----------

Sub you just made me drool on my keyboard with link. :lick:

SC2150
01-08-13, 05:59 PM
What I dont get submariner is I would never think I had more knowledge than you on anything related to the operation or maintanance of a submarine, or even what it is like to live for an extended period on one, but this area I put my experiance and qualifications up with any builders in the country, and have been doing this for over 38 years and do keep up on all new technology as we are one of the most respected perfomance shops in the SE US, and I do this daily with all these different engines, yet you always attack and are beligerent in the few areas where you are not the expert (even though you are 99% of the time right on and a huge asset to this forum). Why cant you accept there are some areas where us that do this day in and day out for a living may have a bit more expertise in these areas? I dont make a dime sharing information that has taken a lifetime to gather....and it takes time to contribute to those looking for guidance that is correct.

I want no quarrel with you yet you throw in the jabs and insults far to often....what is the purpose of this? Just a bug up your but that somehow encourages this? How does this benefit the mebers looking for correct advice? Never do I come into a thread you have given accurate advice in and challenge you, but you seem to make it a priority to do this in my case.

This is not a contest.....this is simply sharing information and for some reason you have the wrong impression that I am not who I am it appears. What is it you want to stop this?

daveyhouse
01-08-13, 07:53 PM
I want world peace.
This is starting to look like the quarrel between Tim Carroll and Jake over at Northstar Performance. I appreciate all info, good or bad. If I go with bad then I have no one to blame but myself, because Google is MY friend.

All that I need is suggestions, there is no need for headbutting.

Maybe there should be another category added on somewhere for members to rant at each other, but then again other members would throw their 2 cents in when they had no business being involved, and then it gets real ugly. I guess that wouldn't work either. Forget that idea.

Anyway I went out and got more sand paper, 320, 400, 600, 800, 1000, and I already have 1200 and 2000.
Lets see what happens.

Thank you ALL :cheers:

daveyhouse
01-09-13, 12:22 PM
Okay here we are with 320 grit and sore fingers later, almost got it all.
I should have separated the rod and weighed it first just to see how much I removed.

http://i100.photobucket.com/albums/m6/daveyhouse/caddy/IMAG0050_zps0fe97ea4.jpg

SC2150
01-09-13, 12:50 PM
That is excelent. I would have no worries now. :thumbsup:

tateos
01-09-13, 08:10 PM
No tend to agree with Sub - no big deal if you had left it - no harm done by lightly sanding. Interesting that the crown did not show the factory machining marks. I used an air die grinder and a steel wire brush attachment to remove carbon on my piston crowns (and combustion chambers/valves). I guess maybe the wire brush could have been a little dull, but it did not seem to cut into aluminum at all and very fine concentric or spiral machining marks were clearly left remaining visible on the top of the pistons - I don't see that in your pictures.

daveyhouse
01-09-13, 08:36 PM
There are swirls. I finger sanded in a circular motion. I guess the phone camera only picked certain angled marks from shadowing something. I dunno. LOL

Ranger
01-09-13, 09:11 PM
Now you've done it. Shortened the piston and lowered the compression ratio in that cylinder. :duck: :hide:

daveyhouse
01-09-13, 09:34 PM
Less chance of detonation :D

Seriously though the piston is now uneven on top because chasing the pits, as mention before a lathe would have been the ticket.

Do you think the uneven top will have a dramatic effect on anything? I had to chase quite a bit.

Ranger
01-09-13, 09:53 PM
BTSOM :noidea: My guess would be no.

SC2150
01-10-13, 08:30 AM
No...you will be fine. This is not a 1000 hp FI build. Just the jagged edges of erosion like that would be where any future detonation would attack.

I would have no qualms installing it as you have it dressed. :thumbsup:

daveyhouse
01-10-13, 09:21 AM
As you can see just above the intake valve relief on the lower right, the dark shadowing from where I was chasing the worse pit. I will try to measure how deep it is when I get a chance today.

http://i100.photobucket.com/albums/m6/daveyhouse/caddy/IMAG0053_zps41e9e39d.jpg

SC2150
01-10-13, 10:15 AM
No worries. It wont affect the CR enough to notice anything. Turned on a lathe would.

:thumbsup:

daveyhouse
01-10-13, 03:10 PM
Okay deepest spot is .018

Tom's Caddy
01-10-13, 03:31 PM
I'm glad you said something SC2150. I have not posted for months because of Subs way of doing things, but i pray for him and feel sorry for him, because hurting people try to hurt others.

SC2150
01-10-13, 03:59 PM
He is usually dead on with most advice so he is a huge asset to the forum so I dont interfere in his threads. Just want peace and all good advice to the members as many of us cant be on very often. Thx for the support Tom's.

davey, you will be fine like that...good job and good luck with the rebuild. Lots of good info here.

:thumbsup:

daveyhouse
01-10-13, 05:36 PM
Thank you for the luck, and thank you keeping the peace.
You can never have too much peace.

Submariner409
01-10-13, 09:45 PM
I'm glad you said something SC2150. I have not posted for months because of Subs way of doing things, but i pray for him and feel sorry for him, because hurting people try to hurt others.

Good for you. Thanks - we all need prayers. I'll light a candle at Mass on Sunday for you, too. (You [apparently] desperately need it). You are perfectly welcome to pity me, but don't ever feel "sorry" for me.

When you get around to trying to build or repair an engine (any engine), call SC2150, me, Tim Carroll, Jake Wiebe, Joe Blau, Mike Lawson - a host of others - it's all in here somewhere.

To put this all in context, click on Tom's Caddy's username in his recent post. Now go back in time and read his recent posts in CF. I stuck a barb in him for posting huge file size pictures of his car and suggested ways to reduce the memory storage space - hardly something to feel 'sorry' for.

Fast Forward to daveyhouse' polished crankshaft thread............