No - Single point boring tool.

"traction in your mind" ???? You've lost me there!

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Beagle

Hard call of what to do with something like this. Basically if the car and engine are really great it probably should have a new cylinder liner installed.

That is quite an undertaking. I would get some opinions from good engine rebuilders on what they think will or might occur from running this as is.

Certainly hot gasses will channel down that scatch to some degree. I have to wonder if the piston is showing any sign of errosion yet in that area. A critical look around the pistons crown area with a maginification device might see it if it has started. The errosion if it ocurs will be the worse at the crown area of the piston probably. Actually I suspect right at the first ring land that is not really visable.

I agree with the boring head idea. In my newbie days I've left scratches on bores when extracting the tool.

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

Ugh, Sue Who? This post pretty much seals the deal that this list is heavily populated with those that know little to nothing about cars / machines / using high level logic.

Ever wonder where juries come from that award millions to a person who picks up their lawn mower to trim hedges? Apparently they come from here!

And now for the rest of the story, if the boring bar was dull and extracted, the rest of the bore would be rough too, even after honing.

OK, now for the high level analysis of the scratch.

Looking at picture 2, the scratch appears to be relatively recent and here is why.

Starting at the bottom of the scratch ( top of piston ) , the left side of the scratch seems to have a raised area ( the silvery edges ) , this goes away where the cylinder is dark them reappears on both sides where the cylinder is light then goes away again. If this area is truly raised, the piston rings would soon wear this area down nixing the theory that it was there since the motor was new.

Next, the scratch is much too clean to have been there long term. The area of the scratch where the rings ride would start to discolor as a concentrated area of blow by would be evident.( the oil would carbonize in this area turning it a brown varnish color ) Compression won't suffer much since the "hole" is a pretty small volume relative to the entire cylinder volume and there isn't much time during the compression stroke for things to bleed down.

Take a look at the area at the top of the bore where the rings don't ride, the bottom has a brown varnish coloration on either side of the scratch but not in the scratch. This brown varnish takes a long time to develop.

If you look farther up, there is heavy carbonization that does extend into the scratch but does not cover the scratch. This heavy carbonization occurs pretty rapidly.

So, when did it occur?

Probably just before the first tear down or just after reassembly. It is pretty apparent that something got caught between the piston and bore. If also has to be above the top ring to make a scratch all the way to the top of deck.

Did the current mechanic run the piston up then shine a flash light between the piston and bore? There might still be something in there. It is normal to have a sizable gap ( 0.010" easily ) between the piston and bore at the top.

Now, what to do?

What were the compression readings pre head removal? Resurfacing the cylinder head won't help compression unless the gasket failed. Did he have the valves ground also?

If the car isn't likely to last another 40,000 miles and is only used for low speed around town driving, put it together and drive. However, if the car is truly nice, pull the motor and freshen up the bottom end. At this point there isn't a whole lot of extra work to do. The cylinder can be sleeved and if the other bores / pistons are not worn too badly, a fresh set of rings , crank rod - main bearings would go along nicely with the rebuilt head.

Remember, when building a motor for a older / worn car, not everything has to be to new specs, some parts can be run again even if they are beyond reusable limits. Build a motor that matches the car.

I'm sure glad there's someone here that knows high level logic.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Perfect.

I agree.

has traction means is believable.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Oh Dear! No sense of humor. Obviously hit a nerve here didn’t I. Care to tell us about who sued you??

And now lets take a closer look at your “high level analysis” and “logic”.

The clean exit of the groove through the chamfer at the top of the liner, less than 1mm from the head face, alone, proves beyond any doubt that this could not have occurred with the head in place. The deeper groove on the relieved section is further evidence that this occurred before honing.

The poor finish on the counter bore is clear evidence of a blunt tool. And just why would the bore be rough after honing?? Have you ANY idea what a hone is??

It is painfully obvious that nothing got caught between the piston and bore (max clearance 0,0018"), at ANY time – not even a trace of damage at edge of piston crown or the liner at top of groove and it would have had to be on top of the piston to cut a groove to the top.Total and utter nonsense!

I could go on……

It is perfectly clear from your “high level analysis” that you have not even the slightest insight into Machine Shop Engineering.
So at least then you are gonna find yourself in good company!
Come on Fess Up – Are you out of High School yet???

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Beagle

Ignore him.

He hasn't a clue of what he speaks.

As usual, you are right on the mark. The boring bar is the only possible explanation for this score mark.

Very likely a boring bar scratch, but it probably has less cross section than a piston ring gap. Put it back together and don't worry about it.

How did the scratch go un noticed though? He scratched it then honed it without noticing it?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I've got lots to do before the day is out and not much time to invest to this thread so I will be brief.



No one has sued me, ever. This list seems to have lots of people that feel wronged / see someone who claims to be wronged during some sort of car repair and their first thought is to sue.

The MD diesel in a Toyota land cruiser guy that claims a too small of a oil filter caused his engine to fail in 2 blocks of low speed driving. Even though the owner had installed a double element filter system.

Someone that bought a car from some distance away, drove it home then to the dealer for repairs. The transmission failed at the dealer and their first thought was to investigate legal action even before the car was diagnosed to see if it failed on it's own. Both of these people have evaporated into the ether when probing questions were asked.

I will give you that the scratch is awfully straight and consistent. The only real way to tell where it came from is to pull the piston and have a look. I don't agree that it was a "idiot mechanic " or a dull cutter.

" The deeper groove on the relieved section . . ." What relieved section?

What " counter bore " A counter bore does _NOT_ exist anywhere in the cylinder bore on this engine. What rough surface? Some of the black bubbly surface is carbon, the brown lines you see are likely not a rough surface but varnish type deposits caused by the area above the top ring. I could explain " Labyrinth " seals but I'm sure you know all about them.




Max clearance 0.0018" ? ( 18 ten thousands of a inch ) You have no clue how and why a piston is shaped the way it is. ( I still hold fast to my claim that there is a significant gap at the top of the piston, at least 0.010" ( that is ten thousands of a inch)

Someone, please measure a new or newish piston. Measure 90* to the pin bore starting at the bottom of the piston then moving up 1/4" and taking another measurement. Also measure 60* ish to the pin bore taking measurements every 1/4". Please post the results.

After someone has posted the measurements, I can then school you on " Barrel " and " Cam ".

Please do

Ah, yea.. . I offered detailed thoughts on many attributes of the scratch. You offered, " Idiot mechanic " and " Sue". You still have not identified who the idiot mechanic is, would it be the person that is working on the car now?


Don't equate advanced age with knowledge, experience or even wisdom. . .

OP: Unless I have missed it-

Is this scratch parallel to the piston travel? I couldn't tell in the pics.


snapped_bolt

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'81 240D For now, a good place to borrow new parts
'80 300TD Probably will be put back into service!
'79 240D BACK IN SERVICE SINCE 09/16; limited use, oil leak. Guide pin r/sealed/replaced. Still a leak. Front crank seal....

See the piston at the bottom of the first photo????