Konstan's 1982 300D Engine Out Thread

[konstan]

Yeah that's kind of what I am thinking barry, that #1 piston/rod may need some more attention before I put it back together...

[jt20]

Originally Posted by barry123400

If you are well satisfied with the bores for reuse. If the number one piston shows excess wear. I would have the number one rod checked for trueness on a jig at an automotive machine shop. A slight bend from being hydrolocked for example at one time might have tweaked it enough to ruin a piston over time.

Or if you decide on a good used piston it will probably come with the connecting rod.

wouldn't that show up on the shallow side of the piston? If the rod was even slightly bent, the wear on the piston would tell that story.

any wear on either side of the piston where the skirts (the longer side) are is typical and warrants replacement of the piston, it does not suggest bent rods.

[barry123400]

Originally Posted by jt20

wouldn't that show up on the shallow side of the piston? If the rod was even slightly bent, the wear on the piston would tell that story.

any wear on either side of the piston where the skirts (the longer side) are is typical and warrants replacement of the piston, it does not suggest bent rods.

All I was suggesting was to check things related to that cylinder if the piston is found to have excess wear. In theory it could even have the bore off centre by a poor boring machine in a previous rebuild. That is too hard to check at home anyways. When you are in this far it is worth the check of at least the rod. Thats of course if it is going to be reused.

I am also not being argumentative in nature. It is just what I would do to satisfy myself that it was straight. Fortunatly it costs little to do as well.

[konstan]

In the course of this rebuild, I welcome all opinions and any advice, and I try to act on it as long as I can afford it. Certainly the #1 has all of our's special attention now

You have all been super awesome! If you are ever in Omaha, I owe you a round of drinks (or three)

[layback40]

Pics Pics Pics !!!!!!!!

[jt20]

Originally Posted by barry123400

Fortunatly it costs little to do as well.

all of these 'little' things add up very quickly.... quicker than you can imagine.

when you are trying to 'rebuild' or remediate and issue (with an engine, that has already passed its serviceable prime) in a fiscally responsible manner it makes little sense to send everything out to the machine shop for peace of mind.

lets face the fact that all of these engines are over 25 years old, inefficient by today's standards, and not worth the perfect rebuild we all imagine in our mind's eye. These cars are cheap because they are on their last legs and no one wants to deal with all the deferred maintenance that has accumulated.

spending $3 - $4K on a rebuild is borderline insanity.

Lets refrain from suggesting that the magicians in the machine shop are the only ones with the knowledge to keep our obsolete addictions huffing and puffing.

[bigblockchev]

Very interesting thread. Lots of relavent suggestions. I am wondering whether the knock got better or worse when the engine was warmed up. I had an engine knock caused by a slightly collapsed piston skirt which would disappear when the engine was warmed up. The pistons are ground in a very slight oval shape at the bottom. They are actually larger across the "slipper" skirt than across the pin. If the #1 piston is all shiny at the bottom and the others still have some machining grooves then I am thinking that excess clearance at the skirt is causing the knock. Good luck Dan

[konstan]

I soaked the pistons in bio-d and cleaned them a little with some emory cloth and a brass brush.

I took a bunch of pics to show the scoring on #1 and to contrast it with #2 (which looks the same as #3, 4 and 5).

Piston #1

Side view, look at the scoring.



Another shot of the same side of this piston:



the other side of the #1 piston; some scoring on the opposite side:




Crown of the #1 piston




Scoring on cylinder #1 walls corresponding to the scoring on the piston #1:




Piston #2:




Crown of piston #2. very very minor pitting, but I think good otherwise:




Cylinder #2 wall, just for comparison (no scoring)




For all this scoring in #1, the car was not smoking.

What do I do with this #1 piston when putting it back together?

[jt20]

Originally Posted by konstan

What do I do with this #1 piston when putting it back together?

you replace it by matching its weight with the replacement. (keeping in mind the mass of the lost material)

that piston is done.

[jt20]

I am very impressed with #2... how many miles on this engine?


why do you think this happened to #1?

[layback40]

What did the rings look like from #1 ?
That piston looks like it has had a hot spot on it or a lack of lubrication causing it to grab. If the rings were jammed it could do that. How deep is that scoring in bore #1 ? Do you think a light hone will remove 95% of it?
Be careful using emery cloth to clean pistons. It can scratch them & damage them.
If you have some solvent based paint stripper try that.
Ideally you would get all that carbon out of those grooves in the pistons.
As to reusing piston #1, If you are able to hone the bore, I would try & get a good second hand piston from a blown motor. Normally there is still a few good pistons even after a major failure. I dont like the scare on the side at all. Others may have had luck with using pistons like that.
I would use #1 piston as a paper weight!

[konstan]

#2 and 3,4,5 are all that good and all look about the same. No scoring, hardly any pitting. 240k on the odometer but it wasn't working when I got the car, so, who knows, really. Other than the knock, the engine seemed to run really well, did not smoke and had lots of power.

#1 is shot as y'all say. What could have caused it? Well, the OIL ring on it was stuck and I had to break . I would speculate that it got stuck because of carbon, and then the piston got scored and it got even more stuck mechanically. What I mean by 'mechanically' is when I got the piston out, the ring groove was distorted enough to bind the ring in one please.

I doubt that this was the source of any kind of knock though. But still, good to fix.

Emery cloth - only to remove larger chunks of carbon. I will give paint stripper a try.

[jt20]

Originally Posted by konstan

#1 is shot as y'all say. What could have caused it? Well, the OIL ring on it was stuck and I had to break . I would speculate that it got stuck because of carbon, and then the piston got scored and it got even more stuck mechanically. What I mean by 'mechanically' is when I got the piston out, the ring groove was distorted enough to bind the ring in one please.

I doubt that this was the source of any kind of knock though. But still, good to fix.

Emery cloth - only to remove larger chunks of carbon. I will give paint stripper a try.

I have a piston from a smaller engine with the same markings. The oil control was broken and half missing, but the second compression ring was stuck.

I also think carbon build up is the answer. As the incredibly hot gases scorch all the oil that is allowed to gather on the sides of the piston and soot is added in, you end up with a big scouring pad.

I do think this could be the source of the knock, though. As the skirts are worn away, the piston is given clearance to wobble around more on the pin. This could definitely cause some piston slap... or the general term 'knock'.

[konstan]

I must've caught it in time, then... the cylinder does not show out of round, using my hole gage and a Fowler vernier caliper...

[kerry]

That's a nasty looking piston. It will be interesting to see how the bore cleans up. I once had a Chevy 283 that I disassembled with the motor in place due to oil burning. I fitted new rings and reassembled. One bore was scored, probably worse than yours but I didn't want to spend the time and money to pull and repair. I probably got another 50-60k out of the motor before that cylinder started fouling plugs frequently.