Konstan's 1982 300D Engine Out Thread (part 2) - PeachParts Mercedes-Benz Forum

konstan · #1 05-11-2010, 10:52 PM

Well, I am starting a new thread, because the old one was getting really long and, well I thought this pic was kind of cool.

(The old thread is here: Konstan's 1982 300D Engine Out Thread)

I finally got around to taking the main bearing caps off. Here is what I found under the main bearing cap of the first (closest to the front) main bearing. That bearing is not where it should be, I think...

vstech · #2 05-11-2010, 11:09 PM

nope, but it got there when you removed the cap.
note the tang. if it had spun, it would be ground off. that tang is intact.
there is however, serious wear on the journal. that band should not be there.

konstan · #3 05-11-2010, 11:17 PM

aah, the tang... i bow to your wisdom sir

kerry · #4 05-11-2010, 11:35 PM

How did it move? Isn't there a tang on the other side? Where was the bearing in the cap?

vstech · #5 05-11-2010, 11:40 PM

very common.
when you pull the cap, the upper bearing falls into the opposite edge, and pushes the lower insert up a bit.
vacuum from the oil skim will pull things oddly as you remove the caps.
the upper (upside down that is...) insert has a tang also, on the adjoining face, so the pivot of the oil skin pushes the bottom insert down, and makes it pop out like that.

konstan · #6 05-12-2010, 12:49 AM

Here is the summary of my measurements.

- Cylinder bore - 90.90 mm, all five (#1 has scoring), measured at varying depths
- Crankshaft - conn rod journals 51.95 mm, all 5 of them
- Crankshaft- main journals #1 is 69.90, #2...#6 are 69.95

of those, the only one that stands out is the #1 crank journal, the others are in spec.

I am ordering a set of main bearings, rod bearings and rings; all in standard size.

konstan · #7 05-12-2010, 01:09 PM

I am thinking of _not_ lapping the journal surfaces. I am concerned that lapping them would only make them worse (because some grit particle will get stuck there and ruin things).

What do y'all think? To lap or not to lap?

vstech · #8 05-12-2010, 01:33 PM

so still no smoking gun on the knock?
.05 mm is not a lot to be out. did you check both sides of the journal? *front and back*
I don't think a set of standard will work with the wear in #1...

konstan · #9 05-12-2010, 02:05 PM

Broken ring in the #1 is the closest to smoking gun I have. Plus layback40 says that the play in the Timing Device bushing could have caused it too (new bushing and washer and spacer have been replaced).

The next size for mains is like 69.71, the "1st repair stage" bearings won't fit without grinding... and I don't think I want to go there....

KCM · #10 05-12-2010, 04:39 PM

Concerning the crank, at the very least you need to polish it. This can be done by a machine shop, or is a do-it-yourself job if you have fine enough emery cloth. This will usually take out any minor imperfections. You should be able to get by with standard size bearings on the mains. In the old days, bearings would come in 0.001" and 0.002" undersize to account for minimal wear.

When measuring the crank journals, did you measure at different locations along the crank length and at different angles? The journal must be round and not oblong.

I sure hope you honed out the #1 cylinder before ordering the rings. From the previous thread pictures, it looked like the #1 piston was unusable and the scoring was substantial enough that it might need reboring. That #1 cylinder looked like the smoking gun to me. Of course all cylinders need to be honed before installing rings.

konstan · #11 05-12-2010, 11:36 PM

Yep, I measured in several places and at different angles; ditto for the cylinder bores.

I am planning to hone the cylinders

What should I use for the crank journals? The fsm calls for 400 grit but that's going to do more than just "polish imperfections"... what should I use?

layback40 · #12 05-12-2010, 11:45 PM

I have used well oiled 1600 wet&dry. The stuff they finish paint with. I think that would be ok for your crank. Make sure you clean it well after !! You dont want any residue left on it.
We are all going to be interested to see a pic of bore #1 after you hone it!!
Its become a bit of an epic journey!!

KCM · #13 05-13-2010, 03:31 PM

Quote:

Originally Posted by konstan

Yep, I measured in several places and at different angles; ditto for the cylinder bores.

I am planning to hone the cylinders

Quote:

Originally Posted by konstan

What should I use for the crank journals? The fsm calls for 400 grit but that's going to do more than just "polish imperfections"... what should I use?

My dad and I have always used well worn emery cloth strips, 1" wide or so. That stuff is puchased in rolls. Did a quick search and looks like belts used for crankshaft polishing are usually 240 to 400 grit, so the FSM is right on. Personally, I would start with a finer grit than that, 1000 or 1600 as layback40 suggested. You can always go courser if it does not clean up easily or quickly, but always finish with a fine grit. Ths long strips work great if you hold one end in each hand, wrap it approximately 180, and pull it back and forth briskly, working your way across and all around the journal.

konstan · #14 05-14-2010, 11:13 AM

That 'band' that you all see on the journal feels like it's only color, you know that, right? I mean, there isn't any kind of ridge there or anything (I guess I'd be in real trouble if I could feel a ridge there

)

vstech · #15 05-14-2010, 12:03 PM

it's likely more a trick in the light from the oil passage to the "polished" surface.
the machine shops I use have 1.5" emery cloth on a belt sander and they ride it on the journals as they revolve the crank in a lathe... ya might wanna see what a local machine shop would charge to lightly polish the crank, and "fit" the inserts to the crank!