Advice regarding cylinder-wall scoring needed
 

Hello and thanks for reading this.
After returning from a 2000 mile trip to Florida while on vacation, I noticed upon my return that my 1985 300dt had developed an external coolant leak at the head gasket above the starter. I have not noticed any coolant loss up until that point, no oil contamination, bubbles in cooling system, or residual coolant sys pressure.
I stripped the head off and sent it to the machine shop for a freshen up and the machinest said all preliminaries looked good from a quick inspection before he did the work. This is the guy I buy BioDiesel from and he was impressed in how the prechambers and the valves had nothing but a surface dusting of carbon.
The question I have is regarding the cylinder walls and to what extent scoring is normal after 185k with religious oil changes and Italian tune-ups every day.
While the car starts really well down to 10F, has normal blow-by, and doesn't consume any oil whatsoever, all the cylinders have vertical scoring that I can feel a little with my fingernail. There is also a slight but noticeable ridge at the top of the chamber. I now realize I should have done a compression test and leak-down before dissambly, but....
The pistons don't have any side play in the bad direction, but a little along the longitudinal axis of the pin, which I believe is normal. I don't have a proper tool to measure the eccentricity of the walls, but thought this rudimentary "feel" test would suffice. The car had not had funny noises at all, except it idled not as smoothly as I thought it should compared to other diesels I have heard that are 617s.
I can get a remanufactured short block from Texas International Motors for 850 with new sleeves, rings, bearings and reman pistons. I know Mr Bibles opinion on pistons, but I think I would be willing to risk it for this price.
I wonder if I should get this reman short block or just simply put my head on, forget about the scoring and watch oil consumption, etc, and be happy.
What would you do?

Thanks so much for letting me bend your ear,
Adam Bush:confused: :confused:

A warped head is very unusual on this engine. Did it ever overheat? Be certain the rebuild includes steel valve guides, not brass ones.
I can't imagine the vertical scoring as serious, but need some measurements to tell you for certain it is or isn't something to ignore.
Since you have the head off, a little more effort would make the engine almost like a total rebuild, by simply replacing the rings. This was offered to me as the easiest solution to a rebuild.
I had a scored cylinder in an '85 that was due to a cracked ring and I had substantial blow-by. I needed rings (or one piston needed them anyway) so I was leaning in the direction of a complete bore and hone, something that you may not be needing. I thing new rings are in order here as long as you are at this point (head off) and if you intend on keeping the car long term.

I decided however to have the cylinders bored first oversize and I installed new pistons, I was advised strongly against reusing pistons because they are known to crack in the turbo models.
I intended to keep the car and really wanted to see how a pristine rebuilt engine operates, so I went all the way. The car now starts in a flick of the starter, its incredible how smooth it idles, and uses esentially no oil.
Oh yes, while you are at this stage you may want to replace the crank seals, and if you pulled the engine the oil lines will be very easy to replace (eventually they will start leaking, if they aren't already!)
Its funny how things start to stack up when you get into a rebuild like this, isn't it?
Dieseldiehard
1971 220 (gas) 4-spd manual 104041
1979 300TD w/ ’85 turbo engine 289560
1983 300D 237490
1985 300TD 206150
1975 300D (looking for an engine)
1987 300D 250K newest addition

The car hasn't overheated nor exhibited any characteristics of having done so. The leak was small and seemed to weap more than leak.
Just a re-ring? If I go that route, I am confident the vertical scoring would come out with a light hone and ridge ream. But, the right thing would be to measure the cylinder walls i guess.
I guess I would put in new rod and mains in the standard size - do you think I should send the crank in to get polished even if it looks good?
Thanks,
Adam

How many miles??
 

If the car has 250K miles or less than I would just put the refurbished head back on and keep driving..

GA-W123 Diesel,

I couldn't help but notice your proud service in our beloved Corps in your signature - thanks for your service!
Right now, I'm just past my ninth year and edcided with my wife to put 20 in to get the retirement when I'm 42.

Thanks for the advice,
Adam

Adam:

Can you still see the crosshatched hone marks? If so, it's fine to just put the head back on and run it. Most often, those marks are from stuck oil control rings or excessive ring gap, but so long as the engine starts well, doesn't use oil, and has minimal blowby, just keep going.

DO NOT use steel exhaust valve guides, they will wear out VERY quickly. The exhaust valves have sodium filled stems, and expand too much for steel guides, the bronze ones (they are not brass) are in there because they expand more with heat, allowing the stem to maintain proper clearance. They also transfer heat to the head better.

Also, make sure the shop does not ream the guides for "clearance" unless it is impossible to fit the valves by hand. Clearance is 0-0.001", the less the better. If the valve can be fitted and the spring will close it, it's fine. Reamed to the "normal" US V8 clearance value (2-5 thousandths), the engine will be an oil pig.

Peter

Psfred,
Thansk for replying...
If I really look, I still see the crosshatched hone marks, but the vertical scoring is more pronounced. I wonder if it would be a good idea to soak the top of the pistons in carb cleaner so as to free up any gunk/ stuck rings? I would of course flush and drain the oil out.
Also, The cam tower brngs aren't smooth looking, but are smooth to the touch - does that make sense? Oil pressure hot after a good hard drive with 15w40 is 1.4 with the idle at about 700-725 - probably need to get it up to 750 I guess.
I finally have to go back to work tomorrow after 2 weeks vacation and have a couple of night flights which should be fun because the weather is supposed to be good. Thanks so much - I hope your trip went well.
Adam

Oil pressure is a bit low at 1.4 bar hot -- the piston cooling jets close at 2 bar, so that is the usual pressure. Well within normal limits, though. It does come right up to 3 bar when engine speed increases, right?

Better bet for freeing sticky rings is to change over to Devac 1 oil if you are not using it.

I'd wait on a new block until this one starts to use significant oil, though.

Peter

Psfred,
I respect and value your opinion, so I am going to just put the head on and keep my fingers crossed.
The OP quickly pegs at 3 when off-idle.
I wonder if replacing the cam towers would help with the oil pressure as I've heard this is where much of the pressure drop comes from? I think I'll bring them to the machinist to see what he think about how they look.
Thanks again, Adam

adamb,

I have a manual for my 1975 240D that has a page with 9 photos of damage and streaking on cylinder walls as examples of different kinds of problems and what the fix is. The criteria for accepting the condition "as-is" or not is whether you can still see the honing patterns on the cylinder walls through the vertical or axial scratches. Personally, from your description I would second PSFred's recommendation - put it back together and run it until something serious goes wrong as the fix is about the same and that could really be several hundred thousand miles away.

The manual goes on to suggest the scratches that do not remove the cross hatching of the honing process are classified as "optical" streaks and all others are siezure streaks where some feature of the piston (ring, wrist pin, etc) has something less than its normal ability to turn, move or slide (they call this "partial seizure"). In the examples, some pretty serious looking marks can be accepted, provided the honing is still there. If your marks are wider, like 1/8 to 1/6 or so of the circumference it is most likely you are dealing with an oil ring seizure. If it is less than that it is more likely the wrist pin (actually called the piston shaft in the text and then the piston pin elsewhere). A complete seizure of either is likely to lead to destruction of the honing patterns.

So, if you can see the honing you are fine. If it has been obliterated for the width of the streaking, you are not. If it is somwhere in between, well, it is your decision. Good luck, Jim

Jim,
Thansk so much for the schooling. My streaks are most definitely of the "optical" variety and I feel much more settled now after reading the one paragraph descrispion in the Mercedes shop manual for my 1985 300d. I wish I had a 9 page one like you have - that's awesome!!!
I searched the web just for fun to learn about the differences between optical and seizure streaks and came up with some funky stuff about astrophysics.
Thanks to all of you who have helped. I should have it all done by this Saturday night and will post the reslults.
Respectfully,
Adam Bush

Hello,
I just wanted to thank everyone who helped me with all the information which has lead to successful top-end job on my 300D. I got her all back together and she's running great. It starts without a thought even below freezing temps on 100% biodiesel.
Now I'll just have to store that complete motor with 130k miles I bought off EBay for 500 bucks and get it ready at some point for a quick swap.
Anyone know of a 123 that needs an engine that they would want to sell?
Thanks, Adam

So are you saying you left the bottom end alone and didn't worry about the scoring? Just want to be sure.

Rick,
I didn't mess with the bottom-end and just left what I thought was "optical" type of scoring alone for now.
I figured since I had normal blow-by and no oil consumption I would just leave it alone. The used motor I got with 130k for 500 is a gamble, but if it runs as the guy I bought it from says, then it'll be cheaper than doing a bottom end job and then I get all the extras that came along with it.
Thanks for asking,
Adam

I got the motor yesterday and power washed it in my driveway. I'm very happy so far, as the timing chain stretch is just over 1 degree and the cam and rockers have no perceivable wear on them whatsoever.
It came with the glow plug relay, reman starter, a/c compressor, p/s pump, fan, etc., etc. I think once I get a flex plate I'll crank her up in my garage on a stand.
Anyone have a flex plate/ ring gear for an automatic that will fit my new 617.952 motor that I can buy or trade you for something?
Thanks, Adam