New rings or not - PeachParts Mercedes-Benz Forum

petecooke · #1 11-01-2011, 01:27 PM

I have a 83 240d which had a bent #3 cylinder intake valve. The head has been fixed but I need to replace the piston. I'm going to get new rings for the piston. The other cylinders were measuring 350-400psi.

Should I replace the rings on the other cylinder since I have the motor apart?

Do the cylinders need to be honed when new rings are installed?

I spoke with a guy that rebuilds engines and he said just to replace the rings when you put the new piston in and not worry about doing anything to the cylinder.

Any thoughts?

Thanks for any help.

pete

leathermang · #2 11-01-2011, 01:58 PM

Quote:

Originally Posted by petecooke

I have a 83 240d which had a bent #3 cylinder intake valve. The head has been fixed but I need to replace the piston. I'm going to get new rings for the piston. The other cylinders were measuring 350-400psi.

Should I replace the rings on the other cylinder since I have the motor apart?

Do the cylinders need to be honed when new rings are installed?

I spoke with a guy that rebuilds engines and he said just to replace the rings when you put the new piston in and not worry about doing anything to the cylinder.

Any thoughts?

Thanks for any help.

pete

No disrespect intended......but that guy is an idiot....
You need to read the Factory Shop Manual for your car...
it lists in detail more anal than you can imagine exactly what you need to do to determine what you need to do to do this whole thing correctly.
This is not an old gas lawnmower where you can slap a set of chrome rings into an old bore and it clean it up and last a pretty reasonable time....
To do this right you need to pull that bore sleeve, put in new once, measure your piston , hone the cylinder out to be the right size to fit THAT piston, and install the rings according to the FSM....
At that psi I would not bother to address the other cylinders....

BUT, what extent do you mean you have the motor apart ?
If you have the other pistons out.. then you need to do that to all of them ...

petecooke · #3 11-01-2011, 02:15 PM

Thanks Leathermang for the reply.

I don't have any of the pistons out but I have 3 pistons from another 240d engine. So, I was planning on using one of the 3 pistons to replace the bad #3 piston.

I have the upper pan off but I have not pulled any of the pistons out of the cylinder.

Are you saying that when rings are replaced, the cylinder needs to be re-sleeved?

pete

leathermang · #4 11-01-2011, 02:29 PM

In practical terms YES.....
now, if the engine was a few thousand miles down the road from a proper rebuild and this happened.... where you could assume no concentricity, ovalness, general size wear...then no..... but old engine, new rings... since it has the great design of allowing the sleeves to be pulled and basically turning the bore into NEW.... then it allows you to take it down to fit the exact piston you are placing into it at the proper fit....
The FSM will tell you exactly where to measure to find the best of those other pistons.... if the lands are worn you may can still salvage a piston by buying a custom ring from someone like Deves.com
This still means cleaning up the lands on that piston to some size to fit the custom ring width... but can save a piston.
HOWEVER, Non Turbo pistons are amazingly cheap compared to TURBO..... and you might want to check that out... new sleeves, new piston,,,, as Candide said... The Best of All Possible Worlds....

1960mog · #5 11-01-2011, 02:33 PM

If the cylinder is not damaged you don't need to replace it.
Make sure the new piston has the same diameter and weight then the old one.
If you replace the rings you have to hone the cylinders.
A Flex Hone works very well.

Why is the valve bend?
What happend to the piston?

47dodge · #6 11-01-2011, 07:25 PM

I going to jump into this one.

If it were mine and I had it apart I would do a total rebuild. However I can do that here at home, i have a full machine shop and the tools to do it.

Assuming you have a budget, and just basically need it fixed, then I think it is a waste to put a liner and new piston just in one cylinder. So in this case leave the liner in and hone it, check your pistons (used?)to see what gives the best fit, and go for it. It will likely last until the engine needs a complete rebuild. You really do not want one strong perfect cylinder and three worn ones.

leathermang · #7 11-01-2011, 07:31 PM

I am sorry you jumped in ..
Did you see the compression readings on the other cylinders before posting that ?
Do you have a paper manual from MB for this engine and read it ?
So you think you or he can ' half A$$ it ' just the right amount to match the other cylinders ... instead of trying to make it as close to blueprint as possible ?
Exactly how much difference in power do you think this ' perfect strong ' one would have compared to the others ? And what exactly would the net effect be on the engine ?

jt20 · #8 11-01-2011, 07:48 PM

Anyone recommending that a 30- 40 year old manual has all the information required to build an engine... is an idiot. The new rings you buy will have a completely different construction than the original ones assumed by the manual.

And the engine re-builder is correct. You can (most likely*) replace the rings and piston on the affected cylinder without honing.

There is no reason to go replacing the rings on the good cylinders if you are looking for a quick fix. However, everything wears, and you have to determine if all that extra work makes sense to you / your budget / your time. Is the car even worth it?

*depends available roughness of the cylinder wall, taper, out-of round. But for a quick fix, he basically making the assumption that the tolerances will be 'good enough'. Worst case is that you will burn a little oil and the rings on that cylinder will take a very long time to seat.

I have replaced rings on these engines without doing any honing, and had excellent results... it really depends on the roundness of the cylinder. Visual inspection will tell you if the out-of-roundness is a concern simply by determining where the honing marks are worn away.

If the original factory honing marks are still quite visible all the way around the cylinder, then you are still well-within specification.

leathermang · #9 11-01-2011, 08:40 PM

" most likely " ... great advice..... so if that bet does not pay off... who has the labor and money penalty....
You are pretty generous with HIS potential money loss....

47dodge · #10 11-01-2011, 09:14 PM

I guess I stirred the pot. I still stand by my statements. New rings, hone cylinder, replace piston. Now if there is severe wear and the piston clearance is to much then that is a differant matter. I am not suggesting to just put any piston in, but he should measure to be sure they are within proper tolerance. As long as tolerances are correct there is no "what if" assuming new rings and honing/glaze breaking. He could get away with not honing, but i would not. that can bring a bit of uncertainty to it. Honing helps the rings seat properly.

leathermang · #11 11-01-2011, 09:23 PM

It is ok to stir the pot.... helps a lot of people learn the different ways of thinking about these things..
*******************************************
I could not find these parts listed here on Fastlane...checked that first... Whunter can probably provide these...
but for this thread .... the logic of one way or another... here is one way to take away some of the myths which are likely residing in some people's minds...... first since these are actual MB parts....and second because many have dealt with TURBO stuff... which on pistons is MUCH HIGHER COST.....

So the thing to do is look at the difference in labor and materials between using the used piston ,honing to fit ( if appropriate according to the FSM specs ) , and getting new rings for that used piston.. which might include cleaning up the lands or using wider custom rings to be correct in the ring fit dimension....

A NEW piston AND matched ring set....

$55 Mercedes Diesel Pistons & Rings 76-86 .8mm 240D 300D 300TD Mercedes Diesel Parts
Piston AND Rings $55

A NEW sleeve ....

http://www.**************.com/node/8974
Sleeve $29

The old bore will still have some honing which will be needed....and we are assuming that the used piston is large enough to fit according to specs in the FSM..
Whereas the new parts WILL FIT properly.... but require pulling ( plenty of stuff in archives of people doing this with just a hand puller..)... and that fits the FSM instructions also...

One thing many people do not understand ... even if they have been good general engine machinists ....is the extremely tight fit called for by MB to have a long lived non smoking engine....

Put the entire engine back together with USED parts to save less than $100 in NEW PARTS ?
I don't think so....

47dodge · #12 11-01-2011, 10:21 PM

the key to being successful really is getting the right fit.. if his used pistons are too loose, then that will not be good. best rings, proper honing and all will do no good if the piston is just rattling around in there.

As I said in my first post, my preferance would be to do a total overhaul using new parts and liners if the budget will allow.

engatwork · #13 11-01-2011, 10:24 PM

Quote:

my preferance would be to do a total overhaul using new parts and liners if the budget will allow

same here.

If money is an issue then I'd try to find a good, used engine. It would be cheaper.

petecooke · #14 11-01-2011, 10:24 PM

Here's a picture of piston #3 and #2. The #3 piston is the bad one. I thought it was carbon build up but the top of the piston melted somehow. I tried to scrap off the carbon and realized it was metal piston that had melted.

1960mog · #15 11-01-2011, 10:28 PM

Quote:

Originally Posted by leathermang

Whereas the new parts WILL FIT properly.... but require pulling ( plenty of stuff in archives of people doing this with just a hand puller..)... and that fits the FSM instructions also...

By "but require pulling" I assume you talking about the cylinder sleeve?

The sleeve that petecooke has installed right now should have an inside diameter of about 90.9mm + wear, given that it is still STD and has no other damage.
If petecooke buys the $55 piston he has to enlarge the cylinder bore to about 91.7mm.
This will give him a straight round cylinder with a new cross hatch surface.
Combined with a new piston and new rings one of the best ways to go.

If he installs a new sleeve he has to press the old one out and then the new one in.
The sleeve will perturb above the blocks parting surface and has to be cut even with the block somehow.
After installation the bore will be about 90mm.
He has to remove 1.7mm to make the new piston fit.

The end result will be the same then just honing the old sleeve to 91.7mm.

Why do you need a new sleeve?