2.5-16V rebuild Info

[Nagilum]

Hold in mind: If your piston stucks, it most likely will be way more expensive than a rebuild now.

Regards

[Cloudini]

Hi all, thanks for your reply's at first !

Ive removed the engine from the car yesterday,
I will start taking the engine block apart tomorrow, and take out the pistons and measure them,
When they are oke, ill leave them, just replacing the piston rings, bigend bearings and crankshaft bearings, i also take a look at the oil pump now, or do you guys suggest the oil pump is not a must ? ,i hope the new piston rings together with the cylinder wall would wear in a healty way,

Or are those vertical lines in the cyl wall that super bad ? As shaq said probably every 16v has them ?

Also do the cylinder head, new valve seals and valve guides, ill clean the valves and post a picture of them here so you guys could see the wear on that too. From my idea the are still fine,

So more to come, thanks everybody so far for the help and support !

[Maki]

2. They are forged (larger coefficient of expansion when hot)
3

This is not correct.
The 2.5-16V's had hypereutectic pistons
Bye
Maki

[shaq]

What do you mean Maki, please explain? Do you mean that they are not forged but only casted?

Problem in my opinion with 990 engine is that relatively short pistons travel quite a long way so they bounce a lot at TDC.

When I said all 16v have them I meant all 990, with 2.3-16 that I opened picture was different as pistons are longer (longer skirt) and they travel a much shorter distance = much less bounce at TDC.

Regards,
Nikola

[Maki]

Hi Nicola,
like stated only the 2.3-16V had forged pistons ( i don't know if all but at least the first versions).
For cost reasons Mercedes changed to hypereutectic pistons on the 2.5-16V engines . That's the reason why in standard form the 2.3-16V engines are better suited for FI and can handle more power.
Here are the differences very good described Hypereutectic pistons

Bye
Maki

[shaq]

Hi Maki,

I have in garage few 16v engines (beside that one in my 2.5-16) Some of them are complete some are taken apart for future rebuild or even my tuning ideas. I remember the old story from 2007-2008 when someone said on Forum that only ECEs have forged pistons and other do not.

Since then I read a lot of literature, and I think that Sales prospect of 2.5-16 says that 990 have forged pistons too. The thing is that I am pretty sure that all 2.5s have forged but now I am looking for evidences to prove it

However I will check later again my more reliable resources than sales brochure is (Einführungsheft 16v and Evo 1, 2 and WIS) the thing is that I never heard of this process you described it is new to me.

As this sounded interesting to me what you said, this evening I went to my garage as I already planned to - do a little cleaning, so I took closer look on 2.3-16 Ruf/ Kat pistons and 990 pistons which I have in a box taken off their engines .

2.3-16 piston is with larger skirt, also from inner side I can not see traces of forging. However on 2.5-16 pistons I can see that they are forged that wide zone is characteristic also it is clearly to be seen on crankshaft 2.5-16 and connecting rods of 2.3-16 ruf/kat and conrods of 990 that they are forged too, as I have them removed too. My ECE engine is now complete so I can't look at the pistons and tell are they forged or not.

Also just thinking of it would it be wise from MB to put forged crankshaft and forged rods but not to put forged pistons but some weaker ones? About ECE pistons I remember that I read that top side of piston is reinforced also thicker then on following engines. I dont remember where I read or heard that.

Regards,
Nikola

[Cloudini]

Hey everybody, it cant be said enough, im very pleased by the information u guys are giving me, for me its an super cool experiance to rebuild this engine, althrough its my very first time rebuilding an car engine, its cool to do an 16V engine !, learning so much too !, so

i didnt had any time to take the engine block appart and check the piston rings, but i did take all the valves from the head and checked them, there is very very very little wear on the valves them self but alot of carbon (engine definatly burned A LOT of oil !!!!), now im kind of looking for tolerance measure numbers !, when the valves are in the valve guides, there is an Very Small amount of play that ive noticed, and since the valve rods barely has any wear on them, should i replace the valve guide with the Original size ? (mercedes EPC shows repair sizes but arent those not bigger ?)

for sure im going to replace the valve seals ! but im not sure about the tolorance measuring on the valves them self. should there be any noticeble play that i can feel or just NONE !?

im working with an workshop book from an 2.3-16V engine, theres info in there but can i thrust the info from that book with my 2.5-16V or is there diffrents in them ?
also need to know this for the Nm torques to tighten the bolts of the piston rods, crankcase bolts, head bolts stuff like that,

here are a few pictures of how the valves and the valve seats in the head looked like

thanks everyone

Cyl 1

[shaq]

Dont touch guides if they are still good!

Valves are leaking between valve and valve seat it is ring that should be between 1 and max 1,5mm wide if I remember correctly you can better find that value in wis or 16v book (the same as for 2.3-16) valves are all the same size but Mercedes themselves were wondering around experimenting with different materials today only allowed valves for all 16v are evo2 valves that means if you change valves buy all from evo2 and if they are not too much shot you can get them remachined to specs.

But valves are very stressed part and if valve breaks apart you have then a big problem piston is destroyed immediately often together with cylinder head, so I recommend to replace them its worth it.

If seats are too shot they can be remachined too but then will valve sink too much in and you will have a los in power output. Important is that as camshaft starts to push them the more gas can flow around it instantly and it wont happen if they are down in hole after regrinding. I think the best way is to renew seats and make them and valves back in factory height

Regards
N.

[Cloudini]

Hi guys!

I need some help here, im measuring the valve guides and valve stems,
The intake valve guide is 7mm and the valve stem should be 6,97mm thats is what the 2.3-16 workshop manual says
But my valve stem is 6,87, that either makes it a play of .10mm or my measuring tool is broken hehe

The exhaust valve guide is 8mm and the stem should be 7,96mm but it is 7,86mm in real,

What is the tolerence of max mm play ?

And i tried measuring the pistons
Cyl 1 is 95,14mm
Cyl 2 is 95,12mm
Cyl 3 is 95,14mm
Cyl 4 is 95,12mm

Doesnt the pistons need to be 95,50mm ? Or are the pistons slightly oval and im measuring them wrong ?

Thnx for the help
Wesley

[Cloudini]

Alright update

I did some wrong measuring, above before !!!!

Pistons are
1 = 95,41mm
2 = 95,43mm
3 = 95,41mm
4 = 95,45mm

Valves are
Intake 6,96mm where the 2.3-16v workshop manual says 6,97mm
Exhaust 7,95mm where the 2.3-16v manual says 7,96mm

Total wear of .01mm but there still seems alot of diagonal play when the valve is in the valve guide, i can video record that so you guys could see and hear ?!

If i replace them with New original size valve guides ? Will that work or will i still have to much play ?

Thanks
Wesley

[Cloudini]

im currently working on an list that actually want to order tomorrow, want to buy new parts so i can start rebuilding this engine again, but i have no idea wich valves guide i should get !, are these measurings displayd on the picture below the outside width of the valve guide ?, than there should not exists any inside repair size valve guides correct ?


Nevermind those are outside valveguide sizes

[Cloudini]

Well Sh*t ! today, Disaster strikes , i had an accident wich im really pissed off about,

how does this end up if i will drive with this, will this be an weak point where the gasket will easly blow ? or will the gasket hold this ?
or could this be repaird by welding an tear on it and let the head be machined flat ? (by welding, aluminium weld if so ? wich type of aluminium is this ?)

here are a few pictures, on the last picture, ive used my old gasket and hit the edge of the damage inside the gasket so you can see how far this is compared to the cilinder wall edge,
really crap this happend !!!!!!!!!!

[Cloudini]

hey guys, ive orderd an entire partlist for my engine, but we are having some trouble ordering new piston rings from mercedes,

are these still for sale ? because EPC still shows them,

what if they are not for sale, any other good replacements ?

thanx
Wesley

[shaq]

Hi Nicola,
like stated only the 2.3-16V had forged pistons ( i don't know if all but at least the first versions).
For cost reasons Mercedes changed to hypereutectic pistons on the 2.5-16V engines . That's the reason why in standard form the 2.3-16V engines are better suited for FI and can handle more power.
Here are the differences very good described Hypereutectic pistons

Bye
Maki

Today I was looking at the literature and found this:

Verkaufsprospekt DIE 190ER VON MERCEDES BENZ, Ausgabe 10/92, Seite 31:

4-Zylinder 2.5-16

"... Auf einen hydraulischen Ventilspielausgleich haben wir verzichtet, zugunsten einer besonders "steifen" Steuerung, die wesentlich höhere Drehzahlen erlaubt.
Da bei solchen Drehzahlen die thermodynamischen Belastungen erheblich höher sind, sind die Kolben aus Leichtmetall geschmiedet. Außerdem ist der Motor
serienmäßig mit einem Öl-kühler ausgerüstet."

So 2.5-16 pistons are forged,

but by looking in 2.3-16 Rüf/KAT Engine manual (page 28)

"The light alloy pistons are manufactured by a hot forging process to provide higher strength."

So Maki it seem that only those are the pistons you were talking about that are not forged in 16v family - only those of 2.3-16 RüF or KAT Models. Because on many places (literature) it can be found that 2.3-16 ECE pistons are also forged.

BR
Nikola.

[16vau]

Stimmt,

hier stehts schwarz auf weiss, "geschmiedete Kolben"

schmiedekolbe.JPG

und hier "Die Kolben sind aufgrund der hohen thermodynamischen Belastungen, die bei einem Hochleistungstriebwerk dieser Klasse auftreten, aus Leichtmetall geschmiedet."

Schmiedekolben.JPG

Gruß Norbert

[shaq]

Also was Ich finde sehr interessant (dachte immer das Zylinderkopfabdeckung 16v ist aus Alu) ABER

16V Einführungsheft MB Service, Englisch, seite 18:

Valve Cover:

"The valve cover is made of a magnesium alloy and is laminated with black plastic on the outside." (Pulverbeschichtung).

Da man weiß was man hat

MfG
N.