Engine Rebuild options

[Vincent guy]

My 67 250 SL just recently started smoking badly, pulled all my SP's and #1 was badly fowled took it to a trusted Mechanic he checked for valve guides or anything valve related no luck. Pressure test showed it running south through the rings, viewed the piston wall with a scope no visual damage, I've since put in a tank with BG in hopes of un sticking a ring, not holding my breath on this one. love to keep the matching number engine, any thoughts?

[Cees Klumper]

Welcome!

I suggest you have full diagnostics done to inform a decision rebuild yes/no. If rebuild is required there are various options; you can check with one of our active member vendors like Joe A (OH) or Dan C (Canada). Then there are the specialized rebuilders like Metric Motors in CA. Check the vendor listing elsewhere on the site, and run a search, you will find many discussions on this topic. I would think any rebuilder can rebuild your engine (assuming it's not been done before, at least not too often) so you can maintain the car's originality, rather than swap it out for an already rebuilt one.

[Paul & Dolly]

Hi Vincent,
Don't Panic..Is your car an Automatic ? Have you checked the Transmission fluid level ?
Is just the one plug fouled ?

These cars have a few unusual features many "trusted mechanics" are unaware of.
I suggest you spend some time doing a search on this site for problems with the auto transmission pressure diaphragm,

If this leaks you can get fouling of  the plug nearest the bulkhead due to transmission oil
being sucked into the inlet manifold here.

It could be so much cheaper than an engine rebuild.

Good luck

Paul

[ja17]

Unfortunately, a bad transmission diaphragm usually causes #6 spark plug to foul. I would remove the cylinder head and have it checked out, just to make sure.

[Vincent guy]

thanks, it's a standard tranny and has a booster leak that raises the idle, the Mech pulled the valve cover and checked the valve seals ran a pressure check and said he could hear it going past the cylinder, I'm in Salt Lake I'm checking around to see if anyone local is competent. I want to keep this engine with this car, if feasable

[garymand]

Oh, so he did a leakdown test -very good.  With a leakdown, you pressurize each cylinder with valves closed and look ast the guage and listen for where the air is leaking from.   I quess the air is leaking past the rings on #1, your front piston. 

Once these rings start to leak there isn't much you can do. The rings wear significantly and they wear the piston ring landings so new rings fit too loosely.  The bores where out of round and with all that tolerance build up you run a high likelyhood that new rings will leak as much as your old ones.   Hopefully you don't have a leaking big hose to the air cleaner, which means much grit came into the intake and mixed with blowby creating an oilly abrasive that scratched the walls.

I've read that no one has much success with just rings.  The recommenfdation is to bore and oversize with new pistons. 

[Vincent guy]

thanks for the tips, and I believe the inevitable rebuild needs to happen Is there a couple recommendations from this forum members that will do a competent job? I want to keep the numbers matching to the body

[mdsalemi]

Metric Motors in CA has rebuilt many of these engines…
If you specifically ask them NOT to mess with any number stampings on the engine, they'll leave it alone…they did this on mine.
Going on 13 years since the rebuild.

[garymand]

Salt lake is a big town, you have to have a few old mercedes guys there.  If no one here has a recommendation, go to the yellow pages or Google mercedes repair and find someone along 89.  Call them and ask if they have success rebuilding 1960's  2.5s and what might it cost.  I stopped at an autozone there once to get a MAF for my C320.  I remember there were at least 2 mercedes shops on the way down from I80.

Go in and visit them You will see what kind of cars they are accustom to working on.  Find out what machine shop they use and go visit that guy.  I guess you need the valveguides and some new valves, so ask them how they put the guides in, (the old guys, like me, soak the guides in liquid nitrogen and heat the head.)  If you just press them in, there is chance of deforming the guide.  See if they can give a customer reference or a shop reference.  

I'm guessing your best bet is to find a shop that was in business in the 70's & 80's  And have them recommend a machine shop to do the work.

The issue is the pistons are typically not reusable and the tolerances are tight.  So the shop has to take care at every step and not take any chances on short cuts.

[Vincent guy]

I talked to MM of Cal and like what they had to say about working on my Block and returning it, glad to hear a positive position with them, their is a good group of MB mech's here locally and Have known them all of them, none seem to excited about the local Rebuild and all have refereed MM of Cal thanks for the info

[garymand]

Good to Know.  As times change the local machine shops loose the experienced hands and the new guys don't know the tricks and needs of these older motors, but they are willing to give it a try on your dime. 

[mdsalemi]

Vincent,

When all you do--for decades--is engine rebuilds, you get very, very good at it. That's Metric Motors.
When you need driveshaft work, consider Driveline Service of Portland (OR). Like Metric with Mercedes engines, when all you do is driveshafts, you get very, very good at it.

[Rolf-Dieter ✝︎]

As times change the local machine shops loose the experienced hands .... 

Very true and very well said Gary! The lack of "Apprenticeship Programs" in North America will definitely make it no easy task to find the right people/shops as time marches on .... I feel sorry for the future generations in our part of the world ... we don't make too much any more ... most good stuff is imported.

My Master many moons ago in Germany was 70 years of age and he passed his expertise (he tried anyway) on to me ... and I am grateful for it.