[mountainredneck]

as some of you remember, i posted a while back that i was done with jetronic. well, after pulling out what hair i had left, i had a benz mechanic come over and double check my attempts to repair the car.
he found nothing obvious as i did. we had spark, fuel, timing good, compression 80-100 lbs, etc.
well i paid him, he wanted to take it to his shop for further analysis. we both thought that due to all the cranking etc that the cylinders might be gas fouled. so when he left i poured oil in the spark plug holes to let it set for a few days while i come up with some money for the repair.
lo and behold, guess what i saw? oil was pouring out from 4 of 6 cylinders right at the bottom of the head. blown head gasket!
from my experience with chevys, they would start with <100lbs pressure. appearantly not a benz. so, i have to replace my first head gasket on a 103. i am somewhat excited about it all really, but do any of you have any advice, watch out fors, etc. also, what else would you all replace whilst doing the repair? timing chain, tensioner, valve job, shave the head a little, valve seals, etc?

 

[parad0x_i]

compression 80-100 lbs

This is far too low in my opinion.. and i would be looking for around 150psi at the lowest

do any of you have any advice, watch out fors, etc. also, what else would you all replace whilst doing the repair? timing chain, tensioner, valve job, shave the head a little, valve seals, etc?

I would check the valve guides while the head is off and renew them if necessary. At a minimum.. do a valve job with new stem seals.. get the head skimmed and fit new head bolts..

 

[neanderthal]

If you're gonna take the head off it certainly behooves you to do a complete cylinder head overhaul while you're there.
Valve guides and stem seals, check the head for straightness, valve seats etc

 

[RBYCC]

Factory spec for M103-12V compression:

Normal = 12 bar / 176.4 psi
Low = 7.5 bar / 110.25 psi
Max cylinder difference = 1.5 bar / 22.05 psi

 

[mountainredneck]

thanks for that rbycc, i was wondering about that.

 

[mckellyb]

Yeah, thanks for posting the high and low.

Had it been me, anything below 160 PSI would have had me gasping and reaching for the head gasket instructions.

 

[Jayare]

Our new DIY section has a link for the complete workshop manual. This is a two man job to get the head off Mountain and you'll need a chain hoise of some sorts. Head comes off with exhaust manifold attached and intake. Way heavy. Do as others have suggested and get the valve guides replaced, stem seals etc. and have the head decked.

Good Luck partner,

Jayare

 

[coldfoil]

How much to do when replacing head gaskets???? We'll I gues it all depends on how much money you have. If money is not and issue, I would have the heads completely rebuilt, If it is, I would at least replace the valves. Anything else you can replace with with head installed in the car in a later time when you have more money.

 

[mountainredneck]

Our new DIY section has a link for the complete workshop manual. This is a two man job to get the head off Mountain and you'll need a chain hoise of some sorts. Head comes off with exhaust manifold attached and intake. Way heavy. Do as others have suggested and get the valve guides replaced, stem seals etc. and have the head decked.

Good Luck partner,

Jayare

hey jayare,

how you been. boy was i wrong on the jetronic thing. i had been checking and rechecking all kinds of stuff and even the benz guy missed it. it was worth the money for him to come over just to know that somebody who does this everyday still couldnt fiqure it out. i have learned something about the 103. its a good day. i have just got it torn down to the cam gear with valve cover off, TDC, etc. this cold weather has moved in and i came in to build a fire. man i miss the beach, i am afraid that i will end up in florida before long. cant do a thing when its cold outside.

 

[Clarkz71]

i am afraid that i will end up in florida before long. cant do a thing when its cold outside.

Come on down, besides helping you with your Benz we can go shooting.:thumbsup:

 

[augapfel]

Call me skeptical but something is not making sense here. You pulled all 6 plugs and poured a bit of oil down each plug hole, right? And oil ran out the head gasket area below the plugs?
You do realize that there is a 1/8" hole cross-drilled at the bottom of each spark plug recess and that the hole dumps out the exhaust side of the cylinder head below the manifolds? I presume that the holes are there to give any accumulated oil or water a way to drain out of the plug recess.
I can't believe that 4 cylinders would be blown on a 6 cylinder engine. And with the pistons at various height in the cylinders, you'd have to add a whole lot of oil to at least a couple cylinders to reach the head gasket area.
Something to think about...

 

[mountainredneck]

very interesting, i didnt know that about the cross drilled holes. i thought it odd that the head gasket would be THAT blown. i havent totally pulled off the head yet. just the wires, cover, etc. what do you suggest?

 

[Jayare]

Pull a compression test before you go any further Mountain.

Jayare

 

[mountainredneck]

will do, i have had oil in cylinders for a couple of days now, i will report findings tomm.

 

[augapfel]

Yes, compression test. For reference, I did a compression test on the 3.0L engine that I installed in my 260E before I pulled the head. I knew that it needed guides due to the smoke screen but I wanted to see if I had any bad cylinders. I did my test with the ignition system disabled, the throttle blocked open, and a battery charger hooked up and set to boost.
What I found was that all cylinders were slow in coming up to the max pressure. The first compression cycle pulse resulted in only about a 30 psi reading. Each successive pulse resulted in a 15 psi increase. Ultimately, 5 of the 6 cylinders maxxed out at 190 psi and one cylinder reached 185 psi. It took almost 30 pulses (yes, 30) to reach that max pressure.
I know that isn't the way a compression test is supposed to work but I had an unknown, possibly junk engine that I didn't care about and also an expendable starter motor. After doing the head and replacing the injectors, I put that engine and trans in my 260 and it has been running great for 40k miles.

 

[mountainredneck]

we noticed the same thing about slow to rise. we turned engine over about 12-15 revs, BUT, i didnt think of holding the throttle open.
i will try all the above today and report back.

 

[augapfel]

If I were to do a compression test again I would find a way to hold the airflow plate down a bit as well. Pushing the plate down and sticking a small block of styrofoam between the plate and the housing should suffice. Having that plate block airflow must have an effect.

 

[mountainredneck]

results... left air flap as is, held throttle wide open. no cylinder was less than 170PSI...
what the heck guys??? i will start putting it all back together tomm. let me know what you all think. it could be that the gauge was bad. first test this morning resulted in 300+ PSI!! i assume it was oil loaded up in that cylinder.. anyway, gauge didnt act right after that, so i replaced it with a brand new one rated up to 1000 PSI. tested them all and as stated, ranges were between 170-200.

 

[augapfel]

So compression is definitely NOT the problem. And the engine won't start?

 

[mountainredneck]

before all this fiasco, no, it wouldnt start. but who knows, maybe it was gas fouled. all i know for sure is the compression is good, spark was hot, timing was good, fuel was good.
i will put it all back together tomm. and start at square one.
i want to say a special thanks to augapfel and jayare for your wisdom and assistance. you both saved an unemployed man alot of money. thanks again.