new head, #5 low compression
 

I had my head rebuilt last week. New everything. Headgasket, intake gasket, plugs, wires, exhaust gaskets, valves, guides, seals, and valve cover gasket.

Engine does not run very smooth; less smooth than it did before, actually. Did compression test and 1,2,3,4, and 6 were 130 psi. # 5 was 60 psi.

I made sure that the cam timing did not move, looking at it I think it would be hard to mess up anyway. I did not move the crank and the cam and gear have a pin and hole that require proper alignment.

Anyway. What should I check? I also have an exhaust leak... I did not remove any of the exhaust system, just removed the hardware that bolts the head to the manifolds.

Kyle

I would inject some air into the cylinder to see if it can be determined where it is coming out at. Or put a little oil in that cylinder to see if compression rises. Perhaps both tests and just compare it to any other cylinder for refference if required. Double check your valve clearance as well on that cylinder. Tough luck. As matter of habit I always put a littlle very light oil in my heads combustion chambers after the head comes back and leave it overnight. That way if the valves or a valve is not seating properly I know.

Let me get out my crystal ball to find out the year and model of your car...:o

ASSuming that the engine is a M103?
Since the compression is lower on only 1 cylinder, I would remove the valve cover & rocker arm assembly on that cylinder & try removing the valve lash shims on those 2 lifters..re-install the rocker arm assembly & re-check the compression...that should show if the problem is a lifter OR a valve that isn't sealing properly.

MB does supply different size valve lash shims...both the ones above the lifter & the lower ones as well.

It sounds like you had a mechanic do the work right? Take it back and make him fix it!!!

i agree with mb doc --check that cyl & all related to that cylinder..
the valves might not be seating correctly.. or the lifter caps might just be mia??

Sorry, I used to have that in my sig...

1991 300e 3.0L m103.

Thanks Doc.

I am a tech in training, school of hard knock... BMWs are my thing, however.

I had planned to do a leak down at TDC in the morning... I will do the valve lash thing first. I reinstalled everything I removed, but my old valves had already been ground (?) once before so I would think things would change with brand new valves.

I have older guys I work with and they all say, "Its been so long since we worked on those things..."

Any way I will keep you guys updated.

Also, does 130 psi seem high enough? before I did the head job, though it was a different gauge set, I got 185 psi....

I was going to say, 130 is rather Low.. Are you Sure your timing is spot on? Did you move/change valve shims? Do you have a leak down tester handy? Who did your machining?

Jonathan

Stan from Lauck (sp?) in Roswell. He does this kinda thing in his sleep.

I know Lauck..I've chatted w/ a fellow there, can't remember his name but he's been around for some time. Did they do the work for you or did you just give them the head to have the machining done? I have yet to find a machinist down here that I feel 100% comfortable with. I did find one that does top fuel engines but they stopped taking on new clientèle a few years ago:-/

Jonathan

Leak down is bad. #5 is good now, however.

The vavles are not seating properly.

I drive the car, it is smooth and has the amount of power I remember. But every other stop it idles rough.

I also replaced teh plugs with Bosch Supers, as it had platinums before...

I also get a lifter tick every now and then. by friends says since teh guides and vavles are all new, everything may be too tight.

Don't really know waht to do at this point...

I am calling my machinist
monday. I will update from there.

Machinist came over. Lifters were all locked as he described it. This was causing the valves to come no where near closing. We removed them all one by one and squeezed them to free them up. One still ticks every now and then. He also said the rockers had seen better days, so he brought me a better set, and I am ordering new lifters.

I picked up another camshaft from my other Mercedes tech friend... he was appauled that we had forced the lifters closed.

#1 Is it bad to have forced the the lifters closed?

#2 I am getting aforementioned cam ground for higher lift and duration. The lifters should compensate for the slight difference in the base circle, correct? Or will I have to "shim" the lifters?

<<getting aforementioned cam ground for higher lift and duration. The lifters should compensate for the slight difference in the base circle, correct? >>

Why would the base circle change ???