compression check with oil
 

Does anyone know of a diy guide for doing compression check? i.e. where do you squirt the oil? glow plug or injector hole?

either one is fine.

tom w

those look pretty high. i dont know what is called for on that engine but i am guessing you might have some carbon buildup.

tom w

thread update
 

I went ahead and go the head work done. Two valves were visibly destroyed (one burnt, one split :eek: ), and all 8 of the exhaust valves need to be replaced because of 'mushrooming'. All guides were done, along with timing chain and tensioner and one cam gear (although I don't know which one!). I don't remember the last time the engine ran this smoothly (at least 80k ago), the idle is rock solid, but does dip a little low when you engage the clutch and let off the gas (i.e. coasting to a stop).

Brutally expensive, but the shop owner said he was impressed with the rest of the engine, and believed this would keep me on the road for another 150k+. I go back in after 500 miles to get the valves checked/adjusted against initial wear on the valve seats (to my ears, they sound loose, we'll see). For anyone in the cape coral/ fort myers area, i do reccomend 'Better Cars Service Center'

cheers,
dan r.


On a slightly more philosophical note-part of the mystique of Mercedes reliability is that owners are willing to pay more to keep the car on the road...hence there are more oldies with high mileage out there. If this sucker was a honda, i'd have trashed it.

Trust the gauge?
 

I've always been told to disregard the number on the compression gauge, and just look for no more that 10% variation between the high number and the low number. Someone once explained why the actual psi number can't be trusted, but it has done slipped my mind.
As an aside for gizmo heads, large diesel engines often have pressure taps so that you can attach a gauge and check cylinder pressure while running. Really big engines (the three-story tall ones that power ships) have cylinder pressure gauges permanently hooked up.
In the good old days they had a gizmo like a recording barograph (revolving drum with paper on the outside, pen connected to pressure bulb, so the pen moves with pressure, and marks it on the moving paper) anyway, one of those, connected to the combustion chamber, and would make an "indicator card" showing the profile of pressure rise with compression, then pressure spike with injection/combustion, then pressure fall as the cylinder stroked, then pressure drop as the exhaust valve opened. One boat I worked on had an english Sun-Doxford engine, with all this gizmo, and in the engine manual there were indicator cards from the engine's acceptance trials.
Now they do this with an ultra-sound thing that bounces sonic beams through the engine, and instantly plots out a pressure curve on the display of your PC. The theory being that air under pressure is denser, therefore transmits sound faster, while the rest of the iron, coolant, etc, transmits at the same rate. For something like $15,000 you could be the first kid on your block to have one, and amaze your friends.
What will they think of next.
seo

final addendum
 

After about 500 miles, I started getting a very rough idle-definitely a miss somewhere in the engine, along with an un-even acceleration and a miss on de-accel. At first I thought something had gone wrong in the head, and took it back to them for the 500 mile checkup....

As it turns out, the fuel distributor was failing on cylinder 2, the SAME cylinder with the burnt and split valves. So, most likely that cylinder was running lean for some time, causing the failed valve. This is a relief to me because I am usually pretty good with the valve adjustments, and was ticked that i somehow messed them up!

A new fuel distributor later, and I have the smoothest idle in the tri-state area.

cheers,
dan r.