DD 8V92Ti cylinder Temp.

[osprey]

Hello, I am seeking advice. In the effort to get the most out of my old engines, I have preformed a couple complete tune ups. Rebuilt the blowers and turbos, bought a couple exhaust manifolds, and a set of injectors. (No, I did not have the injectors flow checked before installation, this I learned later, was the thing to do). At any rate. I borrowed a infra red thermometer and thought I would check the different temps around the engine. I took the engines up to temperature then brought the boat back to trawling speed and went down into the engine room. On the starboard engine I did my very best to measure the temperature at the same spot on each exhaust manifold to cylinder port..... The readings where like this, L1-237 R1-230 L2-199 R2-187 L3-212 R3-212 L4-240 R4-257. (measuring in order L1,2,3,4 then R1,2,3,4. Can any of you interpret these reading into something useful?

Regards, Pete

 

[captddis]

Checking them at cruise would be a better test.

 

[MikeP]

I did something similar back when we bought our 53MY - 8V71TIs. I did an IR test at each exh port approximately 1" out from the head at the exh manifold. There was considerable variation - on the order of 30 degrees. I carefully marked the manifolds/shot the IR gun at the same spot from the same distance multiple times to ensure as consistent a measurement as I was capable of. I then did a very careful tuneup which took into account the fact that there is some "flex" in the rack if you do the tuneup strictly by the DD service manual and got the max temp difference to 9 degrees.

Re flex in the rack - the movement at the far end is not the same as it is at the close end so just setting each injector height with the correct gauge does not actually end up with the same injection stroke. In reality, on a DD in the real world it probably doesn't matter at all but years of building competition engines makes me anal about such stuff. Added to the fact that it probably doesn't matter, it also makes the tuneup take a lot longer. But death marches and pointless Jihads is part of my mechanical makeup...usually to no useful effect.

 

[rsmith]

I did something similar back when we bought our 53MY - 8V71TIs. I did an IR test at each exh port approximately 1" out from the head at the exh manifold. There was considerable variation - on the order of 30 degrees. I carefully marked the manifolds/shot the IR gun at the same spot from the same distance multiple times to ensure as consistent a measurement as I was capable of. I then did a very careful tuneup which took into account the fact that there is some "flex" in the rack if you do the tuneup strictly by the DD service manual and got the max temp difference to 9 degrees.

Re flex in the rack - the movement at the far end is not the same as it is at the close end so just setting each injector height with the correct gauge does not actually end up with the same injection stroke. In reality, on a DD in the real world it probably doesn't matter at all but years of building competition engines makes me anal about such stuff. Added to the fact that it probably doesn't matter, it also makes the tuneup take a lot longer. But death marches and pointless Jihads is part of my mechanical makeup...usually to no useful effect.

"Re flex in the rack - the movement at the far end is not the same as it is at the close end so just setting each injector height with the correct gauge does not actually end up with the same injection stroke."

.???? The rack has nothing to do with the injector height or stroke. The injector is directly actuated by the cam lobe cam lifter push rod and rocker arm. The rack moves the fuel rod in and out to regulate flow,there not much resistance on this rod and I can't see any meaningfull twist or movement in the rack tube.
IMHO these external heat gun tests are a joke. Without a thermocouple actually in the exhaust flow there are too many variables. If you really want to test the injectors pull the valve covers and hold each injector plunger down on at a time check engine sound and rpm drop with a digital tach.

 

[MikeP]

You are right re the injectors - it was the fuel rod clearance that changes from front to rear Cyls I got injectors in my head for some reason. Thanks for the correction.

And yes, you are right re a thermocouple vs an IR gun but I was much more comfortable seeing 9F between the high/low port than I was with 30F+. Sometimes we do what makes us comfortable...even if it doesn't matter.