8v71ti Compression Test Protocol

[SeaEric]

A well respected Detroit Diesel Surveyor advised me that DD compression tests are performed with the engine at a minimum of 140 degrees, and running at 600 RPM's. If this is indeed correct, then a compression test performed with the engine at 100 degrees will yield incorrect readings. What say the DD Brain Trust here?

[Captain Ralph]

It is hard to keep an engine @ 140° while dock side. I know some guys choke down on the raw water sea-cock but I prefer against that.

IMO;
The important thing to keep in mind, all readings are done at the same warm temp.
Engine oil is warm and flowing, thermostats are a lil open ensuring all the lungs are at the same temp. IR gun at the water manifold above the head will help determine this.

This is a hot and sweaty job.
Labor intensive also.
New fuel pipes are old school required.
The injector timing height should be checked (Preferably the next morning cold) when reassembled also.
I may catch some grip about that but That is the way I did it and some were off.

Are you troubleshooting an issue or going for survey documentation.

An IR gun shot at the exhaust port can tell you quicker if you have a weak cylinder.

[SeaEric]

Engine survey at the dock today on a pair of 900 hour SMOH engines that start easily from cold, little smoke which clears
quickly and they run out beautifully. She made 20 knots at WOT on sea trial this past Monday. Mechanic today checked
compression on only 2 of the 8 cylinders on each engine. Port was within spec but on the low end with one (of the 2 tested) Stbd had cooled to 100 degress by the time that one was tested and one (again of 2 tested) was reportedly below spec at 420 PSI.

[Pascal]

I thought compression checks were part of a standard survey ? Only with red flags like smoke or observed wear on the liners.

[Captain Ralph]

was reportedly below spec at 420 PSI.

Oh sheet.
How do you convince the buyer NFBD??

Any liner inspection, standard part of a DDC inspection.
One of 2 lungs tested dock side, IMO, I would not worry about 420PSI.
For all anybody knows, his pressure test tool was leaking in the tube (a little).

Bottom line, did it run out per spec??
Clean exhaust?
Sell that boat.

[SeaEric]

Buyer has decided to have another compression test done by the DD guru. Good plan IMHO.

[Captain Ralph]

Buyer has decided to have another compression test done by the DD guru. Good plan IMHO.

Good plan.
Sorry for the extra expense but if the boat is in good shape, shame to let an error detour a good sale.
Please keep us up on the outcome of the next engine survey.

[SeaEric]

A properly performed compression test was executed today. As expected, engines are well within DD specs.

[Captain Ralph]

A properly performed compression test was executed today. As expected, engines are well within DD specs.

So, What was the correction?

Run between cylinders test to keep temp up?
Just warmed up and a few lungs tested quickly?
Or just a different tech?

[SeaEric]

So, What was the correction?

Run between cylinders test to keep temp up?
Just warmed up and a few lungs tested quickly?
Or just a different tech?

Different tech. Performed the test at operating temp. The block heaters helped keep them where they needed to be.