Performing compression test on Penta

bobmcgov · #1 11-23-2012

We have the original MD6A Volvo Penta on our new-to-us boat. Whether we keep it and go to the trouble of converting the cooling and exhaust systems has a lot to do with the condition of the pistons and valves. It has the Bosch injectors (held in by yoke washers) and no glow plugs; what adapters do we need to perform a simple compression test? The engine is already winterized, so we'd like to do the test cold. The specs in the owner's manual are 285-340 psi at starter/generator RPM.

Faster · #2 11-23-2012

The volvo part number appears to be 9988539-4 compression gauge..probably not cheap... and maybe even not a match for your model...

dabnis · #3 11-23-2012

Have done lots of comperssion tests on gas engines, but none on diesels. If it starts without excessive cranking or ether and runs well without smoking the compression may be within specs. I read where someone added a little oil, as can be done with gas engines when worn rings are suspect, and it made the diesel fire. Seems like a bit of a stretch but diesels do run on thin oil?

Paul T

bobmcgov · #4 11-23-2012

Yeah, we're trying hard to avoid anything with the name 'Volvo' attached to it. These are pretty standard Bosch injectors, tho I can't measure the length or aperture until they are pulled. Probably 24mm. I just need the right adapter so any garden-variety diesel compression gauge can read it.

When we change over from raw to fresh water cooling and wet exhaust, we'll be fabricating our own mixing elbow, too. If you can even find a Volvo elbow, they cost ~$500.

Doesn't take too many OEM Volvo parts to make a total re-power the preferred option. We want 4 seasons or so out of this engine before we swap out. If the internals are solid. No hour meter, sadly.

Capt Len · #5 11-23-2012

Real carefull there, Not much room for oil at TDC.

Capt Len · #6 11-23-2012

Better to start and run. watch for smoke and oil pressure from cold to hot. (shows condition of bearings) Mixer easy to make with adapter plates and NPT pipe fittings. Make a second at same time to make sure you're good for the 4 years. Weld the nipple at a good angle well below the hot part.

CalebD · #7 11-23-2012

So Bob, where will you be sailing your new-ish Albin 30'?

You are right about the Volvo OEM parts. Enough of those and you could buy a Beta marine brand new diesel (~ $6K). Kubota tractor dealers carry most of the replacement parts at a major discount.

PorFin · #8 11-24-2012

Bob,

Not sure if it will help, but I faced a similar challenge on our Perkins 4.108 which also uses yoke style injector hold-downs.

I picked up a cheapo diesel compression tester at Harbor Freight. It has a quick disconnect (QD) fitting, but no adapters that were usable on the 4.108.

What I wound up doing was to disassemble an old injector to remove the guts. I swapped out the fuel inlet fitting with the QD fitting. I reassembled the injector body leaving out the needle & springs. I also blocked off the fuel return/overflow path.

It took a couple of test runs to make sure it was holding, but ultimately it worked fine.

dabnis · #9 11-24-2012

Before going to all that work, you might consider an oil analysis, supposedly it will show worn bearings and/or rings in addition to unburnt fuel contamination.

Paul T

bobmcgov · #10 11-24-2012

Quote:

Originally Posted by CalebD

So Bob, where will you be sailing your new-ish Albin 30'?

You are right about the Volvo OEM parts. Enough of those and you could buy a Beta marine brand new diesel (~ $6K). Kubota tractor dealers carry most of the replacement parts at a major discount.

Three or four years to refit completely, then down to the Pacific. Probably keep the boat in San Carlos, MX. Would like to hit Vanuatu, Tonga, someday. That's a ways off. Need to replace those sketchy thru-hulls first.

Adore the Beta engines. Outside our refit budget, tho.

PorFin: Thanks! I might try that approach. We also have a huge number of eager, impoverished young diesel mechanic trainees in town (big technical college). I might find a couple of them to run the diagnostics, maybe overhaul the injectors, maybe even the whole engine. Tho again, we don't want to pour too much into an engine that has a) been fresh-water cooled its whole life, albeit in the Great Lakes; and b) will be an ongoing source of trouble/expense. I'd like a solid notion of what hours it has left before we commit to major repairs or modifications.

Suppose "ongoing source of trouble/expense" pretty much describes marine engines in general....