8v71ti-air System

[JCG]

Several weeks ago, a number of forum members suggested that I look at the emergency air shutdown system as a potential problem for insufficient air flow resulting in black smoke and rpms limited to about 1500.

I spent the day removing the air horns and as usual the advice on this forum is excellent. I definitely have a problem with the system, but I dont think it's causing the original problem with the lack of air because they are stuck wide open. Someone has removed any control cables but the spring loaded trip device was still engaged. I tried to trip them and found them to be stuck, so I pulled the air horns to make sure they were open and so I could get them working properly. They were fully open on both engines.

I found a couple of things that bothered me. First there were no screens on either engine. I thought that there was suppose to be a final screen to protect the blowers. Secondly I was surprised to find that blower rotors could be turned by hand quite easily about 10-15 degrees of rotation.... both engines were about the same... is this typical? And last of all, one engines blower was completely dry while the other had a light film of oil. I am not sure which is correct but they are certainly different.

Since I was in the "grease monkey mode" I went ahead and pulled the intercoolers and may have found the problem. On both engined the intercoolers are contaminated with an oily residue that could be restricting the airflow to some degree. They appear to be ok just need a good cleaning but now I am concerned about the source of oil.

If the oil is a problem I would think the only possible source is the turbos. I can understand this on the engine with light film on the blower but not on the one that was completly dry.

I remember reading something about leaking exhaust being pulled back through the intake and contaminating filters and intercoolers ... does this sound feasible...

Thanks in advance for the advice.

JCG

 

[MikeP]

The current DD airhorn to blower gasket has an integral screen as part of the gasket. I don't know if old gaskets did not have the screen or if someone perhaps made their own gasket for your airhorn. It would be good to get the current gasket on there.

As far as oil on the blower vanes - this can be caused by a leaking blower seal OR a leaking turbo seal (or both). If you have oil on the intercoolers, it is likely coming from the turbo(s) but, of course you could have turbos AND the blower with bad seals. Do you have airseps? They can fail in a way that allows oil to be pulled into the intake.

There is usually some observable back/forth play in the rotors because of the backlash between the various gears driving them. I have never seen a published figure for maximum play in degrees though the DD service manual has the specs for the gear backlash - I seem to recall that .010" is the max but I could be wrong.

Leaking exhaust is known to be quite abrasive due to the soot. You can spray a soap/water mix on the various exhaust hoses/collector joints and see any leakage. Obviously this won't work on exhaust port to manifold joints due to the heat immediately boiling off the water but leaks there can usually be seen and heard.

 

[Brian Degulis]

The Blower is driven by a flexible drive so it's normal to be able to move the vanes by hand. Some oil on the vanes is also normal it's being pulled in thru the valve cover vents. Most turbo engines with intercoolers do not use a screen the intercooler itself is the screen gaskets are available with or without screens. Call your DD dealer with the serial # and he can tell you if it calls for a sreen. Assuming you don't have a lot of oil on the vanes I would clean the coolers and also the valve cover breathers then keep an eye on it to see if it's a bad seal or just normal oil vapor being drawn in.

Brian

 

[REBrueckner]

It's significant that you have the same problem on both engines.... as stated in your earlier post. You mentioned the engine room was pretty dirty...just years of no attention or soot??? Smoke is the likely result incomplete combustion...poor compression, lack or fuel or lack of air.....

I'm going to disagree with the experts here, probably a mistake, but it seems to me most likely common source is a FUEL problem....it's would be unusual to have the same air problem with both engines unless your hull intake vents are sealed...

You did replace ALL fuel filters, and drain your RACOR filter bowls....right??? And the fuel supply and return valves are in the correct OPEN position...handles not loose on the valve stems????

 

[Traveler 45C]

I was told by a DD mechanic not to use the blower screens on marine engines because:

1. No need. There isn’t a lot of debris that can be ingested in our engine rooms and
2. The screens are prone to corrosion/deterioration and could be ingested.

Thoughts?

 

[MikeP]

I disagree - the common thought that there is not much debris to be ingested is foolish. There is probably more possible debris in a boat engine room than any car ever has to deal with. True, you have an air filter or screen on the air intake but if a turbo comes apart - where is that debris going to go? I'd rather replace the turbo than the turbo AND the blower...

The screen is SS and isn't going to corrode and disintegrate. It's called for by the current DD service manual and is cheap insurance.

But like everything else, it's all a personal decision...

 

[yachtsmanbill]

My 12s have the screens, Even if working with the airhorns off its worth it to save yer bunz if a screw or anything else falls in. Murpy's law ya know. ws

 

[Brian Degulis]

All naturals call for screens most TI engines do not just look in a parts book. The screens make sense to me and I don't know why they would be omitted the intercooler would prevent anything from reaching the blower rotors but still the screens make sense. I don't put screens in unless the spec on the engine calls for it.

Brian

 

[MikeP]

Yes, that's true, the inter/after coolers will act as screens and DD may have originally speced the screen for the NAs and an unscreened for the T motors.

OR, since the screen gasket will work on any engine - natural or turbo - It may be that they just decided to reduce gasket inventory. In 2004, when I purchased engine gasket sets for my TIs from DD by engine serial number, the sets came with the screen gaskets.

The screen is also a good "routine maintenance" thing - if you pull the airhorn for whatever reason; I've had one of mine off twice. With no screen there is a HUGE opening which is just begging to have small (or large) parts dropped into it! When I pulled my airhorns, the previously installed screen gasket was gasket-sealed to the blower lid but NOT to the airhorn which is a good way to do it...

 

[Traveler 45C]

All very good points.

I didn't think about the screens being SS. Duh...

I wonder why the guy told me not to use 'em?

 

[JCG]

Thanks for the information, and all the questions. I'll try to address them.

My main problem is lack of rpms on both engines. Both begin to smoke (black) at about 1500 rpm and fail to reach cruise 1800 or WOT about 2250? problem was evident on first run with fresh bottom job.

Both engines start easily cold with a cloud of blue/smoke that completely clears in just a few seconds , once warm both start instantly with no smoke whatsoever.

Boat set for 30 months while being restored, fuel was old a full 600 gallons since dilluted with about 170 gallon of fresh.

Main racor seperator/filter replaced, engine final filters replaced. Air filters replaced, and removed none of which seems to make much difference. Investigated possibility of air emergecy shutdowns being closed.. both stuck open. Pulled intercoolers and both engines have black sooty oily residue.

As for return lines valve positions I don't know, I'll have to go back down and take a look. This is one area that I have not looked at.

I am currently cleaning intercoolers and will reinstall in a week or two. I hope this resolves the problem. If not, I'll be posting again looking for help!

 

[REBrueckner]

Another possible next step after engine reassembly would be to drain your smallest fuel tank and refill with fresh fuel, then run both engines from that fresh fuel tank.

If you have the fuel capacity available, you might pump the old fuel from your smallest tank to other tanks, then refill with fresh....that way if it's not fuel related, you have retained all your old fuel...

Would be a good idea to filter the fuel as you transfer it and inspect the filter as you go...maybe at the 1/3 and again at about 2/3 the pumping....

I'm still thinking there is a common problem..one souirce...causing two engines to misbehave in the same manner...

And don't be discouraged if your investigations appear "useless"..they are not!!!. Every step you take insures one more component is ok and removes that from your list...and you also know those items are likely to be good for years to come....
Good luck,
let us know what you discover...

 

[JCG]

Just a quick note on my progress, cleaned the inter coolers and no more black smoke!!!!!!!!!!!!!!!!!! RPMs now 2100 @ WOT. Problem resolved!!! now time to fine tune,

 

[Nonchalant1]

8V71TIs are spec'd for blower screens. It's the double rectangle gasket under the adapter that goes from round to rectangular.

There's play in the blower due to the flex drive shaft but no play between the two blower rotors, which rotate extremely closely without touching. If you move one, the other should move equally without any play. You should not be able to move one blower rotor without equal movement in the other.

Doug

 

[REBrueckner]

Ok, so it sounds like the air intakes were restricted because the intercoolers air passages were partially blocked, reducing air flow..how does "black sooty residue" end up in the air INTAKES?? Is this a sign of turbo issues??

So what are the causes of such blockage in the intercoolers.

I just had my starboard engine intercoolers out early last year; they had not bee inspected in about 1,000 hours over about 9 years....I saw no residue/soot/no blocakge of any kind...but one had a tiny water leak and had to be replaced....

 

[Nonchalant1]

If you have AirSeps, there will be oil residue on the intercooler which looks very black and sooty, however, this usually won't build up enough to restrict air flow. Because the air is filtered, it should not be restricted on the air side of the intercooler.

Raw water restriction AFTER the intercooler can cause very high water pressure in the intercooler water pipes and can expand the normally oval copper pipes to a more round shape, reducing the interstitial space between pipes, substantially reducing air flow. This can be seen by inspecting the intercoolers.

Doug Shuman