AlpineRAM

The smoke screw sets the max fuel available until boost starts.
No smoke at WOT and no boost, if engine is sluggish to accelerate, adjust smoke screw.

Starwheel controls the spring preload - how far the plate of the afc goes forward for each psi of boost.
If engine seems to hang at 5-10 psi of boost at WOT and does not smoke.. reduce spring preload on the afc.

Those adjustments only affect running at WOT or close to WOT,

Your boost being too low has already been re-hashed several times in this thread. It has also been determined that adding fuel is not the solution there.

The timing will be quite close to correct if the pump hasn't been tampered with, but the 22degrees or 24degrees of the marine engine stem from the use at 3000 to 3200 rpm under max load.
Truck engines use 14degrees to achieve good off the line performance, but have high egts and more smoke at high rpms (above 2800)

You can not directly translate truck timing to marine timing due to different shapes of the combustion chambers, but the principle should be visible.

Could you check your boost gauge for accuracy? (I usually use regulated air with a known good manometer to check boost and fuel pressure gauges)

JKosinski

The boat floats on the 17th. I can start working on the engines then.

What would you think the boost should be? How much boost is too much? I assume that boost beyond a certain point will blow the head gaskets.

If I make any changes, I will document them so I can go back if necessary.

If a turbo spins freely, whines under load, and produces boost what could be wrong with the turbos that would cause low boost? Could the wheels be dirty?

I will verify the boost gauges. I will run the boat and check for boost leaks under load.

Thanks
Jack

AlpineRAM

The turbos can have worn bearings, then the compressor wheel starts to rub the housing and this slows down the charger and leads to low boost.
Also the exhaust housing can be too big for the application and keep you in the lugging zone where there is not enough energy in the exhaust gas to produce boost.
(on a truck you would shift down one or two gears, but that is not an option in your case)
The 210 hp version runs approx 25psi boost at max torque, the 330hp about 27.5 psi.
The HX40 is efficient up to almost 40 psi, but has it's sweet spot around 30-32.
Head gaskets with stock bolts usually go up to 35 psi without problems, but this is for new or almost new engines. Head gaskets with a lot of wear will blow out at lower boost.

Since you report only 6 psi of boost ... check the gauge first, if the gauge is correct search for the cause of the low boost. (Turbo, leak or restriction)
A boost restriction or leak can be found by plugging a gauge directly to the compressor housing and another into the intake manifold- the difference should be very small.

JKosinski

This is good info. If the boost should be 27.5 at peak TQ (2000 RPM 683 LB-FT) not max speed, 2800 RPM, then I have serious boost problem.

I will verify my boost gauges and check for leaks under load. There is no way to check boost between the turbos and the aftercoolers. Because there is no wastegate there is no port on the turbos. I have thought about welding a bung onto the pipe that connects the turbo to the aftercooler. That is the only way I can think of to get pressure readings before the aftercooler.

Last year I checked the turbo shafts for end play and side play by hand and found no free play. The turbo wheels spun freely with my fingers.

Thanks
Jack

JKosinski

I spent the day working on the boat getting ready for launch. I checked the engine timing with engine pin and the pump pin. Since they aligned I assume the timing is close. I know that is not very accurate, but the timing shouldn't be too far off. I checked the valve adjustments. Both engines had four cylinders with zero valve clearance on intake valves. There was one exhaust valve that was very close to zero clearance. Couldn't tell if there was preload on the intake valves to the point that it was holding the valves open slightly. I also do not know how much the valve clearance changes when the engines are up to operating temp. If one of the valves were not completely closed would I see high manifold pressure of fluctuating manifold pressure? I thought Cummins engines increase valve clearance over time because of normal wear?

Jack

AlpineRAM

Ha, Valve clearance!

The plot thickens. Intake valves staying slightly open will reduce the amount of air in the cylinder until you are up to boost. So the AFC may well work, but was fooled by that.
The valves do not get wider usually if you run high loads, mostly the seats recess quicker than the rocker wears.

I'm curious what your test of the boost gauges will show.

AlpineRAM

Any news??

JKosinski

I was able to perform some tests. Got the boat floating and set up at the dock. Weather was windy, rainy, and about 50 degrees. It was choppy on the lake and very cold. I could not spend much time testing because I was getting tossed around in the engine room. I recorded the pressures from my Maretron installed gauges. I was able to measure boost on both sides of the aftercoolers. There is no pressure drop there. I used a Snap-on pressure gauge. The tool does not have many graduations so I had to guesstimate the pressures. I think I got enough to see the issues. It was too rough on the lake to safely spend more time testing. I removed one of the air filters to see the compressor wheel. It appeared to spin true, fast, and loud.

After returning to the dock and letting the engines cool off, I removed the air filters to check the shafts. I can flick the wheels and they will spin about 3 revolutions before stopping. There is no end play, the shafts are not loose side to side, but if I push very hard I can feel some side to side play.
as much as it moved the wheels did not make contact with the housings.

I called a turbo shop looking into a rebuild kit. He believes the turbine housings are bad. He thinks the housings are corroded and pitted causing too much clearance between the housing and the wheel. He recommended checking the clearance on the exhaust side. A new turbo will have a clearance equal to the thickness of a business card. A used but serviceable turbo will as much as the thickness of three business cards. Of course the exhaust flange bolts won't come out. I need to go back with a torch to heat up the housings. I will clean the housings with break-clean and see what they look like. Does this sound plausible? These engines only have about 600 hrs.

If the housings are corroded can they be fixed? If I need to replace them can I have the new housings coated to prevent future corrosion? If the housings are not badly corroded and the turbine wheel isn't fouled, what could cause the low boost readings?

Rebuild kits are inexpensive and it appears straight forward doing the work. Some say the turbine shaft and the compressor wheel are independently balanced and there is no issue taking them apart. Others say that these two parts are balanced together? I read that I can mark the shaft and the wheel, then aligning the marks will keep them balanced?

I plan to verify the calibration of my test gauge.

Gauge readings Test gauge
RPM Port STBD P S
1800 1.77 6.76 2400 5.0 15.00
2000 2.27 7.67
2400 4.87 13.13
2950 24.00 24.00

Thanks
Jack

Rare1

Do you have a coolant leak into your combustion chambers? Why would your turbo housings be corroded?
Your turbo shaft bearings seem OK.
I'm guessing you tested at 100% throttle. Where was the test gauge connected? at the aftercooler? Your pressure readings at 2400 RPM of panel gauges vs test gauge are a good match. Where are the panel gauges connected?
Looks like stbd engine pulls a lot more than port, at less than max rpm. Do you feel the difference in thrust at the wheel? Can you center the rudders to test this?
I don't know your injection setup, but my truck does not need max rpm to get max boost. It pulls strongly a little after 1500 rpm and seems to level out at 2000 with gobs of power.
I googled a 6bt marine engine and found a 24 valve 330 hp unit (I know not your engine) and the torque and HP curves were nearly maxed at 2000 rpm. Your engines could not be much different.
Turbo housing clearance should tell you something, but why are they equal at max rpm?
Lastly, is your engine compartment sealed tightly so that intake air can not enter?

AlpineRAM

I would check the turbos as recommended by the shop, and if you need new housings I'd suggest looking for a little smaller ones.
(less cm²)- if available.
Visually inspect the turbine wheel, if it is damaged in any way I would get a replacement and let a shop verify the balance. The "supposed balancing" does not cut it at over 100 000 rpm..
In the excavators we found that well balanced chargers lasted more than five times longer than the same kits without balancing.

The turbo mounted seems to be made for optimum running at high load and high rpm, but that makes them lag at lower rpm.
The problem is that you need a lot of torque to get the boat to plane, then torque demand is reduced and will only catch up to the torque needed to get into plan at a quite high speed. (Which you don't seem to want to run for noise and comfort reasons)
With a smaller turbo you can easily get boost at 1500 rpm, have gobs of torque there and with a wastegate it will not choke out the engine at higher rpm.
Ideally you would get an HX35W marine. (I don't know if they are available)

JKosinski

I apologize for the way the numbers look. I had them spaced and sending made a mess of it.

I was simply bad day to be on the lake so my testing was limited. I did get a pressure gauge that measures in one lb increments. I had it certified in 5 lb increments from 5 lb to 70 lb and this gauge is spot on. I tied in this gauge with the test gauge I used to a compressor that has an adjustable regulator. I verified that the test tool is also accurate. I am certain of the pressure readings.

No coolant leaks I am aware of. The coolant tanks are full. The theory is that there is condensation in the exhaust system after shut down. That is causing the corrosion. I have not read about these engines having turbo problems? If condensation does occur I would think that would happen to some extend in the truck engines?

The sensors for the panel gauges are in the intake manifold near #2 cylinder. I installed my tester in the other port near the middle of the engines. The pressure readings were the same at the manifolds as before the aftercoolers. My engines peak TQ is 2000RPM and peak HP is 2800 RPM. When the boat is starting to get on plane beginning about 1800 RPM I need to wait for the boat to get on plane. Pushing the throttles forward does nothing. The engines won't continue to increase in RPM and the boat won't speed up. Pushing the throttles to full speed at this point will make the engines blow black smoke. Although the boost is equal at 24 PSI full speed I do not know if that is a good number or a low number? The boat is getting enough air into the engine compartment because I have run the boat with the engine hatch open to ensure there is plenty of air.


My plan is to go to the boat tomorrow with a torch and get the flange bolts out. Then I will know more about the condition of the exhaust side.

If I mark the wheel and the shaft, would that keep the balance as good as it now? I know that is not ideal, but I am not sure if I can find a local shop to balance the wheels while I wait. I am concerned about the down time. I read that some turbos have independently balanced turbine shafts and compressor wheels, does anyone how to determine if mine are? I have searched the net and I have not found a turbo with same mounting flange as the marine HX 40.

Does anyone have experience using the E-Bay turbos? A complete new turbo is less than the price I was quoted for just the exhaust housing. I know they are made in China, but I would not assume they are bad or poor quality. Not everything made in China is junk.


Thanks
Jack

AlpineRAM

24 psi at full speed sound quite right.
You know that the governor reduces fuel per revolution so you don't rev over max speed, so if the boat needs less than full torque at that speed boost will also be lower than full boost.

Corrosion problems in those turbos come mainly from salt water through the exhaust housing, sometimes they get eaten right through and then the material of the housing and the wheel gets eaten away.
Be very careful with the torch- if you overheat the center section you can destroy o-rings like on the oil feed and coke the oil somewhat bad..

Talking about the amount of air I always mean the mass of air in the combustion chamber at a certain time.
Torque is a function of the mass of fuel being burnt per power stroke.
Since you have insufficient torque at 1800 rpm, but have black smoke you see that you do not have sufficient air in the cylinder at that time for your load. You also see that you have more than enough fuel.
On a turbo engine this is usually caused by too big a turbo for the application.
At this point of operation the turbine is too big to produce power with the amount of enthalpy available in the exhaust gas. So it can not power the compressor, and not enough air mass is available to A increase rpm and B create more enthalpy in the exhaust gas.
This situation is called lugging below boost threshold. The problem can be solved by different means.
Increase engine rpm (downshift, change prop etc) - therefore increasing the flow of air in the "naturally aspirated" engine.
Decrease turbo size- make it work with the energy available, accept choking out at higher rpm/load scenarios (which can be alleviated by a wastegate)
Use a VG turbo- adjust turbine size to the requirements.
Inject nitrous to increase fuel burn and generate enough enthalpy in the exhaust gas to spool the turbo.

About the chinese turbos- I have seen very mixed results, and I would not use a rotating assembly from them.
Not all are bad, but the damages caused by a bad one are really bad.

Rare1

I have not read in this forum of turbo housing corrosion in our trucks. There is much discussion of exhaust systems but no mention of rust.
I am seeing a clearer picture of your situation now, and thanks to Alpine too. My conclusion for simplest fix is that you are over-propped. I.e. too much pitch. You can't spin the engines fast enough to get over the plane hump because the turbos are not in their best boost zone.
Alternatively, a smaller turbo if you must renew your turbo housings. This might result in less gph at your desired 25 MPH.
But I still don't understand why the engines have such different boost at part throttle. Housing clearance? A difference in the intake paths? Blockage?
Full throttle boost looks adequate, and surprisingly equal.

JKosinski

I removed the frozen turbo flange bolts after many hours of heating them with a torch. I think the coolant in the water cooled turbine housings was absorbing the heat. I will try to attach a pic of the STBD turbo. I cut a business card into strips. The STBD turbo has a clearance of 4, 5 won't fit. This turbo has the highest pressure. The Port side appears to have a clearance of 2. It took so long to get the bolts out that I ran out of time. The Port housing faces away from where I stand and it was still hot from the torch. I plan to recheck the clearance. I am, struggling to understand how that additional gap would totally kill the turbo performance. This boat only floats during the summertime in Michigan. If the corrosion is the problem, it seems to me that this would be a very common problem. Every Cummins marine engine in the great lakes region should be having the same trouble?

I need to know what the boost pressure should be? Getting on plane should be the highest load and I would think then the highest boost? Someone must know? Because the engines have different pressures at least one of them has a problem. Where do I find the clearance spec for the housing? If this corrosion wear is the problem then there must be a clearance spec?

My boat runs up to 2950 RPM, that means the boat is not over propped. There is no other way to determine prop size. If the boat was over propped I would not be able to reach that engine speed. Because these engines have a high speed throttle stop, the boat may rev faster which would indicate then that I could add more pitch. After I resolve this boost issue I plan to set the stops to 3200 and see if the boat will run that fast. The boat has always run in fresh water.

I could buy new turbos, if that fixes it great, If that does not fix it I will have wasted thousands on work that did no good. If new turbos do fix the boost problem it will likely happen again. There needs to be a permanent solution to this. Can the housing be sleeved? Perhaps a stainless steel sleeve or some type of coating would not fail because of normal use. I do not see an option to replace these turbos with anything else. No other turbo I have seen has the same mounting flange.

My turbo data: Assembly 3536620, Serial number H1995536, Customer number 3536621, MDL: HX40-l8294. T/J 1683.

Thanks
Jack

AlpineRAM

This consistent boost difference can easily be caused by a slightly misadjusted throttle linkage, so that one engine has a bit more throttle with both levers parallel.
On the older Volvos I usually synced the throttle through the boost gauges to get a smooth and straight running boat.
To verify a problem in one engine I usually compared running only on left with running only on right, if boost and rpm and smoke are quite similar at this test you know it is a linkage or AFC/Plate mismatch between the engines.

Nevertheless, insisting on the prop "wisdom" derived from gassers when talking turbo diesels will not work.
The combination of hull and prop determines the necessary tuning of the engines, or you can fit the props to hull and engine tune.

And you can retard timing a good bit to increase torque and exhaust enthalpy at lower RPM as it is seen in the trucks. (Where these engines run 14 degrees to perform good and spool the charger below 1500 rpm, where in the boats the timing is very high but these engines are built to perform best at high loads at high rpm - higher rpms than the truck version will rev even without significant load..)