DIY tunnel drive

[liki]

Originally Posted by CDK

Unfortunately I do not have the VW filters and valves because the engines came from a recycler where they used bolt cutters to free the engine from its environment.

Hello again, your missing part is:

(41) 068130157 banto bolt with return flow restrictor / ABL - (41) is not part of the spare part code.

You might want to first ask your local VW shop for the price or ask other recycle yards for that bolt. Likely you'll be surprised by the price, either way. Vagcat lists it at 9,2 EUR in Germany but it is not at all reliable with prices.

[CDK]

Originally Posted by liki

Hello again, your missing part is:

(41) 068130157 banto bolt with return flow restrictor / ABL - (41) is not part of the spare part code.

You might want to first ask your local VW shop for the price or ask other recycle yards for that bolt. Likely you'll be surprised by the price, either way. Vagcat lists it at 9,2 EUR in Germany but it is not at all reliable with prices.

Thank you Liki. No local VW shop within 80 miles, but I'll search the internet. Is the ABL code part of the component description? And why do my engines not have it? I never unscrewed them before and I doubt very much that the vehicle owner(s) exchanged them for the wrong ones.

[baeckmo]

CDK, not only is the injection timing upset, the short time for each injection stroke makes the housing pressure a critical factor for the filling of the pump cylinder. The plunger of the 4-cylinder distributor pump is working with a 4 times higher stroke frequency than each pump element in a 4-cylinder line pump, hence the high housing pressure necessary for filling during the inlet period.

Just spoke to a friend who is in charge of servicing a fleet of MAN-vehicles. He confirmed that there had been a fuel system with the VE-pumps, where part of the pressure restrictor was "displaced" to the shunt valve in the filter housing.

Normally, a pump for ~75 hp would pump about 23 liters/hour at full load. Of this the engine consumes about 15.5 l/h. The rest, 7.5 l/h is recirculated mainly in order to cool the injection pump. All the friction and turbulence within the pump itself generates heat that must be removed. If you plan to make two orifices, the nozzle bore would probably be something in the 0.5 to 0.7 mm range.

PS: Your banjo bolt does not have the same small restriction as the pumps with "normal" fuel return to tank. In your system, part of the restriction lies in the filter housing! DS

[pistnbroke]

back leak off from the injectors usually goes stright back to the tank without restriction ....3-4 mm bore

[liki]

Originally Posted by CDK

Thank you Liki. No local VW shop within 80 miles, but I'll search the internet. Is the ABL code part of the component description? And why do my engines not have it? I never unscrewed them before and I doubt very much that the vehicle owner(s) exchanged them for the wrong ones.

Those bolts were located atop the fuel tank on the transporter, wasn't it so that you didn't get the other end of the fuel lines from the recycling yard?

The exact description is:
Spare part code: "068130157"
Description: "banto bolt with return flow restrictor / ABL"

[baeckmo]

CDK, Went down to the yard and unscrewed the return banjo from an Iveco 8041 MO8, that has the same pump as you, and about the same fuel flow. There are two holes, diameter 0.35 mm (NOTE: NOT 3 to 4 mm as suggested by the p-and-b man) in the cylindrical part of the bolt. This adds up to almost exactly the same effective orifice area as the single 0.5 mm I proposed earlier.

Of course it is by far better if you can get hold of the original parts, but with your tooling and machining skill you may come up with a useful compromize if the VW parts are unavailable.

[CDK]

Originally Posted by baeckmo

CDK, Went down to the yard and unscrewed the return banjo from an Iveco 8041 MO8, that has the same pump as you, and about the same fuel flow. There are two holes, diameter 0.35 mm (NOTE: NOT 3 to 4 mm as suggested by the p-and-b man) in the cylindrical part of the bolt. This adds up to almost exactly the same effective orifice area as the single 0.5 mm I proposed earlier.

Of course it is by far better if you can get hold of the original parts, but with your tooling and machining skill you may come up with a useful compromize if the VW parts are unavailable.

Rest assured, I'll make something. A 0.35 drill isn't in my box, but 0.4 is there.
With just one fixed restriction, the flow will change with temperature and viscosity, but it is a good starting point.

[pistnbroke]

Being a smelly diesel person ie thick ..I thought we were of the opinion that engine output was low /wanted checking ....I dont quite see how restrictions in the back leak off line are going to affect performance.... this is just the fuel not required by the injectors and as I said on cars the pipe goes straight to the tank or back to the filter to keep the fuel warm in winter .

did the boost pressure ever get checked ? diesel ...got enough air ?..yes tick that box ..so still low on power ....you aint got enough fuel .....KISS

[CDK]

Originally Posted by pistnbroke

Being a smelly diesel person ie thick ..I thought we were of the opinion that engine output was low /wanted checking ....I dont quite see how restrictions in the back leak off line are going to affect performance.... this is just the fuel not required by the injectors and as I said on cars the pipe goes straight to the tank or back to the filter to keep the fuel warm in winter .

did the boost pressure ever get checked ? diesel ...got enough air ?..yes tick that box ..so still low on power ....you aint got enough fuel .....KISS

No need to get grumpy.
You missed a crucial point in this conversation. We are not talking about the injector leakage but the fuel return from the pump. The internal pressure is used in the pump for the injection advance mechanism; without the proper restriction there is zero pressure, the injection start may be up to 24 crankshaft degrees retarded, so ignition starts way after TDC.

[CDK]

Today we did a full throttle test with the starter levers still pulled to the max. I didn't do that until now because idle rpm increases and the gearboxes don't like switching above 1000 rpm. The levers advance injection by 4.8 degrees (crankshaft).
The boat reached nearly 11 knots at 2600 rpm, see attached graph. We could make just one test because of the upcoming bora )* and had to return to the bay, but the result proves that the lack of power is caused by injection timing.

)* Bora is a local wind caused by air masses falling down the mountains at the coast. Gusts well over 100 km/h. are normal, in extreme cases up to 240 km/h. There are no reliable telltale signs.

[Ad Hoc]

CDK

ah, so, slowly honing in and ticking off the boxes now, Good...progress

Nasty wind you have there...not referring to eating too many beans either

[baeckmo]

....The levers advance injection by 4.8 degrees (crankshaft). .....AND increases max injected fuel!!!!

Feels fine to have a confirmation of our thoughts; interesting to see coming results from return restrictor tests. Now I will be gone for a week (youngest daughter getting married....), so I won't upset any of you with comments for a while! Good luck Cornelis!!

[Frosty]

[QUOTE=pistnbroke..I dont quite see how restrictions in the back leak off line are going to affect performance.... this is just the fuel not required by the injectors and as I said on cars the pipe goes straight to the tank or back to the filter to keep the fuel warm in winter .

You are still in the stone age, things have moved on, this is not a 108 with leak offs.

My brand new Yanmar 6 LP's would not run with the return back to the filter. Well they would fast idle only. Simply fitting the returns back to the tank as per the book cured it.

I figure that the fuel supply from the tank offered more resistance than the return so fuel was being sucked from the return and was starving itself of fuel.

[pistnbroke]

good I like the stone age ..no technology....I think I said that returns to the tank are normal ...

[Guest625101138]

Originally Posted by CDK

Today we did a full throttle test with the starter levers still pulled to the max. I didn't do that until now because idle rpm increases and the gearboxes don't like switching above 1000 rpm. The levers advance injection by 4.8 degrees (crankshaft).
The boat reached nearly 11 knots at 2600 rpm, see attached graph. We could make just one test because of the upcoming bora )* and had to return to the bay, but the result proves that the lack of power is caused by injection timing.

)* Bora is a local wind caused by air masses falling down the mountains at the coast. Gusts well over 100 km/h. are normal, in extreme cases up to 240 km/h. There are no reliable telltale signs.

CDK
Taking the data points from your speed v rpm curve I have produced the corresponding estimates for the power and drag.

The good news is that each engine is now producing 22kW providing the props are not aerating. A substantial improvement over the situation at 2200rpm - almost double the power. It also gets you into the maximum torque region for the engines once you get the fuel sorted.

The bad news is that the drag, calculated assuming no aeration, is now higher than my prediction. This could be due to the sinkage being greater than I am allowing.

It would be useful to know the actual angle of inclination. It would also be useful to know the water level on the side of the hull just before the transom. Not at the transom but slightly in front so sinkage can be estimated.

It may be worthwhile looking for the aeration as well. Is there any noticeable change in the flow out of the tunnels - bubbles noticeable.

Rick W