6711 Manuals and questions

[snowfish_]

Hi, just 'joined up'! And also just read the brake rebuild guide - very informative!

Just a few things for now re my 6711;

- Anyone know where I can download an operators manual / workshop manual / parts manual?

- It makes a couple of 'unusual' noises: firstly, the gearbox makes a very faint tap tap tap which stops when the clutch is pressed. And, if you rock the back end of tractor side to side HARD there is a slight clonking like you'd get from a slack TRB. I'm thinking a bit of endfloat on the shaft maybe? I doubt most people would notice either thing! Thoughts? Leave well alone being top of the list.

- I'm not used to a crash box, what's the deal, can you change on the move?! There's a bloody steep hill near me!

- Lastly for now, and laughably.... I've got a very unloved turbo looking for a home. If I left the pump stock and set the turbo up for about 5psi?! A cleaner exhaust and a teeny bit more power or a very bad idea?!

All thoughts and comments gratefully received. I'm really looking forward to sorting the old girl out, I've had a few tractors but this is my first zetor , and I love the combination of advanced technology and basic engineering. Shame it's so damn ugly.

 

[Renze]

On our 5245 the diff spider pins were worn due to oil starvation. It survived brutal abuse with a one yard 3pt hitch bucket, quarrying sand for construction from the forest, despite the wear.

Even when not worn, the final drives usually have a fair bit of teeth clearance. They are so overbuilt that theres nothing to worry about, they use the same gears in the 120hp Proxima these days...

About crash gears, yes they grind a little. Be too soft and they only grind and dont take, be too harsh and you get tired, and the shift fork breaks eventually.

You apply enough pressure on the shift lever when it stops grinding (and engages the gear) in about 1.5 second. If you push harder you wear both yourself and the tractor out. If you push less hard, it will keep grinding and not match up speeds between the shafts.

Nonetheless, allways apply the brakes and disengage the gear at standstill when going from forward to reverse, so the gear will be standing still too when you shift. if you take it out of gear on the move and then roll to a standstill, the layshaft will keep turning due to bearing and oil drag, and you have to slow down the layshaft by grinding gears against each other. If you only depress the clutch and then brake, you put the entire mechanism to a standstill so you can shift with a simple click.

Some tractors had the optional synchro 4th and 5th. if you push them too hard, the bronze synchromesh ring will break and you're back to a crash gearbox. They are old school synchromesh, give them a second before pushing through them, and still grinding gears.. Once youve pushed through it, it doesnt do its job anymore and youre grinding the gears like an old fashoned crash box. They only work because the slant surfaces of shift coupler and synchromesh ring push the synchromesh against the gearwheel to slow it down silently, so you dont have to create this friction by grinding the splines of the gearwheel and shifter coupler to each other. When you push through the synchromesh, the slant surfaces dont cause the synchromesh ring to rub against the gearwheel to slow it down so then it does nothing anymore.

About that turbo, from what engine did it come originally ?

The 6711 is a 3.5 liter engine at 2200rpm max... A suitable turbo would come from a 1.8 diesel at 4400rpm (displacement x rpm is a basic guideline for airflow) If you put on a turbo of a 14 liter Scania engine, your 3.5 liter is not going to pump around enough air to get the turbo to spool up, unless you ran it at 5000rpm (at which the connecting rod bearing caps will come off because the bolts arent designed to take that much acceleration force when the piston has to be stopped when it meets top dead point, and then ripped downward by the crankshaft to make an intake stroke)

In fact old slow running ship diesels didnt even have bearings in the bearing cap... they had a bearing in the connecting rod half, but the bearing cap below it was just steel directly on the crankshaft, because these engines ran so slow that the piston would come down on gravity, even when it hit top dead point between exhaust and intake stroke, with no compression in the cylinder...


....anyways i'm getting carried away... you dont intend to run high rpm...

Just, pick a turbo that has a similar displacement x max rpm, or you will overspeed the turbo and kill your engine when it eats a disintegrated turbine wheel, or you will only create more exhaust backpressure because the engine cant generate enough airflow to get that turbo to actually build pressure in the intake side...

 

[snowfish_]

Thanks for that Renze, just a quick one re turbo - of course you are right re size, although I think when using an automotive turbocharger it's a compromise - as I understand it the average car turbo has to spool up relatively low in the rev range, so then at say mid range it's running at full speed, - and at full engine rpm the wastegate will be open? - preventing the unit overspeeding.

I have a unit from a 2.5 litre engine which is probably on the large side, and one from a 2 litre which I think could be ok.

So 2 litre car starts to get boost at say 2000 rpm (or before) = 4000lm

Maximum boost at say 3000 rpm = 6000 lm

On the zetor that would equate to boost available from approx 1150rpm and maximum boost available at 1700 rpm.

Would you agree?

My main issue was the inherent strength of the engine - is it up to it? Maybe 0.5 bar pressure, a bit of extra fuel maybe, and 5-10 hp?! I'd run an intercooler I guess but probably not an oil cooler.

 

[Renze]

Its a four stroke engine so divide the airflow in half. Then use factor 0.85 because a fast running engine doesnt have time for the incoming air to reach exactly the same air pressure as outside the engine, before the piston travels up again.

Cylinder fill rate is better at lower rpm. In old fashioned diesels, max torque is where rpm is high enough to let the compression cycle last short enough to not loose too much air, but not so fast that a huge vacuum occurs in the intake manifold.

The engine can take 90hp alike the 7745 turbo, which has the same journals bearings and connecting rods. The factory turbo engines just had hardened valve seats, valves, and a gel type head gasket.