Target Revs for 330 Diamond 6BTA

[Stephen Oliver]

Hi Guys

What revs am I looking at achieving WOT for the 6BTA 330 Diamonds ideally (approx 1700 hours)

Boat is back in the water finally with new props (20×21 4 blade mikado) Port engine is topping out just over 3000rpm and starboard side wont run that high as the throttle is at max before it gets there (its out position wise compared to port engine much further forward at same rpms – so think its just a cable issue – something i’m going to look at soon) it only gets to 2750 so I suspect the port engine will get to 3100 if the starboard engine was running up to speed. I suspect a bit underpropped – but would rather have scope to load the boat (not that it was empty) but we generally cruise at about 2200rpm (16ish knots) boat repairer is suggesting cupping the props a bit but i’m looking for advice…

By the way are there any guides to adjusting throttle position etc on SBmar?

Thanks in advance

Steve

Topic

[Stephen Oliver]

Well this is why Tony is the guru…

Got a laser tach today (cheap one but seems to work ok – if not a little sensitive to cummins white!)

Results as follows

Port Starboard
Tach Laser Error Tach Laser Error
1000 870 130 1000 960 40
1600 1390 210 1600 1535 65
2000 1740 260 2000 2000 0
2400 2100 300 2400 2400 2340

The error on the Stbd side is purely from a lazy cable and a very damped reaction to revs – you can clearly hear the rev change and very little shows on the tacho.. in contrast the port side is very reactive and bouncy and also enormously out!

Fortunately there is an adjuster on the back of the tacho – a small plastic screw that when turned adjusts the gain / readout 0 I cannot find anything out about the tacho on the web – but its a standard Cummins panel and VDO tacho Any help would be appreciated on these as I am assuming they are pulse driven – but maybe not?

So end result is I have the rev counters to within a hairs breadth of each other.

There was a good chance that when testing the other day that the revs were actually around the 2750 mark so with another test run and WOT for a longer period I should be able to get better readings.

So thanks for your help guys and if anyone had any info on the VDO gauges – i’d appreciate it.

Steve

[Stephen Oliver]

Thanks Phil

I have verified this as you can feel the levers hit their end travel and then spring on the sprung lever section.. i also did a visual check. The only thing left to check is cables so I will change them both to make sure they are the same.

The only other thing is that the throttle position gives different rpm per engine, but I would imagine that would require some in depth technical pump knowledge and would point to another issue?

Steve

[Philip]

Might be worth checking your throttles are full against the high stop. You don’t even need the engines running to verify full open. Just peg the throttles at head down to inspect and adjust. If you have dual stations verify from both stations.

Get some lube in the cables to loosen them up or replace them if needed.

Without verifying full lever travel you can verify rpm.

Phil

[Stephen Oliver]

Hi Rob

Thats is the only thing I found wrong – the lever positions were mismatched by one spline (probably due to the different cables) so I have re-positioned them but still no joy. As Tony suggests the mismatch may be tacho’s but engine revs ‘sound’ about right – not very scientific though!

Its hard to describe but the port engine revs are very ‘bouncy’ levers are very easy to move and the revs bounce up quick when the lever is moved in neutral. The starboard is very different. Very sluggish to respond and stiffer to operate. Revs increase more slowly and i can return the lever back a fair amount with no effect on the reported revs – so backlash or could be something else… I’m new to these controls so am still learning.

Having looked at a video of how the levers work i’m going to see if the cable being stiffer is effecting the operation and ‘damping’ the throttle position.

Steve

[Rob Schepis]

Can you pull one lever off of its spline and reposition it to get it to match the position of the other?

[Stephen Oliver]

Thanks Tony – once I get the laser tach – i’ll get the testing done.

is there a way of calibrating the tach or is it caused by a dirty pickup? Just surprised me something that is essentially ‘digital’ ie counting pulses can get something wrong.. Still new tachs are on my list as the hour meters have stopped working.

Steve

[Tony Athens]

After the engine are warm, check tach accuracy at 2400 & 2800 in neutral… Write it down and differences..Then run it back up to about 2500, let it stabilize and then run it up all the way for a second or so…….Write down what the tach said and report back…

My reasoning is this– I don’t think I have even seen a 315/330 go over 3000 RPM under any load.. I suspect your tach is at least 100 RPM higher than actual………………………………… No-load is typically 3100-3200 max…

[Stephen Oliver]

Thanks Tony I haven’t confirmed that I assumed as they are the standard Cummins gauges ran from mag pickup, that they would be ok. I’ll grab a laser tach and confirm.

Spent half a day trying to get the levers syncd with no joy. I suspect the stbd cable is sticking a bit as it’s a lot stiffer than the port and it’s a different cable to the port one too.. have checked Morse control setup and the engine end, all identical apart from the cables.. the only thing left I can try to get them closer in position and revs.

Currently have them better matched at low rpm just above 2k they go out of sync by a bit..

still to get no load wot rpms but they will see well above 3k with no load but until I check tachs I’m wasting my time ?

Steve

[Tony Athens]

Just a simple question–Have you checked your tach for accuracy? If so, what is your WOT No-load RPM.. Needs to be checked…

Nothing what so ever to worry about with your engine running up to 3300-3400 RPM for a few seconds when you are “verifying things”, or when running under load for checking purposes… Your “not to exceed” RPM is close to 4000……

Tony

[Stephen Oliver]

Hi Rob

Makes perfect sense. Until I get the STB engine sorted I cannot really tell what both engines will pull up to – I suspect it will be somewhere around the 3100 – 3150.

I know you say they are rated to 2800, but at what point does the limiter kick in? just worried i’ll be doing some damage by running them up over 3000rpm while testing.

Reason for testing (she is pretty heavy at the moment – about 25000lbs (11,5t)) is that the workshop that did the reef hit repairs want to close it off so they want the revs correct – so it means re lifting and cupping the props to drop some revs if its required. We have all gear on board and half a tank – so I want to be looking for 2900-2950rpm ideally.. i guess?

Thanks for the link. I suspect the throttle may have been connected do different holes on each engine – easy to check so will do that tomorrow and see what the idle etc is set to.. as they differ. Is the idle meant to be 650rpm?

Steve

[Rob Schepis]

You’re engines are rated at 2,800 and a good target rpm is 2,900-2,950. If you are just over 3,000 I would wait and see where she settles in later in the season with the boat FULLY loaded with all your gear, fuel and water topped off and a dirty bottom.

Splash day can tell you if you are overpropped because if you are overpropped on splash day you will only be MORE overpropped as the season progresses because the boat will only get heavier and the bottom will only get dirtier as the season progresses…..

For the same reasoning, splash day cannot be a true indicator of being underpropped…

Make sense?

Here’s the IP throttle arm pic and a link with more…

https://www.sbmar.com/articles/cummins-bosch-p7100-injection-pump-throttle-arm-adjustment/

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