Beta 25 Repower- Cannot Reach Specified RPM Issue

[Marc G]

Hello All,
I'm hoping I may get some insight to my issue after repowering Spellbound this Spring with a Beta 25. The engine install went well with minimal issues and I performed initial sea trials last week. Warranty requires among other things operating at WOT and reaching 3600 RPM.  After the 15  minute runs at a 50% rev and 75% rev, my 1st trial failed with a max of 2950 RPM, at which point the engine was working quite hard and oil pressure fluctuated and start dropping. I throttled back slowly, rnas at various rpm's for another 15 minutes a tried WOT again with the exact same results.  Terminated tests and returned to port.  I pulled the boat a d prop and had it repitched and balanced at HAle propeler here in Old Saybrook, CT.  The prop is a 2004 sailor style 3 blade, 15". It was 15 x  and they re-pitched it to 15 x 7.5 based upon all the input data. The second sea trial was performed yesterday and it again failed, topping out at 3200 rpm with the same high load and fluctuating and dropping oil pressure.
I had the prop pitch reconfirmed by a third party as correct for all loads by Beta in NC.
My fuel system is all new with 60gpm rated Racor (10Uc) and a parallelled electric lift pump on a bypass for priming and backup to the Beta mechanical pump.
My exhaust riser is the original MX25 Universal riser slightly modified to fit the new engine location. The riser had the aft leg shortened about and inch and the port leg to the water box shortened about an inch. It is 1.25 inch SS material in quite good shape.

I am at a loss as to what to look for with the low engine RPM.. Beta marine is looking at a set of photos of my installation, and I am waiting to hear from them.  Local mechanics said the prop pitch is not correct yet, and/o,r there is too much back pressure on the exhaust at high RPM due to the 1.25 inch riser. Mt calcs say this 1.25 dia. riser equates to a loss equivalent of about a 48 inch long straight piece of pipe after accounting for the three 90 degree bends in the riser.  With the higher rpm of the Beta over the MX25 I think this may be the issue.
Where to spend the money?  Re-pitch the prop again, or make a new riser in a 1.5" diameter, or any other suggestions?

Thanks for listening.
Fair winds and weather.

Marc

[mainesail]

Have you confirmed the tach is correct at WOT using a digital photo tach?

[Marc G]

Mainesail,

Yes, I have a laser tach that I have used to check several boat Tachs.  The VDO tack on the Beta instrument panel is spot on at 3 rpm levels.. First Tach I have ever seen so accurate! I actually used it against the panel tach during the sea trial.

My real concern is the failing oil pressure when to engine tops out under load at 2900.
I RPM tested per the  factory warranty test sheet as well at WOT in neutral with a warmed up engine twice, and got 3700-3750 RPM as was listed on the Beta factory engine test report at 3750 max.
In this test the oil pressure was steady at 60 psi with no fluctuation.

The oil fluctuation and drop only occurs under the operating WOT test. I am thinking back pressure in the cylinders?
I tested from the water lift box out and I can easily puff air out thru the stern.
No test ports between the riser and manifold.

Marc

[Stu Jackson]

Marc,

What was your original prop pitch?  What transmission and ratio is on the new Beta 25?

[Ron Hill]

Marc : I believe that your best answer is going to come from Beta marine - the manufacturer!!

I'm traveling and can't measure the inside diameter of the M25XP exhaust riser, but looking at a ruler I'm sure it is closer to 2 inches than it is to 1.25 inches.  Something is amiss!!

My other question is  - is your 15" sailor style 3 bladed prop a Catalina prop or a Michigan Wheel or another makers??  The reason I ask is because a Michigan Wheel Sailor props that I've seen has a much greater cord surface area than a Catalina 3 bladed sailor style with much narrower blades!!  
The Catalina 3 bladed 15" comes pitched to 9" and most C34 owners repitched up to 10".  I can't believe that you repitched down to 7.5"!!!  
We are surely talking about two different props!!!

A few thoughts

[Stu Jackson]

I'm traveling and can't measure the inside diameter of the M25XP exhaust riser, but looking at a ruler I'm sure it is closer to 2 inches than it is to 1.25 inches.  Something is amiss!!

From the C34 Tech wiki:  Engine / Exhaust Riser Replacement

http://www.c34.org/wiki/index.php?title=Exhaust_Pipe_Replacement

... the original exhaust ... failed due to corrosion at the weld between the 5/8 inch water injection pipe and the 1 1/4 inch nominal size pipe (actually 1 5/8 inch OD).

The ID of the hump hose and the OD of the inlet and outlet ports of the muffler are 1 5/8", too.

[lazybone]

How old is the fuel?

[Ron Hill]

Guys : Now that I've engaged brain - the exhaust hose is 1 5/8" ID, so the exhaust riser must be about 1 1/2" ID.   

[Marc G]

My 1987 Catalina 34.
STU:
Original pitch on prop was 9 inches and the transmission ratio is 2.0 to1.
The pitch calculations included: Engine HP, Mfg WOT RPM spec at load (3600 rpm), Trans ratio (2:1), LWL, Displacement, 60 gallons H2O tankage, 22 Gal fuel, 21 Gal. waste and four people with gear.
Mfg. spec for WOT with No Load, engine at temp. (gearbox in neutral) is 3750 rpm.  This test passed exactly as noted with no change in oil pressure.  The engine just purred at 3750.  The engine included the factory test data sheet.

Lazybones: Fuel was from Sept. 2013, full tank, with biogard added for winter storage. All new fuel system this spring with Racor 500 filter.

Ron: 1,
My MX25 had a 1.25 inch ID welded stainless pipe riser, with a 5/8 inch water inlet nipple and a 1.5" OD outer diameter discharge end piece to accept a 1.5 inch ID Hi-temp blue silicone flex hose to the water lift box.  I had the 5/8 OD inlet machine off and a 3/4" OD inlet installed for the Beta 25 3/4" hose requirement. The riser was threaded into a bolt-on flange adapter on the MX 25 engine.

2. I do not know the prop manufacturer but from your description I would say it is Michigan as the chord is wide, not narrow.

Thanks,  Marc

[Ron Hill]

Marc :  2. I do not know the prop manufacturer but from your description I would say it is Michigan as the chord is wide, not narrow.
Thanks,  Marc

Bingo!!!  You've found your problem!! 

[Marc G]

Update.
Ran boat 2 days ago and with no changes, the engine ran up to 3400 at WOT. Just 200 shy of desired max.
Spoke to Beta in NC and they told me to keep running engine to get 30-50 hours on it to allow break in. Make no changes till then. Just don't abuse WOT.  Engine hums at 2800 with 6.6 knots. Hull speed is about 7.4.
I'm going sailing! With more engine use the I would normally do.
Marc

[Stu Jackson]

That's great news, thanks for reporting back.  I hear your oil changes are a snap! 

[Marc G]

True!  Built in hand piump right up top.
Engine is rung great. quiet and smooth.

[Ron Hill]

Guys : The real key to a diesel engine oil change is not the handiness of the extraction pump, but it's where that pump draws the oil from in the oil pan!! (the lowest point??)

My thought

[Marc G]

The Beta oil pump is an option that includes a special oil pan with the pump pickup at the very rear bottom of the pan ensuring proper evacuation of all oil. Without this option it is a standard pan with center drain lie most universal engines. Worth the extra $$.