Differences between twins in performance

[Lake Erie Boater]

OK Diesel Pro's: Here's my question.

Today I sea trialed a 2001 34 Amberjack with twin CAT 3126 TA's. The port engine would only get to 2700 WOT with tabs up on flat water. The starboard made 2800 (which I understand to be what they are supposed to make). The engines were both on new filters and the props were just prop scanned.

I also noticed the starboard engine running about 10 to 15 degrees hotter and the oil pressure at WOT was about 20 psi higher as well when comapared with the port engine. This was as observed on the Sea Ray dash guages.

Should I be concerned, or will the two engines be just that, 2 different engines??:huh:

Any feedback appreciated.

 

[Pirate]

These engines need to turn to their MIN rated RPM when the boat is FULLY loaded with fuel, water, gear, people, etc. and you need to account for a less than pristine bottom.

As for the differences in RPM.... I am a bit OCD about things like that and I would pursue the problem, however minor, until I discovered the cause and corrected it. The 3126 is good engine and will provide good service unless it is overloaded. If those engines are barely meeting MIN RPM during a sea trial, you can bet that the props are too much for it.

 

[Hampton]

My first suspicion would be the tach's. Of all gauges on these boats, they seem to be the least accurate and/or reliable.

 

[Four Suns]

That would be a big differnce in temps and oil pressures on my engines. Do you have the ability to get boost pressure measurements on each engine?

I don't have Cats but my engines (with recently cleaned heat exchangers) run within 1 degree of each other and the oil pressures are exactly the same per the digital readouts. When I did have problems with the engines not matching, I had a blown intake manifold gasket leaking air. I'm not saying that is what your issue is but I think you should try and track it down.

If you are looking to buy the boat, get a certified Cat shop to do an engine survey...

 

[Pirate]

Hampton and Gary both had good points. Get a photo tach on the engines to verify the accuracy of the tachs. Next in line might be boost pressure. That will take a tech with the right tools since those engines do not have digital info.

 

[Lake Erie Boater]

Guys, thanks for the quick responses.

My bad, I guess I did not provide all the pertinent information.

The rpm's were digitally checked. The results were Port was turning 2059 rpm when the dash tach said 2000 and the Starboard was turning 2083 when the dash tach said 2000. Maybe they actually are making the 2800 on port and slightly over on starboard. It did seem annoying as the little synch needle between them kept calling for more rpms to even them up, which I could only do by backing off the starboard throttle.

Never having owned a boat with all this hardware, I guess I am quite a bit green??

Keep your comments coming please!!:smt001

 

[fwebster]

The Teleflex tachs and gauges used on Sea Ray boats are subject to variances or tolerances in manufacturing. Even though they may be slightly off perfect, he dash gauges are usually quite functional and will tell you when something bad is going on, however, your temp and oil pressure gauges are too far off. You have engine mounted gauges which are mechanical unints supplied by Caterpillar and are usually right. Compare the dash readings to those on the engines and you will know if you have a problem. The usual fix is just cleaning the sending unit electrical connection or replacing the sending unit.

If you are worrying about a 24 rpm difference at 2000 rpm, brain surgery may suit you better than boating. This difference is likely nothing more than your ability to see 2000 on a mechanical gauge or the fact that the tach needs to be adjusted slightly.....screws on the back. If you have a digital tach to aid in the adjustment, you are almost done.

The sync gauge is also adjustable. But, I'll tell you I run a lot of different boats and I just don't find them accurate or dependable from one day to the next in some cases. If a boat has a mechanical syncronizer like a Glendenning, I use it not the gauge. If it doesn't, I sync the engines on a diesel by ear and by feel.

Any way you cut it, the 340AJ with diesels is one nice boat..........you will love her.

 

[Lake Erie Boater]

Thanks Frank and all you CSR guys.

One of the temp. guages on the engine is not working and a replacement has been ordered (part of the survey findings). I will compare them both at the engines once the bad one is replaced and go from there. Regarding the tach's, I did not know they (and the synch. needle) can be adjusted. I assume that's on the back of the guage.

 

[Hampton]

Frank wrote that there's a screw on the back for adjustment.

 

[Lake Erie Boater]

Ya, I noticed that after I replied to his post. Proves I'm no brain surgeon either!!

 

[Hampton]

Not at all - Just trying to help.

 

[osd9]

You said you are having a survey. Is that a Hull survey you are talking about or a very detailed engine survey by a certified CAT techinician? I would STRONGLY recommend the latter, in conjunction with the hull survey. It will cost an additional $1K, but will pay it's dividends down the road.

As to the tachs, I replaced my analog tachs with a set of Aetna Digitals, and I absolutely love them. They are spot on, and accurate (measured against an optical tach). If you search Aetna tachs here you can see some pics I posted.

Good luck .....

 

[Lake Erie Boater]

I have had both a hull survey as well as engine surveys done. The engine surveyors are not certified CAT mechanics, but are a well known in the area for servicing all types of marine diesels. In hind sight, having gotten into some of these questions, I think I would have been smarter to have gotten Ohio CAT themselves to look them over for piece of mind. Maybe I will go ahead and do that anyway.

 

[fwebster]

A Caterpillar dealer has access to the service history of the engines if any repairs or recalls were done under warranty or by a Cat dealer. You can still gain access to that info by going to the Cat dealer with your engine serial numbers and asking their service manager to look it up in their system for you.

The other reason to use a Cat dealer for engine surveys.........and this isn't a criticism but others following this thread in the market for a Caterpillar powered boat should be aware of it...........is that Caterpillar has several proprietary tests that a dealer has the tools to do on Cat engines. One, for example, is a 30 minute ($50-75 cost) blow by test that measures in a quantitative manner how much blow by an engine has, and for a diesel, that is as good as a compression test and saves the cost of removing and reinstalling injectors.....about $1200 on 3126's.

 

[Lake Erie Boater]

I did contact Ohio CAT during my investigative process. They did provide me with the history. All of it was during the 1st year as the boat appears to have been maintained thereafter by the marina where she was kept. Catawba Island Club is a very nice facility for those with the big boats on Lake Erie. Anyway, all the warranty reports show was a replaced heater wire harness, and a couple of coolant leaks, and 1 oil leak at the port turbo. The last line item showed the boat with 88 hours in Oct. of 02. The boat now has 290 hours. CAT was nice enough to provide me with these reports.

Why I didn't have them survey, I don't know. I guess that's what I get for trying to do this deal so fast at the end of our season. The boat is being hauled for the season the end of this week and I am trying to figure out if I buy, or if I pass.

I am going back out with my engine surveyor tomorrow morning to digitally measure RPM's at WOT, check engine temps and oil pressures at the engines themselves. Will see what they are and if not similar between both engines, try to figure out why? If they are similar, at least we will have narrowed it down to the senders, guages etc.

Again guys, thanks for the information, pretty cool how this CSR forum works!!! :thumbsup:

 

[Lake Erie Boater]

Good news, when checking the oil pressure at the engines themselves, they are both the same. We determined the sender in the port engine was actually reading too low. It will be replaced. Likewise the same for coolant temp readings. Each engine was within +/- 3 degrees of the other. Regarding RPM's, we could only get 2710 RPM's though out of the port engine. The starboard was making 2810 at WOT. The suggestion was to slightly repitch the port prop if I am that concerned. Any thoughts on that one??

 

[osd9]

You should definitely be "that concerned". Only one thing...have both props scanned...not just the one. If both engines can't turn 2800++ then you still have work to do. All this should be done on the sellers nickel BEFORE you write any more checks....IMHO that is.

good luck and keep us posted.

 

[Four Suns]

I would agree with Dominic. Don't repitch one prop to fix a problem one engine is having with the load on it. If both props have the same pitch (scan BOTH) then they should handle the same load.

 

[Lake Erie Boater]

Today's sea trial was the 2nd as the engine surveyor had noted the less than optimal RPM's previously (Port 2600, Stbd 2700)

Both props were then prop scanned prior to re-launch and re-sea trial. With that and new filters, washed bottom, etc., the boat picked up 100 RPM to get to the numbers we are at now. The props are 20" X 22.15" per the prop scan summary report.

Any thoughts as to what may be robbing it of power, or what may be loading it more?? Sorry if this is way to general of a question?

 

[fwebster]

Almost, except..............

Here's how it should work: Your engines do not counter rotate, but your shafts do. Sea Ray gets the counter rotation by turning one transmission in forward and one in reverse while the engines turn the same direction. The final ratio out of the transmission is slightly different on some models in forward than in reverse and Sea Ray usually takes this.....usually 1.5% to 1.7% into consideration when tweaking the props. If the prop on your slow engine was replaced with a generic replacement and not dialed in for the ratio difference or for matching the opposite side, that could explain the rpm, difference.

Your Caterpillar tech should have run both engines unloaded at WOT rpms to see if both engines turn up rated rpms as a part of the survey. IF he didn't, then it should be done. Unloaded, the engines should turn up to 2800 to 2850 rpm. Once you are sure they do that then fixing the rpm issue is a matter of a clean bottom, straight running gear and prop pitch.

Most Sea Ray props are tweaked at the factory with 2 adults, a CG kit, no water, no waste, and 50 gal of fuel on board whioch is a lot lighter than most of us load a boat. Most owners end up repitching their wheels to remove a little pitch or cup to increase rpms to keep engines from overloading. with your normal load, full fuel and full water, the Cats should turn 2800 rpm.

I'd say you don't have a major problem going on, just some tweaking to do, but the first thing to do is to run up the engines at the dock and see how many rpms they turn. If there is still 100 rpm different, then its time to get Cat involved and evaluate the pump and injectors on the slow engine.