Starting Up a repaird engine

[21121956]

Hello everybody:

In a medium speed Diesel engine we have performed a machining job on a connecting rod journal, reducing the diameter in aprox. 5 mm. We are almost ready to start up this engine.

Would anyone in this forum give me any advice regarding with the care we have to take at that moment and during the normal operation? Is there any possibility that the nominal capacity of this engine could be reduced by this reparation?

Thanks

 

[jayskind]

Hi: treat the engine as normal. Clean Oil/good pressure etc. Way too much is made of initial start ups in enthusiast magazines. You go tour a G.M. plant at least when I did in the eighties and they just start up a vehicle and drive it off the line. One thing that does make a difference,but not in your case is camshaft workhardening during break in especially with high valve spring pressure. Since you are using the same cam don't worry about it. I usually whenever possible fill the vertically mounted oil filter if that is the kind they have. I am a medium to high speed diesel engineer on tug boats and mega yachts (man I have seen engines that would make you cum when you see them), and I have worked on a bunch. The factory guys do the same break in proceedure I do. Lastly don't do what I did a dozen years ago aqnd tear up perfectly good main and rod beariongs by using a break in grease that does not disolve in oil. I was on drugs building a racing gas engine.
D.A.R.E. really means drugs are really expensive.
Jason

 

[patprimmer]

5mm seems a lot to take of a crank journal. Do you mean 0.5mm or 5mm.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[21121956]

Hello everybody:

patprimmer, yes it is, the connecting rod journal is 5 mm undersize, in an engine of 17.000 kW (17 Mega watts). Any comment that comes up about this subject, is really appreciated.

 

[waross]

Hi 21121956
Just wondering, could you get a 5 mm undesize con-rod and bearing shells from the manufacturer or did you have to build them?
respectfully

 

[patprimmer]

OK

17,000kW is a whole new ball game re my experience, so I have no idea of journal dia nor overlap, but I guess it is a lot more than a few inches.

What is the %age reduction in journal overlap. Have you changed the fillet radius. How was the fillet rad formed originally and on the repair, ie ground or rolled.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tmoose]

Break-in is mostly about ring "seating", and maybe about parts like pistons and bearings getting used to each other. The finish diameters of the rod journals does not have much to do with that. If 5 mm undersize is an unusually aggressive amount required by severe crank distress, then the hidden dangers are stress cracks in the crank or too sharp radius in the journal fillets, and a gentle break-in can not defuse them.

 

[taylorg]

Hi 21121956,

Have done this a few times myself although mainly on slow speed engines. Just run it in nice and gently, the same as you would do after a normal major overhaul and in accordance with the OEM running-in schedule. Keep a close eye on the bearing temperature for a while, and, most importantly remember to highlight in your manuals that it has oversize bearings! Otherwise the guys who overhaul it many years in the future will get a surprise!

Given the output I guess it is a Wartsila 18V46? I'm curious - which journal required machining and why? Did you seize a piston or wipe a bearing?

 

[21121956]

Hello everybody:

Thanks for your comments.

waross: The manufacturer has achieved this job and, under the circumstances, new especially elaborated con-rod big end bearing shells were provided.

patprimmer: The work we are talking about is the result of a guarantee claim, so, the manufacturer has performed the job at site but has kept in secrecy the technical data. Unfortunately, legally they are not obliged to release these data.

taylorg: the journal is the Nº 8 of an 18V46 and the failure was a seized piston. How about the load this engine can deliver after the reparation?

 

[taylorg]

It should deliver the same load.

If the repair has been carried out under a guatantee claim and you find the engine will not give the same output then you have the right to reject the engine...

Your statement that "the manufacturer has performed the job at site but has kept in secrecy the technical data. Unfortunately, legally they are not obliged to release these data." concerns me as they regularly say this nonsense to their customers when things go wrong.

What exactly caused the failure?? - You have the right to know. What info are they keeping secret? If they are repairing it under guarantee it suggests they accepted liability. Are they checking your other engines for the same fault?

 

[Fabrico]

Pre-lube the engine. Pressurize the oiling system with oil just before you start it.

 

[waross]

If you have exhaust port temperature monitoring I would watch the temperature on the repaired cylinder very closely. If the original problem was caused by an injector over-fueling you don't want to repeat the problem. I would be watching the temperature as I was increasing the loading for any sign of cylinder overloading.
respectfully

 

[wr180561]

After extensive pre-lubrication of the engine (liners & bearings), start the engine at low idle for less than one minute then stop it. Using an infra red thermometer, measure the temperature of the main and conrod bearings. Make sure that all bearing's temperature are nearly at the same level ( +/- 2 deg. C). If the temperature of any bearing is comparatively shooting up (including the machined one) you know you have a problem in this bearing. If all at the same level, start the engine again for 1/2 an hour and repeat the above procedure.

This is just to ensure that machining, clearances, installation and lubrication of the bearings are adequate.

By the way, an engine with 17,000 kw seems to be a low speed engine, what is the nominal rpm ?

Regarding power deration, you did mentioned a machining of 5 mm, can you tell us the nominal diameter of the conrod journal ?

Best Regards, WR

 

[Metalguy]

I was involved with a 7,000 HP V20 turbo diesel that had a repaired main journal. It was repaired via plasma spray, and several attempts to start the 600 RPM engine resulted in shutdowns because the bearing temp. got very close to the limit.

We finally resorted to wiping high-moly grease all over the journal and running the engine at 400 RPM/no load for a while. 400 was a safe RPM, and the bearing got close to the shutdown point as we all held our breath. After ~30 min. the temp. started to go down a little. Another 30 min. and it was near normal. We then went up to 600 and had to hold our breaths again. Another 30 min. and the bearing was cooling down well. Same story as we increased load, but today the bearing is fine.

 

[21121956]

Hello everybody:

To all once again, thanks for your comments.

wr180561: the nominal speed for this engine is 514 RPM @ 60Hz; the original connecting rod journal was 450 mm in diameter.

 

[taylorg]

21121956 - have you started it yet? Please let us know how you get on!

 

[21121956]

Hello everybody:

taylorg, we are still overhauling this engine and, according to the planning, the start up will be in the next few days. I will be in contact with the Forum and I will share our experience on this subject.

 

[21121956]

Hello everybody:

The engine was started up.
Check outs before starting: stop tests (trip tests) of Oil Mist Detector, low lube oil pressure, local and remote emergency stop.

- Cold deflexion of crankshaft.
- The Oil Mist Detector was checked, specially serviced and adjusted to its lower value.
- Starting and stoping the pre lube oil pump for lube oil circulation through all bearings, crankshaft, etc. and to see where this lube oil comes from and goes to.
- Pre heat the engine with the High Temperature water system.
- With the lube oil pump on, pre heater pump on and fuel oil on, rotate the engine with the turning gear during 15 minutes.
- Rotate the engine with starting air blow for around 30 seconds.

Starting up.

- The engine is started up and run idle during 1 minute, then is stopped with the Oil Mist Detector.
Once the engine has stopped, we proceed to open the crank case covers and check the temperature of all the bearings: main bearings, big end and small end bearings. For this activity we use an infrared meter and a thermal camera.

We verify the free axial movement (along the connecting rod journal) of the big end connecting rod.

- Everything was OK. Start and run idle during 5 minutes, then stop with the low lube oil pressure trip setting.
At this moment, we achieve the same controls stated above.
Besides that check outs, we check for leaks of: fuel oil, lube oil, water and starting air.

- Everything is OK. Start and synchronize the unit taking 1.000 kW load and run during 3 minutes. Stop the unit with low lube oil pressure trip setting.
Here we check one more time the temperatures and the free movement of the con rods.

- Everything is OK. Start and synchronize, then run with 3.000 kW during 5 minutes. Stop with the local emergency shutdown.
Check out once again.

- Start and synchronize, then run during 30 minutes with a load of 5.000 kW, then with 6.800 kW, 10.200 kW, 11.900 kW, 13.600 kW, 15.300 kW and finally, with 17.000 kW.

After the 30 minutes with each level of load, the engine was stopped and left run idle for 5 minutes after which, the check outs of temperatures and movement were achieved.

- After the unit ran at the nominal capacity, Hot deflexions of crankshaft were taken.

- After 10 hours of operation at full load, the main bearings A8 and B8 were checked out and the big end bearings A8 and B8 were replaced for new ones.

The crank case covers A8 and B8 were painted in yellow and red in order to warn that a special condition on that side has ocurred. An inscription was properly painted on these covers indicating the modifications and showing the part numbers of the new elements.

 

[21121956]

Hello everybody:

Sorry but I forgot to say that, at this moment two days after the latest check outs, the unit is operating at full load under normal conditions.

 

[Fabrico]

44 minutes to full load, quick break-in. Detroit Diesel 2-stroke truck/boat engines are no more than about 5-10 minutes checking things, then it's full load and speed. Otherwise the rings never seat right.

Good for you. Thanks for sharing.