11-17-2013 10:57 PM
Almost all of the G3600 engines are used in gas compression. The history of gas compression packages of this horsepower is not to dowel the engine to the base. The compressor is usually grouted to the base or fixed in a similar way so the engine has to move for coupling alignment.
The most reliable mounting is to use the Cat sole plate mounting group and grout the sole plate to the skid using a correct procedure to get the location in relation to the compressor (driven equipment) correct. Grouting the sole plate to the skid procedure wil result in all of the engine mounting locations being parallel which will make it easy to shim the vertical location for coupling alignment. Engine jacking screws are used to move the engine laterally. The engine has to be located so that the engine crankshaft and the compressor crankshaft do not have the end play inhibited. The usual practice is to tighten the rear engine mounting bolts to the highest torque (650- ft. lbs), then the center bolts to 450 ft. lbs. if used, and the front bolts to 350 ft. lbs. This allows the engine to grow forward away from the compressor. The G3600 will grow in length as much as 0.125" as the engine cylinder block warms up to operating temperature. We have in more recent times indicated that the mounting bolt torque should be supplied by the mounting bolt supplier since he knows his product. The sequence of rear bolts tighter than the front bolts still apply to allow engine block growth.
We recommend that alignment checks and engine mounting bolt torque be checked at least yearly. Some people don't do this until it is sometimes too late.
The quick mounting adjustable chocks are just that and many packagers are using them to save money. But they are not good for the life of the engine and will probably have to be replaced, maybe more than once. The grouted in sole plate is the best configuration in my experience.
08-27-2013 11:53 PM
In therory diligent bolt retorqueing could likely assure the package stays in proper alignment. In my own experience I find hardly anyone actually knows how to properly check the mounting feet for soft foot and then properly torque the feet to the base, even with the available literature in the A&I Guides and Special Instructions. Also don't know of too many engine users who diligently perform alignment checks unless they suspect a problem, certainly not many do it as a part of a regular PM program.
Ideally the engine doweling system provides for a consistant reference point at the rear of the engine to maintain alignment and still allow for thermal growth in both directions, this is why the 3600 series has the fixed dowel in the rear and the "sliding" dowel in the front on the same side. I have also done a couple of industrial drive packages where we had the fixed dowel at the front of the engine and the slider at the rear, both ends had loads being driven off them but the most critical alignment was at the front end driven piece of equipment.
I would also think coupling selection would contribute to the decision as to dowel or not, if you have a driveline with a metallic element coupling, like a Geislinger you have to maintain better alignment tolerences than you would if you were using a rubber element coupling like a Vulcan Rato.
In my own experience, I have seen a number of packages that required realignment after the initial startup. I think it is likely due to the base stress relieving in service and have found in some cases the alignment to change over 40 mils. Personally i won't dowel the driven equipment for the first 1500 to 2000 hours, then recheck alignment and then dowel. And yes, I have also found mounting bolts loose after 1000-2000 hours, although in most of those cases a soft foot condition existed, and when corrected the issue of mounting bolts loosening appears to have reduced significantly.
My two cents worth. Mike L.
08-27-2013 04:13 AM
A question of philosophy and real need... There is the opportunity to install the G3600's on the base frame by using the engine mounting plates with or without the dowl pin and keystone and the engine on the engine feets w/o doweling, but torqueing it down to the base frame. The installation rules, provided by CAT would allow to go for all three of these options, which makes it hard and easy for the packager. The most sophisticated way would be to dowel the engine after alignment to a ridgid base frame, but is this really necessary? Would'nt it be good enough to apply the torque pattern to the engine mounting feets and check every 1000/5000 hrs torque and alignement?
What are your thoughts? Has anybody seen real or even any misalignment after 5000 running hours or dedicated bolt loosening after 1000 hours?