Thursday, December 24, 2015

Engine Mounting Bolts Retorqued & Grounding Modified

Today, the DOG Aviation procurement department was able to find a sale on a torque wrench which will fill in the gap between the two torque wrenches already in the shop. The new torque wrench has a range between 10 to 75 foot pounds in half pound increments, which nicely fills the range of 12 to 20 foot pounds the other two wrenches can’t cover.
The new 10 to 75 foot pound torque wrench fills the gap the other two torque wrenches couldn’t cover.

Due to seemingly week long obligations, only had enough time to take the new torque wrench to the hangar and retorque the engine mounting bolts and begin another minor project discussed later in this post. The castle nuts for the engine mount are to be tightened to a torque range of 160 to 190 inch pounds (13.3 to 15.8 foot pounds) … however, they should to be torqued to the lower limit of 160 inch pounds and if the cotter key fits onto the hole in the bolt great … if not, the castle nut is to be tightened further until the castle nut is clear of the hole in the bolt so the cotter key can be inserted through the mounting bolt to lock the assembly. To accomplish this, the new torque wrench was set to 13.5 foot pounds and the castle nuts for the two lower engine mounts were tightened … of course, the holes in the bolts were covered by the castle nuts so they required further tightening before the cotter pin could be inserted.

To torque the upper two engine mounting bolts, the sheer size of the head on the torque wrench will not allow it to fit into the “V” of the WD-1221 engine mount standoff so a crows foot wrench attachment was required. As covered in a post on January 8, 2014 when using a crows foot wrench attachment on a torque wrench, it changes the overall length of the wrench which affects the applied torque. There is a formula and instructions on how to calculate the offset here:

Using the formula and measuring technique that can be found in the above link, my 9/16" crows foot wrench attachment adds .9 inches from the center of the bolt to the center of the 3/8" drive on the torque wrench, so the required the torque wrench setting needs to be adjusted down to 151 inch pounds or 12.59 foot pounds to achieve the desired applied force of 160 inch pounds (13.3 foot pounds) at the bolt.
Torque wrench with 9/16" crows foot attachment requires a lower torque setting on the wrench of 12.5 foot pounds.
Finalizing the torque setting on the right upper engine mounting bolt.

After the desired torque was achieved, the castle nuts were tightened further until a cotter pin could be placed through the hole in the bolt.

Onto the battery grounding modification: One of the items ordered a few weeks ago was a grounding block manufactured by B&C Specialty Products. The rational behind this is to move the electrical system grounding to the RV-12’s firewall as opposed to keeping it on the powder coated battery box components as suggested in the plans.  Frankly, I feel grounding the electrical system to the firewall just makes good electrical sense. Was actually searching for a small grounding block assembly but could not find anything suitable, so decided to order the 24 pin unit in the photo below ... which is total overkill in that nowhere near that many grounds will actually be used. The grounding stud is the main item of interest but the additional spade connectors will allow making solid ground connections for sensors and other electrical items on both sides of the firewall.
B&C Specialty GB24/24-Tab firewall grounding block kit.

The grounding blocks will be mounted on both sides of the firewall with the stud becoming the main grounding point for the battery and starter. Because the grounding block is way bigger than necessary, decided to cut off half of the grounding tabs and trim the unit down a little so there are now only 12 tabs (and that is way more than necessary).
Both grounding blocks after being cut down a little.
Approximate position of the modified B&C grounding block ... this will be the firewall grounding point for the battery.
I would have liked to have been able to drill the mounting holes for the grounding blocks prior to mounting the engine while access was straight on … but the engine hoist needed to be returned, so will now need to use an angle drill to make the necessary holes. Fortunately, access is still quite good so this should not pose any problems.

Friday, December 18, 2015

Rotax 912 ULS Engine Mounting Completed!!!

Yesterday was another monumental occasion at DOG Aviation marking another major milestone … the Rotax 912 ULS engine was successfully mounted onto the firewall of the DOG Aviation RV-12.

With the assistance of Bernie and later joined by Mike, we were able to mount the Rotax engine onto the RV-12 with relative ease once some preparations were out of the way. The tail cone was propped up a little to place a downward force on the front landing gear and the weights that were hung over the nose gear so the RV-12 could be rolled outside during canopy fiberglass work were removed to make way for the engine.

Tom, (a fellow local builder nearing completion on his Van’s RV-10), loaned me his engine hoist a few weeks ago ... so we had a hoist available to lift the engine in position. The hoist worked great!!! Thanks Tom! … your hoist sure made things much easier.

The Rotax 912 ULS engine was lifted using a couple of ratcheting cargo tie down straps … one attached onto the engine mount and the other on a pipe inserted into the prop flange. The ratcheting cargo ties came in handy to level the engine once all the weight was supported by the hoist.
Bernie stabilizing the engine while I slowly lift it off the workbench with the engine hoist … at this point the engine is a couple of inches off the table.

Once we got the engine stable and off the workbench, it was wheeled over to the front of the airplane. The engine is mounted onto the firewall at four mounting points. Each mounting point has a large rubber isolator with steel sleeves and aluminum bushings that are slid into the sleeves. With the engine on the hoist, the mounting isolators and bushings were test fitted along with the mounting bolts and it was discovered the bolts would not go through the powder coated washers until the powder coating was removed from inside the hole in the washers.
Test fitting of the isolators to make sure all the parts fit correctly prior to attempting to install the engine onto the firewall.

There were also a couple of engine mounting bushings that did not want to slide into the male isolators, so they needed to have some tiny burrs removed … then a very thin film of slippery Corrosion X was also used to help slide stubborn bushings into the sleeves on the isolators. After a little tweaking, all the parts began playing nicely together and it was time to actually mount the Rotax 912 ULS engine onto the RV-12’s firewall. The engine was lifted to an approximate position by eyeball and moved sideways into position. We elected to install the engine from the side as opposed to installing the engine from the front. Basically, it was cold outside and we did not want to open the hangar doors … plus it would have required moving the whole airplane aft in the hangar because there is a large ridge by the door that would have hung up the wheels on the hoist. Sliding the engine in position from the side was the easiest option … nothing had to be moved and the access was good.
The engine was raised to an approximate eyeball position and ready to be slid sideways across the front of the firewall to get into position to be slid aft to the mounting points.

As luck would have it, the height of the engine was almost perfect it only needed to be raised about a 1/4" to achieve a perfect alignment. The lower mounts were installed first as suggested in the plans, followed by the upper mounts. The upper mount took a few moments to bring into alignment. Basically, after the castle nuts on the lower mounts had a couple of threads captured, the engine/mount was slid forward so a small gap could be created at the WD-1221 upper mount so it was possible to look in and see which way the assembly needed to shift to allow the upper mounting bolts to slide into the holes on the WS-1221 upper mounting point. All and all, the end result was almost anticlimactic in that the engine mounting did not put up much of a fight and all things considered, the engine mounted onto the firewall quite easily.
The engine is now mounted onto the firewall. Bernie was rotating the mounting bolt a little to get the hole for the cotter pin vertical while Mike began removing the tie down straps.

The bolts were torqued and the cotter pins were placed into the holes but not bent. The DOG Aviation procurement department needs to locate a different torque wrench. Lately there have been required torques that are too high for my 150 inch pound wrench and too low for the foot pound torque wrench which starts at 20 foot pounds. As an example, the engine mounts are to be torqued between 160 to 190 inch pounds which equates to 13.3 to 15.8 foot pounds and the M8 bolts used on the engine required 18 foot pounds so I need to find a torque wrench that fills that gap. Of course, in a pinch, a one foot long ratchet wrench or breaker bar can be used and pulled from the end with a fish scale until the scale reads the desired torque say 18 pounds (which is what I did for the M8 cap screw that needed tightening to 18 foot pounds). It would be nice to have the proper tool for the job.
Installed Rotax 912 ULS engine right side view.
Installed Rotax 912 ULS engine left side view.
A major milestone at DOG Aviation, the Rotax 912 engine is installed on the RV-12’s firewall and nobody got hurt and nothing was broken. A job well done!

Thanks to Bernie and Mike for all the assistance and to Tom for allowing me to use his engine hoist.

Thursday, December 17, 2015

Engine Reassembly Completed – Ready To Install

Yesterday, the Rotax 912 engine reassembly process began. The first step prior to reassembling all the parts that needed to bo removed to custom fit the FF-1207 air shroud is to lay down two beads of high temperature silicone along the marks made on the engine casing. Some care should be taken to only apply the silicone to the crankcase area and not apply it onto the cylinders. The FF-1207 air shroud will be seated in the beads of silicone which will serve as an air seal and also to help secure the air shroud.
Two beads of silicone applied to the crankcase and ready for the FF-1207 air shroud to be seated into it.
View from above … one can see how the air shroud is seated into the high temperature silicone.

From this point on, the reassembly is a reverse order of the steps taken to remove the parts from the engine. First the coolant expansion tank and the four water lines are temporarily installed and marks are to be made on the air shroud for a dollop of silicone between the air shroud and water lines. Once the high temp silicone is applied, the water ports are seated and the M6 Allen screws are torqued to 90 inch pounds. Next the ignition module bracket is returned to its original position and the M8 Allen screw receives Loctite and is torqued to 215 inch pounds (18 foot pounds). Lastly, the carburetors/ intake manifold assemblies are installed onto the engine and the M6 intake manifold screws are torqued to 90 inch pounds.
Screwing the right carburetor/intake manifold assembly onto the engine … once the screws are torqued, the engine will be ready for instillation onto the firewall.

Although not told to do so, I also tightened up the bolt and nut that secure the ignition modules. If this poses a problem, I will try to come back from the future and edit this post.  At this point the engine is ready for instillation. Although, at this point, the plans instruct the builder to remove the carburetors for the installation of drip trays. Unfortunately, I do not have the luxury of time and need to move onto hanging the engine because the gentleman I borrowed the engine hoist from needs it to install an engine in his RV-10 … and I don’t want to hold him up since he was kind enough to loan me his engine hoist. Feel removing the carburetors is a task that can be just as easily done with the engine mounted … possibly even easier so will move onto that next.

WD-1220 Engine Mount Bolted On Engine

Yesterday, the engine mount was installed. Prior to installing the WD-1220 engine mount, the plans instruct the builder to remove the powder coating from the area on the engine mount that contacts the engine along with using masking tape on the inside of every leg of the engine mount to prevent against scratches … hah!
Sanding the powder coating away from the inside of the WD-1220 engine mount.

The plans imply installing the WD-1220 engine mount is a tight fit and that it will only go on one way … this is highly understated. To install the mount, the right side of the engine mount is placed around the starter and lower water port on the right side … OK, so far so good. Then the left side of the engine mount is supposed to make it past the lower water port on the left side. The words snug fit is an understatement. I fought with this for over a half hour hoping to find that magic sweet spot there the engine mount would slip past the water port without contact. Of course, while twisting and maneuvering the engine mount attempting to find that elusive sweet spot, the masking tape was getting scuffed like crazy and a couple of places on the powder coating got dinged before the mount was finally PUSHED past the water port. Also now know why the lug was removed from the starter the engine mount needs that space during maneuvering.
Finally!!! … the engine mount went past the water port my finger is pointing towards.

The engine bolt dilemma: Some history -- 5 years ago a builder identified an issue with the RV-12’s engine mounting cap screws coming lose. As word spread on the forums, more of the fleet was checked and it was discovered this was NOT an isolated issue … quite a few builders discovered lose bolts and, in a few cases, even missing bolts! Van’s was slow coming up with a fix … most likely due to the fact Rotax needed to get involved because the cap screw torque values were set by Rotax. Before an “official fix” came about, builders tried two different methods to keep the bolts in place one being blue Loctite and the other installing Nord-Lock washers (same washers that are used to bolt down the propeller). Both methods appear to work fine but each has a down side. Once applied, using Loctite prevents the cap screws from being torqued during inspections because torquing after the Loctite sets will brake it free thus negating its effectiveness. Nord-Lock washers are slightly larger in diameter than the head of the cap screw and need to be trimmed down a little prior to installing them so they will fit inside the engine mount ... a real pain. However, after the Nord-Lock washers are made a little smaller (a hassle), the up side of using them is the torque on the cap screws can be checked during inspections without negating the lock washer's ability to hold the cap screws in place. Thus far, builders who have employed either method have reported no subsequent lose bolts.

In the mean time, Van’s and Rotax decided the 26 foot pounds of torque on the cap screws was too low, so the torque has now been upped to 30 foot pounds and although not positive, I believe this is also when the recommendation came out to remove the powder coating from the mating surface on the engine mount as well. DOG Aviation is going to make a preemptive strike and use the higher torque setting of 30 pounds and ALSO ditch the smooth split lock washers and use Nord-Lock washers instead … something I can do now since the DOG Aviation RV-12 is being built under E-AB rules. And should a cap screw ever get a little lose (truly doubtful) … they will all get slathered with blue Loctite.

Photo of a Nord-Lock washer - they come as pairs, comprised of two thin washers with “ramps” that are placed back to back. The ramps lock with one another when the bolt is rotated in reverse keeping the bolt secure. They also have serrations on both sides and get a better purchase on the metal than an ordinary smooth split lock washer.

Unfortunately, prior to using the Nord-Lock washers for the Rotax 912 engine mount application, the washers need to be made slightly smaller in diameter so they will fit into the recesses in the engine mount. To do this, a metric bolt was used and electrical tape was wrapped around the shank so the Nord-Lock washers could be kept perfectly centered on the bolt. The Nord-Lock washers were sandwiched between some split washers and tightened on the bolt using a nut. The assembly was chucked up in a drill press and spun while a file was used to trim away some of the excess diameter. I filed away and checked with a micrometer until about 30 thousandths was removed bringing the diameter of the washers down to .630 thousands.
Fixture used to clamp to pairs of Nord-Lock washers so a file could be used to make the outside diameter a little smaller when the fixture was spinning on the drill press … my finger is pointing to the Nord-Lock washers.

Bernie came by to give me a hand with installing the engine but it was quickly realized the time spent shopping for parts to make the Nord-Lock filing fixture, checking the air gap on the trigger coil, sealing the FF-1207 air shroud with silicone and reassembling the engine meant there was no way the engine was going to get hung this work session.
Bernie threading the M10 cap screw and Nord-Lock washer into the upper left engine mount.
The WD-1220 engine mount installed and torqued ready to hang the engine onto the RV-12’s firewall.