912 Big Bore

[BigJohn]

big john , since you are in wa , are you going to make it to arlington?

Not this year, probably be heading S on Wed or Thur after a few hours on the new lower end and Cam.

[cap01]

too bad , would have been nice to chat with you about the zipper . I've been following your updates of the mod with interest and becoming more interested in trying it out .

[BigJohn]

In Washington at my Sons place, Hal flew in this weekend and we installed a new lower end with a modified Cam, Cams design is for the 1622 BigBore to increase the valve opening by approx 40 thousanths and approx 6 more degrees overlap. Innitial tests today showed a much smoother idling, at one point we saw smooth at 1100 RPM not that you would want to idel there due to gear box. To early to report pro or con on the flight testing yet, Plan on significant testing the next couple of days.

Flew down to S CA and now have 17hrs with the new Cam, Low RPM is smoother than stock Cam even with a slight loping, not that you want to run the Engins super low or the gearbox but I can get the idle down to 1100 RPM with no issues. We did have to initially increase the Main Jets to 190's for a richer thus cooler EGT's at full throttle and move the needle jet clip to the lowest setting raising the needle jet for richer mid range, this all worked with the exception that we are a little rich between 2000-3300 RPM so we will be doing some fine tuning with the needle jets and clip settings.

I don't have any real significant reporting with the new Cam as all my flying thus far was at or near Gross with the Cargo Pod on, I will be checking it out fully once we are satisfied with the Jetting.

On another note some of you have heard or may hear that I had an Engine failure on takeoff requiring a turn back landing, This was due to a Stator issue and was not related to the Big Bore Kit in any way, required a new stator and we were back in the air the next morning. An unknown item took out both ignition coils at the same time at 300 AGL on departure, Good thing we practice Engine outs and those impossible turn backs.

[BigJohn]

Glad your engine out turned out OK BigJohn.

Me to, Glad I had been practicing for it but not Glad it happened. .

[BigJohn]

Flew down to S CA and now have 17hrs with the new Cam, Low RPM is smoother than stock Cam even with a slight loping, not that you want to run the Engins super low or the gearbox but I can get the idle down to 1100 RPM with no issues. We did have to initially increase the Main Jets to 190's for a richer thus cooler EGT's at full throttle and move the needle jet clip to the lowest setting raising the needle jet for richer mid range, this all worked with the exception that we are a little rich between 2000-3300 RPM so we will be doing some fine tuning with the needle jets and clip settings.

I don't have any real significant reporting with the new Cam as all my flying thus far was at or near Gross with the Cargo Pod on, I will be checking it out fully once we are satisfied with the Jetting.

On another note some of you have heard or may hear that I had an Engine failure on takeoff requiring a turn back landing, This was due to a Stator issue and was not related to the Big Bore Kit in any way, required a new stator and we were back in the air the next morning. An unknown item took out both ignition coils at the same time at 300 AGL on departure, Good thing we practice Engine outs and those impossible turn backs.

Right at 90hrs on the 1622 BigBore and 30hrs with the new Cam. As I mentioned in an earlier post the smoothness of the engine with the new Cam is superior to the stock Cam, The Cam also allows the carbs to perform better with a longer duration and greater opening, Have been able to dial in the Jetting to 180 mains from185's with stock Cam, needle setting next to last bottom clip setting, temps are all good with mid 1400's at or near sea level at mid range and low 1400's on hard climb out leaning still is viable at cruise rpm's from 3000' and above.

Performance is slightly better with the new Cam, climb and Innitial throttle up at take off improved just to a noticeable amount but much smoother overall. I have only taken it to 13,500 with the new cam, was still climbing at 500' min and able to get up to 5600 Rpm.

Now it will be a duration test to see just how things hold up over the long run, my Innitial feeling is as we'll or better than a stock engine.

[WWhunter]

I finally got my Zipper kit installed but due to other commitments have not been able to take it up for a test flight yet. I just returned from the Black Hills to see my son one last time before he heads to the sandbox. He flies out on Monday and like any parent I am worried and my mind was just not into flying.

I had done a 15-20 minute test run and retorqued everything along with checking for leaks. Picked up all the extra parts I had left over...doesn't everyone have parts left over??.... and then closed the hangar door.

Well, I was finally able to take the plane up for a flight last night. I flew 0.8 hrs. with the engine at 5500 RPM nearly the entire time. All temps and pressures seemed to stay lower that what they were previously. The water temp never went much over 200, as I installed a 180 degree thermostat. Oil pressure was close to 60 psi with oil temp eventually hitting a peak of 220 but stayed around 200 for most of the time. I was cruising at just a touch over 100 mph and this is with 29" Bushwheels and also dual external fuel tanks.
I had LOTS of throttle left available. I was easily able to bump it up to 6,000 rpm!! I definitely need to repitch my prop. I am speculating I will get a small increase in speed that will be great for those crosscountry flights.
With the previous pistons installed I wasn't able to overspeed it as easily as it does now.
I did notice a slight vibration after a bit of flying and by the time I landed it was getting worse. I removed the cowl to recheck everything and removed all the plugs. The spark plugs of both of the front two cylinders were very black and sooty looking. A sign of a rich carb. The weird thing is that both rear cylinders had the brownish/tan looking plugs of a correctly burning cylinder.

My question is, what the heck would cause only the front cylinders to run rich and the rears to run fine? Since I am a neophyte to these Rotax engines and their dual carb setup I am curious as to why this is occurring.
I do have a complete carb rebuild kit I purchased for 'just in case' so I guess it may be time to install it. The engine only has 200 hours TT.

[BigJohn]

Make sure to check top and bottom plugs as the top front and back bottom and etc are on the same ignition, also if it has been 200 hrs on those plugs I would suggest new plugs. Not sure why other than checking these areas first, May need to give Hal a call. I had to increase jet sizes since I was initially running lean yours sure shouldn't run rich I wouldn't think.

I have about 102hrs on the 1622 Zipper and all has been running great.

[WWhunter]

Both the top and bottom plugs are fouled in each of the front cylinders. All of the plugs on the rear cylinders are good. Yes, I am stumped. :-(

[BigJohn]

Both the top and bottom plugs are fouled in each of the front cylinders. All of the plugs on the rear cylinders are good. Yes, I am stumped. :-(

Spoke with Hal and Wayne, Innitial thoughts are make sure new plugs and gap no more than 24, with break in and especially break in oil expect some minor fouling especially in front cylinders. Run hard 5500+ during most of innitial break in. This should resolve issue. They did ask what your EGT's we're running.

[WWhunter]

BigJohn,
I do not have an EGT.
The readings at a continuos 5500 RPM from other gauges are:
Water Temp-210
Oil Temp- 250+
CHT- 200
Oil Pressure-55
I kept the throttle at 5500 most of the time on these flights. I did wind this little screamer up to 6000 a couple of times and let it run for a few minutes at that speed.
Spark plug gap is set at 0.22.
Fly over an hour on Saturday and it started running very slighty rough so I cancelled my flight and returned home to check things over.
I removed the plugs again yesterday after Saturdays flight and they are slighty better looking than the first couple of times I checked them. I think, as you state, that this issue may work itself out with time.

I probably should call Hal and inquire if I need any jet changes. Not a professional by any means but it stands to reason that an increase in engine volume would require an increase in fuel flow.