Johansson´s Pocketbike

racketmotorman · Post by **racketmotorman** » Fri Apr 13, 2007 9:40 pm

Hi Anders

So it was just poor combustion causing the pulsing ........interesting :-))

Your TOTs at 550 C @10 psi P2 sound pretty good , they'll probably exceed 600 C at higher P2s with the sized jet nozzles you have at present , so need to change their diameters just yet .

Developments going well :-))

Cheers
John

Johansson · Post by **Johansson** » Sat Apr 14, 2007 7:05 am

Yup, when the lube/air problem for the bearings is solved I will concentrate on building a reliable tacho. Fricke sent me a drawing and some parts needed to convert a frequency counter to a tacho so I will try to get it working before running it at higher P2Â´s.

Even at 10 psi the jet thrust is enough to get the bike rolling with me on it, so I am excited to find out what the bike is really capable of!

//Anders

Johansson · Post by **Johansson** » Fri May 11, 2007 9:12 pm

Developments are actually going slow, now as the summer approaches I am trying to catch up some time with friends and myself since IÂ´ve spent the last 6 months in the garage...

I fitted a larger bleed air tube to the engine today, it will allow more air to enter the bearings and hopefully keep them cooler than before. The syringe needle in the lube restrictor didnÂ´t stick to the solder so I had to fit the old carburator jet instead until I have time to silver solder it.

When I assembled the turbine I found that the preload was missing, the rear bearing outer race got stuck in the housing when the bolts were fitted so I will have to take a few 0.01Â´s away so the preload starts to work again. A bit strange perhaps since it had a nice sliding fit before, but I guess that heat can mess with things...

//Anders

Johansson · Post by **Johansson** » Sat May 12, 2007 8:14 pm

The engine is back together after some tweaking, I found that the rear bearing got stuck when the six bolts that hold the engine together were torqued down so I had to take some material away from the bearing tube so the bearing could slide more freely. Now the preload works perfectly even when assembled, hopefully it will stay that way even when it is at running temperatures...

New bearings are fitted and should hopefully last longer than the old ones did with the improved cooling and lubrication, I will not run the engine above 10 psi before I know how fast the shaft is spinning at that pressure.

Video clip will be on Youtube when it is tested, hopefully I will have time to do it tomorrow...

//Anders

Johansson · Post by **Johansson** » Sun May 13, 2007 12:10 pm

I ran the bike today with an interesting result. With the old lube restrictor the bearing noice and EGT fluctuations are back, so the main reason why it behaved strange earlier must have been flooded bearings. IÂ´m still glad that I made the syringe fuel nozzles since the fuel pressure is way lower now than before...

//Anders

Johansson · Post by **Johansson** » Sun May 20, 2007 1:03 pm

I made some flow tests today with the old lube jet along with a new one with a 5mm long syringe.

Since I have no idea on what the pressure difference over the jet is when the engine is running I decided to test the flow at 1 bar pressure, and found that the old jet flows 108ml/min and the new one 57ml/min. I assembled the engine and ran it only to get a bit confused...

The EGT fluctuations are gone and the exhaust puffs are less frequent, but the bearing noice is still there above 5 psi P2. The battery was almost empty so I don´t know if that could have affected things, when the main fuel pump was activated I could hear that the idle pump lost power.

I will have to do more tests when I get back home from work two weeks from now...

//Anders

Ash Powers · Post by **Ash Powers** » Mon May 21, 2007 1:46 am

Anders,

I'm a bit confused as to how you are distinguishing bearing noise over the sound that the engine makes - how are you hearing it?

In ballbearing turbochargers, we usually place 0.035" restrictors in the feed line and our engines operate with between 30 to 80psi, dependent on engine RPM. The cartridges in the GT BB turbos we use have galleys that direct oil to the front and rear bearing and the drains for the bearings are just on the other side of each bearing - a cutout in the wall of the bearing bore for each bearing that runs to the drain port on the cartridge.

I recall in one test, we left the return lines disconnected to see how much oil was actually coming out of the drain - we didn't measure it like you did, but there was a thin continuous stream - I would estimate somewhere around 300mL per minute or so.

The bearings in these Garrett GT turbos use a phenolic ball cage and interestingly enough, they aren't ceramic balls. Regardless of their material makeup though, I would think that mimicking the flowrate seen in an automotive application would put you where you want to be. I know the bearings in the GT turbos aren't as large in diameter as the ones you are using, which would lead me to believe your bearings can deal with even larger oil flow rates.

By the looks of your bearing tube assembly on page 15, I'm not led to believe you are using the original turbine shaft seal and your setup is a total-loss type configuration. Perhaps the surging noise you are hearing is the quick bursts that occur when the lube oil "flashes" as it works around the turbine and into the hot gas stream - or perhaps the flow of bleed air isn't moving as a continuous stream through the bearing tube and causing the bearings to experience some sort of oscillating loads?

do you have any drawings that show how all the parts come together and where the air bleed line is connected and where the oil is coming into the bearing tube at? Something that also shows the clearances of the parts; namely the area around the back of the bearing tube that surrounds the thick header on the backside of the turbine as well as the area just behind the compressor?

Johansson · Post by **Johansson** » Mon May 21, 2007 10:28 am

Hi Ash,

Thanks for the feedback. The noice that I believe is coming from the bearings is a quite loud whine that comes at a certain rpm, then it just gets worse if the revs are increased further. The strange thing is that it wasn´t there during the previous test when the rear bearing failed, so it is either flooded bearings or imbalance in the rotor since I don´t know how the compressor wheel was oriented on the shaft when it was balanced. Do you know if there use to be any grinding marks or such on the wheel and shaft that indicates how they should be assembled?

You are right about the shaft seal, the rear seal is removed and a new piston seal is located on the spacer between the compressor wheel and the front bearing. Unfortunately I have no access to my computer at the moment, but I will check tonight if I can find any detailed drawings of the shaft arrangement.

Perhaps the surging noise you are hearing is the quick bursts that occur when the lube oil "flashes" as it works around the turbine and into the hot gas stream

The burning lube is heard at idle as frequent "fluffs" from the exhaust indicating that it gets a bit too much oil, with the larger restrictor the EGT gauge went crazy from these streaks of burning oil but with the new and smaller one EGT is steady...

//Anders

Johansson · Post by **Johansson** » Mon May 21, 2007 3:43 pm

You have got me thinking, perhaps the space where the air and oil goes through to the turbine is too narrow? If I remember it right all I did was to remove the piston seal from the shaft, so the total open area around the shaft might be on the small side.

The oil, no matter the flow, will pool up after the rear bearing since it cannot drain from the bottom of the bearing as you can see on the attached picture. If I also mill a slot at the bottom of the hole so the oil can flow into the turbine housing and keep the guiding edge on the turbine plate intact it might just do the trick...

Late night Edit: When I think of it it all seems clear now, the only time that the engine throttled fine without bearing noices was when the bearings didn´t get any lube at all, i.e. without a flooded rear bearing due to the pocket of oil collecting behind it. With a larger but not too large restrictor the noices appeared again since the pocket filled up with oil again.

I am very eager to get back home and try this modification out, I will run it without making any other changes to the engine so I can find out if the mod affects anything! Thanks Ash for pointing out the possible problem source!

Unfortunately I haven´t got any accurate drawings where clearances can be found, I made drawings of the engine as I intended to make it and modified the clearances along the way to get a working engine. I´ll post a crude drawing anyway of the core where you can see where the lube/air enters. I will have to disassemble the engine and take some measurements to find out if I must make any changes to the section after the rear bearing, double-checking the preload pressure might be a good idea while I have it apart so the noice isn´t just a loss of preload.

This is really the best part of the project. If everything went smooth and the bike ran like a dream on the first attempt I would not have a chance to learn anything by trial and error so I´ll keep changing bearings and work on the lathe with a smile on my face! :-)

//Anders

racketmotorman · Post by **racketmotorman** » Tue May 22, 2007 4:55 am

Hi Anders
Bearings need very little "lubrication" to work , even at extremely high rotational rates, BUT, they need good cooling .
In industrial gas turbines they use oil for cooling as well as lubrication , but the average model jet engine only uses ~3-5% of its fuel flow to lubricate the bearings and has copious supplies of air bleed air for their cooling .
If you're running a fuel flow of perhaps 500 ml/min , then 3-5% would equate to only 15-25ml/m, BUT you will need plenty of bleed air , and that bleedair must have a free flow right thru into the turbine wheel , so no restriction to air flow ,especially at the turbine end where the lubricant will have almost turned to vapour on those hot bits .
The "lubricant" , once having passed thru the first bearing at high rpm will be a very fine mist in the bleed air flow, and will continue as such thru the second bearing and out into the turbine scroll , it shouldn't come in "bits and pieces ", it should be a continuous flow .
I'd be looking at possible "centrifuging" of your excessive lubrication flow against the bearing housing wall causing it to collect and "puddle" . This could then be "moved on" as intermitent large fluid flows .
Perhaps you need a "drain channel" under the turbine end bearing joining the space between the bearings and the turbine wheel space , so that "puddled" lubricant can pass into the turbine space without going thru the bearing . You only need mist going thru a high speed bearing as "chunks" of fluid will cause bearing problems .
A bearing , especially a hybrid with ceramic balls, will survive with minimal lubrication , but NOT without adequate cooling .

High speed bearings need cooling first, and lubrication second :-))

Cheers
John

Johansson · Post by **Johansson** » Tue May 22, 2007 4:41 pm

Perhaps you need a "drain channel" under the turbine end bearing joining the space between the bearings and the turbine wheel space , so that "puddled" lubricant can pass into the turbine space without going thru the bearing.

I was thinking of something like on the pic below, if I extended the hole to the other side of the rear bearing wouldn´t that make some of the air bypass the bearing through the hole?

//Anders

Ash Powers · Post by **Ash Powers** » Tue May 22, 2007 6:09 pm

Anders,

In my current GT build I came across a few issues with the rear bearing - one of which was too little clearance between that large diameter shaft header on the back of the turbine wheel and the bore it resided in. I ended up opening the bore to give it a good bit of clearance - the bore is almost as large in diameter as the bearing - it is actually the same diameter as the inner lip of the outer race and provides a good amount of annular space for the cooling air and fuel/oil to move out of the bearing tube.

I think your proposed fix will get rid of the oil wanting to pool at the rear bearing and likely fix your problem nicely. You might even want to drill three holes back there like that - one at bottom center and two others about 60-degrees on each side of the bottom hole. You want to make sure the cooling air and oil have every opportunity to get blown out of the bearing tube to keep those balls from skidding in the races as well as keep things cooled down. As John also noted, you dont need a whole lot of lubricant in there - my fuel/oil feed tube is only delivering in the likes of ~30cc/min into the bearing tube but a good bit of air is passing through.

Johansson · Post by **Johansson** » Tue May 22, 2007 6:51 pm

Thanks a lot for your advice guys. It is great to be able to bounce ideas with experienced people, learning from others mistakes can be just as rewarding as learing from my own... ;-)

What about this? I won´t have to drill any holes and the oil will still drain easily.

//Anders

Ash Powers · Post by **Ash Powers** » Tue May 22, 2007 8:10 pm

That's actually the same as what I did in my GT. I just opened up the bore as well. :)

Johansson · Post by **Johansson** » Tue May 22, 2007 8:40 pm

Perfect, now I know what to do next time I come home!

I really hope that this mod will do the trick, the shaft seems balanced enough so as soon as this problem is solved I will fit the cheramics and do some thrust measurements at 10 psi. Without the tacho working I won´t go much higher but it is hopefully enough to get the bike rolling with me on it, can´t wait to do the first road test!

//Anders