ScottsCrazyBuilds Jet Kart

[slittlewing]

Many thanks for giving this more consideration John 😁

I am finding it hard to visualise the lack of fuel mainly because after the test, I connected the drain hose and plenty of hot liquid kerosene came out of the bottom of the engine! The afterburner lookalike flames on the spool up are probably residual fuel burning off from my failed starts (not all fuel comes out when you drain it). Having said all that, it’s got to be worth a more thorough check on the nozzles. I have a good idea of how to do this, more to follow 😎

The machinist at work did not disappoint, and has recovered the turbine to a state way better than I was imagining 😀 really really pleased with what he has managed to achieve.




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Cheers,

Scott

[racket]

Hi Scott

Nice cleanup job :-)

Cheers
John

[slittlewing]

A little video update



Cheers

Scott

[Sweetenough]

Soon back to making noise again!

[racket]

Hi Scott

LOL............where can I find a mate like Carl ??

Nice lathe , wouldn't mind that in my shed :-)

Cheers
John

[slittlewing]

Carl is awesome!! I am very lucky to have him as a mate.

One random question, obviously the journal bearings only have holes every 60 degrees or so for oil to get through to the ID. I see on Anders engine he used a Dremel to scallop out a longer section so oil could always reach a hole.

s231.photobucket.com/user/Anders811017/media/Anders%20projekt/Johansson%20Unit%2002/JU-02%20342.jpg.html

The bearing tunnel of the kart has a smaller scalloped area but not long enough to reach from one hole to another:



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Rather than trying to add extra oil path to the bore like this, Would it be suitable to instead cut a small groove in the standard journal bearing outer diameter, axially in line with the holes so that there is oil feed to all holes continually?

Cheers

Scott

[racket]

Hi Scott

Your current setup should be OK , I've seen no scallop on some turbos.

I just checked the TF15 centre housing and its scallop goes from one bush hole to the next .

I wouldn't cut a groove in the bearing , the scallop produces a "wedge" of oil that "forces" oil thru the bush hole , we need plenty of pressure to counteract the centrifuging of the lube in the other direction, if you'd like to change something , increase the scallop rather than cut a groove, but your current setup should suffice .

Cheers
John

[dieselguy86]

John,

I believe I read in a rotor dynamics book that the grooves were used to decrease the length of the hole, which decreases the bearing pumping forces.

Not sure why some bearings have them and others don't.

[racket]

Hi Joe

Yep , the groove in the OD of the bush does that , ............maybe theres a Patent issue for the reason why some do and some don't ,I don't know .............I like to have lotsa lube pressure and then it doesn't matter :-)

Cheers
John

[slittlewing]

Thanks for the confirmation John and for checking your TF15 housing. I will probably have a go at extending the scallop!

One other question, does anyone know what Torque I should use for the HX82 Compressor Nut?
The Holset service data sheet says 45Nm for a standard HX82, but there is a one variant 4044033 which should be done at 80Nm.

Given the much larger than standard Compressor, and higher P2 of the engine, I am tempted to go for 80Nm. When I removed the comp, I measured 95Nm to undo the nut, but it had been fitted with loctite.

Cheers
Scott

[racket]

Hi Scott

You have a left hand threaded nut which should "tighten??" under load so doesn't need as much torque as a right hand threaded nut such as we used on the Garrett TV94 rotors which can undo under load, perhaps the 80Nm unit has a right hand thread .

Somewhere in one of my build threads I did a nut torque vs comp slippage test and found that I had nearly a 100% safety factor , your comp might need 300 HP to spin it , but at say 63024 rpm that 300 hp represents only 300 divided by 63024/5252, or 300 divided by 12 = 25 ft lbs being transmited by the turbine wheel/shaft.

Yeh , we need to heat our comp nuts to soften the loctite before undoing , the heat will help to slip off the comp wheel as well .

A tad more initial torque shouldn't be a problem , maybe an extra 15Nm at most .

Cheers
John

[dieselguy86]

There's one variant that has a titanium wheel, that could be the one that takes the higher torque

[slittlewing]

Thanks for the replies all! I will go for about 55Nm then, it does indeed have a left hand thread. Don’t want to over torque it and damage anything as they are expensive parts 😬

I have cleaned up the bearing housing and made longer oil grooves that just about span 2 holes on the journal bearings. A fiddly job, small ball ended burr on a dremel seemed to do it.





I also found the front journal bearing was pretty scored on the OD, same for the bore in the housing. I have lightly cleaned up the housing with 1000 and then 1500grit wet sandpaper to make it smooth again.




Rebuild kit now on order from abroad which will have fresh bearings, thrust washer, oil slinger etc.

In the meantime I am looking at modifying the comp back plate oil feed sealing arrangement.

Cheers

Scott

[andym]

does the comp plate oil seal not work... ?
The bearing kit is easy to get in uk,
you clocked the NGV up the wrong way,

As for starting the engine, dispite what you think of the method i explained, its the right way to do it. Doing it your way will let oil past the seals and into the can and burn, along wit any unburt fuel from failed starts if you dont have the drain pipe on
As for the drain pipe, it should be on for the start.

You have never shared the picture of inside of the engine case

I would think the best thing to do, is put every thing back together the best you can, and in a configeration it last best worked in, remove changes you have made, prove all is good, and go from there

[slittlewing]

The oil seal I will be changing is the main oil feed through the casing into the diffuser plate.
At the moment, there is a 10x1 o-ring on a 9.86mm tube, sitting in a 12.2mm bore. That makes 0.35mm of air gap around the o-ring. You have used a shoulder on the tube and the external case compression fitting to push onto a backup ring and then squeeze down onto the o-ring to squash it and fill the gap. This is not a reliable method and has no way of controlling the amount of compression, which should be tiny at about 0.3mm. If I put the engine together and back in the frame and this doesn't seal under pressure, I will have to remove the engine and casing again to fish out the o-ring etc. Or if the casing expands under pressure, the squash will relieve itself leading to an oil leak at high boost.



Using a new feed tube with an accurate groove machined into it will control o-ring compression to a specific value (~25%) and axial location or movement wont matter - this is the normal way o-rings are used.


Since stripping the engine I can now see why you mention oil can leak into the casing without the engine running. Thats because on the oil drain tube, there is no seal to the diffuser housing and a 0.2mm gap. At the moment it relies on boost coming through this gap to prevent leakage which will also flow a load of air into the oil tank. I will fix this by using a piston type seal same as above, so the engine can be started with full oil pressure and no concerns.

Not much to see from engine case but heres a picture:


If you are making another engine I have another tip for you. The back of the shaft tunnel o-ring groove is broken through by a bolt thread:


If you use 6 bolts to hold the NGV instead of 5, you would have lots more space and even room for a bigger oil drain path.