Nitro engine air leak and Mid needle setting

[Steve-O2021]

Did a leak test on my K5.9 and found a leak at the rear (most likely due to a missing bolt lol...)

 

Noticed there was also air coming from the front bearing but I read this is OK  as long as you don't have splattering out around the flywheel / clutch area as the oil from the fuel creates a seal here. 

 

Also what's the stock setting for the Mid needle? I read flush but this needle has 4 holes in it, do you line it up with the HSN inlet hole?

 

Thanks

 

 

[wolfie1]

When i set mine up i just made sure it was perfectly flush using a straight edge and all was good, i did put a spot of loctite on the threads as the only reason i was messing about with it as it fell out

[locky]

A small air leak at front is common depending how you perform the air leak test . The MSN should be flush, you can try to line up its holes to be inline with HSN when near flush. Just make sure its orings are still good as they will harden with age and the needle can then rotate during use.

[Steve-O2021]

2 hours ago, wolfie1 said:

When i set mine up i just made sure it was perfectly flush using a straight edge and all was good, i did put a spot of loctite on the threads as the only reason i was messing about with it as it fell out

 

Thanks 👍 

 

1 hour ago, locky said:

A small air leak at front is common depending how you perform the air leak test . The MSN should be flush, you can try to line up its holes to be inline with HSN when near flush. Just make sure its orings are still good as they will harden with age and the needle can then rotate during use.

 

Quite a basic test, blocked the exhaust port and carb port then put it in the sink and blew through some pipe connected to the fuel inlet by mouth and looked for bubbles lol

 

What would a more involved test be?

 

Thanks

[locky]

The front bearing isnt designed to be an air tight seal, if there isnt much oil build up around it then not an issue.  The seal is internal between the crankcase, crank and fuel boundary layer.  When engine is at idle  spray carb cleaner or brake cleaner from an aerosol at potential leak points. If there is a leak then aerosol spray will be sucked into the engine and the rpms will drop or it will stall due to insufficient oxygen. It is often recommended to use rtv sealant on the backplate and carb when reassembling, which should ensure an air tight seal, allow the sealant to go off before running.

[Steve-O2021]

6 hours ago, locky said:

The front bearing isnt designed to be an air tight seal, if there isnt much oil build up around it then not an issue.  The seal is internal between the crankcase, crank and fuel boundary layer.  When engine is at idle  spray carb cleaner or brake cleaner from an aerosol at potential leak points. If there is a leak then aerosol spray will be sucked into the engine and the rpms will drop or it will stall due to insufficient oxygen. It is often recommended to use rtv sealant on the backplate and carb when reassembling, which should ensure an air tight seal, allow the sealant to go off before running.

 

Thanks for the tips

 

Is the starter shaft supposed to have a o ring on that groove in the image

 

 

 

[locky]

No

[Steve-O2021]

13 hours ago, locky said:

No

 

Thanks, my next question is what o ring material is best for a nitro engine?

 

Nitrile of viton?

 

Thanks

[locky]

Buna/nitrile. Let us know if you find a source that has a range of sizes suitable for carb needles.

[Steve-O2021]

6 hours ago, locky said:

Buna/nitrile. Let us know if you find a source that has a range of sizes suitable for carb needles.

 

Been using this seller on eBay, arrives next day usually

 

https://www.ebay.co.uk/itm/141455807147?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=UXpgn1gJSJe&sssrc=2349624&ssuid=eHUxVO3MTke&var=&widget_ver=artemis&media=COPY