jett qm40 - possible pressure leak??  
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All Forums >> RC Airplanes >> Pylon Universe - RC Pylon Racing >> QM-40 Racing >> jett qm40 - possible pressure leak?? Page: [1]

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jett qm40 - possible pressure leak?? - 6/21/2007 12:17:21 AM   
izzy


 

Posts: 98
Joined: 4/24/2003
From: REHOVOT, ISRAEL
Status: offline 		I bought a QM 40 a few months back from Jett Engineering , and now that i am removing the engine from the plane for check up, i found someting very interesting

1 of the 6 bolts that hold done the head , seems th have its thread go though the casting and into the exhaust port chamber, such that when i put my finger over the exhaust port , there is a pressure/leak sound of air coming out from where the bolt is threaded . since the bolt does not extend into the port, the air is escaping from there

this seems very strange , as i am sure that this will cause me to lose pressure in the head

i will post pics of the hole , but wanted to hear any comments you might have (for now i have made a drawing to try and explain the position of the leak)

i will also send Dub a mail and post his reply

the engine has had less than 10 flights on it , so it is new and never crashed



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< Message edited by izzy -- 6/21/2007 12:19:47 AM >
       Post #: 1

RE: jett qm40 - possible pressure leak?? - 6/21/2007 8:12:29 AM   
izzy


 

Posts: 98
Joined: 4/24/2003
From: REHOVOT, ISRAEL
Status: offline 		here is the picture of the motor , and the hole i am talking about where the pressure is leaking from
the arrow points to the exhaust port , where the thread reached , therefore allowing pressure to leak from there

any comments ?



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(in reply to izzy)
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RE: jett qm40 - possible pressure leak?? - 6/21/2007 1:21:53 PM   
Ed Smith


 

Posts: 2855
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: online 		I have looked at both of my Jett engines and the hole does not break into the exhaust outlet. Does the hole to the front of the exhaust break through as well? It apperas as if the hole is drilled too deep. I would think that there is no need for that deep a hole as the thread dos not go that deep and the screw is nowhere that long.

The person to ask would be Dubb Jett.

Ed S

(in reply to izzy)
       Post #: 3

RE: jett qm40 - possible pressure leak?? - 6/21/2007 5:27:05 PM   
rmenke


 

Posts: 1822
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline 		izzy:

Give Dub a call on this. Have looked on the 35, 50 and 60 Jett engines, no noted hole into the exhaust port noted. I would think a little "locktite" would cure the problem, or other non binding seal would do the trick. This is Jetts question to answer, I know Dub would resolve any problem you may have. There is no one out there more anxious to keep his customers pleased. Always give him a chance to make any very rare problem with his engines right. I now have 5 of his engines and feel they are the best in the world at any price. ENJOY

(in reply to izzy)
       Post #: 4

RE: jett qm40 - possible pressure leak?? - 6/21/2007 8:37:14 PM   
izzy


 

Posts: 98
Joined: 4/24/2003
From: REHOVOT, ISRAEL
Status: offline 		thanks i sent him a mail today , so i hope he replies soon

thanks all
izzy

(in reply to rmenke)
       Post #: 5

RE: jett qm40 - possible pressure leak?? - 6/21/2007 9:05:58 PM   
Ed Smith


 

Posts: 2855
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: online
quote:

I would think a little "locktite" would cure the problem, or other non binding seal would do the trick.


I think that Loctite would not do it. The screw is not long enough to plug the hole.

Ed S

(in reply to rmenke)
       Post #: 6

RE: jett qm40 - possible pressure leak?? - 6/21/2007 9:20:45 PM   
fizzwater2


 

Posts: 812
Joined: 8/16/2004
From: Paola, KS, USA
Status: offline 		about the only thing you'll lose out of that hole would be a little exhaust gas.. there's no path from there to the combustion chamber when the piston is covering the exhaust port, so you won't lose any compression.

You say the engine has been running fine? If it was me, I probably wouldn't worry too much about it, unless the exhaust leak was troublesome or it was messing with the performance of the tuned exhaust.

_____________________________

no matter where you go, there you are..

(in reply to Ed Smith)
       Post #: 7

RE: jett qm40 - possible pressure leak?? - 6/24/2007 6:13:48 AM   
Trnnbrn


 

Posts: 4
Joined: 4/9/2005
From: Oklahoma City, OK, USA
Status: offline 		Izzy,
Dub's email account is flooded with spam constantly. He has his spam filter cranked up pretty strong so he has told me to only send email without a subject. Those are the only emails he sees, all others are ignored. I suggest you send the mail again with the subject line blank.
Chuck A
quote:

ORIGINAL: izzy

thanks i sent him a mail today , so i hope he replies soon

thanks all
izzy


(in reply to izzy)
       Post #: 8

RE: jett qm40 - possible pressure leak?? - 6/24/2007 7:17:50 PM   
rmenke


 

Posts: 1822
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline 		izzy:

Go to the Jett forum and Bob"s 27 and ask your question to Bob. He is sharp on the engines and will contact Dub if he does not know the answer.

(in reply to izzy)
       Post #: 9

RE: jett qm40 - possible pressure leak?? - 6/24/2007 9:20:21 PM   
daven



Posts: 7013
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		Bob is on vacation for the next week, so he may not get back to you soon. Dubb is getting ready to head to Muncie this week also.

Dubb answered several of my emails this week.

I personally don't think it will effect anything, but I can understand your concern after purchasing an expensive engine.

_____________________________

Dave Norman

klasskote.com
supertrc.com

(in reply to rmenke)
       Post #: 10

RE: jett qm40 - possible pressure leak?? - 6/25/2007 1:41:06 AM   
izzy


 

Posts: 98
Joined: 4/24/2003
From: REHOVOT, ISRAEL
Status: offline 		here is dubs answer in red


Dub hi

I am not sure if we are talking about the same hole

since the hole is near the exhaust port, the exhaust pressure also escapes from this hole as well as the muffer , which obviously decreases its performance

(“when you assume the obvious, you are often wrong”----a dub saying….)

It does not decrease it performance. Try a test. Plug it up with silicone and watch nothing change.

i guess the only thing then is if there is a small leak it is exhaust gas, which in turn will in due time leave burnt oil residue /marks on the engine, which is a pity as i would have like to keep a clean engine
in all honesty i dont think the threads should have gone so deep in the first place so silicone should not have been needed( that and the fact is silicone will probably fall away after a few flights leaving me with the same leak




(in reply to daven)
       Post #: 11

RE: jett qm40 - possible pressure leak?? - 6/26/2007 6:32:40 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Arvada, CO, USA
Status: offline 		Izzy,

I have no idea how or why that hole is there, but I can recommend JB Weld to plug it. Clean the inside of the hole with lacquer thinner first, then stir up a drop of JB Weld and insert it with a toothpick or a small piece of wire and wipe away any excess with a cotton swab. Problem solved, it'll last forever, & it's practically invisible.

Duane Gall
RCPRO

(in reply to izzy)
       Post #: 12

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