steve@innoviator.com Posted August 25, 2014 Report Posted August 25, 2014 Does anyone have an explanation for a MAP line weep hole? Typically weep holes are near the bottom of lines, not the top. Quote
MB65E Posted August 25, 2014 Report Posted August 25, 2014 My understanding is that it's a hole for excess moisture, oil, residual fuel to escape. I've had an install on a MVP-50 that didn't have the weep hole... Constant Manafold pressure issues! I'm sure there is more technical reason. -Matt Quote
cliffy Posted August 25, 2014 Report Posted August 25, 2014 OK I guess I need an education, MAP line weep hole? Quote
MB65E Posted August 25, 2014 Report Posted August 25, 2014 Usually with in about 6in on the #3 or 5 cylinder manifold pressure line. In the 1/4 alu hard line, Bottom side, sometimes right next to a clamp. Maybe too it's a faster way for the guage to read Ambiant pressure? -Matt Quote
carusoam Posted August 25, 2014 Report Posted August 25, 2014 On my C, the small 1/8" aluminum line from one cylinder's intake ran directly through the firewall to the back of the instrument... The intake is full of dark blue gooey deposits coating everything... The tiny hole (vent) is drilled in the 1/8" line. It is a calibrated hole dimension. Too big the gage will read low, too small the gage reads high. My experience comes from the vibrations cracked the soft aluminum. While searching for the problem, I broke the line open (in flight). This is also the moment that I lost faith in instruments that bring hot or flammable liquids into the cockpit. OK for high priced planes back in the 60's. Not so good for a family flying on a budget... I had heard of the weep hole, but could not find any documented evidence. Mine was broken in half and really hard to measure. Bill Wheat was probably my best resource for this... The hole is documented in one of the IP drawings for the older Mooneys, but not in any of the C drawings... Bought drill bit, had mechanic take care the details...requires cutting the tube, flanging the end and reinstalling... The instrument is under vacuum until the engine shuts down. Without the vent hole, fuel/air mixture would be drawn towards the instrument... Overall, with the proper details, it's a fifteen minute job....? Best regards, -a- From my hand written notes.... 0.023" drill. Keep in mind 1/32" is .032". This is tiny....! Also keep in mind, I am not a mechanic.... Quote
Guest Posted August 25, 2014 Report Posted August 25, 2014 The weep hole allows fuel, oil etc to drain out of the map line on shut down. It is usually at the bottom of the rigid MAP line as it exist the intake port fitting. Clarence Quote
steve@innoviator.com Posted August 26, 2014 Author Report Posted August 26, 2014 Thank You Gentlemen, Very good explanations.. steve Quote
cliffy Posted August 26, 2014 Report Posted August 26, 2014 OK learn something new every day Now my question is- If it only shows on earlier than C model drawings why would we assume it would be used (required) on Cs and later? Quote
carusoam Posted August 27, 2014 Report Posted August 27, 2014 Cliffy, I was less than clear... C,D,E, and F were produced concurrently. All had the same weep hole. I believe the F drawings have the detail captured on the drawing. I was looking as an owner of a C. The 1/8" flexible aluminum line is barely documented, never mind the weep hole. I tried to buy the line from my MSC, they sent me one for a J? instead... 1/4" rigid tube? I believe it may have the same weep hole. My memory wasn't that good then either... Best regards, -a- Quote
cliffy Posted August 27, 2014 Report Posted August 27, 2014 This is interesting as I've never heard of it before. At first glance I would think the hole would affect the MP reading at lower MP setting. I would think it would act like any other induction leak but would have a direct effect on the MP gauge reading. I'm going to ask a real old timer A&P friend of mine if he ever heard of such a thing. Interesting, very interesting. Quote
carusoam Posted August 28, 2014 Report Posted August 28, 2014 Cliffy, Now you're being funny... It does act like any other induction leak allowing excess air into that particular cylinder. Unlike any other induction leak, it is directly affecting the instrument with the improper air flow. Without the hole the MP indicates off the instrument... With the hole cracked open slightly, the MP is off a couple inches... With the hole broken open, it reads atmospheric pressure even while idling... Hence the word calibrated being used. The instrument is sensitive to the small hole. Knowing MP and RPM is key to proper power management. My C lost the MP this way. It lost The rpm gauge via a worn drive cable, it wobbled until the needle fell off... Great trivia for the non digital instruments guys... You'll need to find that drawing for proof. My digital instruments still have analog needles... Best regards, -a- Quote
Andy95W Posted August 28, 2014 Report Posted August 28, 2014 Cliffy / Carusoam - thanks for posting. Nice to learn new things. Does anyone have a copy of the engineering drawing that has this weep hole? Cliffy, please let us know what your "real old timer A&P friend" has to say. Quote
cliffy Posted August 29, 2014 Report Posted August 29, 2014 Waiting to hear back from the "old timer" but this is something I want to learn about. Lost my MP once due to broken 1/8" line Makes no difference to as I'm full throttle or pulling back for landing :-) I may also have a contact for the drawing on the line but it might take a while to get it. Quote
Piloto Posted August 30, 2014 Report Posted August 30, 2014 The orifice on the manifold pressure line is for dampening the pulsating vacuum caused by the intake stroke cycles. Without the orifice the MP reading would be fluctuating about 1"rapidly, specially below 1,000 RPM. Check: www.grtavionics.com/MANPRES.pdf par. 4 José Quote
Guest Posted August 30, 2014 Report Posted August 30, 2014 Jose, Two different animals. A restrictor orffice is within a fitting in the MAP line, the weep hole is drilled into the side of the line. Clarence Quote
carusoam Posted August 30, 2014 Report Posted August 30, 2014 Additional info... From the parts Manuel... Figure 17 Instrument Panel Assembly. Page 74 This drawing depicts all the wires and hoses going to the backs of all the instruments. Figure and index nos... 17-41 FP and MP gauge 17-42 hose, snubber, and hardware list... 17-43 MP line and hardware list... Gives two part numbers for the lines.... 660061-3 for C,D,E 660121-3 for F I think the part numbers may give a hint to a drawing number with the reference. Now, how does one get an engineering drawing for the individual part? As José points out above the instrument manufacturer would be the one with the knowledge of the hole dimension. Note that the FP indicates a need for a snubber, the MP, nary a hint! Why is the F different than the others? Hope that helps, -a- Quote
Piloto Posted August 30, 2014 Report Posted August 30, 2014 Clarence has a point, but the hole is too small to drain any oil plus it will need positive pressure to get it into the line. On my engine the hole is located on the top side of the line. It looks to me more like the hole is for vacuum bleed off. José Quote
Andy95W Posted August 30, 2014 Report Posted August 30, 2014 Carusoam said his hand written note said .023 drill; Poloto's PDF noted a #70 drill bit, which is .028. Think we are talking about the same thing here. Still curious to see what Cliffy's old time A&P buddy says. 1 Quote
MARZ Posted August 30, 2014 Report Posted August 30, 2014 Timely. My large tube broke in half at the adel clamp. I didn't see any weep hole on inspection have to take a closer look Sent from my iPhone using Tapatalk Quote
carusoam Posted August 30, 2014 Report Posted August 30, 2014 Mike, what year is your F? At some point in history the F evolved away from C and E... From dusty memory... The C's weep hole is about 2" from the instrument. -a- Quote
MARZ Posted August 30, 2014 Report Posted August 30, 2014 67. Guess I'm slow. I've got a larger tube off the engine ends just back of the right rear cylinder. Then a much thinner tube that connects and goes to the gauge. Where is the hole? Sent from my iPhone using Tapatalk Quote
carusoam Posted August 30, 2014 Report Posted August 30, 2014 From dusty memory... The C's weep hole is about 2" from the instrument. -a- Quote
triple8s Posted August 31, 2014 Report Posted August 31, 2014 The hole may be obscured by a clamp. The C I owned had a tiny hole that was very close to an adel that helped support the line as it made its way back towards the firewall. Quote
Yetti Posted June 12, 2017 Report Posted June 12, 2017 Per chance does anyone know anything about snubbers say on an F model Quote
MB65E Posted June 12, 2017 Report Posted June 12, 2017 They leak, they don't seal. They are supposed to drain excess fuel in the intake sump. Don't over prime and they are not needed. The ball type ones are better than the Piper diaphragm type. -Matt Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.