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Old 10-16-2005, 05:39 PM   #1
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Default Airleak?

What are the symptoms of an airleak? Today was my first race with my new P5. During practice I was richening the carb quite a bit to keep temps under 250. I ended up with 3 1/2 on the hsn, 3 on the lsn and it was running great. At the end of the second qualifier it was running 290! and revving pretty good at idle. Not enough to engage the clutch though, although it's a werks clutch and it sert to engage pretty high. Anyone know why it was so hot and revving? I was thinking maybe an airleak somewhere, would that cause this? Will 290 for a couple minutes hurt my new baby?
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Old 10-17-2005, 10:40 PM   #2
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well it for sure isnt good on it..but a few seconds shouldnt hurt..air leaks usually make it rev up,and just will not tune..did you do your tuning at full tank of fuel or what..sometimes if you do your tuning when its not at a full tank the tune will not be right..and it will heat up when it is low on fuel and get hot..have you checked your linkages and trim and idle screw to see if they are all set right?and sometimes fuel line will get tiny holes in it and cause it to have an airleak..i would try setting the idle and richen it a hair and see how it does.
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Old 10-18-2005, 05:26 PM   #3
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Well I dunked it in the sink while blowing through the fuel line. Everything sealed great except the front bearing, major bubblage. Has anyone had this problem with a new P5X? Is there a better bearing to use than the stock Novarossi rubber sealed bearing or was this just a freak deal? Also the motor had no head shims, that isn't right is it?
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Old 10-18-2005, 06:35 PM   #4
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The front bearings in any RC engine are not air tight. The seals are only there to keep the dust out and most of the fuel in.
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Old 10-18-2005, 07:10 PM   #5
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You dunked a new P5 in a sink??? Man you're crazy! The thing probably just isn't fully broken in yet. Was there a big temperature change from the beginning of the day to the end?
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Old 10-18-2005, 07:13 PM   #6
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So How does the crankcase keep from sucking air? No bubbles came from anywhere else. I hope it's the bearing 'cause I'm at a loss as to where else the problem is. At 4 turns out hsn and lsn the motor still idled great and screamed, running about 260 -270. I would think it would barely move from being so rich.
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Old 10-18-2005, 07:16 PM   #7
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It did seem to change at the end of the 2nd heat. I had running rich when the day started and after the race it was 290+ and revving high.
even today when I kept richening it still hit 290 after minute or two on the track.
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Old 10-18-2005, 07:29 PM   #8
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It sounds to me like the low end needle is to lean, that can make it rev up and heat up.
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Old 10-18-2005, 08:22 PM   #9
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Hey speedbump I was just looking at motor and I see what you mean. The bearings don't need a perfect seal. When the case starts to pull a vacuum(piston going up) the inlet on the crank is opening so air rushes in from there.

Well that sucks, it must have been just too lean. Today when I was tuning it, when I got 4 turns out on both needles it finally started to act rich. Then the horn on the throttle servo stripped and I packed up. I was probably on the right track when I left and didn't know it. Already ordered the unneeded bearing too ($18). And shims ($20). Which I found were on the button, they were aluminum and i just didn't notice they were there.

And the real icing on the cake: I forgot the backplate had a groove for the piston skirt at BDC. Yep, I yanked out and took a chunk piston with it ($105).
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Old 10-18-2005, 08:37 PM   #10
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Quote:
Originally Posted by augerpro
So How does the crankcase keep from sucking air? No bubbles came from anywhere else.
I believe it is the tight tolerance between the crank journal and the case that keep it from sucking air. The chances of the engine sucking air from the front bearing are pretty slim and if it did it would not be because of the seal on the bearing, it would be because of a worn out crank journal. Bearings are not air tight! Engines made for RC boats sometimes donít have but a metal shield on the front bearing and they donít suck air! If you really think you have an air leak here are places to look & seal up.

1. Tank, tank lid and fittings
2. fuel lines
3. Fuel filter.
4. Seal carb to case with RTV
5. Seal back plate with RTV
6. Seal pinch bolt with RTV
7. Seal fuel inlet on carb around banjo.
8. If necessary seal carb boot at both ends
9. Make sure all the o-rings on all adjustment needles are in good shape and not loose in there housingís.
10. Make sure head bolts are tight
11. Make sure your exhaust gaskets are making a good snug fit and are not torn.

I know some of these things are obvious; I just listed all the things I could think of that might help. Does the engine idle well and for a long time?
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Old 10-18-2005, 08:46 PM   #11
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Man that SUCKS! Don't feel to bad though as that has happened with the back plates more that you would think. As far as your tune that is where I was going next. I think you are still to lean on the bottom end. If you do get it back together remember this, it is always better to tune from a way rich setting then from a lean one and also much easier. I'm sorry you have been having such bad luck but it does happen to most at some time or another.
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Old 10-18-2005, 11:49 PM   #12
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Well I WAS rich leading up to the race. The motor only had 1/3 gallon through it at most. I wanted to keep it rich since it has more power than I can use anyway. So maybe the race loosened it up and my lean condition came out?

As far as idle that's what was wierd. Before the race I had to screw in the idle screw a bit so it could get enough air. Now with the idle screw out I can even push the slide closed and it still idles fine. Like it's getting plenty of air from SOMEWHERE. I did rtv everything you suggested yesterday and it passed the bubble test.

This is my first "nice" engine so maybe I should have expected more change in tune as it broke in and loosened up. Oh well, got a new sleeve and piston coming, guess I'll try it again. Thanks for the help!
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Old 10-19-2005, 02:12 AM   #13
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3 on the LSN? they are around 5 or 4.5 stock... so i would say rich LSN by 1 turn...
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Old 10-19-2005, 03:18 AM   #14
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Well that would explain some things ! I had no idea what was stock, and my motor definately did not come set like that. Oh well, I'll pay closer attention this time.
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Old 10-19-2005, 06:50 AM   #15
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I noticed that you said you only had 1/3 of a gallon run through the engine. Everybody that I know that has a P5X did not get theirs broke in until well after a gallon of fuel.
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