TRX250R.ORG
Workshop => Engine and Bottom End => Topic started by: 937ampd on July 31, 2013, 12:24:29 AM
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Got your attention? Now get your mind out of the gutter. Lol. Ok I bought an ESR 310 bolt on, going to do a leakdown and was wondering if I should blow air into it with a bicycle pump or suck the air with a handheld brake bleeder putting negative pressure in the case rather than positive? Does it really matter? Any insight on this is greatly appreciated. Aaron P
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Blow.....then suck. Repeat. :encouragement: In all seriousness most pressurize the cylinder. But I can see benefits to both, such as with the crank seals. If you pressurize it can help the seals seal even if they are worn therefore hiding a possible leak. However a vacuum wouldn't have the same effect and the worn seal may leak. If you have the capability give both a shot!
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Lol, I figured that'd get somebody's attention. I was worried about possibly blowing the seals but know just about everyone and their momma pumps air into it. Plus 6-8 psi isn't a great amount of air. Just playing it cautious, I don't want to be the reason it fails. Great advice Polonda, I will do both just for sh*ts n giggles.:positive:
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I really don't think there is a great deal of benefit of doing one versus the other. I have read the pros and cons, and there is not much in favor of one versus the other. I will say that most of your big name engine builders pressurize instead of using vacuum. There may or may not be a reason for this. Regardless, 6psi for 6 minutes with no loss is a proven method and used by the majority. Can't go wrong with that.
937ampd, You can used up to 8 psi without any issue of damage to the seals. If you are using some sort of small pump, 6 - 8 psi is easily attainable without going over.
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This is interesting. If you used vacuum to measure negative pressure would the reading be 6-8 inHg?
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6psi would be 12.22 in hg
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Over the years, 10 psi has been the amount not to go over, so most will go somewhere between 6 & 8 psi.
Years ago how to do a pressure test proper, was to seal the engine openings (exhaust, spark plug hole & intake), pressure it then submerge the whole engine under water. I've never done one like that to date, but I do use a hand sprayer filled with soapy water to check for leaks any where theres a seal or gasket.
Now some may look down on it, but I use Three Bond 1211 sealant on every gasket when building an engine. I'll not take a chance of a gasket leaking, because after all these years have past & as many owners have past parts of 250R engines from one to the other, I seriously dont think theres a perfect gasket surface left.
Now if it was a new machined part, that a German machinist had just perfectly finished, then I would probably trust that gasket surface with only a gasket.
Every engine builder has their own way of pressure testing, no problem with that at all, I just shoot for 7 psi, walk away & leave it & will try for no leak at all. I figure if it sits a hour & still on 7 psi, I've done a good job on the build getting every thing sealed up.
Neil
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Awesome, great info here. I had a feeling this could open a can of worms with different procedures of leakdown but the general consensus is to pressurize to roughly 7 psi and hold for an hr/spray with soapy water. I did use Honda gasket maker along with the gaskets because as C-Leigh stated the mating surfaces have been around the block and this is a low budget build. Thanks for the replies fellas. Hopefully this holds air and I can pop this new 38 a/s and cm trx5 on and start jetting. I'm having 2stroke withdrawal...
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Like Neil said, I use 1211 as well. It is just hard to find around here for some reason.
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I pressurize because its easier than vacuuming but either would work.
IMO I honestly do not think if you lost a couple pounds over a a 10-15 minutes time period on a used motor to be of any concern, new motors with fresh grease on the seals will seal much better than a motor that has time on it.
I have never had a jetting issue/engine performance fixed because I fixed a small leak of that amount (couple psi over 10-15min) after it was repaired
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IMO when you use 3bonds 1211 if you have white globs oozing out from the gasket mating surfaces you have used to much, I just barely skim it on by working it on the gasket between my thumb and index finger.
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^^^^ yep, whatever squeezes out also squeezes in.
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One last question. BDC or TDC during leakdown?
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At BDC, the whole engine is open to pressure, where as if the piston was up, the pressure would have to squeeze past the rings to get into the head dome area.
Pressure would get there in a short time, but with the piston down it would be no waiting.
Either way is fine, you do it like you want to do it, because its you testing not us, so make yourself feel good.
I'm just glad you got a TRX250R to test :eagerness:.
Neil
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I'm just glad you got a TRX250R to test :eagerness:.
Neil
I'll raise a glass to that:very_drunk:
BDC it is, thanks Neil and you other guys for the sound advice.
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Very interesting thread. Just curious, how do you plan to keep the constant vacuum to gauge the test itself?
I was thinking about pulling vacuum and holding it with a valve somehow. Make something similar to your normal homemade leakdown tester, just pull instead of push. This would work, correct?
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Sure do, for those easy one man brake jobs. Have vacuum covered just have to go buy a bicycle pump to put air in.
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The tester I made, used a hand pump from an old blood pressure cuff.
Neil
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The tester I made, used a hand pump from an old blood pressure cuff.
Neil
Mine as well.
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Got the leakdown tester complete. Couldn't find a gauge I was happy with, it reads to 160psi. Pretty big to get a real accurate reading but I made sure I didn't go past 10psi. Held pressure without leaks so I'm pretty stoked. Also can't find a gauge to read vacuum so that's on hold. Just happy this held air. Here's some pics of what I set up.
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Was able to take the inHg gauge off my bleeder pump and just plugged the void on the pump with a brass fitting. I was also searching online and Grainger carries a gauge that reads psi and inHg for $10. They have bankers hours so I was s.o.l. this weekend, gonna go buy it for future use. This motor did very well though, held 6.5 inHg for well over an hour. Time for break-in, my least favorite part.
*update*
Just realized I should have tested at 12.22 inHg not 6.5 inHg. I feel stooooopid!!! Oh well, live and learn.
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I wouldn't rule out a carb problem especially if its old. worn out carb will cause endless grief. hard to say where your problem might be but if theres no visible signs of leaks ,either at the seals or gasketed areas and the engine holds pressure then I would probly look elsewhere. even if you had a slight leek I don't think it would be a big deal. ive had the left seal leek a alittle and it didn't seem to affect anything that I could notice. allitle oil behind the stator clued me in but i never did bother to pressure it up, mostly because it still ran fine