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leak down?

This is a discussion about leak down? within the Turbo Nitrous section, where you will Drag Racers sharing info on Turbo and Nitrous applications; I use a leak down test almost every single day at my job on internal combustion engines, maybe more like once every two to three days. Either way my point is that I have alot

  1. #16
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    I use a leak down test almost every single day at my job on internal combustion engines, maybe more like once every two to three days. Either way my point is that I have alot of experience with using the leak down tester as a diagnostic tool. I almost think that this tread is people over thinking about it. I can promise you that if you have a any valve issues or ring issues you will know it! if it is over 20% there is a problem somewhere period. i have seen cars with 15% leakage with almost 200,000 miles on them and still running fine considering the wear on cylinder walls and rings, so i believe that a fresh motor with even too much ring gap wont even hit 10% on an up too temperature engine, would almost put money its not even to 5%. of course, i dont use cheap tools not that they dont work will cause i dont know that, its just when it comes to any measurement type tool I only use will known name brand tools. your engine will most likely have more than normal crankcase pressure so you may end up need to use a catch can on the crankcase vent. burnt exhaust valves will usually put the percentage around 30-40% and bent valve or damaged seat will be 80% or more. for those that are interested, OTC is the company that makes most of they tools similar to leak down testers for other tool companies like matco, mac, cornwell, and so on. so if you buy OTC brand you cant go wrong.

    And the comment about the not tearing into unless its more than 20% i would agree with ONLY if you can hear or feel the are coming from the crankcase breath hole, if its blowing out that exhaust or intake then tear it down and dont spray it but i would put money that if you got a valve seal issue its going to be well over 20%. this much past the rings will only make the engine down on power and excessive crankcase pressure.
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    Quote Originally Posted by Moody View Post
    And the comment about the not tearing into unless its more than 20% i would agree with ONLY if you can hear or feel the are coming from the crankcase breath hole, if its blowing out that exhaust or intake then tear it down and dont spray it but i would put money that if you got a valve seal issue its going to be well over 20%. this much past the rings will only make the engine down on power and excessive crankcase pressure.
    I agree 100%. I don't use the tool professionally and I assume I am adding some measure of error. I know the spark plug thread isn't sealed as tight as I'd like. I know when my gauge gets over 20%, I gotta start digging. 10 or 15% past the rings, no big deal for me as long as the valves are good. 20% sounds like a lot, but I don't think it is. That's MY number. It's a compromise with my wallet. I can't afford to keep it much tighter and I can't afford to let it get any worse. If I do, bad things can start happening in the ring lands.

    I agree that if the valves need attention, it's fairly obvious and rarely have I caught them leaking 'a little'.

    If I were running total seal rings and a vacuum pump, I would log crankcase vacuum data and have a much better idea where I was. I'm just not willing to go that far for where I'm at.
    Sometimes nuthin' can be a real cool hand.....

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    StrokeThis, Steve Knecum is on here a bit...I'd guess you all know his credentials.
    I'd suggest you contact him for a pro's point of view.
    Some of what I'm reading here doesn't line up with my perception of good practice and I'd suggest getting Steve's opinion on it.
    Hank

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    Which parts and why?
    Sometimes nuthin' can be a real cool hand.....

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    Thank you 1216 bandit

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    Quote Originally Posted by 1216 Bandit View Post
    StrokeThis, Steve Knecum is on here a bit...I'd guess you all know his credentials.
    I'd suggest you contact him for a pro's point of view.
    Some of what I'm reading here doesn't line up with my perception of good practice and I'd suggest getting Steve's opinion on it.
    Hank
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    the ONLY reason i spoke up on this tread is because i can give someone my actual experience and knowledge and not just a theory which is what you will get from most poeple on here. Good luck.
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    Calm down, Big Guy...no one and especially myself was trying to offend anyone.
    I mentioned Steve as I know, as Bob Carpenter's engine guy for years, he had assembled well over 1000 motorcycle engines, and continues doing the same thing today, years later. His motors hold a good number of records of LSR records including the fastest motorcycle in the world, Bill Werner's. He is familiar with NA, Turbo, and nitrous motorcycle motors. He has over 5000 1/4 time slips of his own and has run over 250 at the Bonneville Salt Flats and he's a hell of a nice guy to boot. His credential's speak very well for him, don't you think?
    And for another example, a friend had a turbo kit built by Richard at RCC on a streetmotor with miles. The first thing Richard did was leak it down and said if it wasn't tighter than 6%, he wouldn't do the kit. He's got some pretty good motorcycle credentials too.
    My point without getting into a pissing match was I though there was a bit of misinterpretation of when a motorcycle needs to be looked at and I only offered Steve as someone I'd qualify as an expert, on motorcycles.
    I've built some motors myself and am well familiar with leak down...If I get a motor that leaks more than 10%, it gets fixed period, but that's just me.
    Hank

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    Lots of things can affect the readings, basic leakdown tester setup, no 1 ,
    from a practical point of view , as mentioned above occasionally, if its not breathing excessively its fine
    too tight in the rings will cause major problems as the ends can meet when the piston gets hot, damaging piston and cyls
    my turbo motors are set to .020, and i can't tell you what the leakdown is at that,
    the landspeed bikes don't get small problems , if i have a leakdown issue i can hear it at cranking and or see evidence of excessive blow by

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    Thanks moody and oz

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