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Post by fuzzyruttin on Apr 27, 2019 8:01:19 GMT -5
The engine has close to 4000 miles and I figured it's time to check valve clearances. Intake = 0.0025, exhaust = 0.005. One site said intake should be 0.002 - 0.004, and exhaust should be 0.003 - 0.006. According to this (if it's true) then my engine is still within tolerance, but I'd like to readjust to optimal settings. What does everyone else normally run?
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Rune 75
Scoot Enthusiast
Posts: 441
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Post by Rune 75 on Apr 27, 2019 8:38:18 GMT -5
Personally I would go for the widest spec. 0.004 in and 0.006 out. They get tighter by time/wear so that will give the biggest margin.
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Post by fuzzyruttin on Apr 27, 2019 9:04:55 GMT -5
Personally I would go for the widest spec. 0.004 in and 0.006 out. They get tighter by time/wear so that will give the biggest margin. That makes sense. Do you know if that is the correct spec?
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Post by fuzzyruttin on Apr 27, 2019 9:06:01 GMT -5
For what it's worth, I have a compression tester from Harbor Freight that I do not have a lot of faith in, but it only read 60psi. Hence the valve check. 0.0025 may be on the tight side for the intake, but the fact that it's not flush leads me to believe perhaps my rings are shot. Ugh. Maybe it's time for a BBK.
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Post by snaker on Apr 27, 2019 9:29:09 GMT -5
Why jump into a rebuild just because of a questionable tool? I buy a pretty diverse range of tools from cheapo stuff to some expensive equipment. But I would never keep a tool that I didn't trust. I would sell it, give it away or toss it. Use your rebuild money and buy a better quality gauge or at least see if you can borrow/rent from a auto parts store for a comparison to yours. Also study up on the use of a compression tester if your not experienced in it.
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Rune 75
Scoot Enthusiast
Posts: 441
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Post by Rune 75 on Apr 27, 2019 10:05:08 GMT -5
For what it's worth, I have a compression tester from Harbor Freight that I do not have a lot of faith in, but it only read 60psi. Hence the valve check. 0.0025 may be on the tight side for the intake, but the fact that it's not flush leads me to believe perhaps my rings are shot. Ugh. Maybe it's time for a BBK. Compression test is to be done at WOT. More air is sucked in giving higher and correct reading.
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Rune 75
Scoot Enthusiast
Posts: 441
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Post by Rune 75 on Apr 27, 2019 10:07:18 GMT -5
Personally I would go for the widest spec. 0.004 in and 0.006 out. They get tighter by time/wear so that will give the biggest margin. That makes sense. Do you know if that is the correct spec? Dont know the correct spec is but im absolutely sure 0.004 and 0.006 will work just fine.
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Post by fuzzyruttin on Apr 27, 2019 11:16:23 GMT -5
Why jump into a rebuild just because of a questionable tool? I buy a pretty diverse range of tools from cheapo stuff to some expensive equipment. But I would never keep a tool that I didn't trust. I would sell it, give it away or toss it. Use your rebuild money and buy a better quality gauge or at least see if you can borrow/rent from a auto parts store for a comparison to yours. Also study up on the use of a compression tester if your not experienced in it. Just an excuse to go big bore, that's all. I bought the compression tester about three years ago when I was having problems with my car. I ended up borrowing a compression tester from a guy at work. IIRC, my tester was reading a little low compared to his. I put it on the scoot just to get a general sense of what's going on, but did not expect such a low reading. But yeah, as Rune 75 suggests, I forgot to open the throttle. Whoops, of course.
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Post by jackrides on Apr 27, 2019 11:35:53 GMT -5
A couple minor points. One member suggested holding the vacuum slide open so it does not interfere with the intake drawing air. A proper compression tester has a valve (just like a tire valve) at the spark plug fitting, and so should any adapter between tester and spark plug hole. Otherwise, the volume of the hose effectively becomes part of the combustion chamber and lowers the reading. I've always adjusted valves toward the wider end of the specified range to be sure they still have some clearance when the motor gets as hot as it ever can during operation.
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Post by fuzzyruttin on Apr 27, 2019 15:38:24 GMT -5
For what it's worth, I have a compression tester from Harbor Freight that I do not have a lot of faith in, but it only read 60psi. Hence the valve check. 0.0025 may be on the tight side for the intake, but the fact that it's not flush leads me to believe perhaps my rings are shot. Ugh. Maybe it's time for a BBK. Compression test is to be done at WOT. More air is sucked in giving higher and correct reading. Thanks for the reminder. Owning a scoot is certainly a good means to keep your basic mechanical skills honed without a lot of effort! I'm loving how easy everything is... one carb, two valves, I can physically lift the entire bike, on and on. Anyway... I re-ran the compression test and now get 85psi. Still seems low. I will adjust the intake valve to 0.004 and probably just keep the exhaust at 0.005. Take another compression test after that and see if it makes any difference. Sorta got my doubts, but interesting test nonetheless.
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Post by fuzzyruttin on Apr 27, 2019 15:46:32 GMT -5
A couple minor points. One member suggested holding the vacuum slide open so it does not interfere with the intake drawing air. A proper compression tester has a valve (just like a tire valve) at the spark plug fitting, and so should any adapter between tester and spark plug hole. Otherwise, the volume of the hose effectively becomes part of the combustion chamber and lowers the reading. I've always adjusted valves toward the wider end of the specified range to be sure they still have some clearance when the motor gets as hot as it ever can during operation. Good suggestions. I tested with and without shimming the vacuum slide open, and did not see any difference in measurements. Kept WOT for these tests this time. The compression tester does _not_ have a valve at the spark plug connecter. Not sure how much psi loss that would actually contribute... no more than 5?? Regardless, it gained 25 psi just by opening the throttle. (Did I say whoops already!)
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Post by fuzzyruttin on Apr 27, 2019 19:01:41 GMT -5
After adjusting the intake valve to 0.004, compression went from 85psi to a hair under 90. But I also have to mention that the valve cover was off when I did the pre-valve-adjustment reading. Does that matter? Might this indicate a possible blow-by issue?
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Post by lilpinny on Apr 27, 2019 21:57:06 GMT -5
I use .004 and .007
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Post by jackrides on Apr 29, 2019 10:25:18 GMT -5
Valve cover off has no effect.
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Post by fuzzyruttin on May 1, 2019 17:11:25 GMT -5
Borrowed a couple compression testers from guy at work. He has an "old" one and a more expensive new one.
Old tester: 155 psi New OTC tester: 168 Mine (US General): 115 ^ All of these were taken using same plug adapter. Using my plug adapter with my compression tester, it reads 85psi. So yeah, 70psi low reading. I knew it was bad, but didn't realize it was that bad.
Nonetheless, ~160psi cold cranked on a GY6 seems pretty good.
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