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Post by tortoise on Mar 25, 2016 10:18:13 GMT -5
Valve lapping may be "less than optimal" . . but definitely acceptable. Unbalancing crankshaft rotational dynamics with a big-bore-kit installation significantly enhances the odds of bearing failure . . so engine reliability and longevity is probably compromised anyway.
One technique is to chuck a tire valve stem in a reversable electric drill to press against the valve head. |
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Post by rockynv on Mar 25, 2016 21:56:22 GMT -5
YA I knew someone would come up with a Chinese manual that say to lapp even tho the same OE Does Not at the Factory. Pure Bunk. the "Book" is simply passing down misinformation of Old school thought. Currently the Big Five makers Do not advocate Lapping, were dealing with Allot of TI in Offroad and want to ruin a TI Valve fast lapp it. Why would someone think there perfecting fine machined surfaces with Lapping compound. Unreal and have No Clue what There Doing. I have work with every Factory MC Pro Show and None Ruin a Valve Job with Lapping compound. Yup, I'm one of those who gets Paid to be at races every weekend. You are pointing out that you simply have never done a proper valve job and don't know how or know what you are looking at. Piston guy didn't move from TX to NC for the BBQ. I have been involved with one of the Nations Highest End manufactures of Valves, Valve Seats, Valve Guides and retainers. Turn the TV on this weekend and you can watch a few thousand of that Valve Train Not Lapped. A Service Station Manual from Piaggio Aircraft Corporation or its subsidiaries is not "some Chinese manual". Not everyone has a full race shop with machinery for milling valves so grinding with lapping compound is the final step followed by a leak test especially when servicing an old head that's being re-used when your Joe Average working on a shoe string budget. How many here would have a clue on how to apply and then read Plasti-Guage or Prussian Blue to ensure a proper engine rebuild when checking bearing clearances or valve contact patches? You would have to be pretty much insane to pay for race machining of valves when installing an $89 BBK on a $399 scooter. On a $150,000+ Moto GP bike with a purse and endorsements at risk that's a different story but on a 50cc Chinese scooter that someones put a BBK into that's a bit extreme. |
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Post by mopojo on Mar 25, 2016 23:07:08 GMT -5
Was that a new head that you put your old valves into or did you reuse the existing head when you installed the 72cc BBK? The 72cc (just checked eBay purchase and says it's 80cc - 47.7mm - not good with doing the math to come up with actual CCs) came with new head with valves pre-assembled. Ran it a while today and no smoke... may have a bit of an issue with pre-detonation now as when I give it gas (hard) I hear some knocking or pinging. Will try richening up tomorrow and see if it helps. Seems as if there is a bit of hesitation around 1/4 throttle but take-off is quick and low-end is screaming. lol Think the clutch is worn out and will slap a newer one on as well. @ pisonguy: Yeah... thanks for the input on machining the heads and all but it only cost like $50 and it was all a "get a donor scoot running" type of project. Refusing to put out thousands of dollars on some unknown metal that may or may not last long. Lapping the valves did the trick, though. |
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Post by rockynv on Mar 26, 2016 10:03:47 GMT -5
Was that a new head that you put your old valves into or did you reuse the existing head when you installed the 72cc BBK? The 72cc (just checked eBay purchase and says it's 80cc - 47.7mm - not good with doing the math to come up with actual CCs) came with new head with valves pre-assembled. Ran it a while today and no smoke... may have a bit of an issue with pre-detonation now as when I give it gas (hard) I hear some knocking or pinging. Will try richening up tomorrow and see if it helps. Seems as if there is a bit of hesitation around 1/4 throttle but take-off is quick and low-end is screaming. lol Think the clutch is worn out and will slap a newer one on as well. @ pisonguy: Yeah... thanks for the input on machining the heads and all but it only cost like $50 and it was all a "get a donor scoot running" type of project. Refusing to put out thousands of dollars on some unknown metal that may or may not last long. Lapping the valves did the trick, though. New head with the valves factory machined and pre-installed. So much for leaving the factory machining of the new valves alone without lapping them. Don't forget that a loose valve is a happy valve. You need to have a little valve noise at idle or the valve may not release/seat completely at high rpms. Yep, sounds like you need to upsize the jets to burn richer especially at high throttle. |
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Post by mopojo on Mar 29, 2016 9:56:49 GMT -5
All is well with the build. Guess all that "smoke" could have been unburned gas or vapor (from valves not seating/closing completely)?
Got some clanking under heavy load... think it is a loose (worn) boss-pin in variator. Had this noise before on a different build and a new variator assembly work it out.
For some reason the auto-enritcher does not seem to do it's job... tried two known good ones. Starts without issue and runs good. Anyone had an issue with auto-enritcher after installing 47mm "80cc" BBK? Or any other build? Just don't get it: Wired right (AFAIK).
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Post by pistonguy on Apr 4, 2016 22:02:47 GMT -5
Valve lapping may be "less than optimal" . . but definitely acceptable. Unbalancing crankshaft rotational dynamics with a big-bore-kit installation significantly enhances the odds of bearing failure . . so engine reliability and longevity is probably compromised anyway.
look ill advocate this in One Area. Your Scoot is your only means of transportation, you have to get to work in the morning to not get fired and eat. Then Lap a valve to get to work. Other than that it is Barn Yard Butchery. Did you actually Lap the valve in lieu of a Proper valve job? unreal. Your guides are clapped out. The Valve Face is now concave and it has lost a large % of being able to transfer its heat to the seat to cool it, Now a Hot Valve. and now what gotta do give it extra lash clearance so she won't close up? Destroys you port flow, Just a nice Lazy motor now. good work Just because you made it run does not mean that you accomplished much other than barnyard mechanics. |
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Post by powerzombie on Apr 5, 2016 7:26:00 GMT -5
Wow....
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Post by mopojo on Apr 5, 2016 10:24:23 GMT -5
Yeah, right? My word(s) exactly.  |
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Post by powerzombie on Apr 5, 2016 19:26:45 GMT -5
Sometimes barnyard mechanics is all you need.
These scoots aren't top fuel dragsters, ralley cars, F1, or even rocket (science).
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