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Post by walleye1963 on Jun 18, 2015 15:17:34 GMT -5
Hey shield.I put that bbk on about a week ago and when I was torqued the valves down.I started at 8 did 4 then moved up too 10 lb did 2nuts when I got to the 3rd one it just crushed it.had to send for a new one glad it only took2 days to I get here.
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Post by Fox on Jun 18, 2015 16:42:46 GMT -5
You are over-thinking it shield. Cheap casting failed. End of story.
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Post by runningbuck on Jun 19, 2015 9:01:20 GMT -5
humanshield I just read your bikes stats and that sounds exactly like my Lil Scoots setup minus the Uni filter I hit about 48 to 49 mph tops around hear unless you count down hills then it tops out at about 55 I have about 3000 miles on the bbk with no problems yet how is yours holding up
as to the issue if one of the nuts was not tightened it would be worse that over tightening them it would allow slack and could have been the problem by too much play flexed the rocker arm and snapped it just a thought
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Post by humanshield on Jun 19, 2015 9:42:04 GMT -5
You are over-thinking it shield. Cheap casting failed. End of story. Fox, I respect your knowledge my man, but at the very least I think it deserves "some" thought....just in case it was something else. Would hate to put it all back together, new head and all and after fishing the lost piece of metal from the crankcase only to have it happen again due to a stupid oversight. I Googled this A LOT and came up pretty much empty. I don't think it's all that terribly common.  |
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Post by humanshield on Jun 19, 2015 9:47:41 GMT -5
humanshield I just read your bikes stats and that sounds exactly like my Lil Scoots setup minus the Uni filter I hit about 48 to 49 mph tops around hear unless you count down hills then it tops out at about 55 I have about 3000 miles on the bbk with no problems yet how is yours holding up as to the issue if one of the nuts was not tightened it would be worse that over tightening them it would allow slack and could have been the problem by too much play flexed the rocker arm and snapped it just a thought You know, that makes sense. I actually did find some studs loose and that could have caused a lot of stress with each stoke banging the head against the rocker assembly. Brilliant !!  My BBK is doing fine so far. If I get to 3K miles I will consider this a done deal. I have no problem doing a top end OR engine swap every 3,000 miles for the benefits the BBK gives you. I'm still working on a way to get the big valve head to work. From my experiments so far, it will make a huge difference if I can get it working right. Reason I say this is because even with only 115psi compression withthe big valve head it performed almost as good as with 180psi and the non big valve head. With correct compression on the big valve head I'm 100% certain it'll hit 50+ and probably 55mph. With that and a better exhaust and head pipe and a gearing change...60 - 65 I think is a reasonable expectation. Theory at this point tho. |
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Post by humanshield on Jun 19, 2015 9:51:03 GMT -5
Hey shield.I put that bbk on about a week ago and when I was torqued the valves down.I started at 8 did 4 then moved up too 10 lb did 2nuts when I got to the 3rd one it just crushed it.had to send for a new one glad it only took2 days to I get here. ok. Thanks! |
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Post by walleye1963 on Jun 19, 2015 11:10:24 GMT -5
Are your valves loud. after I put bbk on they got loud I reset them twice with no change.any thoughts.
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Post by Fox on Jun 19, 2015 12:45:29 GMT -5
Well if one of the nuts was loose it could cause the thing to flex a little bit and that could have caused it I suppose. If you make sure the new one is tight all around then I doubt you will see this issue again. I have no clue how many scooters I have opened up over the past 9 years but other than the two I cracked from over-tightening I have seen only one instance of a rocker assy broken on it's own and that was when a cam bearing had failed allowing the cam to wobble in there. It's rare and I think as long as you install everything right and make sure all the bolts are tightened properly it's gonna be fine.
On just about every single scooter I worked on with a 4 stroke engine I have found head bolts that were barely tightened and case bolts that were loose. I used to tell people to go ahead and check the head bolts before doing a valve adjustment. I guess it's still good advice and I should start saying it again.
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Post by niz76 on Jun 19, 2015 16:23:34 GMT -5
Humanshield- Have you considered shaving the head down to bring your compression back up? I'm sure u have, but I thought it may be worth mentioning if even for future readers... I shaved mine (it was a 2t head though) home brew ghetto style on a piece of glass with sandpaper taped to it. I'm sure it'd be a lot more difficult to do at home with a 4t head since the 2t heads have the spark plug centered and makes for a convenient place to use a drill with spark plug socket attached to turn the head on the sandpaper. Maybe somehow affix a sanding disc into a drill press and bring it down squarely onto the surface?? Just a thought....  |
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Post by runningbuck on Jun 20, 2015 7:47:34 GMT -5
ok now I am not sure on this but I have been told to replace the rings if the jug is removed but since you just did a head swap I would inspect the head and install a new head gasket I think one of the valves is not seating correctly you could try and lap the valves to ensure a good seat and better quality if done by you than the under payed china man now this is just my opinion I do have the taller gears in my bike but they did not seem to make much difference I seemed to only gained about 1 to 2 mph not saying my setup is all tuned but runs good enough for me if I want faster I get on my 125 which tops out at inbetween 65 - 70
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Post by humanshield on Jun 20, 2015 8:48:26 GMT -5
Humanshield- Have you considered shaving the head down to bring your compression back up? I'm sure u have, but I thought it may be worth mentioning if even for future readers... I shaved mine (it was a 2t head though) home brew ghetto style on a piece of glass with sandpaper taped to it. I'm sure it'd be a lot more difficult to do at home with a 4t head since the 2t heads have the spark plug centered and makes for a convenient place to use a drill with spark plug socket attached to turn the head on the sandpaper. Maybe somehow affix a sanding disc into a drill press and bring it down squarely onto the surface?? Just a thought.... Niz, The information is not in this thread, but I had several big valve heads professionally machined to varying degrees from about 30 thou all the way up to 70 thou. At 70 thou the compression was coming up nicely...BUT...the timing chain was getting dangerously loose. I need to find a chain one link shorter or figure out how to shorten the chain. Problem is...shortening the chain one link could make it far too short. (arghhh). The ideal solution (that SD is working on) is a domed piston to compensate for the 13cc combustion chamber in the big valve head. Stock is 5cc |
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Post by humanshield on Jun 20, 2015 8:49:48 GMT -5
ok now I am not sure on this but I have been told to replace the rings if the jug is removed but since you just did a head swap I would inspect the head and install a new head gasket I think one of the valves is not seating correctly you could try and lap the valves to ensure a good seat and better quality if done by you than the under payed china man now this is just my opinion I do have the taller gears in my bike but they did not seem to make much difference I seemed to only gained about 1 to 2 mph not saying my setup is all tuned but runs good enough for me if I want faster I get on my 125 which tops out at inbetween 65 - 70 I sent ahead and bought a new head. There is a binding issue with the intake valve and after about 5 tries lapping it, it still leaks like a sieve. I think the valve seat is burned. |
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Post by 90GTVert on Jun 20, 2015 10:47:36 GMT -5
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Post by runningbuck on Jun 21, 2015 7:12:48 GMT -5
some times poor china quality is just too poor LOL glad you found the problem and A fix is going on better than some who just give up and leave them that is when I snag them up cheep and is why I have 7 scooters lol
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Post by humanshield on Jun 21, 2015 8:20:34 GMT -5
some times poor china quality is just too poor LOL glad you found the problem and A fix is going on better than some who just give up and leave them that is when I snag them up cheep and is why I have 7 scooters lol lol. That's exactly how I got this one. |
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