Had a customer bring me a Yerf Dog 3206. Top end was shot, rings gone, burning oil, low compression, etc. He also had a 155cc big bore kit that he brought in with the kart that he wanted installed. We pulled the old cylinder head, cylinder and piston off. Yep they were worn out. I then compared the old parts to the NEW "big bore" kit. EVERYTHING looked EXACTLY the same, except the bore diameter was bigger (of course). Kit came with new piston, rings, cam and cylinder head. We put all this on and set the valve timing. Now we rotated the engine by hand a few times after setting the timing. After every 2 turns, the timing gets off. After about 10-12 turns the timing is so bad, the valves start hitting the top of the piston. Stumped!!!! We compared the new cam to the old. We counted the teeth. Both the same. We measured the cam, the height of the new cylinder vs the old, etc, etc. Everything looks the same....the valve timing just walks off!!! Ideas?
Thats a new one It's mechanical impossible when the system is assembled correctly. Take a closer look at the new cam. check if the cam gear is the same diameter. may have the same number of teeth but spaced slightly different. Is the gear indexed to the lobes correctly? That would throw the timing off. put the old cam back in, see what happens. A change in the gear ratio between the crank and cam would be the only mechanical factor that would cause the cam to rotate faster or slower in relationship to the crank. just throwing out ideas here. keep us posted on what you find. _________________ 3206 yerf. too many mods to list. easier to list what has not been modified- seats and steering wheel. plus one set of kidinme's hand made special collectors edition fuzzy dice. We support pole dancing.
Hows the cam chain? Can you compare it to a new one?
Hows the gear on the crankshaft, mark the chain at
the crank, and mark the chain at the cam, make one
full revolution, if your mark lines up perfect on your
crank , then check your mark on your cam to see if it
lines up, if it does, and the valve timing is off, then I
would say the chain is stretched. _________________ 05 Blade SX-550 Suzuki
07 Sand Viper 250 ( SOLD )
89 Honda Pilot
The valve timing can wander only if the sprockets are the wrong diameter - Even a stretched chain will not cause this. If the cylinder height were different this also would not cause timing problems - Only chain tension issues. Is it possible that the timing chain is no longer seated on the crank sprocket? _________________ 08 Joyner SandViper 250
07 Joyner SandSpider 650
06 Tank Urban Touring 150SE
04 Yerf-Dog Spiderbox 4209 GX150 (SOLD)
04 Yerf-Dog Spiderbox 3206 GX150
81 Honda Passport C70B
Start putting the old pieces back on until the problem goes away. That'll tell you where the problem is.
Let us know what you find. _________________ Chris Dierkens
'04 Yerf-Dog 3206 10g Rollers, 1500# Spring, Reverse, SuperTrapp, Uni
'04 KPX Xterro: pumper carb, oil cooling, 10g rollers, Junkies pipe, Uni
'05 Blade 150 DX: 4 Valve head, 10g rollers, East Side pipe, Uni
www.northeastbuggy.com
155 with stock cam, everything was fine. Put in the A12 cam, exhaust valve hits the piston.
Was yours an A12 also?
We compared the old cam with the new one. Don't see ANY differences at all. Diameter and tooth count the same. I'm thinking it has to be the cam chain is not riding on the crankshaft gear correctly cause I see no differences in any of these parts (other than the bore is bigger on the new cylinder). I won't be able to mess with it till this Saturday, but will post an update. I plan on checking the cam chain again.
Funny, (not really) my bro-n-law's having the same problem on their yerf.
155 with stock cam, everything was fine. Put in the A12 cam, exhaust valve hits the piston.
Where did the cam come from?
Was yours an A12 also?
I have been running my A12 cam from Buggy Depot for over two years on a stock head and cylinder without issue. _________________ 08 Joyner SandViper 250
07 Joyner SandSpider 650
06 Tank Urban Touring 150SE
04 Yerf-Dog Spiderbox 4209 GX150 (SOLD)
04 Yerf-Dog Spiderbox 3206 GX150
81 Honda Passport C70B
I had a similiar problem. the sprockets on the cam shafts are pressed on they have no key way. it is possible for the camshaft to become loose and the sprocket will start to shift positions causing your timing to be off. My sprocket loosened up becuase a nut fell into the head and got stuck between the camshaft and the cylinder head. i used jb weld epoxy on it and its been fine ever since. If this turns out to be your problem, the trick will be getting the sprocket back in the correct location. There is a groove cut into the shaft. If you line it up with the middle timing mark on the sprocket it should be fine.
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It's mechanical impossible when the system is assembled correctly. Take a closer look at the new cam. check if the cam gear is the same diameter. may have the same number of teeth but spaced slightly different. Is the gear indexed to the lobes correctly? That would throw the timing off. put the old cam back in, see what happens. A change in the gear ratio between the crank and cam would be the only mechanical factor that would cause the cam to rotate faster or slower in relationship to the crank. just throwing out ideas here. keep us posted on what you find.
