gx200 clone knocking

#1
Hello. First post here. I have been modifying my gx200 clone in a baja mini bike. At first i put in a flat top piston, ported the head, air filter, exhaust, but left the governor in. It has a torque converter so is rarely over 4500 rpm. The next step was to get a vm22 carb, remove the governor, and mill the head. I did all of that and now it has a knocking sound. I tore it back open and cant find anything hitting. I did remove the governor gear from the crank as well. Could that cause too much crank end play? I havent measured but it seems like it has alot. Is the only way to change end play with removing the side cover gasket? Thanks in advance!
 
#2
End play is controlled with shims. You need a dial indicator to check it. If you can move the crank back and forth say 1/8" inch it could be your issue but if you milled the head then put on a different head gasket that is thinner you piston could be hitting the head. You need a minimum of .030 piston to head clearance.
 
#3
End play is controlled with shims. You need a dial indicator to check it. If you can move the crank back and forth say 1/8" inch it could be your issue but if you milled the head then put on a different head gasket that is thinner you piston could be hitting the head. You need a minimum of .030 piston to head clearance.
Thank you. The shims go on the side cover side? I will check the head. I am running a thin head gasket as well. If I have to run a thicker gasket that kinda defeats the head milling :(
 
#4
OK so i took it all apart again today. Crank end play is .016 which seems good. I checked the piston to head, and the clay didnt work out. Kept ripping. So the piston is .006 in the hole, and was running a .010 head gasket. Went to a .020 head gasket which should be .026 clearance. I ran it a bunch trying to get the jetting figured out but still sounds real bad. I even took the fly wheel off again to make sure the key was still there and good. I think it has to be the rod. It is just odd that this started after the governor removal. I was going to buy a billet rod today, but then decided to run it till it blows. Then can get a 212 block. lol. But if anyone has any other ideas i would love to hear. Because i am at a loss. Thanks.
 
#5
so it still has a knocking sound? Did you try moving the rod to see if it moved on the crank journal? Did you remove all of the governor parts?
 
#6
It is still knocking. The rod does have some play. Did not Plasti gage it. It has to be that. Maybe I will check it. Is there any chance the crank journal is worn? I don't want to get a new rod and then have that issue. Do you know the correct measurement on the crank journal?
 

SAS289

Well-Known Member
#7
It is still knocking. The rod does have some play. Did not Plasti gage it. It has to be that. Maybe I will check it. Is there any chance the crank journal is worn? I don't want to get a new rod and then have that issue. Do you know the correct measurement on the crank journal?
If you think there's a rod knock tear it down and you should see the wear on both rod and crankshaft. If the crankshaft is not worn the measurement to look for is 1.180" measured at several places on the journal. If you find more than .0005" too small the crankshaft should be replaced. If the wear is obvious the crankshaft should be replaced. Unlike the Predator, clone crankshafts are usually in stock everywhere for around $30.
 
#9
Well looks like the crank is shot. Measuring 1.167-1.170. rod measures 1.183-1.185. here are some pictures. Seems odd that the crank wore so much but not the rod. Oil was very sparkly.
question - how did you mill the head? equipment, set up, etc.

thanks,

phil
 

SAS289

Well-Known Member
#11
OK so i took it all apart again today. Crank end play is .016 which seems good. I checked the piston to head, and the clay didnt work out. Kept ripping. So the piston is .006 in the hole, and was running a .010 head gasket. Went to a .020 head gasket which should be .026 clearance. I ran it a bunch trying to get the jetting figured out but still sounds real bad. I even took the fly wheel off again to make sure the key was still there and good. I think it has to be the rod. It is just odd that this started after the governor removal. I was going to buy a billet rod today, but then decided to run it till it blows. Then can get a 212 block. lol. But if anyone has any other ideas i would love to hear. Because i am at a loss. Thanks.
Seen something here that caught my eye. What did you do to get the .006" in the hole?
 
#14
do you have any pictures of your milling setup? i am wondering how you maintained the head being square and perpendicular.
No. It is pretty primative. The valve cover is parallel to the head surface. Drill press table is flat. Did it in 4 passes just holding it on the drill press table. Then finish on glass.
 
#16
It was for sure the crank. Got a new crank and decided to get a billet rod. Sounds much better! now i just need to figure out the clutching. Thanks everyone.
 
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