I will be buying a new engine in a few weeks because my old one was ruined by a thief how put regular gas in it and ran in the rain after the air filter fell off. I got the bike back but it needs an engine. I will be taking it apart to do some mods and upgrade bearings. I want to port match the bottom end and top end transfer ports because the bottom end transfer ports are smaller. Also replace the bearings and stuff the case. How do you stuff the crankcase? Has anybody made a tutorial? Can somebody tell me about the power gains? Also, where did you get your bearings from? I'm on a budget so I don't want to spend more than $30 on the bearings. I will also match port the top end and lighten the piston, I don't want to go to the trouble of balancing the crank. There are a few spots on the piston you can grind away and it will not affect heat transfer or strength. I will make a small tutorial on that. I will also paint it black and file the paint off the edges of cooling fins and stuff so it looks awesome. I will make a build thread when I get the engine. First I need to get some $$ out of the punk who ruined my engine. Very lucky a cop recognized him riding on it so I got his balls in a vice. You can't pay for it? Then you go to jail, dirtbag!
crankcase stuffing and other bottom end mods
- Thread starter young grease monkey
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- crankcase stuffing porting sbp
Stuffing the cases means adding material to the inside of the crankcase halves to better ur crankcase compression ratio. Around the main bearing bosses is good. After preping the cases u will need to create 2 circular molds slightly smaller than the hollow side sections of the crank that the bosses fit into. The molds will need to be coated in a release agent then centrally placed over the bosses & filled with JB weld to the height of the bosses. After curing, remove the mold & check for fit. Remove any material that fouls the crank. Cheers
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Thanks! I tried to take apart the old engine so I can melt down for casting, but I couldn't get the small gear off. How is that done? I ended up taking it apart the caveman way. About 100 impacts from 20 ft in the air did the trick. And how do you get the bearings off the crank and countershaft? Heat maybe? And how do I know if the bearings that I buy are high quantity? One place I looked at said they are deep groove. What is the best type for a crankshaft?
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Maby these can help you out.
http://motorbicycling.com/showthread.php?t=36334
http://motorbicycling.com/showthread.php?t=31010
http://motorbicycling.com/showthread.php?t=36334
http://motorbicycling.com/showthread.php?t=31010
I found jaguar's tutorial on stuffing cases, and I think I will do it. What kind of power increase can I expect? I read that low end will decrease because the higher pressure will just shoot the charge out the exhaust. How do you cure this? Will it happen if I don't increase the ratio too radically? Jag says you don't want a ratio lower than 1.2, and most China's are at 1.1 so if I only add maybe a little less than both tubes of jb weld I think it will be ok. How much should I stuff in the cases on a 66cc grubee? I don't really want to do all the calculations and measuring stuff. I think I will stick with stock seals and leave the outer seal on my replacement bearings. One last thing I need to know is how do you align the crank and clutch shaft? I read that you have to do it to have a quiet and smooth engine, but never found out how to do it.
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the roof of port can be reshaped to direct flow where u want it. I image that members of this forum could contribute quite a bit in that feild, & xpansion chambers r made to take advantave of this scavenging mixture & reurning it to the combustion chamber. To calculate ur crankcase compression ratio, & save on math, get an old piston u have n drill a hole thru the crown & put a fuel tap in there. Fill the crankcase with kero to do ur calculations
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to align the countershaft, (ur gunna have the cases together & apart here, coupla times). First have the crank & the 1 countershaft bearing that ISNT a kinda loose fit in the case, in the cases & the crank centralized & end floated to between 0.003" & 0.008". 4thou is good. This is done with shims. I've got an interuption so get that done & I'll get back to u. Thats a couple of together/aparts, fun hey. Cheers
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ok, now the case halves have a register to align the crank, (1 case has a groove that the register on the other case fits into, around the crank area, right where the cases join ). Notice with them held together, u can twist the 2 cases round on the crank axis & the crank bosses r still alligned, Not so the countershaft.. U do know to "pull" he crank thru the bearings in the cases with packing washers & the nut on the end of the shaft, right, to avoid distorting it. U'll have to have a couple of goes at each side, but its worth all this effort Now ur cranks done, split it for the last time.
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so now the cases r split with the crank in 1 & 1 countershaft bearing in. Fit the other bearing to the correct end of the countershaft & pull the other end of the countershaft thru the bearing thats already seated in the case. Now apply bearing retainer to the case where the bearing that u put on the end of the countershaft (the 1 thats not seated in the case) will seat & pull both crank & countershaft thru to bring the cases together. Now u need to "snap" spin the countershaft to make sure its aligned.
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if it is aligned it'll spin for a couple of revolutions. If missaligned u'll need to lightly tap 1 case to make it twist on that crank alignment register till it is, then torque the cases to 75 inch/pounds in 3 steps, 25, 50 & 75, then leave to let the bearing retainer cure & ur done. I hope u put the crankcase gasket in there to end float the crank, or its now got too much. Now u've got a reliable bottom end. Notice how less ratly that bearing retainer makes it when its all done. Cheers
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Thank you so much! I will need to read this I few times to understand it. I finally got to look at the teardown on photobucket, thanks Fisher! It didn't show how to take the old bearings off the crank and clutch shaft, though. The page crashed on my phone, even when I used the photobucket app. I think I can figure most of this stuff out easy enough, though. I hope I can order the engine soon, I gave some paperwork to the police officer, it was a print out of the price of the replacement engine and air filter. I should get my money in a few days.
another way to do the crank bearings is to freeze the crank (in plastic bag in deep freeze) & heat the bearings in hot oil, then drop them on. Make sure they're on all the way, u'll get 1 go at it, but b4 u can u have some precision measuring 2 do 2 centralize & end float crank in cases. Unless u have eqipment 2 do get a shop 2 do this. U still need to pull the bearings/crank into the cases. Cheers
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Hey here are a couple of youtube tutorial link for the type of bearings you want as well as removal and installation.
