cylinder threads stripped

GoldenMotor.com

Houseworth_t

New Member
Feb 20, 2011
13
0
0
San Clemente
Breaking in the engine had a sudden loss of power up hill found out exhaust was leaking through head gasket tried to tighten head bolts up while warm with torque wrench to 10ftlbs when one bolt kept turning Crap! taking cylinder off found block threads were stripped or so i thought threaded the bold it with cylinder off it went in fine and got tight seemed fine i put thread lock on too to be sure went to tighten all up and kept turning along with another bolt CRap! now I am frustrated spec is 12 ftlbs im at 10. this thing has cost so much and so many problems out of the box with carburetor clutch throttle assembly chain coil pack and spark assembly everything the other bike went together great what should i do thread it out and helicoil it? I know this is cheap stuff but am i over tightening it? oh and the peddle strippend out and fell off while i was peddle starting any hints there (was probably funny to watch) HELP thanks for your time this a brubee 66 cc kit.bf.
 
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skjjoe

Member
Mar 9, 2009
393
1
18
Boerne Texas
if you go 1/4 20 that is bigger than the 8mm bolts..so yes you will need new studs. this is not an easy thing to do .if you get any metal shavings at all in the case you might at well throw it away .If you dont know what you are doing a machine shop could probably fix it at a reasonable cost.
 

buzbikebklyn1

New Member
Jun 3, 2009
207
0
0
Brooklyn N.Y.
Welcome to the wonderful world of the china girl engines!
Cheesy, poorly cast aluminum parts a specialty!
#1, Are you talking about the long head stud bolts that thread into the crank cases?
#2, the stock fiber exhaust gaskets and exhaust spigot sometimes leak, dont sweat it, we can fix that easy.
#3, Is the case cracked were the head stud threads into it?
If it is cracked, it can be welded up, re drilled and tapped.
Its a pain in the butt but it will save the cases
If its not cracked your in luck, a Heli coil insert is your best bet to repair the crank cases with out to much drama.
Ok now to the original problem, the exhaust leak.
2 strokes are very sensitive to any exhaust problems so this parts important,
#1- Once the cases are fixed you'll need a new cylinder base gasket and an old school product called Gaskacinch gasket sealant or a similar product, with the mating surfaces of both the cases and cylinder surgically clean and totally free of any trace of the old gasket(i use acetone for this) brush a THIN coat of the gasket sealer on the gasket its self and hang it up to dry over night, it will still be sticky to the touch.
#2- Lay the base gasket over your fresh head studs and slide the cylinder CAREFULLY over the studs.
#3- The Cylinder head/cylinder barrel interface is designed to work with a metal head gasket and NO sealer, lay the new head gasket in place CAREFULLY over the studs.
#4- now lay the cylinder head over the studs, make sure everything is lined up correctly and add the big washers and hand tighten the head nuts as tight as possible.
#5- using a criss cross tightening pattern step up to the indicated torque value incremental, a little bit at a time until you arrive at the right torque value.
Congratulations, you just did a partial rebuild of your china girls top end... feels good dont it?
Ok, now for that exhaust spigot and gasket

I use the thick aluminum exhaust gaskets available from several suppliers, they just plain old seal better.
#1- clean off the exhaust port mating surface of any remains of the old gasket, make sure its perfectly flat.
#2- look at the mating surface of the exhaust spigot, is it welded properly? put it on a flat surface and see is its warped or bent, if it is it will rock, this causes 90% of exhaust leaks.
Depending on how bad the warpage is you might need a new one, if its not to bad you can fix it.
#3- put the spigot in a vise mating surface up, make sure its sitting straight in the vise, then useing a large flat file, file it flat, keep standing it on your flat surface till it doesnt rock any more, then use a sanding block and fine sand paper to smooth the mateing surface.
#4- lay on the new exhaust gasket clean, no sealer, exhaust port studs should be fully seated in the cylinder port holes, install the spigot over the gasket and studs then lay on the large washers to evenly distribute the torque and keep t from warping agian as its tightened down, TIGHTEN EACH SIDE A LITTLE AT A TIME!
You just finished tweaking and installing a exhaust spigot.
Good luck, feel free to ask questions...
BBB
 
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Houseworth_t

New Member
Feb 20, 2011
13
0
0
San Clemente
SKIJOE, BUZ,
wow lots of good info.
yes i an talking about the long studs that thread in the crank case.
The case is not crack. Saves me!
I apologize I should have worded this differently the "exhaust" leak came from between the cylinder and the head on the intake side in the middle of the studs not from the muffler or muffler mount.
I like your procedure for rebuilding the top end i will follow that. What do you torque them down to? everything I saw said 12ftlbs i did 10ftlbs working up to 12 and this happened. Probably like SKIJOE said dont tighten while hot. And dont let metal get in lower case. Aside from the problem just a thought I know these are two stoke so oil in gas but does the lower end need any grease/oil for the crank drive gear and all or all strickily come form 2 stroke mixture (thats why break in is heavy on the oil to gas mix)
 

buzbikebklyn1

New Member
Jun 3, 2009
207
0
0
Brooklyn N.Y.
I'm just glad it helped-
I'm such a clean freak when im diving into an engine, I take for granted that it should still be mentioned, My bad. Stuff clean rags in that open case! and be careful pulling them out.
12 ft lbs is the figure I keep getting on those head stud nuts, all readings done on a cold engine.
Dont sweat the exhaust spigot leak, the extra info was free, no charge...lol and it might help you some time.
No, the China girl engine does not need a separate crank case lubricant, the main bearings also are lubed by the same oil mixed with the gas.
Try a good synthetic oil, mind your mix ratios, it really does wonders for these tiny terrors.

Enjoy the ride, you never know how long it might be till the next one.
BBB
 

shanefoster

New Member
Feb 23, 2011
2
0
0
usa
Once the cases are anchored you'll charge a new butt abject gasket and an old academy artefact alleged gasket adhesive or a agnate product, with the alliance surfaces of both the cases and butt surgically apple-pie and absolutely charge less of any trace of the old gasket besom a THIN covering of the gasket sealer on the gasket its cocky and adhere it up to dry over night, it will still be adhesive to the touch.
 
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beentryin

New Member
Apr 24, 2010
208
3
0
goshen,ohio
Once the cases are anchored you'll charge a new butt abject gasket and an old academy artefact alleged gasket adhesive or a agnate product, with the alliance surfaces of both the cases and butt surgically apple-pie and absolutely charge less of any trace of the old gasket besom a THIN covering of the gasket sealer on the gasket its cocky and adhere it up to dry over night, it will still be adhesive to the touch.
huh i didn't catch all that???
 

Joey

New Member
Sep 29, 2010
58
0
0
Australia, Syd
i suggest you put a pin into the bolt, solved my problem perfectly..
i can get you a picture if you want.. but basically, tap a hole in the side of the engine, then just put a pin into it with jb weld :)
 

buzbikebklyn1

New Member
Jun 3, 2009
207
0
0
Brooklyn N.Y.
66cc taco... i don't know the exact measurements of the exact bore out of the cylinder or the turning down of the sleeve.
(because they wouldn't let me near the machine shop! Im lucky they let me watch. lol)
I saw a flurry of measurements with various tools, Watched as the grizzled old machinist grumbled to himself as he rummaged for the new sleeve, then more measurements, then he set up the barrel in the boring machine, then measured some more, then set the sleeve in the lathe, turned it down, then measured some more, the trimmed it to length then threw the cyl. in an oven and the sleeve in a freezer, then he put them in a huge ancient hyd. press and pressed them together, then he pinned the sleeve in place at the base opposite the ports, then measured some more , then honed out the sleeve to fit a brand new 66cc piston and rings.He blasted it all clean and hant it to me 2 hours after i walked in, it took him about 1 hour and 15 minutes. I was astounded and amazed at his speed. Thats workmanship.
Ill be getting another one as soon as my next shipment of engines come in...
glad you liked the thread.
BBB
 

Houseworth_t

New Member
Feb 20, 2011
13
0
0
San Clemente
Solved!
I doulbe helicoilded it then another stud un helicoilded broke so drilled them all out and helicoilded them works great not BUT not it seems to be too tight the engine does not turn over very easy . I did not let any shaving get into the case.
 

flybytaco

Metal Molding Madman
Oct 17, 2009
1,170
8
0
seekonk MASS
lossen all the studs and turn the motor over a few times by hand then tighten the bolts down turning the motor over will help straighten out the jug