Chinese engine's head bolt sizes

alhickabee

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Apr 27, 2009
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Chandler, Az
Hello everyone,

My 67cc engine kit from bikeberry.com is supposed to get in tomorrow and I've been reading up on all of the little stuff that needs to be done before running these motors. Just wondering what size the head bolts are so I can get the right sizes from Sick Bike Parts (I'm thinking they're 6mm). I'm planning on ordering the following from them:
Engine hardware kit
Head stud kit
Head gasket
NGK BPM7A Spark Plug
Spark wire
Fuel valve
Fuel filter
Carb o-ring
gas cap o-ring

And doing most everything advised in these two threads:
http://www.motoredbikes.com/showthread.php?t=13287
http://www.motoredbikes.com/showthread.php?t=11986

I plan on using loctite on everything, torque specs, exhaust mount, using higher grade bolts on the rear sprocket, remove petcock screen after removing as much rust as possible, clutch alignment, heat-shrink/solder all the connections and anything else I can think of.

I also plan on doing a lil port matching while I have the engine apart, any reason not to do this? Also any more tips or links would be appreciated.

TIA
-Matt
 
Unless you plan on pulling the head to do some mods to it, I would just avoid it unless you run into problems. I've ran mine fine for over 400 miles without doing anything to the head bolts. I did have to snug them up once about 2 weeks in, but haven't needed to touch them since.

If you do need them later on, you can just run down to the hardware store and pick up some all thread. I haven't even done half that stuff myself and considered myself cautious. The way you break these in, you'll likely find your problem areas "places you need lock tight etc.." just by breaking in the motor. The first few rides just go over your bike each time checking everything. I really never encountered engine stuff working loose, it was always the bike parts.
 
I finished my build today. I used the SBP engine hardware kit. It was a great upgrade. One thing I noticed was the gasket mating surfaces on both the intake and exhaust were anything but flat. I turned to motor till the piston was blocking the ports then packed the inside (edit: of the port) with t paper. I took the studs out to do the upgrade but before I put the new ones in I used a wide flat file and slowly worked the gasket faces till they were flat. Did the same to both ends of the intake tube, and with a piece of sandpaper on a mirror did the mag cover till it was flat on the gasket side. Then I siliconed the intake tube (edit: just the intake tube not the motor) where it meets the motor put the gasket on and lightly bolted it to the jug. The next morning I took it back off and used a round file to cleanup the inside edge and the gasket at the same time. now the gasket is glued to the intake. Just a lil grease on the gasket surface before you put it back on the motor and it won't stick or shrink. No leaks. Did the same to the mag cover (except the gasket trimming). It seemed to fit alot better. Also check the engine mounts, Mine had an 1/8" of flash, easily trimed with a half round. Oh and I cut inner tube pads for everything that touched the bike frame. I cut them to size and used weatherstrip glue to bond them to the engine mounts etc so I didn't have to fight keeping them in place while I was installing everything. It worked great. This is my first build but it went really well. Rode it 4 times today. Longer trips each time after it cooled. You could feel the ring seating about halfway thru the 4th one. Hope I didn't get carried away here. This is way fun.
 
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Thanks for the help guys. This engine has to reliably get me to and from school and my internship, so the engine's gotta be built-proof. I'd rather spend the money now:D!! I'll have the engine tomorrow so I'll just wait till then to order the stuff from SBP.

Junster I'm jealous. If I can get mine running by weekend after next, I'll be quite happy.
 
I would guess on the 67CC Bikeberry uses 8mm. I have asked them and they did not respond to my email. The problem is, do they use 8mmx1 or 8mmX1.25? You will have to wait until your engine arrives to check yourself. Sure you can buy allthread if it's 1.25, but then you'll need to cut it, and get the hardware, and of course it will be whatever grade the store has and the price will be a wash if you count your time. If it's 8mmx1, I doubt your local store has it.
 
just the facts -- fun little THINGS -- when good

This engine has to reliably get me to and from school and my internship,

so the engine's gotta be built-proof.

just the facts -- fun little THINGS -- when they are running good

these little Happy Time engins fall just a ((slight bit short)) of being called reliable

just a rough figure to throw out here
thinking that a RELIABLE engine should start right up and get me there and back
at least 24 out of 25 trips ((rides)) out
from what I have seen regarding the HTs
this will not be happening -- not for very long anyway

just don't want you to get your hopes set too high

must remember also -- what one paid for the little THING -- not much

ride that MB thing
 
Maybe the statement - should be: They can be made to be MORE reliable. I've actually never been stranded or anything nasty. There are are a couple things at play: a) preparation on the part of the owner - there ARE things you can do. We all know this. b) luck of the draw. If you get a winner from the factory or you get a loser from the factory. There is no polite way to say this: Some of the engines are **** from T=0. Some go the full expected life. 50 miles into an engine usually will tell you if you have a winner.
 
that's the difference

preparation on the part of the owner

If you get a winner from the factory or you get a loser from the factory

that's the difference -- between true quality and a so so so

preparation -- with the quality engines -- needing almost none
I just jump on mine and ride and ride -- nothing ever goes wrong

plus with the quality engines -- just a guess here
99 out of a 100 are a winner

I like those odds as I ride that THING
 
I've got years and many miles on my HT bikes. the only one that I've had fail me was one that i abused and overrevved by going full throttle downhill on a single speed. All others have been very reliable provided I upgraded some parts/hardware during my install.

One reason I replace the headstuds is because many times the tops have damaged threads by the acorn nuts. I also JB weld my studs now into the block and use a quality replacement so i never have to worry about them snapping if I overtorque them. I've also had too many studs vibrate loose and pull out of the frail bock threads. JB weld with new quality studs fixes the problem.

One of the best reliability improvements you can make is get a SBP shifter kit. Sure, I rev the heck out of my engine while accelerating, but once up to speed, lower rpms should increase engine longeivity.
 
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