popping noise out of front end of engine....

[Legwon]

so i just finished up with the break in period, decided to take it for a good haul.
checked everything b4 i left.
it made it to the final destination just fine(with the exception of the kickstand rattling loose)
when i went to leave about 4 hrs later, i had this weird popping noise coming out of the front end of the engine. sounds like a balloon popping. pretty much every time it sparked.

i did make it home with out too much hassle. but it died about half way and wouldn't fire:s ...
had to walk up the bridge. and decided to try again on the way down the bridge(large bridge over a river).... took a bit but did fire up.. again with the popping.
had to keep revving the engine to keep it running at idle, and once i let it settle for a coast the engine revved down and just quite.

Ive checked the plug cable, its solid.
i pulled the head and found that the upper gasket was cracked. replaced that.
checked that all the casing bolts were tight.
and checked the plug, and spark while i was at it.

when for a test ride and had to get up to about 15km/h to start it...
again with the popping noise. its not a compression popping... as i said above, its like a balloon popping.

anyone have any ideas??

 

[crassius]

probably the exhaust gasket (did you put on the muffler strap that keeps it tight?) - best thing to do now is clean it well, then look for oil leaking out - tighten or replace gasket at the leak

 

[2door]

The kit supplied gaskets, both intake and exhaust are notorious for early failure. I agree with crassius, the noise is probably the exhaust manifold gasket. Replace it with a good quality automotive gasket material and torque the fasteners to about 60 inch pounds.

Tom

 

[Kioshk]

Mmmm...it may be that exhaust-gasket, although it sounds like classic loose-head behavior. I notice you mentioned that the head-gasket was "cracked"...I expect that the noise you were hearing was the hot-gasses escaping between the head and jug. You also mentioned that you had trouble getting it back home and that it wasn't firing...the exhaust-gasket failure wouldn't cause difficulty firing...a loose head would. Have you tried lapping the mating-surfaces of the jug and head? You gotta get those surfaces good and flat before you attach 'em to assure good compression.

 

[Legwon]

no i havnt lapped it yet.. that was my next teardown procedure, for this weekend coming.. one way or the other.
the cracked upper gasket was the original, replaced with one from gasket set for rebuild.
i have 1 other good gasket i got with a head to rebuild my old motor (66cc also) but i would prefer not to use that on this one :s

the exhaust gasket is a new one.. just replaced it about 3-4 days ago. had issues with the old one.
neither of my kits came with a muffler strap

 

[crassius]

neither of my kits came with a muffler strap

that sounds like the root of your problem then - the muffler is way too heavy to hang from just two little studs

get a piece of coat hanger wire and wrap it around the output pipe of your muffler, then wrap the other end around your frame and back down to the muffler again - then put a screwdriver between the two parts connecting the muffler to the frame & twist them until the muffler is pulled up tight

 

[2door]

Kioshk makes a good point. Your "popping" might well be another head gasket problem.
Are you using the kit supplied chrome acorn nuts on the cylinder head? They are bad about not allowing the head to be torqued down properly. Some of the cylinder studs are a little too long and the acorn nuts bottom out on the stud before clamping against the head. Also torquing the head is important. 120 to 140 inch pounds is about right.

If you're planning on lapping the head and cylinder replace the acorn nuts with flanged hex nuts while you're at it. I'd also check the studs for tightness. Put two nuts on a stud (double nutting) and torque the stud into the case to the same value as the nuts. Do this while you have the head off.

Do you know the proper procedure for lapping the head?

Good luck.

Tom

 

[Legwon]

that sounds like the root of your problem then - the muffler is way too heavy to hang from just two little studs

get a piece of coat hanger wire and wrap it around the output pipe of your muffler, then wrap the other end around your frame and back down to the muffler again - then put a screwdriver between the two parts connecting the muffler to the frame & twist them until the muffler is pulled up tight

right.. same as rebar tying. got it.

Are you using the kit supplied chrome acorn nuts on the cylinder head? They are bad about not allowing the head to be torqued down properly. Some of the cylinder studs are a little too long and the acorn nuts bottom out on the stud before clamping against the head. Also torquing the head is important. 120 to 140 inch pounds is about right.

If you're planning on lapping the head and cylinder replace the acorn nuts with flanged hex nuts while you're at it. I'd also check the studs for tightness. Put two nuts on a stud (double nutting) and torque the stud into the case to the same value as the nuts. Do this while you have the head off.

i will be changing the nuts and bolts when i lap the head. have new bolts already waiting for it

Do you know the proper procedure for lapping the head?

ive seen a video floating around here for a (i believe) motorbike head. same process, right??

 

[2door]

Lay down a flat surface, preferably glass and a sheet of 280 sandpaper. Paint the gasket mating surface of the head with something like magic marker or lay-out ink and run the head over the paper a few times. You can quickly see any high or low spots that need to be removed. Keep working the head using the old "wax on wax off" method while rotating the head in your hand so as not to sand an angle into the gasket surface.

You won't want to lap the cylinder with it on the case. Remove it completely so you don't get abrasives down between the piston and cylinder wall. Use the same procedure as you did on the head. Clean the parts well before reassembly.
Good luck.

Tom

 

[Kioshk]

Legwon, here's a video demonstrating the proper technique that 2door mentioned:
http://www.youtube.com/watch?v=3PycZtfns_U

 

[Legwon]

this is the one that i found floating around here ..
http://www.youtube.com/watch?v=cQHdXcqAo-k

 

[Legwon]

good news and bad ...

start fine now that tighten up exhaust and put wire on it ...gasket almost blown apart :s

but idle still out ...Im assuming that has to do with the fuel mix change since break in ?

 

[2door]

Legwon, here's a video demonstrating the proper technique that 2door mentioned:
http://www.youtube.com/watch?v=3PycZtfns_U

LOL, Same same, I just use one hand though. But I do breath in through my nose and out through my mouth.

Tom

 

[Kioshk]

I first thought it was "wax on, whacks off"...boy, was I embarrassed. My second-favorite favorite scene from that movie was the "paint-uh deh fence" where Miagi gets POed at Danielsan for painting sloppily: "Noh 'hea hea hea hea'!". My FAVORITE scenes where any with Elizabeth Shue...especially the one where she's running around in the bikini. GEEEZUS, did those pleasant thoughts of her get me through my teens!

 

[crassius]

good news and bad ...

start fine now that tighten up exhaust and put wire on it ...gasket almost blown apart :s

but idle still out ...Im assuming that has to do with the fuel mix change since break in ?

yep,time to try adjusting your needle & float level

 

[Legwon]

awesome

Thx everyone

 

[supercub]

The acorn nuts can be bottoming out on the studs, replace with grade 5 hex nuts and new washers.

 

[Bikeguy Joe]

yep,time to try adjusting your needle & float level

Not a good idea to adjust anything until the gasket problem is resolved.
The "needle and float" are not going to do much for an idle problem either.

 

[crassius]

Not a good idea to adjust anything until the gasket problem is resolved.
The "needle and float" are not going to do much for an idle problem either.

?????

as I read it, the gasket is fixed & the bike is starting & running fine now with just an idle problem left

did I miss a post somewhere?

 

[2door]

?????

as I read it, the gasket is fixed & the bike is starting & running fine now with just an idle problem left

did I miss a post somewhere?

I believe the OP was going to lap the cylinder head and install a new gasket and would get back to us.
I think he has an air (vacuum) leak. Probably the carburetor or intake manifold.

Tom