Decompression

[Bbqjoe]

I'm starting to believe I might be having a problem with the decompression system on my 6.5 clone.

Sometimes I have to pull so hard, the bike and myself come up off the ground. (ok, not really, but close)

I went to check the valve clearance, and I could probably use a 1000th or so adjustment (if that has anything to do with it). I can't get the intake valve nut to turn without fear of snapping something.

I installed a petcock to shut off fuel as I get close to home so that there isn't a whole lot of fuel in the carb when I shut down, but still, a lot of times I **** near pull my arm out of the socket trying to start it either cold or warm.

I'm very open to any suggestions here.
Also, I've never been inside this engine.

 

[chancer]

sheared flywheel key?

 

[KartFab]

If it turns out you have a performance cam, you can turn it slowly by pulling the string to the compression stroke, reset the pull start by letting it go back in, then give it a yank after pulling it up to the part where you feel resistance from the compression.


Also, there is a nut on the rocker arm rods? That you have to loosen prior to adjusting the lash.

 

[Bbqjoe]

If it turns out you have a performance cam, you can turn it slowly by pulling the string to the compression stroke, reset the pull start by letting it go back in, then give it a yank after pulling it up to the part where you feel resistance from the compression.

Hmmmmmmmmmm. Ok


Also, there is a nut on the rocker arm rods? That you have to loosen prior to adjusting the lash.

Yes, it didn't want to give, skeeeeeeered me.
I gotta look again.

But I'd rather it just pull start like it should. I don't think the Chinese built this with a performance cam.

 

[itsid]

The thing with 6.5 clones is there are simply too many..

some are decent and work reliably and a handfull fail on short order or need more maintenance than others right from the start

So check the lash again just check for now..
do NOT trust the marking on the starter cup alone; have that lined up with the marking on the air shroud and remove the spark plug.

drop a drop a chopstick in the cylinder (to test how far up the cylinder is..)
now slowly turn the engine over degree by degree and see if it goes up or not..
best in both directions.
if you found the TDC, make another mark with a sharpie on the starter cup for the next time.

Now just check the valve lash.. if it's within specs.. no need to adjust anything, if not...
well I'm afraid you'll have to ..

Take a look at the pushrod tips.. they should be sticking out equally.
If not, you might have an issue with your cam or lifters *shrugs*
(it's unlikely but unfortunately not impossible )

In order to ease the whole process, add some penetrating oil and patience to the seized adjusting screw;
and if that doesn't work out either..
you can remove the complete rockerarm assembly (should be four bolts holding the shaft in place the rockerarms rest on)
wrap the assembly in aluminium foil, put it in an oven (200°C) and leave it for half an hour or so..
take it out, and apply another squirt of penetrating oil to only the seized bolt..
the magic dragon will fly by, so be aware...

then get a good wrench and apply some steady force.. the bolt should cool slightly slower than the rockerarm and loosen up eventually without any excessive force.
I'd NOT back it up with the screwdriver, that tiny slots may snap indeed if it's seized.
but as soon as the counter nut and adjusting bolt are free from the rocker arm, they should seperate rather easily.
Oh.. if you have two nuts.. the smaller 10mm is the one you care about first of course.
but when heat is applied the 14mm one is the one you should apply mild force upon to get it to loosen up.

reinstall, reset lash, try again..

But again, if your pushrods are not aligned nicely, that will not solve the issue;
and you'll have to split the crancase open anyways

'sid

 

[mckutzy]

That thread is fine... Be careful as it strips easily as it threads on...
I have a half completed motor in need of a rocker stud and nuts, as a result of that fine thread...

 

[Bbqjoe]

sheared flywheel key?

I've read that in a few other places, but if that was the case, assuming the engine started, wouldn't it run like a mess?

 

[itsid]

depends on how offset the flywheel is as opposed to it's ideal position...
within a few degress (say +/- 4°) you shouldn't feel too much of a difference if you're not going for some speedruns.

But you can tell rather easily if the key is sheared..
just remove the air shroud and the nut (and startercup) and use a penlight to look for the key..
you should see both keyways nicely without actually removing the flywheel;
if they're not aligned.. sheared key.. if they are.. cup and nut back on.. no harm, no foul

'sid

 

[Bbqjoe]

depends on how offset the flywheel is as opposed to it's ideal position...
within a few degress (say +/- 4°) you shouldn't feel too much of a difference if you're not going for some speedruns.

But you can tell rather easily if the key is sheared..
just remove the air shroud and the nut (and startercup) and use a penlight to look for the key..
you should see both keyways nicely without actually removing the flywheel;
if they're not aligned.. sheared key.. if they are.. cup and nut back on.. no harm, no foul

'sid

Ok sid. Will do.

 

[itsid]

Frankly personally I don't think the key will be sheared.. not that it won't cause issues, or it can never happen..
it's just a more likely IMHO that a part moving in respect to it's neighbors fails before a mechanically static part will.
a shaved or offset key.. sure... you haven't installed or messed with your woodruff key; so yeah... possible but unlikely (again : in my opinion)

Anyways, a quick look will tell and at worst you ruled that out to be the cause of trouble.
While the shroud is off, it might be a good idea to check the magneto distance to the flywheel as well, maybe it grinds slightly and catches on the magnet *shrugs*

but since the decompression system is "cam, lifter, pushrods, exhaust-rocker, - valve and finally the exhaust"
and that's where I'd assume the issue to be or at least a direct neighbor on an unmodified engine.
according to the gx manual jerking is normal when you're not gently pulling the engine into the compression stroke like KartFab described.
Nothing that'd feel like someone's ripping your arm out though.

Good luck, I hope it's just something minor (like a flake clogging the flywheel on the camshaft)

'sid

 

[Bbqjoe]

Frankly personally I don't think the key will be sheared.. not that it won't cause issues, or it can never happen..
it's just a more likely IMHO that a part moving in respect to it's neighbors fails before a mechanically static part will.
a shaved or offset key.. sure... you haven't installed or messed with your woodruff key; so yeah... possible but unlikely (again : in my opinion)

Anyways, a quick look will tell and at worst you ruled that out to be the cause of trouble.
While the shroud is off, it might be a good idea to check the magneto distance to the flywheel as well, maybe it grinds slightly and catches on the magnet *shrugs*

but since the decompression system is "cam, lifter, pushrods, exhaust-rocker, - valve and finally the exhaust"
and that's where I'd assume the issue to be or at least a direct neighbor on an unmodified engine.
according to the gx manual jerking is normal when you're not gently pulling the engine into the compression stroke like KartFab described.
Nothing that'd feel like someone's ripping your arm out though.

Good luck, I hope it's just something minor (like a flake clogging the flywheel on the camshaft)

'sid

It's really nothing like you mention. It feels like nothing more than compression holding it back. I'm sure I could pull the plug and it'd rotate just fine. It's not jerking or trying to pull back, it's just a mother to pull sometimes.

 

[itsid]

with "jerking" I meant the sudden increase in pulling resistance when you start anywhere but the compression stroke; then you'll feel the aircushion you're building up working against you, even if the compression release is working properly.
If the compression release is not working
that air cushion building up can feel like you're hitting a wall (or better a giant spring) trying to dislodge your shoulder

And since you said

a lot of times I **** near pull my arm out of the socket trying to start

That sounded like a match to me

'sid

 

[Bbqjoe]

with "jerking" I meant the sudden increase in pulling resistance when you start anywhere but the compression stroke; then you'll feel the aircushion you're building up working against you, even if the compression release is working properly.
If the compression release is not working
that air cushion building up can feel like you're hitting a wall (or better a giant spring) trying to dislodge your shoulder

And since you said


That sounded like a match to me

'sid

I'm going to tackle this thing today.

 

[Bbqjoe]

Ok, here we are at the flywheel. I tried a zillion times but this is the best pic I can get.
I believe I see the key, but I see no signs of a keyway looking around the shaft as best I can. Then again the keyway might no go all the way to the end of the shaft? I don't know.
Maybe you see something I don't?

Baja said this engine calls for 5 on the intake, and 7 on the exhaust. I'm nowhere close.
I have like 1.5 on the intake and 3 on the exhaust.

[/IMG]

---------- Post added at 12:10 PM ---------- Previous post was at 11:51 AM ----------

Pulled flywheel. All is good there.

 

[itsid]

wow.. that is indeed odd!

from what I remember I was able to see the key quite well actually
on that image I can barely make it out...

But I think that dull grey 'light' inside the keyway you see is indeed the key.
take a strand of wire and see if it is and not just a confusing reflection perhaps..
it's really hard to tell on the pic.

Anyways, IF that grey spot there is indeed the key, it'll be fine..

if you bent a 90° hook (short) on the tip of the strand of wire.. you should even be able to hook into the crrankshaft's keyway to verify it's properly lined up.
(that dark creased shadow right below on the pic)

I hate removing flywheels, they're brittle.. but if you want to be absolutely sure and are carfeul with it..
screw on a nut (to protect the threads) and tap the crank with a rubber or wooden mallet to free the flywheel
slide it off and there will be no doubt if it's okay or not.

Personally I think it will be.. even though that pic is indeed not too clear about the integrity of the key...I'd still say it's where and as it should be.

Sorry, I really thought it was much clearer on mine when I took a glimpse *shrugs*

'sid
[EDIT]

Ahhh I was dawdling..
So key ruled out, that's good!

back to the compression release then

 

[DeathMachine]

Have you pulled the plug and tried pulling the rope? At least that will confirm compression vs something mechanically jamming up.

 

[Bbqjoe]

wow.. that is indeed odd!

from what I remember I was able to see the key quite well actually
on that image I can barely make it out...

But I think that dull grey 'light' inside the keyway you see is indeed the key.
take a strand of wire and see if it is and not just a confusing reflection perhaps..
it's really hard to tell on the pic.

Anyways, IF that grey spot there is indeed the key, it'll be fine..

if you bent a 90° hook (short) on the tip of the strand of wire.. you should even be able to hook into the crrankshaft's keyway to verify it's properly lined up.
(that dark creased shadow right below on the pic)

I hate removing flywheels, they're brittle.. but if you want to be absolutely sure and are carfeul with it..
screw on a nut (to protect the threads) and tap the crank with a rubber or wooden mallet to free the flywheel
slide it off and there will be no doubt if it's okay or not.

Personally I think it will be.. even though that pic is indeed not too clear about the integrity of the key...I'd still say it's where and as it should be.

Sorry, I really thought it was much clearer on mine when I took a glimpse *shrugs*

'sid
[EDIT]

Ahhh I was dawdling..
So key ruled out, that's good!

back to the compression release then

The keyway and key are good and where they should be. (Removed flywheel.)

Reset valves. I just kinda closed my eyes, and torqued. The exhaust nut came loose.

I saw one video that I can't find again, and also read that when starting, the exhaust valve should open briefly on the compression stroke.
No such thing that I saw.

 

[Bbqjoe]

The excitement! The drama! I love this minibike thing!

Put it all back together, still a hard pull, but started.
I went about a mile and a half, took the dogs for a swim, went to start it, and I think I got about eight inches of rope. That's it, the engine doesn't want to budge. Pulled the plug, engine doesn't want to budge. It was running great before I stopped.
Gotta recoup from the walk, get under a trailer, and go get it.

Well, I returned and started at the recoil assy, hoping maybe the rope got jammed up or something. Then I took off the fan.

Holy banoonies!
I found a phillips tip, stuck to the magnet, jamming up the flywheel.

Very strange. It must have been picked up off the bench when I set it down earlier, but I would think I would see something like that.

But what's weird, is it didn't keep me from first starting it up, nor did it make any noise, or even scrape up anything, but hopped into place when I stopped.
It's back to running. :yaysmiley:

Another thing that freaked me out is that I've never held or looked at a flywheel.
At first I thought I was missing a magnet when I saw that empty pocket. Then I did an image search.

It's no wonder these engines have a vibration with a big chunk of flywheel basically missing.
I can hardly imagine these things are balanced.

It's still tough to pull start.

 

[chancer]

Previously on BBQJOE I said:

Naw it wont self destruct if you are taking it easy.
All these warnings are 100% true. But most guys remove the governor for the sole purpose of achieving max RPMs and speed. So lazy, Dumb, young guys bypass the linkages to go fast and break their engine. Unless you are holding that thing WFO alot, you will probably be fine.
I NEVER tell anyone to do this.

BTW: The plastic gov, gear is made to run at 3600 RPM, Stock valve float is 5300-5500 (depending) so Valve float would not save the Gov gear from breaking.
The engine itself is not harmed... yet. It is the piecesof the internal gov gear when Broken that will break the engine internals.

Now guys will probably yell at me for typing this bad advice.

Well turns out the plastic internal Gov gear DID brake and was screwing up the operation of the compression release.

NEVER BYPASS THE GOV!

 

[itsid]

See Eric, THAT's why we never tell to do so

This one's on you I understand... so hop into that kart, visit joe and fix your mess buddy

Luckily nothing worse happened, imagine it'd got ejected into the cylinder and got caught by the piston coming down...

'sid