Strange Compression loss..

[brettLo]

Hey,

So gotta question about compression. Awhile ago I replaced my piston and rings and have been riding numerous types with the bike running flawlessly, well until yesterday when I went for a ride. I had a minor stack and basically it was more or less just laying/dropping the bike on it's side. When it eventually stalled and I picked the bike back up to kick it over to re-start it, there was no compression what's so ever, I can now push the kick starter with ease using my hand and the bike wouldn't fire back up again I was just wondering if anyone would have any advice/ideas ? As I said the bike basically just got laid down and I find it really weird to lose compression from something like that. Before the stack, the bike had been running perfect!!

Cheers

 

[my67xr]

hmmm, not to sure there ?

but, have you checked the valve clearances since you changed the piston/rings etc?

 

[brettLo]

Hey,

Yep! I had given the bike a full service when I done the piston and rings. It's probably only just due for it's next service now..I haven't checked the valves yet however..as I haven't got around to doing the current service etc.

Do the valves open right up to lose compression or is it the opposite and close right up ?

Cheers

 

[my67xr]

if the clearances are too small, then the valves wont shut properly, so you will loose compression.

same thing when the engine heats up, clearances get smaller.
most engines are set up in China with very tight clearances from new, then they get warm riding them/running them in and they become hard to start.



here is a video/how to
the only thing is i would run tighter clearances than they suggest,
use .003" on the intake and .004" on the exhaust


[video=youtube;QJciyJRJh8Q]http://www.youtube.com/watch?v=QJciyJRJh8Q[/video]

 

[brettLo]

Hmmm ok maybe they had just closed up due to nearing it's service. I might go have a look shortly and post back. I usually run .003 and .005 that should be fine, yea ?

Cheers

 

[my67xr]

yeah, everyone has their own preferance when setting them up.
i have never had a problem running .003" and .004"...

 

[zwebx]

Also is it piss easy to roll start it? is the kick starter actually moving the motor?

 

[brettLo]

Hey ,

Just in the middle of checking the valves now. And yep kick starter is moving valves etc. I attempted a push start when I couldn't get it started. But had no luck. So right now I'm doing a full service hopefully this can resolve the issue, by checking timing and resetting valves etc.

Cheers

 

[motorman]

Hey ,

Just in the middle of checking the valves now. And yep kick starter is moving valves etc. I attempted a push start when I couldn't get it started. But had no luck. So right now I'm doing a full service hopefully this can resolve the issue, by checking timing and resetting valves etc.

Cheers

If it's you valves a good way to check is to push start it. If it does start with a push start but not kicking, it's your valves for sure.

 

[brettLo]

Hmmm ok thanks for that. I couldn't get it to push start although I was in a pretty foul mood and didn't try to much. I'm just about to reset the valves so I'll post back anyway and keep the thread updated on my progress.

Cheers

 

[Blender]

I was in a pretty foul mood

Damn bikes, they always bring out the worst in people sometimes aye! Damn wheel spacers annoy the hell outta me! but all part of the fun i guess!!

 

[brettLo]

Haha your not wrong blender!!

Ok, so reset valves and still bugger all compression?! Grrr

 

[brettLo]

When cranking the motor the valves seem to be moving as normal. Anyone got any other suggestions at all ?

 

[motorman]

When cranking the motor the valves seem to be moving as normal. Anyone got any other suggestions at all ?

To me it sounds like your rings have gone or your missing a bit of your piston.

Time to strip down the top end and have a looksy.

Was the bike smoking a lot before it stopped going?

 

[brettLo]

Thanks for the reply.

As far as I noticed there was no smoke at all..bike was running flawlessly ...

 

[motorman]

Not really much else to check without pulling the top end down.

Well not that I know of. Only a few things you can check compression wise.

One other thing would be too check the timing. Have you done that?

 

[brettLo]

Ok no worries thanks man.

Yea checked all the timing etc when I reset the valves. Everything there seems normal. I've put it in the to hard basket until after chrissy. Then I'll rip the top end down again and have a closer look at the piston and rings. They were replaced not to long ago though. When I get it pulled apart I'll repost here to keep the thread updates as always.

Thanks for all the quick replys, I'm spewin it wasn't just a matter of resetting the valves! Haha if only things were meant to be easy...

Cheers again guys!

 

[my67xr]

what engine was it again ?
and is it a start in neutral only ?

 

[brettLo]

Hey mate it's lifan yx140...

 

[my67xr]

ok,
if it was a Ducar 125 engine, they have a built in decomp that can cause problems.


pull the spark plug out, and hold your finger covering the hole in the head, then kick it over.
is there any compression then ?