Lack of Compression

[jmadden91]

Hey guys so my motor is severely lacking compression at the moment. I tore down the head today as to inspect the piston rings, but I noticed that the gasket sealing the head to the body of the engine and the one sealing the cylinder head are severely damaged.

So two questions,
Is it likely the damaged gaskets are the cause of the lack of compression?
How do I tell if the piston rings are shot?

Cheers guys

 

[Dreadful]

yeah the damaged gasket will reduce your compression all day mate I'd say that's ya problem.

As for piston and rings ?

I usually do gasket piston and rings .... just to be safe and keep it all tight.

 

[DvDRip]

while you've got the head off you may as well clean off all the carbon build up, lap the valves in, replace gaskets, replace piston and rings (don't forget to get a hone if you replace rings).
maybe even port it a bit if you're keen

 

[jmadden91]

Awesome thanks for the help guys, I think I will give it a bit of a tune up while the head is off. Btw is there a thread on here about pit bike store locations throughout Australia? I found the online stores ones Im just after a local place or two.

Cheers guys

 

[Dabomb]

carbon build up doesnt win races.

 

[jmadden91]

Lol just bought the motor mate, haven't even turned it over yet let alone raced it

 

[bulldog93]

It was a statement. You might be able to getthe gaskits off DHZ:
- DHZ Mini Moto - Home

I'm not sure if he stocks gaskets. Just send him an e-mail or a private message on ths site:
- Mini Dirt Bikes & Pit Bikes Forum - View Profile: pitsterproAUS

This is just here in case you don't know how to do it.

Checking valves:
- YouTube - How to check valve timin on Honda 50 70 cc motors
- QingQi (Qlink) 200GY Illustrated Valve Adjustment - MyChinaMoto - Chinese Motorcycle Forum
- http://www.miniriders.com.au/motor-tutorials/24965-how-set-valve-clearances-horizontal-engines.html

Setting the timing:
- http://www.miniriders.com.au/motor-tutorials/24388-setting-adjusting-timing-irk.html
- http://www.miniriders.com.au/motor-tutorials/24347-how-set-timing.html

 

[jmadden91]

Wow. Thanks for all that mate, cheers

 

[sean01]

hmm i dont see anything abnormal in the picture...
carbon build up looks normal..
no real evident scuffing on the piston
base gasket (cylinder to engine) breakage due to removal of the barrel..
unable to see if rings are worn... need to be measured in the barrel with feeler blades...
altho they still look nice and thick.
but thick rings need good tension to operate properly

lack of compression can be several things and totally not related to bad gaskets or rings..
if gaskets are the cause then usually they will leak oil...also if the base gasket is sus it wont change the compression it will only leak oil...
compression is built from the piston rings and above...not below..

valve clearance is a major issue with any of these small engines...
if the valves arent set correctly then there going to leak compression...

another thing tho.... your thread lacks the relevant pics to diagnose better...
as im just shooting in the dark

 

[Dreadful]

yes good work Bulldog ... won't let me raise ya rep anymore till I rep a few others but well done
young man .... I think I'll start calling you link dawg

 

[Th3D3v1Ly]

Yeah bull you are farely good with the links ive noticed.

 

[Cactus Jack]

Yes , good work Bulldog ... The missing link has baffled mankind for monkeys years ...

It was most likely only the valve clearances as Sean is pointing to ... but it doesn't hurt to do a rebuild to know where you're at ... Just make sure no dirt gets into things ...

 

[jmadden91]

Awesome thanks for the help guys. btw does anyone know what a yamoto 125cc is a copy of?