low compression?

[Minibiker05]

Ok so I got my bore lightly honed and put a new piston on but it has almost no compression what could be going on cheers

 

[sean01]

hard to tell mate..

valve clearance!! ring gap!! poor head gasket sealing!! and the dreaded wrong cam timing..

 

[Minibiker05]

ok well the valves are bang on and cam timing is bang on too so how do i check for head gasket sealing

 

[sean01]

does it run?
all im getting at is a light hone wont decrease comp.. id be back tracking what you've done..

oh one other thing.. you've put a tb 60mm piston in hey!! check you didnt put that in wrong, will bend a valve straight up.. did you have to re adjust your valve clearances??

you are talking about your z160ho right?

 

[Minibiker05]

it does run and no its my yx150 dont even get me started on my z160 just spent over a grand on it and now ive got no spark but thats getting off topic

ok so all i did was take the glaze off the bore put a new piston in its all in correct put back together set timing and did valve clearances now its got stuff all compression like before i rebuilt it

 

[sean01]

oh ok. so new piston n rings im guessing you mean??

does it feel down on power to wat it originally had? does it kick back at all..

if your certain its down on comp, id be pulling the head and do a leak down test on the valves..

 

[Minibiker05]

yer it kicks back like crazy and i havnt riding yet just started it

 

[coolmodee01]

you timing may be out one tooth

i'd say advanced it's easy to do and hard to spot sometimes it just looks right

take a photo of the donk at top dead for us

 

[Minibiker05]

ok ill do that now

 

[Minibiker05]

It seams like its got fairly good compression when cold but once its been started and ran for a min it has no compression and is really hard to start

 

[sean01]

just gotta cover the basics..
cam timing
valve clearance
failing those you have to dig deep and remove the head and do a leak down test.

does it puff thru the carb at all

 

[Minibiker05]

Ok ill check them agian and do know what this timing mod terry was talking bout is coz this thing has the worse kickback

 

[sean01]

yes its in one of my threads

 

[Minibiker05]

Ok so I checked timing agian and valve clearances and were perfect so pulled head down and did a leak test and both valves have a slight leak but nothing I would call major and it takes forever to start but once started it runs perfect and it starts back up straight away so idk what it is

 

[clunky64]

it does run and no its my yx150 dont even get me started on my z160 just spent over a grand on it and now ive got no spark but thats getting off topic

ok so all i did was take the glaze off the bore put a new piston in its all in correct put back together set timing and did valve clearances now its got stuff all compression like before i rebuilt it

"its got stuff all compression like before i rebuilt"
so your saying the new piston hasnt changed anything but it does run with no compression
doesnt have an automatic decompression unit on it does it?

 

[Minibiker05]

No it hasn't and it donst have any kind of auto decomp

 

[DHZ_XR8cing]

How hard was it to slip the piston and rings back in the bore when you put it together?

 

[Minibiker05]

about as hard as when i put my new piston in my revmx

 

[DHZ_XR8cing]

I would be double checking the ring gaps are not lined up together.
What did you use to lubricate when you were giving her a hone?
With the head off does the piston move side to side much when you try to move it with your finger?

 

[loace]

The piston you used fornthe new one ,is it exactly the same?