With clutch out bike has little to no compression

[mapbike]

Hey Mapbike look at the picture above, if that is top dead center it shouldn’t have much compression. I hope its ok I used the picture of your engine to show what it should look like

Yep, allnthe Half breed engines I've seen look exactly like thatbat TDC

Why they made those engines I have no idea.

and of course its fine to use that pic...

anything that may help someone

 

[Blizz]

How do you know you have little or no compression?

Just curious about what has lead you to believe this is your issue ..??????

When you pull the cyl. look and see what the makings on the side of the connecting rod say, if its marked ZAE50 then you have what is called a "half breed" geometry engine, these engines are 38mm stroke but use the Type A piston with what we call a "low hole" piston.

The piston in these particular engines that I've had myself and seen lack around .060" reaching top of cyl. when at TDC.

When everything is right, good rings, good cyl. with no gouges in wall, etc.... they will still run "OK" not great power, but OK...

Judging from what I see in the pic you posted here, Im guessing you have an engine with a rod marked ZAE50 but I could be wrong... its for sure if I am, its not the first time...LOL

again, how do you know that you have little or no compression?

I know for a fact that I have no or barely any compression to the fact at which I can pedal with clutch disengaged where as before I got a new crank case I couldn’t even pedal a meter without putting all of my strength into it I’ve been around motorised bikes for around 2 years now learning and researching them so I understand them slightly more than a new comer to motorised bikes but this really threw me off as I have not had this problem ever before I have ordered what I believe to be a type A piston and will check back if this doesn’t fix the problem at which I will be completely unsure and unaware as to why this is happening

 

[mapbike]

I know for a fact that I have no or barely any compression to the fact at which I can pedal with clutch disengaged where as before I got a new crank case I couldn’t even pedal a meter without putting all of my strength into it I’ve been around motorised bikes for around 2 years now learning and researching them so I understand them slightly more than a new comer to motorised bikes but this really threw me off as I have not had this problem ever before I have ordered what I believe to be a type A piston and will check back if this doesn’t fix the problem at which I will be completely unsure and unaware as to why this is happening

Well Blizz, I hope you get it figured out and get back up and ripping down the road.

I will add this, and that based on the pic you showed of where the piston sits in the cyl. at TDC you engine sgould have plenty of compression to run if all else is correct and of course as long as combustion chamber in the head you're using isnt so large that its the cause of compression being so low.

I'm curious to know what it is you figure the problem out to be and Id really like to know what marking the connecting rod in your engine has on it, based on you TDC pic. I woulf guess it says ZAE50 but maybe not.

No matter what you find the fix to be, I hope you will share all the results here so others can also know.

Best wishes, Map

 

[Blizz]

Well Blizz, I hope you get it figured out and get back up and ripping down the road.

I will add this, and that based on the pic you showed of where the piston sits in the cyl. at TDC you engine sgould have plenty of compression to run if all else is correct and of course as long as combustion chamber in the head you're using isnt so large that its the cause of compression being so low.

I'm curious to know what it is you figure the problem out to be and Id really like to know what marking the connecting rod in your engine has on it, based on you TDC pic. I woulf guess it says ZAE50 but maybe not.

No matter what you find the fix to be, I hope you will share all the results here so others can also know.

Best wishes, Map

My connecting rod has the markings ZMN 40mm which just confuses me a whole lot more but won’t stop until I have this engine running not gonna give up!

 

[Greg58]

I just thought of this, take the intake off and use a screwdriver on the bottom of the piston to raise the piston to TDC. That’s what I do to check deck height.

 

[mapbike]

My connecting rod has the markings ZMN 40mm which just confuses me a whole lot more but won’t stop until I have this engine running not gonna give up!

Well, OK now we know its not the "half breed" engine so that possibility is ruled out.

If that has the "zeda" type crank which uses the high pin piston but is a 40mm Stroke

Seems like the low pin piston is gonna cause the piston to come way up out of the hole.

Again, im curious about what you figure out

I've nevwr seen a 40mm stroke engine with a piston that sits that far down in the hole..

 

[mapbike]

What Greg suggested above is a good way to know for sure the piston is at its maximum height.

Just know Blizz, no on here is doubting you, we're just throwing everything we can think of out on the table to hopefully leave no stone unturned.

All of us who have tinkered with these engine over the years have had the scratch our head moments when weird things happen and we haven't dealt with that exact issue before.

We're curious and pulling for you while teying to be helpful in any way that we can be.