Just set up a new lower engine, and now the rear wheel locks when clutch is engaged

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sergman89

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Jul 7, 2012
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First, thank you for your time.I just bought a lower engine from thatsdax.com and then I bought a new piston as well because my old piston had an arrow shaped chip of metal missing from its top side. This will be a HUGE help guys, and I swear give me 1 more year and ill be a pro returning the favors!
Below are all the factors I feel may be effecting this.

The issue is that the piston seems to get stuck and locks the back wheel instead of turning over. I thought maybe some starting fluid, but that only works if the piston is moving inside.

When I was trying to put the chain on the motor, I had to loosen the head bolts because there was to much pressure and it kept me from turning the bolt WITH the sprocket.

Apparently there are quite a few different kinds of pistons though or its just a way for them to market. When installing the new piston and everything I only used a little bit of oil supplement to glide the piston into the upper engine.
 

MotorBicycleRacing

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Jul 28, 2010
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

When I was trying to put the chain on the motor,
I had to loosen the head bolts because there was to much pressure and it kept me from turning the bolt WITH the sprocket.
Removing or even just loosening the spark plug will let the engine turn over.....
No need to touch the head bolts.

Apparently there are quite a few different kinds of pistons though or its just a way for them to market.
When installing the new piston and everything I only used a little bit of oil supplement to glide the piston into the upper engine.
There are only 2 kinds of 47 mm pistons now with a low wrist pin location for PK 80's and a high location for Skyhawk types.

Not enough info from you to answer your other questions.

Do you have pics of your damaged piston and other parts?
 

Greg58

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May 1, 2011
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

Did you compare the pistons? There are at least two different piston that are popular. I would take the head off and rotate the engine to top dead center and see if the piston comes out of the cylinder. You do have a base gasket under the cylinder don't you?
 

Greg58

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May 1, 2011
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

Sorry MBR, but we basicly said the same thing!
 

mapbike

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Mar 14, 2010
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Central Area of Texas
Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

First, thank you for your time.I just bought a lower engine from thatsdax.com and then I bought a new piston as well because my old piston had an arrow shaped chip of metal missing from its top side. This will be a HUGE help guys, and I swear give me 1 more year and ill be a pro returning the favors!
Below are all the factors I feel may be effecting this.

The issue is that the piston seems to get stuck and locks the back wheel instead of turning over. I thought maybe some starting fluid, but that only works if the piston is moving inside.

When I was trying to put the chain on the motor, I had to loosen the head bolts because there was to much pressure and it kept me from turning the bolt WITH the sprocket.

Apparently there are quite a few different kinds of pistons though or its just a way for them to market. When installing the new piston and everything I only used a little bit of oil supplement to glide the piston into the upper engine.
Pix would help so we can see exactly what you have, but I'd like to add here a question.

You do know that all you need to do is remove the spark plug from the head to relieve th compression?

You never need to loosen the head inorder to relieve compression for turning the engine over.

Im not sure what you mean by "oil supplement" you should always lube piston and cylinder with a light coat of 2 stroke oil before installing piston.

Some pistons are made with an arrow shaped indent in the piston top.

A new engine is gonna be a little tight and be sure that with all else done right that you have the clutch cable adjusted correctly.

Map
 
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mapbike

Well-Known Member
Mar 14, 2010
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Central Area of Texas
Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

Dang......! By the time I got my response posted there were three ahead of me.... are we on top of this or what......?

Lol....!

Map
 

sergman89

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Jul 7, 2012
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

Do you have pics of your damaged piston and other parts?
This is the piston from the original kit.




So when I grab my rear wheel and force it to start rotating without pulling the clutch handel, it makes a "wwwwwhhhhrrrrrrr" sound instead of what im used to hearing "pump-pump-pump" ....
 

sergman89

New Member
Jul 7, 2012
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

You do have a base gasket under the cylinder don't you?
Base gasket is the green one (when new), yes. Theres a gasket between the lower and upper engine. Also a metal gasket between the engine top (with spark plug hole) and the upper engine.
 

Greg58

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May 1, 2011
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

Remove the spark plug and rotate the tire again and see if the piston moves.
 

maniac57

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Oct 8, 2011
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

This is the piston from the original kit.




So when I grab my rear wheel and force it to start rotating without pulling the clutch handel, it makes a "wwwwwhhhhrrrrrrr" sound instead of what im used to hearing "pump-pump-pump" ....
That "chip" is NOT damage. It's the piston orientation mark for assembly.
Nothing wrong with it unless there damage the pic does not show.
 

Greg58

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May 1, 2011
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

I'm wondering if the lower is a 40mm stroke and the piston isn't. Did you get the piston from Dax as well?
 

MotorBicycleRacing

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Jul 28, 2010
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

I bought a new piston as well because my old piston had an arrow shaped chip of metal missing from its top side.
That triangle mark is to indicate where the ring pins are so points to the intake side.

All my pistons have them.
Other pistons have an arrow that points to the exhaust port.

There was nothing wrong with your piston.
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
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Central Area of Texas
Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

That triangle mark is to indicate where the ring pins are so points to the intake side.

All my pistons have them.
Other pistons have an arrow that points to the exhaust port.

There was nothing wrong with your piston.
Ditto........

Map
 

sergman89

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Jul 7, 2012
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

I'm wondering if the lower is a 40mm stroke and the piston isn't. Did you get the piston from Dax as well?
No I did not buy it from thatsdax, but I should of. I called them and they answered on the 4th ring, and he was so kind to answer some of my questions.

http://www.ebay.com/itm/321415387043?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Thats the piston set I purchased, to be honest with you guys im not sure what a 40mm stroke means. I tried incorporating that into my search for a new piston, but I couldnt find anything.

I did eye this piston up with the other one and visually I cannot see a difference in size.
 

Greg58

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May 1, 2011
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

The stroke means the distance the piston travels from tdc to bdc, a 66cc engine has a 38mm travel or stroke the 69cc has a 40mm travel or stroke. MBR and Dax both supply 40mm stroke lowers. Since you are comparing the new piston to a piston that has never run on this engine dax will have to tell what you need. Did you take the head off and see if the piston comes out of the cylinder?
 

MotorBicycleRacing

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Jul 28, 2010
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

http://www.ebay.com/itm/321415387043?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Thats the piston set I purchased, to be honest with you guys im not sure what a 40mm stroke means. I tried incorporating that into my search for a new piston, but I couldnt find anything.

I did eye this piston up with the other one and visually I cannot see a difference in size.
The pistons are all the same size as in diameter and height.
Check the wrist pin hole heights.

The eBay add is for a "SkyHawk" high hole piston.

The triangle marked piston is a PK 80 low hole piston.
 
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MotorBicycleRacing

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Jul 28, 2010
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

Sounds like your replacement piston is hitting the head and stopping because the wrist pin hole is higher than the original piston.

Put your original triangle marked piston back in the motor and hopefully you haven't damaged anything.

PS: Now I understand why you had to loosen the head bolts to get your motor to turn over!
 
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greaser_monkey_87

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Mar 30, 2014
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

The bottom end is either called a bottom end or a case, sometimes a crankcase, the part that goes on top of the case is called a cylinder or a jug, and the part that goes on top of the cylinder is called the head. The gasket between the cylinder and the case is called a base gasket, and the gasket between the head and the cylinder is the head gasket. The bolts that hold the cylinder and head to the case are called the head bolts.
 
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MotorBicycleRacing

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Jul 28, 2010
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Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

The bottom end is either called a bottom end or a case, sometimes a crankcase,

the part that goes on top of the case is called a cylinder or a jug, and the part that goes on top of the cylinder is called the head. The gasket between the cylinder and the case is called a base gasket, and the gasket between the head and the cylinder is the base gasket.

The bolts that hold the cylinder and head to the case are called the head bolts.
You didn't check what you wrote.... :)
the gasket between the head and the cylinder is the HEAD gasket.