***Slipping Clutch*** - **Piston Seizing?**

GoldenMotor.com

Vinoy Thomas

New Member
Sep 12, 2012
42
0
0
Brampton,Ontario
Hi Everyone,

I want to make this as to the point as possible for a hopeful quick fix!!!

I have a motorized bicycle a friend asked to repair. The problem is the bike won't start because the clutch slips.

I took off the head at first to see if the piston was seized, but when the head was taken of the clutch caught on and the piston moved with ease. I ruled that out.

But when the head was placed back on the clutch would catch on for the piston to move around 1.5 times then the clutch being slipping. Take note, I tried using a flat head screwdriver on the small gear (behind the clutch cover) and the piston would not move even then while I turned the gear, I have a feeling something is jammed...

Lastly, the large gear is loose when the plate is taken off. I have multiple engines in my garage and not one of them has a loose large gear.

Would appreciate any help/tips on how to go bout solving this.

Attached a few pics too.






Note: Please assume I have a poor knowledge of the terminology.

Thanks in advance,
Vinoy

zpt

:-||
 

Huffydavidson

STREETRACER/MANUFACTURER
Jan 29, 2012
1,076
4
38
st.louis,mo.
Hey Vinney, go into Norm's repair shop and take a number, **** down and do some research it's what the fourm is far. All your clutch answers are there I know I've read them go and sit down take a number and read and then apply what you learn you can fix this . Then if you still can't figure it out then ask for help .this form is kind of based on a self help self improvement bases thing .
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
pics are hard to see. but it looks like you got the red clutch pads & they look like they've spread a bit - sometimes when this happens, the pads won't grab both plates - take each pad out & file or otherwise trim it a bit so it goes all the way thru the slot to press on the back plate
 

fatdaddy

New Member
May 4, 2011
1,516
4
0
San Jose, Ca.
The clutch has a little wiggle in it, this is normal.
Before ya start taking stuff apart try this. Take the small screw out of the clutch plate, Pull the clutch lever in to make adjustment easier, Then screw in the flower nut a couple or three notches. This is only a simple clutch adjustment problem, But you should check out the rest of the site anyway. I'm SURE there's a post or two on adjusting a clutch.
The only time you need to take out the pads is if you are replacing them or, sometimes, if you burn the pads a little you can bring them back with a little sandpapering. Even if they do spread a little the large internal clutch spring will push them in place, no problem.
This area is to help guy's in figuring out what is wrong with their stuff, (read the header,) SO, HELP FIRST, THEN send them elswhere to learn more.
fatdaddy.
 
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2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
I don't believe your piston/crankshaft is seized. I think your only problem is a clutch that needs adjusting. You need to understand how the clutch works BEFORE you take it apart or at least read some of the good information here so you'll understand what you're doing and why.

Here's one of the best posts available which will guide you step by step through the proper procedures for adjusting the clutch. http://motorbicycling.com/showthread.php?t=22729

I'm a little concerned that you removed the cylinder head. Did you replace and/or inspect the head gasket? Did you torque the head fasteners down after you replaced the head? These points are critical.

If I understand correctly you can't rotate the crankshaft with the cylinder head installed but it does turn with the head off. Was a new spark plug installed? If so you need to compare the 'reach' or length to make sure the piston isn't contacting the plug. Compare the old plug with the new one if that's the case.

Keep us informed as to what you find.

Tom
 

biknut

Well-Known Member
Sep 28, 2010
6,632
411
83
Dallas
Try removing all of the red clutch pads, and file the edges down a little so they fit into the clutch gear better (looser). See if that cures all the problems.
 

fatdaddy

New Member
May 4, 2011
1,516
4
0
San Jose, Ca.
2door is right about everything, Listen to him. The only thing I might ad is that you can simply take out the new plug and THEN see if the piston moves. This WILL NOT tell you anything about the clutch adjustment, only about plug lenght and if you have the right size spark plug or not.
And again, You rarely need to take ALL the pads out, trim them, then replace them. Doing this won't hurt anything, Just a lot of wasted time. ANYONE thats EVER had one of these apart knows that there's a HUGE internal clutch spring. A little bit of pad spread is not going to keep the pads from seating. Worse case, The spring will force the edges off the pad and you wind up with some pad dust in your case. You can then just blow this out.
The engine should have quite a bit of compression, so trying to turn it with a screwdriver may or may not work. So FIRST, Adjust the clutch, put the old plug back in, (the one YOU KNOW was the right size,) Then try starting it. If the piston STILL wont move and the clutch isn't slipping, then check for piston seisure.
And again, LISTEN TO 2door, 99.99999% of the time he's right.
fatdaddy.
P.S. Shoulda put more 9's in that last sentence.
P.S.S. You might want to ask your friend how he was mixing his fuel. If he was running straight gas the piston MIGHT be seized.
 
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Vinoy Thomas

New Member
Sep 12, 2012
42
0
0
Brampton,Ontario
Hi Everyone,

Sorry I wasn't here to reply earlier (I was out).

Firstly, I want to thank all of you for the very detailed and helpful replies. Much appreciated.

Excpecially 2door for his reply, because of your suggestions I was able to fix the issue very quickly. The issue was that the piston had been hitting some part of the head preventing the engine from turning over.

To solve this, I placed another head gasket to provide a teeny bit of clearance between the piston and the head. To my surprise the clutch caught on and I was riding in a few minutes.

Just for anyone else who has this kind of issue (before you tear apart your engine):

-Check to see whether the piston is hitting the head, preventing it from moving any further.
-Read 2door's reply a couple of times.

Again thank you for all your help, it is ALWAYS appreciated.

.shft.

Thanks again,
Vinoy
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
We're always glad when we can help solve a problem. In fact its one of the primary reasons this forum is here.

I have a theory. The original owner might have installed the cylinder without a base gasket. That will lower the cylinder/head by few thousands of an inch. If the head gasket was used several times it might be compressed enough to allow contact between the piston and the head. Just a theory but installing two head gaskets would raise the head enough for clearance. I'd keep an eye on it however and retorque the head after the engine has reached operating temperature a couple of times. 120 to 140 inch pounds will suffice.

Enjoy your bike and you know where to come if you have any problems. Thank you for getting back to us with your results.

Tom