ScootDawg Scooter Forum - compression problem

« compression problem »

Welcome Guest. Please Login or Register.
May 21, 2013, 1:54pm

ScootDawg Scooter Forum :: The Garage :: 50cc Scooters and up.... :: compression problem

Author

Topic: compression problem (Read 372 times)

david3336
Great Big Dawg

member is offline

Joined: Jun 2011
Gender: Male

Posts: 102
Location: virginia

compression problem
« Thread Started on May 6, 2012, 2:45pm »

I have the 50mm bbk it has been running fine till today i road it about 2 weeks ago seem to be fine. took it out the house today very hard to start wouldnt idle cut off . has not cranked since i checked the compression and it was only 60. took engine apart everything looks fine no play in crank no scaring in wall or piston valves seem to open and close well. have seen no smoke or anything to explain this. any help on all things that could cause this problem would be nice. im thinking needs new rings but this build only has about 300 or so miles on it. it has been sitting alot here latly the weather been too cold to ride much.

« Last Edit: May 6, 2012, 2:48pm by david3336 »

Link to Post - Back to Top IP:

Logged

1-sunny 50cc yy50qt-6
1000 torque sping
ngk iridium plug set at 0.6mm
orange perf. cdi and coil
5.2 gram rollers
93 octane gas
43mph top speed (GPS)
120 mpg

2-2008 peace sports
83cc bbk
big bore head
a9 cam
20mm carb
6 gram rollors
modded stock air box and muffler
stock idle and 88 main jet
custom paint job
93 octane gas
top speed -53 mph
90 mpg

skuttadawg
Great Big Guru Dawg

member is offline

[avatar]

Joined: Jul 2011
Gender: Male

Posts: 5,396

Re: compression problem
« Reply #1 on May 6, 2012, 7:45pm »

Adjust the valves

Link to Post - Back to Top IP:

Logged

CFMOTO Echarm 150 with EFI
Ngk Iridium

david3336
Great Big Dawg

member is offline

Joined: Jun 2011
Gender: Male

Posts: 102
Location: virginia

Re: compression problem
« Reply #2 on May 6, 2012, 8:18pm »

that was the first thing i did.. and would that cause compression to be only 60lbs

Link to Post - Back to Top IP:

Logged

1991toyota
Junior Dawg

member is offline

Joined: Apr 2012
Gender: Male

Posts: 11

Re: compression problem
« Reply #3 on May 6, 2012, 8:45pm »

60 with the throttle wide open? If so the valves might not be seated correctly or misaligned or broken rings. Pull it back apart and see if u notice and issues. How did it run before?

Link to Post - Back to Top IP:

Logged

1991toyota
Junior Dawg

member is offline

Joined: Apr 2012
Gender: Male

Posts: 11

Re: compression problem
« Reply #4 on May 6, 2012, 8:47pm »

Sorry I overlooked where u said u had already pulled it back apart. What do the rings look like

Link to Post - Back to Top IP:

Logged

dude
Great Big Guru Dawg

member is offline

[avatar]

Joined: Oct 2008
Gender: Male

Posts: 488
Location: Mooresville In.

Re: compression problem
« Reply #5 on May 7, 2012, 12:09am »

When you had it apart did you pour gas into the ex. and in. ports to check for leaks? Was there blow by (oil in air breather) or smokin?
Twice Ive had motor no signs of nothing (low comp. reading) then hone the cyl. Rebuited with the same gaskets and rings. worked fine, maybe the cyl wash down with gas. I was at lost.

« Last Edit: May 7, 2012, 12:16am by dude »

Link to Post - Back to Top IP:

Logged

Run Your Scooter Not Your Mouth
www.twistandgone.com
05 Zuma, TPT 70cc, ZXR Exhaust
04 Vento Zip R3i MRP 70cc, Stage6 Street Exhaust
http://www.AntiSocialSC.com

skuttadawg
Great Big Guru Dawg

member is offline

[avatar]

Joined: Jul 2011
Gender: Male

Posts: 5,396

Re: compression problem
« Reply #6 on May 7, 2012, 12:15am »

Compression should be 120 to 150 yikes something is wrong with your engine

Link to Post - Back to Top IP:

Logged

CFMOTO Echarm 150 with EFI
Ngk Iridium

david3336
Great Big Dawg

member is offline

Joined: Jun 2011
Gender: Male

Posts: 102
Location: virginia

Re: compression problem
« Reply #7 on May 11, 2012, 8:37pm »

no i didnt put gas in ports.. it seem to have been running fine last ride i took. maybe lil slower than normal i thought it may had come from setting. no smoking or blow by. just took it out to ride it and it was hard to start and when it did start it wouldnt idle it cut off then hasnt cranked since. im thinking about ordering a ring kit and try that.

Link to Post - Back to Top IP:

Logged

Stash
Great Big Guru Dawg

member is offline

[avatar]

Flyin blind on a rocket cycle!

Joined: Mar 2012
Gender: Male

Posts: 419
Location: Greenville, SC

Re: compression problem
« Reply #8 on May 12, 2012, 11:14am »

Check out your head gasket. probably need a new one.

Link to Post - Back to Top IP:

Logged

Peace Sports 805 50cc
80cc Kit
Irridium Plug
HP Coil/CDI
Kehin Carb 95/38 jets
Uni Intake
Free Flow Exhaust
Chrome oil Breather
Gates Kevlar Belt
Koso Variator
6g Dr. Pulley Sliders
Tiny Tach
[image]

They call him, "Paperweight!"

Scoot Tech
Great Big Guru Dawg

member is offline

[avatar]

Improvise-Adapt-Overcome

Joined: Aug 2011
Gender: Male

Posts: 267
Location: Terre Haute, Indiana

Re: compression problem
« Reply #9 on May 15, 2012, 10:57pm »

If this is one of thos cheaper 50mm kits you need to lap the valves. I am yet to see one kit come through my shop with properly seating valves. A valve lap seems in order.

Link to Post - Back to Top IP:

Logged

Personally built frame up 150cc
Perf coil
Perf cdi
Perf exhaust
12g sliders
Reversed 30mm carb
Free flow filter
Port and polish

loast
Junior Dawg

member is offline

Joined: May 2012
Gender: Male

Posts: 14
Location: SoCal

Re: compression problem
« Reply #10 on May 17, 2012, 4:42pm »

Question 1: How does one check compression?

May 15, 2012, 10:57pm, Scoot Tech wrote:

If this is one of thos cheaper 50mm kits you need to lap the valves. I am yet to see one kit come through my shop with properly seating valves. A valve lap seems in order.

Question 2: Which kits do you recommend for the DIY'er? I would like to go as big as possible (52mm) but I wouldn't know how to check compression and how to lower it if it did end up being too high.

Link to Post - Back to Top IP:

Logged

Rex RS 450 (German Qing-Qi model)
139QMB
Performance A.F.
88 Main, 40 Low Speed
50mm BBK (installed Memorial Weekend, still not running right!)

david3336
Great Big Dawg

member is offline

Joined: Jun 2011
Gender: Male

Posts: 102
Location: virginia

Re: compression problem
« Reply #11 on Jul 4, 2012, 4:26pm »

just got around to fixin my scooter. it was the ex valve was not closing all the way i had another head laying around put it on and problem fixed. thanks for all the help.

Link to Post - Back to Top IP:

Logged

dude
Great Big Guru Dawg

member is offline

[avatar]

Joined: Oct 2008
Gender: Male

Posts: 488
Location: Mooresville In.

Re: compression problem
« Reply #12 on Jul 4, 2012, 10:33pm »

Good to know you figured it out.

Link to Post - Back to Top IP:

Logged

Run Your Scooter Not Your Mouth
www.twistandgone.com
05 Zuma, TPT 70cc, ZXR Exhaust
04 Vento Zip R3i MRP 70cc, Stage6 Street Exhaust
http://www.AntiSocialSC.com

Click Here To Make This Board Ad-Free