Author Topic: LT500 Spark Plug Piston Problem (Read 1877 times)

MrMendo2 · « **on:** January 06, 2013, 08:07:58 pm »

Hey guys new to the forums, have had this problem took the motor apart and now the motor is just sitting in my house.

So what was happening is the piston is slapping the spark plug out. It is bending the plug and the bike will turn off. When I bought the bike it wasn't happening but after about 2 hours of use it started happening. What I want to do is fix the bike to sell it but I don't want the next person to buy it with problems. It's the 87 with cool head. Let me know if you guys need any more information. On the motor it also says "WEBER" on it if that means anything to you guys.

Stpltn250r · « **Reply #1 on:** January 06, 2013, 08:18:59 pm »

Detonation. What fuel are you running? Carb and jets? How is the head cut? Elevation and temp?

MrMendo2 · « **Reply #2 on:** January 06, 2013, 08:38:43 pm »

Was running 110 because the guy told me it HAD to run race fuel. Keihin PWK (on the side it says 72RA4 TJR) not sure on jets (its been a while since i had the carb opened up) elevation im in Yuma AZ (next to Gordon Well or Glamis California) I'll upload pictures temp can range from 50 degrees to 110 degrees. Was using a BR8EG plug (the nipple came right off.) Was going to try an iridium plug but didnt want to just run through iridium plugs(BR8EIX). The first picture is the plug that got over extended.

MrMendo2 · « **Reply #3 on:** January 06, 2013, 08:41:23 pm »

Last picture in last post was the last spark plug the popped on me(broke nipple).

El Diablo · « **Reply #4 on:** January 06, 2013, 08:52:22 pm »

Yay! another guy in Yuma! What part of town do you live? Anyhoo, not sure if it will make any difference but try an NGK B8EGV spark plug. Who built the engine?

Stpltn250r · « **Reply #5 on:** January 06, 2013, 08:54:32 pm »

Got to be detonation. Its rattling so bad its dropping porcelin. Jerry Hall is closest to you. Might want to get that dome checked. What are you mixing your fuel out? Look around the flat area around the carb whefe thr bowl meets up. Should tell you what size carb it is. Need to see what the internals are in it. Where exactly in the throttle position is this happening? Half throttle cruizing around. Idling or wide open?

MrMendo2 · « **Reply #6 on:** January 06, 2013, 09:06:24 pm »

Throttle will be all around i usually like running wide open but sometimes putt around. El diablo im in somerton bike is in the foothills. The carb is a PWK 39. Mixing 24 to 1 but the guy said to run 32 to 1.

Stpltn250r · « **Reply #7 on:** January 06, 2013, 09:13:41 pm »

Im assuming flywheel and stator are in good shape and tight. Timing marks lined up. Going from 32:1 to 24:1 will lean out the fuel. Need to know what jets are in it.

MrMendo2 · « **Reply #8 on:** January 06, 2013, 10:02:56 pm »

hey guys just opened the carb 180 and 55 jets.

El Diablo · « **Reply #9 on:** January 06, 2013, 10:53:20 pm »

If I remember correctly, I had a 190 jet when I used to have my Kehin. But it all depends on engine mods. Other than the bent tip, how does the porcelin look?

MrMendo2 · « **Reply #10 on:** January 06, 2013, 11:06:31 pm »

Brian I think I know who you are!!! Pedro Sanchez ring a bell?! Porcelain looks okay not **** or anything.

El Diablo · « **Reply #11 on:** January 06, 2013, 11:12:44 pm »

PCS! Yup!

What color is the porcelin?

MrMendo2 · « **Reply #12 on:** January 06, 2013, 11:17:32 pm »

Pretty white. Can't attach with my phone.

MrMendo2 · « **Reply #13 on:** January 09, 2013, 06:40:50 pm »

So did we conclude that this was probably because I went from 32 to 1 to whatever I was running? Should I use only 110 fuel or what kind of of fuel should I use I just have to get some gaskets to get this think back up and started.

PCS · « **Reply #14 on:** January 09, 2013, 07:51:30 pm »

Quote from: Stpltn250r on January 06, 2013, 09:13:41 pm

Going from 32:1 to 24:1 will lean out the fuel.

how would increasing the oil concentration in the pre mix lean out the fuel?

MotorGeek - Jerry Hall · « **Reply #15 on:** January 09, 2013, 10:48:22 pm »

Quote from: MrMendo2 on January 06, 2013, 08:07:58 pm

Hey guys new to the forums, have had this problem took the motor apart and now the motor is just sitting in my house.

So what was happening is the piston is slapping the spark plug out. It is bending the plug and the bike will turn off. When I bought the bike it wasn't happening but after about 2 hours of use it started happening. What I want to do is fix the bike to sell it but I don't want the next person to buy it with problems. It's the 87 with cool head. Let me know if you guys need any more information. On the motor it also says "WEBER" on it if that means anything to you guys.

I have never seen the piston hit the spark plug on a LT 500 unless the pieces of broken piston are hitting it.

Detonation will over heat the ground strap and sometimes burn the end off.

Detonation will over heat the center wire and cause the center wire to expand and break the ceramic cone surrounding it.

Detonation will cause the spark plug to come loose.

Detonation will eat through the head gaskets and o-rings.

Detonation will eat away at the edges of the piston and cylinder head.

MrMendo2 · « **Reply #16 on:** January 09, 2013, 10:59:30 pm »

So how do I this detonation problem?!?

LT250RWV · « **Reply #17 on:** January 10, 2013, 12:34:18 am »

more oil going into the into the jet at 24 to 1 then 32 to 1. More oil means less gas once it compressed around the crank as the gas vapors go up in the ports as the oil suspends out of gas and falls around the crank then the crank spin the oil up and throws it to lubricates rings bearings rod piston.I always heard 1 jets size up or down for 4 oz of oil you put in or take out.

Stpltn250r · « **Reply #18 on:** January 10, 2013, 06:03:03 am »

As stated before. Carb and head geometry checked.

Glamisrider · « **Reply #19 on:** January 10, 2013, 10:54:05 am »

Do a squish test and see how much clearance you have.

Since there is no write up on here on how to do a squish test (hint...hint), here is a link on how to do a squish test.
http://www.rb-designs.com/squish-band-test.htm

You should be .048-.052

How does the piston look?

Has it been impacting the strap on the plug?

MrMendo2 · « **Reply #20 on:** January 12, 2013, 10:12:52 pm »

Sorry I took so long to reply to any posts this are some pictures that I found when PCS took the bike apart and this is what we found. MotorGeek anything? (before i bring it to you?!?!)

GrkGuy · « **Reply #21 on:** January 12, 2013, 11:38:17 pm »

whats up with that clean ring around the squish, is the piston hitting the head,

MrMendo2 · « **Reply #22 on:** January 13, 2013, 07:25:08 am »

Not sure why there was 2 of the same picture.

Julle74 · « **Reply #23 on:** January 13, 2013, 08:42:51 am »

You have piston to head contact. Check Rod bearings and main bearings

Stpltn250r · « **Reply #24 on:** January 13, 2013, 08:47:19 am »

Or you have an invverted squish band. Meaning from the bores edge it gets closer to the piston as it gets closer to the curtains edge or edge of where the bowl start.

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Author Topic: LT500 Spark Plug Piston Problem (Read 1877 times)

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