what caused the air leak that destroyed my engine?

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1/19/2018 11:55 AM

about 2 months ago i had just finished building my 2001 honda cr125. I rebuilt the engine and had everything torqued to oem specs. This was my 3rd time rebuilding a 2 stroke engine and i used all the proper tools. It ran fine at first while on the stand but after revving it a few times it got stuck wide open. it was not the throttle getting stuck, it was an air leak. The kill switch wouldnt work and i pulled the spark plug and that didnt work either. I pulled the gas line and let it run wide open until the gas ran out. By this time the water pump seal had busted. I removed the cylinder and the piston was messed up along with minor scarring of the cylinder. Also the crank seal on the flywheel side had a little drops of oil come out of it. I finally got the motivation to try and rebuild it again and just bought an engine rebuild kit. I just need to know what caused the air leak so that I can fix it this time and not destroy my engine a second time. Info on the bike: I recieved it in a box in pieces. Both crankcase surfaces were very scratched up and one was too far gone so I replaced it with a new one. The other is still scratched but i sanded it until smooth (its not perfect but its good enough to use). When i put it together I used a fresh gasket AND some hondabond gasket to make sure it seals perfect. It didnt leak at all so i believe that cant be the problem. What do you guys think the problem is? How can I find the cause of this incident? Im scared to put it back together and have the same thing happen again.

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1/19/2018 12:28 PM
Edited Date/Time: 1/19/2018 12:30 PM

Interesting, I know you'll likely get more insight on here than I can offer but here are my thoughts.

-It's an 2001, so thinking of age what is the condition of the air boots any chance it came from there?
-You mentioned oil coming out the fly wheel crank seal, interesting being there is no oil on that side from the transmission so I would assume it was gas/fuel mixture coming out.
-Did you install new crank seals when you did the rebuild? If so what is/was the condition of the crankshaft mating surface that meets the seal, nice and smooth and no scarring ect?
-Also, the crank bearings themselves. I had a bike that the clutch side bearing went bad and it was sucking in transmission oil and smoking like a steam engine. If that happened on the flywheel side could be a big issue.
Sounds like you had the case halfs themselves sealed properly......

Anyway, that's my 2 cents......

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1/19/2018 1:08 PM

beamer wrote:

Interesting, I know you'll likely get more insight on here than I can offer but here are my thoughts.

-It's an 2001, so thinking of age what is the condition of the air boots any chance it came from there?
-You mentioned oil coming out the fly wheel crank seal, interesting being there is no oil on that side from the transmission so I would assume it was gas/fuel mixture coming out.
-Did you install new crank seals when you did the rebuild? If so what is/was the condition of the crankshaft mating surface that meets the seal, nice and smooth and no scarring ect?
-Also, the crank bearings themselves. I had a bike that the clutch side bearing went bad and it was sucking in transmission oil and smoking like a steam engine. If that happened on the flywheel side could be a big issue.
Sounds like you had the case halfs themselves sealed properly......

Anyway, that's my 2 cents......

The boots are in perfect shape. It looked like the oil was dripping right from the seal where it touches the crank. I did install new crank seals, but I reused the crank. Also when it was running i took off the exhaust at one point and there was a lot of black oil in the pipe and around the cylinder where the pipe met.

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1/19/2018 1:19 PM

Am I reading that right ? You took the exhaust off while it was running ?? Why ?

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1/19/2018 3:02 PM
Edited Date/Time: 1/19/2018 3:03 PM

My question is?

When you replaced the crank seal did you lift on the crank end whit your hand up and down. To check for play. If not its gone make the seal oval again if the crank bearing had play in it

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1/19/2018 3:44 PM

you DONT use gasket sealer on centercase gaskets they slip out

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1/19/2018 4:06 PM
Edited Date/Time: 1/19/2018 4:12 PM

OldPro277 wrote:

Am I reading that right ? You took the exhaust off while it was running ?? Why ?

Lol no I ran it once then took the exhaust off cause I saw a little black oil coming from it. I didn’t word that very good!

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1/19/2018 4:07 PM

metal_miracle wrote:

My question is?

When you replaced the crank seal did you lift on the crank end whit your hand up and down. To check for play. If not its gone make the seal oval again if the crank bearing had play in it

There was no up and down play

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1/19/2018 4:08 PM

pete24 wrote:

you DONT use gasket sealer on centercase gaskets they slip out

So just use a gasket only? You think it’ll seal ok?

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1/19/2018 4:49 PM

A few possibilities ...
Bad air leak.
Bad crank bearing. ( or crank not running true)
Squish set too tight. ( was it checked?)
You did not mention the state of the carb....Dirty pilot jet?

Paw Paw

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1/19/2018 4:56 PM

pete24 wrote:

you DONT use gasket sealer on centercase gaskets they slip out

z71will wrote:

So just use a gasket only? You think it’ll seal ok?

Yes, some (like a yz 250) only use sealant on the center cases but for your Honda with a gasket, only use that.

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1/19/2018 5:04 PM

pete24 wrote:

you DONT use gasket sealer on centercase gaskets they slip out

z71will wrote:

So just use a gasket only? You think it’ll seal ok?

Gaskets only - no silicone sealant. For oil seals you rub some bel ray waterproof grease around the outside.

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

1/19/2018 5:08 PM

Paw Paw 271 wrote:

A few possibilities ...
Bad air leak.
Bad crank bearing. ( or crank not running true)
Squish set too tight. ( was it checked?)
You did not mention the state of the carb....Dirty pilot jet?

Paw Paw

Carb was freshly rebuilt. Crank bearings were new. The crank might have been out of True since I did reuse the old one. What do you mean squish set too tight?

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1/19/2018 6:44 PM
Edited Date/Time: 1/19/2018 6:47 PM

Squish is the amount of clearance between the head outer compression ring machined into it and the piston crown.
If set too tight it will create pre-ignition and cause the fuel to ignite even with out a spark.
What did the top edges of the piston look like? Was it pitted? Was the ring stuck in the ring land on the piston.
FYI: Do a google search for two stroke squish....Or look up The two stroke tuning hand book on line.

Paw Paw

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1/19/2018 6:57 PM

How did it run with no spark?

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1/19/2018 8:25 PM
Edited Date/Time: 1/20/2018 5:06 AM

The Lord works in mysterious ways... Or not... Maybe ?

You blew an engine up by doing something incorrectly or had bad part(s)... Revisit, revise, retry if you have the $$$. So many variables you put forth to pinpoint where it could have went wrong... 32:1? Fuel type? Post some pics of your efforts. Engine rebuild Kit? From WHERE?

Always take pics during the process to review prior to starting up, even if for your own sake.

Do you have an OEM manual?

One odd bit is driving the crank seals in too far can fuck an 2T engine up as you describe... Sufficient fuel to run, insufficient fuel to lubricate crank bearings. Coupled with an ill-adjusted carb flowing fuel, I guess it COULD happen.


EDIT: Removed troll reference

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1/19/2018 9:50 PM

Are you using a v force?

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1/20/2018 3:20 AM

Rockinar wrote:

How did it run with no spark?

If it sparked enough to start, and the squish was so tight that the gas ignited on its own, theoretically the engine could stay running without spark at least for a little bit.

Quick lesson on gas & compression ratios. Gasoline engines require a spark to run obviously due to low compression ratios. Diesel engines on the other hand rely on compressing the mixture so it ignites on its own. This requires 16:1 compression or higher. So to tie this in with his bike.. if his squish is tight enough to create a 16:1 compression ratio or higher, the mixture will ignite on its own and run as long as its getting fuel.

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

1/20/2018 6:48 AM
Edited Date/Time: 1/20/2018 6:49 AM

If the head has damage pits and lean jetting a hot spot can keep it running WFO.

I would do a leak down pressure test and find exactly where the leak is. Takes rubber plugs for the intake & exhaust and a special hand gaged pump.

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1/20/2018 7:02 AM
Edited Date/Time: 1/20/2018 7:04 AM

Powervalves can make it difficult as they often have leaks so you have to be creative.

The Matco guage I have.

Photo

Rubber plug look for intake and exhaust ports.

Photo

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1/20/2018 7:19 AM
Edited Date/Time: 1/20/2018 7:20 AM

z71will wrote:

about 2 months ago i had just finished building my 2001 honda cr125. I rebuilt the engine and had everything torqued to oem specs. This was my 3rd time rebuilding a 2 stroke engine and i used all the proper tools. It ran fine at first while on the stand but after revving it a few times it got stuck wide open. it was not the throttle getting stuck, it was an air leak. The kill switch wouldnt work and i pulled the spark plug and that didnt work either. I pulled the gas line and let it run wide open until the gas ran out. By this time the water pump seal had busted. I removed the cylinder and the piston was messed up along with minor scarring of the cylinder. Also the crank seal on the flywheel side had a little drops of oil come out of it. I finally got the motivation to try and rebuild it again and just bought an engine rebuild kit. I just need to know what caused the air leak so that I can fix it this time and not destroy my engine a second time. Info on the bike: I recieved it in a box in pieces. Both crankcase surfaces were very scratched up and one was too far gone so I replaced it with a new one. The other is still scratched but i sanded it until smooth (its not perfect but its good enough to use). When i put it together I used a fresh gasket AND some hondabond gasket to make sure it seals perfect. It didnt leak at all so i believe that cant be the problem. What do you guys think the problem is? How can I find the cause of this incident? Im scared to put it back together and have the same thing happen again.

You have to use some high temp grease on the crank seal lips. When rebuilding a two stroke your not finished until you have done a leak down test.

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1/20/2018 9:09 AM

YamahaJT1 wrote:

The Lord works in mysterious ways... Or not... Maybe ?

You blew an engine up by doing something incorrectly or had bad part(s)... Revisit, revise, retry if you have the $$$. So many variables you put forth to pinpoint where it could have went wrong... 32:1? Fuel type? Post some pics of your efforts. Engine rebuild Kit? From WHERE?

Always take pics during the process to review prior to starting up, even if for your own sake.

Do you have an OEM manual?

One odd bit is driving the crank seals in too far can fuck an 2T engine up as you describe... Sufficient fuel to run, insufficient fuel to lubricate crank bearings. Coupled with an ill-adjusted carb flowing fuel, I guess it COULD happen.


EDIT: Removed troll reference

Fuel was 32:1 and I was running 93. I used all balls crank bearings and a namura top end with cometic gaskets.

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1/20/2018 9:10 AM

Bruce372 wrote:

Are you using a v force?

Yeah I have v force 3 reeds and a pro circuit pipe

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1/20/2018 9:12 AM

z71will wrote:

about 2 months ago i had just finished building my 2001 honda cr125. I rebuilt the engine and had everything torqued to oem specs. This was my 3rd time rebuilding a 2 stroke engine and i used all the proper tools. It ran fine at first while on the stand but after revving it a few times it got stuck wide open. it was not the throttle getting stuck, it was an air leak. The kill switch wouldnt work and i pulled the spark plug and that didnt work either. I pulled the gas line and let it run wide open until the gas ran out. By this time the water pump seal had busted. I removed the cylinder and the piston was messed up along with minor scarring of the cylinder. Also the crank seal on the flywheel side had a little drops of oil come out of it. I finally got the motivation to try and rebuild it again and just bought an engine rebuild kit. I just need to know what caused the air leak so that I can fix it this time and not destroy my engine a second time. Info on the bike: I recieved it in a box in pieces. Both crankcase surfaces were very scratched up and one was too far gone so I replaced it with a new one. The other is still scratched but i sanded it until smooth (its not perfect but its good enough to use). When i put it together I used a fresh gasket AND some hondabond gasket to make sure it seals perfect. It didnt leak at all so i believe that cant be the problem. What do you guys think the problem is? How can I find the cause of this incident? Im scared to put it back together and have the same thing happen again.

Hondas4Life3 wrote:

You have to use some high temp grease on the crank seal lips. When rebuilding a two stroke your not finished until you have done a leak down test.

A leak down tester costs over $250!!

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1/20/2018 9:22 AM

Bruce372 wrote:

Are you using a v force?

z71will wrote:

Yeah I have v force 3 reeds and a pro circuit pipe

Did You have to cut the carb manifold to fit it? A common source of leaks...

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1/20/2018 9:52 AM

Bruce372 wrote:

Are you using a v force?

z71will wrote:

Yeah I have v force 3 reeds and a pro circuit pipe

Bruce372 wrote:

Did You have to cut the carb manifold to fit it? A common source of leaks...

No I didn’t cut anything

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1/20/2018 1:26 PM

beamer wrote:

Interesting, I know you'll likely get more insight on here than I can offer but here are my thoughts.

-It's an 2001, so thinking of age what is the condition of the air boots any chance it came from there?
-You mentioned oil coming out the fly wheel crank seal, interesting being there is no oil on that side from the transmission so I would assume it was gas/fuel mixture coming out.
-Did you install new crank seals when you did the rebuild? If so what is/was the condition of the crankshaft mating surface that meets the seal, nice and smooth and no scarring ect?
-Also, the crank bearings themselves. I had a bike that the clutch side bearing went bad and it was sucking in transmission oil and smoking like a steam engine. If that happened on the flywheel side could be a big issue.
Sounds like you had the case halfs themselves sealed properly......

Anyway, that's my 2 cents......

z71will wrote:

The boots are in perfect shape. It looked like the oil was dripping right from the seal where it touches the crank. I did install new crank seals, but I reused the crank. Also when it was running i took off the exhaust at one point and there was a lot of black oil in the pipe and around the cylinder where the pipe met.

Oil on the LH crank seal dripping is probably premix getting past a leaking main seal. May have folded / rolled the lip of the seal during installation of the crank. Lack of grease on the seal during crank install could have also let the crank end eat / burn the seal a bit. Were the crank ends clean, free of roughness where the seal mates on it ?

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1/20/2018 6:40 PM

z71will wrote:

A leak down tester costs over $250!!

You can make one for under $50

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