Got our engine running, jetted correctly, even running a bit rich top and bottom to break in. Local guy slightly bored my cylinder over and ported. Stock head, stock bottom end with no vertical play. I did a leak down test and held 7psi for 10 min. Tried to kick the motor over today after running it for an hour or so, had very little compression. Pulled the cylinder and this is what I found... Is this due to an incorrect bore job? The wear is only on the exhaust port side, the carnage is pretty bad for the amount of time running. Any guesses wtf happened?
Engine trashed in an hour...
- Thread starter RatedM
- Start date
Not good,
I think most on here would ask the following;
What is your jetting?
Air box lid on or off?
Type of air filter?
What exhaust are you running?
The hour is was running, what kind of running did it endure?
Oil injected or premix 32:1?
Temperature elevation?
Slightly bored?
I may have missed something but I think this should be a good start.
I think most on here would ask the following;
What is your jetting?
Air box lid on or off?
Type of air filter?
What exhaust are you running?
The hour is was running, what kind of running did it endure?
Oil injected or premix 32:1?
Temperature elevation?
Slightly bored?
I may have missed something but I think this should be a good start.
slightly bored ?
new piston ?
cast or forged ?
was it bored/honed for the exact new piston and clearances recommended for that piston ?
what was that piston to cylinder clearance ?
were the ports chamfered after the bore and porting ?
leakdown test ...check
3-5 heat cycles and retorque of head/base nuts ?
leakdown test again ?
as mentioned above...what kind of running for an hour ?
heat cycles ?
or start it and rip ?
it got crazy hot/or improper piston to cylinder clearance
also that must have made some crazy noise lol
also that must have made some crazy noise lol
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Doesn't look like proper chamfering, but hard to tell. Did the guy have the new piston to check clearance?
I sure hope you did not add more oil to the mix, if you did you may have leaned out the AFR just enough to cook the piston!
Did you make sure that the header pipe was free of debris before you put it on?
If there was any crap in there it may have been forced back into the cylinder by the back pressure!
I'm with pops on this. Adding oil "richening up" for a breaking in touch aboutsure sounds like it was a kiss of death.
All that adding extra oil does is lean out the AFR, and makes you run terribly lean.
The piston might not have been in the proper tolerances either. If it was slightly bored like you said, that throws up a red flag. You want to bore and then hone to meet the new pistons tolerances.
Best advise I can give you is....don't go back to that shop. Take or send it to someone who knows what tolerances, port chamfering, and ring end gap are. Educate yourself on blaster motors and their specs. All the info can be found here.
Sorry to sound like a dick, but I hate seeing people spend their hard earned money, only to have to spend it again.
Doing things a second time isn't any fun, unless it's a hot chick
All that adding extra oil does is lean out the AFR, and makes you run terribly lean.
The piston might not have been in the proper tolerances either. If it was slightly bored like you said, that throws up a red flag. You want to bore and then hone to meet the new pistons tolerances.
Best advise I can give you is....don't go back to that shop. Take or send it to someone who knows what tolerances, port chamfering, and ring end gap are. Educate yourself on blaster motors and their specs. All the info can be found here.
Sorry to sound like a dick, but I hate seeing people spend their hard earned money, only to have to spend it again.
Doing things a second time isn't any fun, unless it's a hot chick
Using a PWK 28MM, I forget where I ended up on the jets, but from a plug chop I made sure that I was a bit rich for break in.
No Airbox, this engine is being used in a go-kart. I just have a Uni off the carb.
FMF Fatty and FMF silencer
I did 3 warm up cycles just lowly blipping the throttle. Re-torqued all the head/cylinder bolts. Then I drove it around less than half throttle for about 15 min, checked everything again, then let her rip.
Premix 32:1 with Lucas and 93 octane
80deg and sea level here.
OEM cylinder and sleve, just had it over-bored to clean up minor scoring. Forget what spec the builder ended up at, but he ordered the piston himself. It was a Pro-X cast piston with cosmetic gasket kit.
I didn't measure the piston to cylinder clearance, I was told the machine shop made the measurements and all was in spec since they ordered the piston themselves. I could see that the ports were chamfered when I got the cylinder back. I didn't do a leakdown test a second time after break in, but did check the main with a plug chop and it was overly rich, which I wanted. I think the rest of your questions are answered above.
That's the surprising part...No strange noises, and it ran when I put it away! Tried to kick it over today and had no compression.
I'll take some pics tomorrow for you. No strange heat marks or anything on top though. Looks new.
I'll take better pics of the cylinder ports tomorrow. He bought the piston himself for my build, so yes, he had it on hand.
32:1. Just richened up the main for break-in. Yes the header pipe was free of debris when I put it on, as far as I know atleast. I even blew it out with air before the install.
Thank you guys for the help so far!
Richining up the main will do nothing to the AFR until after 3/4 throttle.
You should have set the idle speed at the end of the first heat cycle.
Was the needle in the correct position?
Is it possible to get a pic of the top of the piston please?
You should have set the idle speed at the end of the first heat cycle.
Was the needle in the correct position?
Is it possible to get a pic of the top of the piston please?
I understand, but I adjusted the needle to what I thought was correct too. For the most part, this kart is either WOT or on the brakes. Only time I really let up is to modulate a slide.
It idled fine from the first start up after I adjusted the air screw.
This is the only pic of the top that I have. Will get a better pic tonight.
Attachments
That pic to me shows some melting of the edge of the exhaust side of the top of the piston.
You may have been just a little on the lean side!
On a side note, if you are going to be at full throttle for extended periods you may like to consider altering the oil ratio to 25:1. You of course will have to increase the jetting sizes.
32:1 ratio is great for recreational riding but if you are going to fang it fully, the oil in the mix will not come out of suspension easily enough to provide a pool in the crankcase bottom to bathe the engine parts. You will suffer oil starvation.
You may have been just a little on the lean side!
On a side note, if you are going to be at full throttle for extended periods you may like to consider altering the oil ratio to 25:1. You of course will have to increase the jetting sizes.
32:1 ratio is great for recreational riding but if you are going to fang it fully, the oil in the mix will not come out of suspension easily enough to provide a pool in the crankcase bottom to bathe the engine parts. You will suffer oil starvation.
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would just a LITTLE lean actually do that damage that quickly? or realistically would it have to of been very lean to fry in an hour. I'm still new to this so i'm trying to understand and learn from others mistakes.
A little lean at full throttle, will create quite a lot of heat.
You said you let it rip after 15 minutes or gentle riding, I assume you meant ripping at full throttle!
That combined with a freshly honed cylinder, creating even more heat from friction, may have caused the carnage.
It only take just a little grain or two of cooked piston top to create a major problem.
You said you let it rip after 15 minutes or gentle riding, I assume you meant ripping at full throttle!
That combined with a freshly honed cylinder, creating even more heat from friction, may have caused the carnage.
It only take just a little grain or two of cooked piston top to create a major problem.
Ive kept thinking about this. What kind of exhaust do you have on it? An exhaust flange that isn't sealing up tight running at WOT can create a lean condition as well.
You say this was on a go cart. These motors are air cooled so with it not getting enough air flow = hotter than norm and then being even the slightest bit lean = even hottor.
I think the lack of air flow over an air cooled motor played a big role.
I think the lack of air flow over an air cooled motor played a big role.
WOT may starve the engine from oil if you are using pre mix at less than the 20:1 ratio that the trusty oil pump puts in!
injection ratios should not be compared to mix ratios.
injection oil is of a way thinner viscosity than mix oil, so more is required to do the same job when injecting.
hence why 20:1 is injected versus lesser ratios for the higher viscosity mix oil.
http://www.klemmvintage.com/oils.htm ..............
About Oil Injection - A majority of vintage street and recreational based 2strokes were manufactured with an oil injection system that eliminated the need for pre-mixing fuel. Oils made for oil injection use have a considerably thinner viscosity than oils intended for premix. It is unwise to use a premix type oil in an injector because a premix type oil can have difficulty passing through the small orifices in many oil-injection systems. On the same tack, it is a very bad idea to use an "oil-injection" oil in a premix application because the reduced viscosity will not offer the lubrication needed in a pre-mix situation
injection oil is of a way thinner viscosity than mix oil, so more is required to do the same job when injecting.
hence why 20:1 is injected versus lesser ratios for the higher viscosity mix oil.
http://www.klemmvintage.com/oils.htm ..............
About Oil Injection - A majority of vintage street and recreational based 2strokes were manufactured with an oil injection system that eliminated the need for pre-mixing fuel. Oils made for oil injection use have a considerably thinner viscosity than oils intended for premix. It is unwise to use a premix type oil in an injector because a premix type oil can have difficulty passing through the small orifices in many oil-injection systems. On the same tack, it is a very bad idea to use an "oil-injection" oil in a premix application because the reduced viscosity will not offer the lubrication needed in a pre-mix situation
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