head gasket questions

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mechanickid

mechanickid

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Aug 7, 2008
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Hey guys, so i figured out i had an air leak after i peddled up a hill with the engine off and the clutch engaged trying to start it.

when i took the head off i found a metal spacer where the gasket should be, but no gasket.
im thinking i could just replace the spacer with a gasket and that would improve compression greatly, has anyone tried this? .sno.
 
Bikeguy Joe

Bikeguy Joe

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It's a soft aluminum...it works very well, and in fact most engines have a similar type of gasket...or sometimes annealed copper. The only head gaskets I've ever seen with "gasket material" have an aluminum ring where each cylinder is.

Some guys (Norman) have use a heavy aluminum pigmented paint as a "gasket".
 
mechanickid

mechanickid

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ah, well i replaced it with some cardboard and grease. dumb, i know, but it was worth a try. it did improve compression a bit. but i still have an air leak somewhere between the air filter and the engine.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
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You could always use to "hillbilly chrome" paint or Rustoleum aluminum paint if the cardboard and grease don't hold up.....I think the correct gaskets are cheap though.
 
Bikeguy Joe

Bikeguy Joe

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Thebest thing to do for the air leak is to just remove the carb and intake, make a new gasket out of some gasket paper, or carboard and SILICONE like RTV sealer, and put it back together.

In a pinch, just remove it and goober up the old gasket with silicone....any kind will work, even 100% silicone caulking.
 
Norman

Norman

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Jan 16, 2008
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If you want to use that used head gasket I spray it with the aluminum spray paint the cheaper the better and check to make sure the main ingredient is aluminum powder and not mica. spray both sides and install it or if you want wait until the stuff dries then torque it down in an x pattern start at 40 inch lbs then 80 inch lbs then 1`20 inch lbs. I try to start at the exhaust side and end at the other exhaust side. run it until its hot then re torque it while its hot at 120 inch lbs. starting on the exhaust side and end on the exhaust side.
I've been mulling over the idea of sealing the head with a copper ring by machining the head with a groove in it and installing a home made copper wire ring. I haven't yet but may do so when I can find the time. This might work good or $hit the bed its worked on other hot roded engines in the past and should be kind of fun. I have machined a head for very high compression but haven't tried it I might run into piston hitting the head problem but that is just a challenge to work out.:-||
Norman
 
mechanickid

mechanickid

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thanks. i did a lot of re torquing just like that but i still have a huge air leak somewhere. not the carb though. not the exhaust, not that that would make a difference. the head doesn't have any oil or signs of leaking... cant find any cracks... but terrible compression. its a problem that started a month ago and has been getting worse, any ideas?
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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When you had the head off, how did the walls of the cylinder look?

Also, what happened before it started getting worse? Did you get it really hot?
If you ran it too long with an air leak, you may have put the hurtin' on it....two strokes don't like to be run lean very long.

To find the air leak, run the engine and spray water, WD 40 or carb cleaner around the intake, carb, and the gasket that is between the two case halves. You may also have a leak in the shaft seal on either side where then mag and gears are.

If it has low compression, I'd bet it's hurtin' and needs a re-ring or a new ring/piston/cylinder.
 
Norman

Norman

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Jan 16, 2008
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I don't think a rubber o-ring would hold up to the temp at the head around 450deg.f. but then it might. It could turn into the challenger space shuttle after they went to throttle up POP went the shuttle!
If I was to cut the o-ring groove I'd do just the head and not the cylinder. If you have a lathe you can chuck up the head using a dumby sparkplug to spin the head and do all sorts of heinous things to the head.
I like a challenge so I ordered 2 engines to do some nasty thing to like trying to o-ring the head and maybe some other parts like the intake to carb so the o-ring will be in a machined groove and not stuck betwen the carb and intake and the intake to cylinder head, what about the cylinder to the case?! I got to get a mill the dremel is going to get a very heavy workout.duh.
 
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mechanickid

mechanickid

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the walls of the cylinder looked fine, i didn't take a long look though. it hasn't been running hot because it been cold out and i haven't wanted to take it far since the problem started.
 
mechanickid

mechanickid

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ok... looks like im still not out of the woods...

i've got good compression, everything is well sealed... carb is pretty clean and the spark is nice.

i can get it to start and it will idle at high rpms but not for long.

the *put puts* have a lot of kick to them but they dont last for long.

i've tried lots of choke and idle settings.

the gas mixture is mixed about 24/1 regular (89 i guess) octane

not sure where to go from here.

all help is greatly appreciated.
 
stuartracing

stuartracing

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Dec 9, 2008
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mechanickid said:
ok... looks like im still not out of the woods...

i've got good compression, everything is well sealed... carb is pretty clean and the spark is nice.

i can get it to start and it will idle at high rpms but not for long.

the *put puts* have a lot of kick to them but they dont last for long.

i've tried lots of choke and idle settings.

the gas mixture is mixed about 24/1 regular (89 i guess) octane

not sure where to go from here.

all help is greatly appreciated.
Click to expand...
Hey, I`ve been through this exact problem...(look for air leak thread)....If you spray around the split in the cases(where they put the 2 halves together) when the motor is running I`ll bet that the rpm`s will change alot....
I`ve experimented and sealed all around the case split and the motor runs dramatically different....The motor richens up and can`t get it leaned out enough now....But at least it runs....This was done on two different motors just to see if it was true....
Check it out and see what happens...I used grey si:-||licone to seal the case split....Check under (sealing cases thread too)....
Paul....
 
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