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Old 19th August 2010, 17:16   #1
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Default Bullet 350 Standard Air leak from cylinder head

Dear Teambhpians,

I have a problem with my Bullet Standard 350 1996 model. There is an air leak from the cylinder head where the exhaust pipe meets the cylinder head.

My mech says the problem can be resolved by some welding but I have no idea about this. I was thinking abt replacing the entire cylinder head assembly with a new one. Plz advice and also let me know the price for a new or a good used cylinder head assembly.

Thanks in advance,
Navin.
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Old 19th August 2010, 23:36   #2
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Post a few clear high resolution pictures and circle the part from where the air is leaking. This will give us an idea to exactly what the problem is.
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Old 20th August 2010, 10:40   #3
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Hi,

You know even i dont know the exact location of the air leak, but my mech says it is either from the 1. inside of the cylinder head or 2. At the point where the exhaust pipe meets the cylinder head. I am posting a pic with the pointers for point 1 and 2 respectively.

Thanks.
Attached Thumbnails
Bullet 350 Standard Air leak from cylinder head-airleak-bullet-350-standard.jpg  

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Old 20th August 2010, 11:21   #4
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@Navin, if its the gap between the cylinder head & the cylinder, then replacing gaskets will suffice, may be one more additional cylinder gasket is sufficient. Even if its at exhaust, then there's a gasket, but again, two gaskets cannot be accomodated here.

BTW, what're the problems you're experiencing?
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Old 20th August 2010, 11:36   #5
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Hi, the silencer pipe seat in the head must've become oval. This is a regular phenomenon on old Bullets. When the condition is not too worse what mechs do is to put a thin piece of tin sheet between the pipe and the head. When this remedy no longer works they suggest adding metal to the silencer hole in the head and then grinding it off to match the pipe. No need to change the head.

Btw gases would never leak from the place you've marked '2' on the photo.
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Old 20th August 2010, 11:40   #6
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You don't have to replace the cylinder head man. I faced the exact same problem. It is not too serious. My mech just sealed it, probably with a tin sheet (not sure).
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Old 20th August 2010, 12:05   #7
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Quote:
Originally Posted by aargee View Post
@Navin, if its the gap between the cylinder head & the cylinder, then replacing gaskets will suffice, may be one more additional cylinder gasket is sufficient. Even if its at exhaust, then there's a gasket, but again, two gaskets cannot be accomodated here.

BTW, what're the problems you're experiencing?
Hey aargee, i dunno if the problem is related to the air leak, but my bike misfires when i open the throttle it happens both during riding as well when stationary when i open the throttle.
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Old 20th August 2010, 12:13   #8
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Hey Sankar,

I think you are bang on the right point dude, there is a thin piece of metal between the exhaust pipe and the cylinder head, but it was removed by the mech while installing a flower shaped heat insulation on the exhaust pipe where it meets the head.

About Mark 2 another mech told me there is probably a crack inside cylinder head which even i suspect.
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Old 20th August 2010, 13:23   #9
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Even if there is a crack at the place marked '2' it will not leak gases because its well outside the combustion chamber and valve area. Only thing would leak is oil from the rockerbox.
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Old 20th August 2010, 14:06   #10
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Quote:
Originally Posted by Sankar View Post
Even if there is a crack at the place marked '2' it will not leak gases because its well outside the combustion chamber and valve area. Only thing would leak is oil from the rockerbox.
Sankar i think you are right while saying this coz i have not seen any oil leak from that area Mark 2 till date, so it has to be the area where the exhaust pipe meets the head. Also as you stated the silencer pipe seat in the head must've become oval, how does it happen? I will try giving it to my mech for fixing this so replacing cylinder head for now ruled out. I will ask the mech to get it repaired. Can you explain as to how the repair will be carried out just for my info?
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Old 20th August 2010, 14:24   #11
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Quote:
Originally Posted by navin_v8 View Post
Hey aargee, i dunno if the problem is related to the air leak, but my bike misfires when i open the throttle it happens both during riding as well when stationary when i open the throttle.
I already see a thin metal sheet at the silencer mouth.
Check your spark plug gap. Too much of gap would sometimes lead to misfiring. Also check the ignition timing, probably its in advance.
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Old 20th August 2010, 15:15   #12
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Quote:
Originally Posted by navin_v8 View Post
Sankar i think you are right while saying this coz i have not seen any oil leak from that area Mark 2 till date, so it has to be the area where the exhaust pipe meets the head. Also as you stated the silencer pipe seat in the head must've become oval, how does it happen? I will try giving it to my mech for fixing this so replacing cylinder head for now ruled out. I will ask the mech to get it repaired. Can you explain as to how the repair will be carried out just for my info?
How old is your bullet?
Aluminium alloy used in Bullets (till early 00's iirc) are not of comparable quality to jap bikes. Its kind of soft, easy to strip threads in cases etc. Removing and installation of the pipe for maintenance such as decarb or other work wears out the hole over time. The exhaust pipe seldom goes into the head smoothily often they are whacked into place with wooden blocks and while removing sometimes they're forced out. These are contributing factors. And there are no bolts or screw to retain the exhaust to the head except for a single clamp low down in the bend pipe.

Repair work is carried out by welding aluminium in the hole, to add aluminium, and then the ID of the hole is redone so as to match the OD of the exhaust pipe.

Misfiring can be due to many factors on a Bullet, Ignition timing, clogged jets, lean jetting, spark plug condition, etc Most common cause on an otherwise healthy bullet is very lean idle circuit - set the carb tuning screw to flow a bit more petrol.
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Old 20th August 2010, 15:46   #13
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Quote:
Originally Posted by jeeva View Post
I already see a thin metal sheet at the silencer mouth.
Check your spark plug gap. Too much of gap would sometimes lead to misfiring. Also check the ignition timing, probably its in advance.
Hi jeeva,

The thin metal sheet was removed while installing a flower like heat sync holder, i will definately check the ignition timing once i take it to the mech.

Quote:
Originally Posted by Sankar View Post
How old is your bullet?
Aluminium alloy used in Bullets (till early 00's iirc) are not of comparable quality to jap bikes. Its kind of soft, easy to strip threads in cases etc. Removing and installation of the pipe for maintenance such as decarb or other work wears out the hole over time. The exhaust pipe seldom goes into the head smoothily often they are whacked into place with wooden blocks and while removing sometimes they're forced out. These are contributing factors. And there are no bolts or screw to retain the exhaust to the head except for a single clamp low down in the bend pipe.

Repair work is carried out by welding aluminium in the hole, to add aluminium, and then the ID of the hole is redone so as to match the OD of the exhaust pipe.

Misfiring can be due to many factors on a Bullet, Ignition timing, clogged jets, lean jetting, spark plug condition, etc Most common cause on an otherwise healthy bullet is very lean idle circuit - set the carb tuning screw to flow a bit more petrol.
Hey sankar mine is a 1996 standard 350 model. Also the misfiring might be due to lean setting as i had checked the spark plug and it looked fine.

Last edited by Jaggu : 20th August 2010 at 16:49. Reason: Back to back posts, please use multi quote (Quote +) instead. Thanks
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Old 20th August 2010, 18:08   #14
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If there is a vacuum leak in the cylinder, won't it cause a loss of compression too? Will it not cause the kick lever to be smoother than usual?
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Old 24th August 2010, 10:22   #15
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Quote:
Originally Posted by Gordon View Post
If there is a vacuum leak in the cylinder, won't it cause a loss of compression too? Will it not cause the kick lever to be smoother than usual?
Hey Gordon,

I think you are right in saying that the kick lever has become smoother than usual due to loss of compression. I have felt it while kicking some of my friends have told me that the kick start in my bullet is familiar to a kick start on Pulsar.

These are the symptoms, what should i do to rectify it?
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