Engine noise

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StueyC
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Engine noise

#1

Post by StueyC » Fri Oct 29, 2010 7:41 am

I'm about to start my engine after a rebuild. When I kick the engine over I'm hearing a loud whistling noise as it goes over compression. I'm not sure where the noise is coming from as it's hard to track down. It might be air trying to suck past the carb butterfly? The engine was a non runner and wouldn't kick over when i got it so I don't know if this noise is normal or not.

I know it's a hard question but any ideas?

Thanks.
StueyC



Bosheff
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Re: Engine noise

#2

Post by Bosheff » Fri Oct 29, 2010 8:14 am

Possibly a head gasket or maybe the crankcases venting to the atmosphere or through the oil tank....bosheff

StueyC
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Re: Engine noise

#3

Post by StueyC » Fri Oct 29, 2010 8:25 am

G'day Bosheff. I have a filter on the end of my crankcase breather hose and the noise doesn't appear to be coming from there. The oil tank has a rubber bung in it and I would think the bung would blow out if the oil tank was pressurising. Does my carb theory seem logical?

Thanks.
StueyC

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Re: Engine noise

#4

Post by StueyC » Fri Oct 29, 2010 8:38 am

Don't know why i didn't think of this earlier. I've eliminated the carb and head gaskets as being the cause as the noise is still there even with the plugs removed. The noise seems to come from the front of the engine somewhere. Can the cam chest become pressurised? I'm wondering if there is air escaping from between the generator and cam chest.

Thanks.
StueyC

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Re: Engine noise

#5

Post by old1955 » Fri Oct 29, 2010 9:22 am

G'day Stuey,

Might be your genny, they can howl rather than whistle, if the lash isn't
set correctly.

Pull the genny and kick it over.
Pete

StueyC
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Re: Engine noise

#6

Post by StueyC » Fri Oct 29, 2010 9:41 am

G'day Pete, I'm aware the genny's can howl and I'd prefer not to remove it unless really necessary. If it's the Genny then it will howl constantly once started and then I've have to attend to it. I suppose I'm after a bit of reassurance that it might not be anything serious so I can start her up and then see what I hear.

I suppose if it's blowing air somewhere then the worst I can get is some oil exiting where the air is escaping after it runs for a while?

Thanks for your advise.

StueyC.

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Re: Engine noise

#7

Post by old1955 » Fri Oct 29, 2010 12:17 pm

OK Stuey,

Only other thing I can think of is your breather, is it timed right. which
Bosheff mentioned already. Or did you modify the opening like S&S suggest?
(don't do it)

I know there is nothing worse, you think everything's done right, you make
a huge effort assembling everything correctly, spotlessly clean and tidy,
and you got to open her up again.....sucks!

Pete

StueyC
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Re: Engine noise

#8

Post by StueyC » Fri Oct 29, 2010 12:23 pm

G'day Pete, I did fit a new breather S & S but didn't do any mods. The breater was the same as the one originally fitted except oversize as I machined scouring from the breather bore. The breater was timed and went in in the same postion as the original i.e. all markes lined up.

Maybe I need to "bite the bullet" and start her up.

Thanks.
StueyC

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Re: Engine noise

#9

Post by JR JOHNSON » Fri Oct 29, 2010 2:15 pm

hi,if it was me,i would pull 1 plug out,see if the noise change, if it gos a way,put a compression gauge on the cylinder,see what it do's,may leak down test,our something like that.is the noise comming out of the exhaust?when you take the compresion a way
should tell the story.hope this helps,lets us now....with respect....JR
OPPS ,I SEEN YOU PULLED THE PLUGS, STIIL DO A LEAK DOWN TEST. jr..
also pull the filter off of the vent tube, see if you have puff of crankcase pressure out of it.should have some comming out,hope this helps
Last edited by JR JOHNSON on Fri Oct 29, 2010 4:01 pm, edited 1 time in total.

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Re: Engine noise

#10

Post by Panshovevo » Fri Oct 29, 2010 2:41 pm

Rethinking this


Do you have someone who can kick it while you listen?
Do you have a mechanics stethoscope?

Regards,
John

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Re: Engine noise

#11

Post by Kuda » Fri Oct 29, 2010 2:59 pm

StueyC wrote:I'm about to start my engine after a rebuild. When I kick the engine over I'm hearing a loud whistling noise as it goes over compression. I'm not sure where the noise is coming from as it's hard to track down. It might be air trying to suck past the carb butterfly? The engine was a non runner and wouldn't kick over when i got it so I don't know if this noise is normal or not.

I know it's a hard question but any ideas?

Thanks.
StueyC
This ain't a shortcut to proper diagnosis, but for what it's worth (which is exactly what you paid for it :mrgreen: ) mine's been making that noise for as long as I've had it. And that's with three bottom end rebuilds, 6 top ends, and over 100K miles. Always did it, always ran fine...

-Kuda (I'm just sayin'...)
'49 panchop

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Re: Engine noise

#12

Post by steve_wood » Fri Oct 29, 2010 4:04 pm

Okay, this might be a stupid question, but...

Does the noise change if you change the position of the throttle and/or choke?

If the answer is no, then it probably isn't coming from the carb.

Could it be coming from air whistling as it passes the intake valve? If so, it would appear to be coming from the carb.

Could it be coming from air whistling as it passes the exhaust valve? If so, it should be loudest at the exhaust pipe.

JR JOHNSON
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Re: Engine noise

#13

Post by JR JOHNSON » Fri Oct 29, 2010 4:36 pm

hi,i've notice that you have a bunch of bikes,witch one are you working on?is it posseble that your piston rings gaps are lined up?not sure thats your noise.just make sure you have pressure leaving the crancase breather. with respect....JR

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Re: Engine noise

#14

Post by Bosheff » Fri Oct 29, 2010 4:41 pm

If after all is said and done and ya still can't put yer finger on the problem, ya really only have two options. Either disassemble and give a look/see, or fire it up and go from there. The first option is time consuming and may not be all that fruitful as a wear pattern probably has not had time to appear on the related parts, if it is in fact a clearance issue. Firin' it up should hopefully point ya in the right direction, but may be more costly dollar and cents wise. One thing's fer sure, it ain't gonna go away on its own. Good luck....bosheff

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Re: Engine noise

#15

Post by panhead_kicker » Sat Oct 30, 2010 1:34 am

StueyC wrote: I have a filter on the end of my crankcase breather hose and the noise doesn't appear to be coming from there. The oil tank has a rubber bung in it...
Hey Stuey, I have to ask... when you say you have a filter on the end of the crankcase breather hose, what hose do you mean? There is the case vent nipple that exits just above the oil pump and is normally piped to the oil tank, then there is the crankcase vent stud that exhausts inside of the primary. Mine always makes a lot of asthmatic noises from the vent stud in the primary while kicking.

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