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T140 compression leak at the spark plug hole. #100969
09/28/06 1:55 pm
09/28/06 1:55 pm
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Johnny-B-Good Offline OP
BritBike Forum member
Johnny-B-Good  Offline OP
BritBike Forum member
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
I have been trying to figure out why my right cylinder has been giving me so much trouble with missing and running lean and I believe I have finally got it. After a quick ride yesterday afternoon, I got off the bike with it warm and running and started listening to the engine. I could hear what sounded like exhaust toward the top of the head so I put my hand over the spark plug and I could feel air lightly popping my hand.

I pulled the plug to make sure I didnít forget the gasket and it was there. I am not sure what to do now. I am thinking head replacement if there are no other alternatives. Has this happened to any of you and is there anything else I can do?

Thanks,
Johnny


78 Bonneville T140V
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Re: T140 compression leak at the spark plug hole. #100970
09/28/06 2:16 pm
09/28/06 2:16 pm
Joined: Dec 2004
Posts: 9,483
Scotland
kommando Offline
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kommando  Offline
BritBike Forum member
Joined: Dec 2004
Posts: 9,483
Scotland
Could be,

1. Air cooled engines are hot and hot air rises.

2. Cracked head

3. Porus head

4. Cracked or porus sparkplug

doubt its 1 but just double check.

2 and 3 are cured by welding head at leak point or injecting head with some fancy compound as Norton did to their porus heads.

To find leak, let head cool and using an old sparkplug adapted to take an air line pressurise combustion chamber whilst spraying soapy water on head, bubbles will appear at leak point.

4 is easy, new sparkplug and try this first.

Re: T140 compression leak at the spark plug hole. #100971
09/28/06 2:17 pm
09/28/06 2:17 pm
Joined: Apr 2003
Posts: 127
NSW Australia
S
saxon7 Offline
BritBike Forum member
saxon7  Offline
BritBike Forum member
S
Joined: Apr 2003
Posts: 127
NSW Australia
Johnny,

I'm a bit confused by this; are you saying that the spark plug isn't locating properly? Which gasket are you referring to; the metal ring on the spark plug? Sorry if I've missed any previous threads which the bike was mentioned in, but I assume you've pulled the head off and checked out the head gasket and either replaced it or re-anealed it. If the blow out is actually coming from the spark plug hole..then I am guessing you can helicoil the thread. Not everyone approves of helicoils...but then not everyone has a spare head to just shove on either...

Sean.


51' Thunderbird project
48 Speed Twin project.
85' BMW K100RT and sidecar.
Re: T140 compression leak at the spark plug hole. #100972
09/28/06 2:46 pm
09/28/06 2:46 pm
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Johnny-B-Good Offline OP
BritBike Forum member
Johnny-B-Good  Offline OP
BritBike Forum member
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Thanks for the replies.

My first thought was maybe I am just imagining this. I installed a new spark plug with the metal ring that I called a gasket, and cranked her back up. I laid a napkin over the spark plug and could see it popping caused by air leaking. I then laid the napkin over the other spark plug and no popping of the napkin. I say napkin but used a kleenex. The air escape is that lite.

Would this little bit of air escaping cause the engine to miss and that clyinder run lean?

I have not pulled the head yet but I do need to. I also have a small oil leak at the base of the jugs. I had planned to repair it this winter but I guess I had better start now.


78 Bonneville T140V
Re: T140 compression leak at the spark plug hole. #100973
09/28/06 4:46 pm
09/28/06 4:46 pm
Joined: Aug 2005
Posts: 49
Massachusetts
DaveH Offline
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DaveH  Offline
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Joined: Aug 2005
Posts: 49
Massachusetts
Brush soapy water around suspected area. Slowly depress the kickstarter and watch for bubbles on the compression stroke.
Dave

Re: T140 compression leak at the spark plug hole. #100974
09/29/06 5:59 pm
09/29/06 5:59 pm
Joined: Apr 2006
Posts: 1,708
Virginia, USA
SBoyd Offline
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SBoyd  Offline
BritBike Forum member
Joined: Apr 2006
Posts: 1,708
Virginia, USA
Brush soapy water around suspected area. Slowly depress the kickstarter and watch for bubbles on the compression stroke. DaveH

That sounds like a great, simple idea. Inquiring minds want to know where the leak is.
>>sb


Stop the insanity.
Re: T140 compression leak at the spark plug hole. #100975
09/29/06 6:25 pm
09/29/06 6:25 pm
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Johnny-B-Good Offline OP
BritBike Forum member
Johnny-B-Good  Offline OP
BritBike Forum member
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Quote:
Originally posted by SBoyd:
Brush soapy water around suspected area. Slowly depress the kickstarter and watch for bubbles on the compression stroke. DaveH

That sounds like a great, simple idea. Inquiring minds want to know where the leak is.
>>sb
I will try this tonight. I don't guess soapy water will be sucked down into the clyinder on the power stroke.


78 Bonneville T140V
Re: T140 compression leak at the spark plug hole. #100976
09/29/06 6:31 pm
09/29/06 6:31 pm
Joined: Apr 2006
Posts: 1,708
Virginia, USA
SBoyd Offline
BritBike Forum member
SBoyd  Offline
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Joined: Apr 2006
Posts: 1,708
Virginia, USA
Johnny.......
Suggest you remove spark plug from other side.
That will give you a feel for the compression on the side you're testing. Also, if you hold the throttle open while test kicking it will minimize or eliminate any ingress on the intake stroke..
>>sb


Stop the insanity.
Re: T140 compression leak at the spark plug hole. #100977
09/29/06 11:13 pm
09/29/06 11:13 pm
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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Happy Birthday Tiger  Offline
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Joined: Oct 2004
Posts: 4,429
Melbourne Australia
A mystery indeed ?

I wonder if it is an exhaust leak masquerading as a compression leak ?

I like the airline into the cylinder approach, a compression test may also be usefull ?


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: T140 compression leak at the spark plug hole. #100978
09/30/06 11:50 am
09/30/06 11:50 am
Joined: Oct 2003
Posts: 11,263
North Georgia, USA
RF Whatley Offline
BritBike Forum member
RF Whatley  Offline
BritBike Forum member
Joined: Oct 2003
Posts: 11,263
North Georgia, USA
JBG -
IMHO, if a sparkplug had been leaking that much, that long, then the very hot gasses from the combustion chamber would probably have melted the head enough to shoot the loosened sparkplug clean through the fuel tank and or rider's leg. What's going on inside the cylinder is very HOT and very explosive. Almost like a stick of dynamite going off on every combustion stroke.

I would not be surprised to see a leak after, say, an amateur sparkplug Heli-coil insertion, but never for long on a running bike. IMHO, I believe you'll find the whiff of air is leaking at the base of the rocker box or around a head bolt.

bigt


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: T140 compression leak at the spark plug hole. #100979
09/30/06 5:13 pm
09/30/06 5:13 pm
Joined: Jun 2004
Posts: 411
Columbus, Ohio, 1978 T140E
T
tomterrific Offline
BritBike Forum member
tomterrific  Offline
BritBike Forum member
T
Joined: Jun 2004
Posts: 411
Columbus, Ohio, 1978 T140E
This is nuts. Hook up a leak down tester to teh spark plug hole and feed in some air pressure. The steady leaking pressure will allow you to zero in where it is leaking.

A clever fellow can knock out teh guts of a spark plug and drill and thread for a male air line fitting. Just hook up an air compressor.

FWIW, I saw a Norton rebuild that blew out the paper head gasket. You could see the loose piece of the paper gasket sticking out the side. Much longer and the piece of loose gasket would have completely blown free and the compression leak a mystery.

Well, as is often the case I go and read the thread more carefully AFTER I've written a response. It seems my sugesstion has been given, good advise that.

One otherplace to look is the rocker box. Anything loose? Crankcase pressure from the pistons is massive in a vertical twin and anywhere the crankcase can breath, it will.

Tom Graham

Re: T140 compression leak at the spark plug hole. #100980
09/30/06 6:40 pm
09/30/06 6:40 pm
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Johnny-B-Good Offline OP
BritBike Forum member
Johnny-B-Good  Offline OP
BritBike Forum member
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Sorry about the late update but my DSL has been down and was just repaired.

If my memory serves me right,this problem might be part of the reason I put the bike in mouthballs 5 or 6 years ago.

I sprayed soapy water around the plug last night and no bubbles when I kicked. The bike was cold and only seems to do this when it has been ridden and fully warmed up.

The mechanic I spoke of in another thread had to cancel this morning. I will be there late Monday afternoon to get started. He does happen to have another head but as he put it...For last resort only.

Glad to see you back Professor Whatley. From what I read you had a great time. Wish I could have been there.

Again, thank you all for the advice and assistance. I now have a few more options to check for this leak. It would be nice to have it pinpointed before bringing it to the shop.

Johnny


78 Bonneville T140V
Re: T140 compression leak at the spark plug hole. #100981
10/03/06 3:05 pm
10/03/06 3:05 pm
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Johnny-B-Good Offline OP
BritBike Forum member
Johnny-B-Good  Offline OP
BritBike Forum member
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Update for Tuesday

I got to the shop and the bike unloaded at 5 yesterday afternoon. Being able to work on my bike in a motorcycle shop made this old man feel like a kid in a candy store.

We cranked her up and sprayed a little soapy water around the spark plug and sure enough there were some small bubbles appearing where the plug screws into the head.

Before I could get my manuals out, Tim, the owner of the shop, told me the order of disassembly. Tank, pipes, carbs, rocker boxes, and then unbolt the head. I had brought my own tools and got with the program. In a record breaking 2 and a half hours later, I pulled the head off the bike. Tim would pass every once in a while to check my progress and ask how come I wasnít finished yet. I would just grin and keep on working

There is a heli-coil that had already been installed in the right cylinder that could be the culprit. It could also be that I havenít been tightening my sparkplugs enough.. I was always taught to tighten hand tight. Well I found out last night that hand tight meant put a little more arm into it. We are going to clean the head tonight and check everything. I will also pull the cylinders and fix the oil leak. I will keep you updated as we progress.

Johnny


78 Bonneville T140V
Re: T140 compression leak at the spark plug hole. #100982
10/03/06 4:24 pm
10/03/06 4:24 pm
Joined: Oct 2003
Posts: 11,263
North Georgia, USA
RF Whatley Offline
BritBike Forum member
RF Whatley  Offline
BritBike Forum member
Joined: Oct 2003
Posts: 11,263
North Georgia, USA
I believe most shop manuals list a torque setting for sparkplugs. On my Trophy 900 it's 18 ft-lbs. You always fit sparkplugs by hand for the first couple of threads, then tighten.

Glad to hear good news at the end of the story.

bigt


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: T140 compression leak at the spark plug hole. #100983
10/05/06 3:11 pm
10/05/06 3:11 pm
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Johnny-B-Good Offline OP
BritBike Forum member
Johnny-B-Good  Offline OP
BritBike Forum member
Joined: Jul 2006
Posts: 53
Lafayette, Louisiana
Update for Thursday.

We pulled the cylinder block off last night and I was amazed at how shiny the rods were. We left the pistons in the cylinders. They werenít quite as shiny but in good shape.

I spent 3 hours cleaning gasket material off everything especially where the cylinder block sits on the crank case. We are talking razor blades and emery cloth to polish the case. I didnít think I was ever going to get the nod saying thatís good.

I also had the chance to pull the carbs apart and prepared them for a cleaning. I was surprised to see the floats are made of plastic instead of some type of metal. It has been a good learning experience to see everything up close.

I have been reprieved until Monday while Tim sand blast the head and repaints the block. I still donít have an answer on the leaking head but I should have an update for Monday.

Johnny


78 Bonneville T140V

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