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?
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...
51' Thunderbird project 48 Speed Twin project. 85' BMW K100RT and sidecar.
#100972 - 09/28/062:46 pmRe: T140 compression leak at the spark plug hole.
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
#100973 - 09/28/064:46 pmRe: T140 compression leak at the spark plug hole.
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.
#100977 - 09/29/0611:13 pmRe: T140 compression leak at the spark plug hole.
Joined: Oct 2004 Posts: 4,429Tiger
BritBike Forum member
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.
Don't hide 'em, Ride 'em !!
RF Whatley Cornelia, GA
"Shop Boy" at Rodi British Bikes
#100979 - 09/30/065:13 pmRe: T140 compression leak at the spark plug hole.
Joined: Jun 2004 Posts: 411tomterrific
BritBike Forum member
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.
#100980 - 09/30/066:40 pmRe: T140 compression leak at the spark plug hole.
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.
78 Bonneville T140V
#100982 - 10/03/064:24 pmRe: T140 compression leak at the spark plug hole.
Joined: Oct 2003 Posts: 11,108RF Whatley
BritBike Forum member
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.