Topic: leak around spark plug!!! HEEEELP!!!

[cben750f0]

well here goes, was setting up the carbs for the pod filters i am running, got everything back together, hit the starter(but forgot to hit the kill switch), and the motor turned over, (but didnt fire)... and there was a distinct SSHHHHHH, comming from the front of the motor.

    so left the kill switch off, and turned the motor  over slowly by hand...SSSSSSSHHHHHHH, thought i have a leaking valve there... so pulled the timing cover off , and checked witch cylinders were responsible for the sssshhhhhh

   cyl 2-3... ok... now which on...... turn it over... number two....

pull the valve covers off... check that there is clearance on the rocker arms.... yep they move...

ok.... which valve then..... pull the carbs ... and the exhaust..... get my g/f bros, to turn over by hand... not comming from the back(intake)...  comming from the front... but not the exhaust......

    pull the horn off so i can see the spark plug.... spray dishwashing liquid on to spark plug... get assistant to turn motor over..... BLOODY "ELLL   there is heeaaaaps of air comming out past the spark plug..... remove plug.. and it looks like it has been helicoiled, but on the piss, so the plug doesnt seat properly,is there anyway that anyone can point out that would be able to straighten the plug without removing the engine...(i know i am being lazy, but i dont have any other transport)... i wondered why it felt a bit flat.... any ideas... suggestions...help please....

[Tim.]

I don't have any good suggestions for you, but I'm curious to know how you pulled off the valve cover without removing the engine?  This is your 750F?

[mcpuffett]

hi ben ,are you sure your plug is going all the way in? i had an issue with one of my inner plugs that i did'nt find until i had the head off to put a new cam chain in ,one of the inner plugs had not been tightened fully down in it's hole so carbon had built up in the hole and you could only tighten down till you hit it ,once the head was off and it was noticed it was easily sorted ,just a thought?    mick.

[kaysystems]

After my CB750 K0 was helicoiled I had the same problem. Looked like the tool had tapered the plug seat instead of leaving it flat.

So you either take the head to a machine shop, or do like I did and make a sleeve hat fits neatly in the bore for the plugs and supports a 17mm end mill. Some VERY careful hand turning of the end mill & I'm runnin' smooth.


Yea I know it's a bodge, but I'll get it cleaned up in a machine shop when the head comes off in the winter.
At least it worked.

David
 

[MRieck]

 Sorry to read of your problem. As mentioned, facing the area around the plug with an end mill is about the only thing I can think. I guess you wouldn't be lying to the wife if you say you really do need a new (ported) head. 

[cben750f0]

tintin, the valve covers i refer to are the ones you adjust the valves threw...everyone else thanks for the time... i dunno what i am gonna do... will talk to my mechanic tomorrow and see what he has to say...MRieck, you are right i wouldnt be a lie, my only dramma now is trying to get a head, and then haveing the money to get the work done...thanks all

[TwoTired]

If I understand this correctly, you have a helicoil insert that was installed crooked?  And this doesn't allow the spark plug to seat?
New spark plugs come with a compression gasket that deforms with use ( ie. gets pretty flat), especially when overtorqued.  Would a new spark plug gasket have enough compliance to make the seal?  I suggest you use a torque wrench set for 11 ft Lb. so as not to overcompress the gasket.

Might get you going again...

Cheers,

[cben750f0]

the funny thing is , the bike runs great... and you cant actually hear the noise when its running, you know when you have  an exhaust leak you get a very definate noise, well there is non of that... i only noticed it wheni had the kill switch off and turned it over... so i dont know how long it has been doing this for?.... i had noticed when i changed plugs that the threads were black, and that sometimes even the crush washer had a little black, not alot, but just put it down to not tightening it enough, will give a new plug a try and see if that helps, might also see my local machine shop and see if i can get a soft aloy washer made just to get me out of trouble till i cn get the head repaired....peace

[Quail "Owner of the comfortable k8"]

I would just stack 2 spark plug gaskets and torque it down until you could fix it right.

[cben750f0]

yeah thought of that, but have you ever tried to get those washers off!!!!... would be quicker for a machine shop to make one.. ... yeah am gonna have another try, my mechanic here has so much SOHC stuff that he has shelves of barrels,heads,cases... will see what he wants for a good bar head, and put my valves and  cam and  stuff on it, it will be a weekend job, start fri night, and hopefully have it back together by sun night....will find out monday if i can get a head...its just a pain, if i hadnt turned the motor over, how long would it have gone on for, ??.... NEway will keep ya's posted, thanks for the replies... peace

[dpen]

In my area of Oz (beautiful Central Coast NSW) there's a bloke who goes around doing mobile thread repairs. We've used him at the workshop so we don't have to pull a head to fix some fools' weekend work. This man is good! Check with your local mechanics & engineering shops for someone like this in your area.

[Tim.]

What about aluminum welding?  Chundy had a broken area on his head where the exhaust brackets bolt into it.  One of the holes was broken.  They built it up with new aluminum and then drilled/tapped/helicoiled it.

While this is more precise an operation, couldn't a decent shop basically fill in the old hole with new aluminum and then drill and tap a brand new hole for your plug?

This would be a longer term fix of course.  For now I'd agree with those suggesting you band-aid it with another washer (copper might be a good choice).

I can't imagine you're doing any permanent damage by riding it as-is.  Certainly your compression would be lower in that cylinder, but it shouldn't be hurting anything.

[kghost]

I sort of think all the answers above have some merit.

I would agree that carbon can keep the plug from fully seating.  Its really easy to screw up a helicoil installation in an aluminum head. But even if its done crooked it chould still work.

Why don't you try running a thread cleaner down the hole and reinstalling the plug?

Would recommend careful prudence when doing it but if it goes all the way with minimal force your problem might be solved. the spark plug seats do tend to get deformed by overtorqueing the plugs.

Would also recommend a dab of anti-sieze on all plug threads when reinstalling.

[cben750f0]

have got a mirror into the aream, and there is a big piece broken out of the seat that the plug screws into...   went and got some sump plug washers from the honda dealer, and litle tightened... leaked... so tightened heaps...  there was a big difference... but still leaking,   have got onto a bare head, have ordered a 836 head gasket, and valve stem seals,rocker box gasket... if they all turn up b4 the week end will pull the motor friday night, and hopefully have it back together by sunday night.....then i will repair the original head, and wrap it up for later....am a bit bummed, but you get that i s'pose.... will keep you posted... peace

[mutters]

cben, 
I know of this guru you refer to.
just moved from your town last year to the cold country.
I can guarantee he will have a solution to your problem but it will require lots of beer.
cheers jeff.

[cben750f0]

g'day mate, you know AL... he has everything, and is willing to give me a hand to get it done this week end. all i have to do is get all the parts together, and then a big week end of spanner fun.... BTW if you ever want to get out of town on the bike let me know... i take the CB out all, the time.... PM me if you wanna catch up with another CB owner... cheers

[cben750f0]

NEway, i am resigned to the fact that i am changing a head on the week end, have got one, it is bare but that is ok, will swap my cam and towers over to the other head, i am going to paint the head while i have it, and bake the paint in the oven, while my missus is at work, will also heat proof  clear coat the other rocker cover i have just finished polishing... will get all the parts friday, so will start pulling it appart thursday... here is a pic  i have photo shoped, of what i want to do with the rocker cover... thought it would look good...peace