Forum

[bigpete]

Hi all. I have oil on my 2003 350 bullet cylinder head. It seems to be coming from the cylinder head nut next to the spark plug I,e coming up the thread. This is the short stud that is screwed into the cylinder barrel. The bike is very clean and so I am sure its not coming from the spark plug thread. does the team think that it may be the head gasket ? The gasket is the compost type fitted about 1200 miles ago Thanks for your thoughts on this Pete

[Winkie]

Sounds silly but firstly check the joint on the rocker oil feed. I had a similar problem which was caused by a slight leak at the rocker feed, with the oil blowing back on to the flat part of the cylinder head near the spark plug. I replaced the oil feed washers and problem solved.

[Tim NZ]

The oil will be passing DOWN one of the cylinder head nuts, the washer under the nut will be buckled/distorted and the seat for the washer in the head will more than likely be damaged to some degree.
A new head gasket and a set of hardened head washer will be needed, when the head nuts are out, their face ends needs to be cleaned with a fine file to ensure they are true and square, and when you fit the new head gasket, a light smear of sealant around the stud holes, (And around the push rod tunnels)
Check/retighten the head nuts after a few miles running.

[PeteF]

Very often leaks in that area are just a mist. If this is so and you can live with it, just leave it until the head needs to come off for other purposes.
If you do replace the head gasket, I found the composite type excellent and, on advice from someone who should know, I didn't bother re-torqueing the head. I used a smear of Wellseal. No problems in several thousand miles.
You really need a torque wrench for this job. The head nuts only need 21ft/lbs and it's horribly easy to pull the studs out of the crankcase if you overdo it.

[pd110961]

yup.. you must re torque the head after a few miles.. I didn't (after a top end rebuild) and it blew the gasket

[jefrs]

Have you checked for oil in the exhaust? Oil shows as glossy on a rag held over the end. If not then it's not getting into the combustion chamber and head gasket is probably ok but does not completely exclude it. Moving parts are the next suspect and Winkie probably got it in one.

[Mickey]

Oft repeated, but cylinder head porosity is not unusual, though more often on 500, seen as a weep near spark plug or de-compressor. Doubt it's your problem however IF it has only been present since gasket change. If minor wouldn't worry too much.
REgards, Mick.

[simon]

Had a similar mystery leak on mine and it turned out to be the oil feeds to the rockers. They only leaked when the bike was hot and then only a weep so the oil would get blown around to a different spot. Soft aluminium washers proved to be the complete cure.

[bigpete]

Thank you all for suggestions but I am convinced it is coming up the stud. if I clean it up it takes three or four miles before it starts running into the spark plug recess ,, I might try a dome nut.If the heads got to come of well so be it I would rather do it now than in spring.The bike is running well after 1200 miles since fitting a hi/com piston alloy cylinder and our hosts competition valve set, golde silencer and amal monobloc carb.I was hoping to spend winter time fitting stainless rims and trying to get the front brake to work. cheers Pete

[jefrs]

Simon, you may be onto something. Aluminium is a peculiar metal, under the right conditions of heat and pressure it can form what is known as a "diffusion bond". This is similar to but not the same as soldering where one metal dissolves into the other. It is difficult to achieve a good mechanical bond and I had little success with it in the lab. None the less, the aluminium washers will deform and probably fuse enough to make a good seal as you used them.