Oil leak from head

chiefdeal · May 27, 2009

Put my cylinder head back on yesterday. Bike started 3rd kick. Running a wee bit eratic but wasn't too concernes as I thought it may need a little fine tuning after new guides were fitted. After about 5 mins running (fast tickover with the occasional blip) oil started to drip from the front of the head between the exhausts. This is not coming from the head gasket but from 2 or 3 fins above. I wonder if I've cracked the head (whilst trying to fit new guides) or if the guides aren't seated properly or if I may have needed oversize guides? I took out the front head bolts 1 at a time to check & then re-torqued them. Needless to say I'm a bit frustrated after all the time & effort i've put into this. Any suggestions. I know I'll have to bite the bullet and pull the head again.

Seeley920 · May 27, 2009

It might be worth checking the studs at the front (the ones that come up from the barrel) Sometimes they break through into the pushrod tunnels and oil can weep up through the stud holes.

JimC · May 27, 2009

It's not uncommon for the Commando head to leak such as you described. The problem is usually the 5/16" studs. Oil seems to wick up on them. A fix is to seal the stud threads in the cylinder and a sparing application of sealant on the head gasket around the area of the studs. But first, make sure the head is flat.

I had exactly the same problem you described. Convinced I had a porous head, I pressure checked the head. I put a Schrader valve in a exhaust valve cover and bolted a plate sealed with RTV to the head mating surface. I heated the head an filled the oil chambers with Marvel Mystery oil and pressurized it to 30 psi. I found the only place it leaked was around the stud holes.

cNw · May 27, 2009

Chiefdeal,

Double check the overhead oil line crush washers. If they arent sealing properly the oil, that is very hard to see when clean, will seep down inside, forward, through the head and escape at the third fin from the bottom.

Matt / Colorado Norton Works

chiefdeal · May 27, 2009

Thanks once again for all your replys. CNW, do you mean the banjo bolt washers from the rocker feed?. I took the head off and noticed some debris (particles of sand) beneath the two front headbolt washers (I blasted everything with compressed air but my garage gets covered in sand being on a seaside golf course) where so even when torqued up maybae the bolts still weren't sealing? Another thing is that on the side that was particularly lumpy, the combustion chamber has already started to soot up. Is this a duff guiude or a sticky valve? Thanks for your patience but you've got to start somewhere!

cNw · May 27, 2009

Yes, those washers are sometimes hard to seal. We always use a new washer (they should not be re-used) and also put a thin coat of Permatex #2 (non hardening) on all contact surfaces. Of course be careful when you tighten those bolts as the threads in the head cant take to much torque. Also re-tighten when warmed up.

Matt / Colorado Norton Works

79x100 · May 27, 2009

It is a favourite leak. Also check the rocker spindle end plates and the inlet rocker cover, including centre fixing.

Any oil from high up on the head will find its way down to the front, three fins up. Even if you're riding at 100 mph, the oil will still run forwards (before it blows back all over you

)

Cookie · May 27, 2009

Permatex may be old school but it is still hard to beat in some applications.

cNw · May 27, 2009

Cookie said:
Permatex may be old school but it is still hard to beat in some applications.

Old Scool ?

We have used this Permatex #2 Non Hardening (this is not a Silicone) in this application and have had a lot of luck with it since it allows for a re tighten with out breaking the seal. The crushwashers just dont to do the job very well by themselves.

Matt / Colorado Norton Works

swooshdave · May 27, 2009

Is Permatex #2 similar to Yamabond or Threebond?

cNw · May 27, 2009

swooshdave said:
Is Permatex #2 similar to Yamabond or Threebond?

Its a really sticky, pliable sealer. Little bit goes a long way. It doesnt break down with oil or fuel. It will not act like a glue like the Yamabond does. I have no experience with Threebond, so I cant tell you how it compares to that.

Matt / Colorado Norton Works

Cookie · May 27, 2009

Permatex makes lots of products now but 30 years ago when I was trained it was all we had. It went into aircraft use in WW2 and it was WW2 guys who trained me. There are some things that it is hard to beat on like gas fittings an diesel equipment, very resistant to fuel and oil.
#2 is hard to clean up for reuse but it sure does seal.
I recently tried their newer product called the "Right Stuff" to seal a damaged BMW read end together. Even with bad sealing surfaces that did the job. GM uses it to glue down rocker covers with no gasket or other sealers.

maylar · May 27, 2009

My favorite Permatex sealer is a rattle can aerosol spray called High Tack. Spray those paper gaskets and metal plates at the rocker feeds and they stay stuck.

JimC · May 27, 2009

It went into aircraft use in WW2 and it was WW2 guys who trained me.

Fred Eaton of Old Britts must of went to the same school. He recommends Gasgacinch for the tunnel area on the head gasket. I believe Gasgacinch has been around for over fifty years.

slupdawg · May 27, 2009

I've got a small leak from around the tachdrive housing where it meets the case and puddles in the little indent is right behind the fitting. I've tried tightening it down with no success. Would it be advisable to use permatex #2 to try and seal the leak even though there is a gasket (albeit a non-sealing one) already there? Since it doesn't harden up, I don't see the harm it could cause?

chiefdeal · May 28, 2009

Took the valves out this morning. The inlet valve is really rocky in the guide ( which I think was the one that I had trouble fitting & a friend reamed out the guide) which must have let a lot of oil through. This surprises me as there was zero smoke coming from the exhausts when I ran it. I imagine all this oil would have to go somewhere so would find the easiest escape in the combustion chamber?

Scruff · May 29, 2009

I had the same problem with oil dripping at that location. Removed the head to check if the new valve guides had cracked the head on fitting as it appeared the oil was coming from below the tappet end covers at a flaw in the head. Was suggested by ( cant remember who) to use baby powder to trace the new engine oil track as it is hard to locate when fresh and clean. Vave gear end plates were the problem even with new gaskets and copper washers. Permatex solved the problem and no leakes since.
Ian

chiefdeal · May 29, 2009

I've been told by norvil to do the baby powder check. Anyway when I examined the head, I noticed that there was a small dent creating a raised lump just in front of the right hand side pushrod tunnel. This must have happened during reassembly whilst trying to get the pushrods in. This is definately the cause of the leak. I have scrapped the lump down & rubbed the head with valve lapping paste on a thick pane of glass. Its now as flat as a pancake. Just waiting on parts for re-assembly now. Fingers crossed!

Oil leak from head

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