Leaky valve covers

Kool_Biker · Jul 7, 2013

I have carefully rebuilt my 1972 750 Commando, and take pride in that it has a pretty clean and oil tight motor.
With one glaring exception: The valve covers. 80% fronts and 20% rear (inlet).
Now I've done all the usual like planing the covers, using new OEM gaskets AND sealant, even using carefully planed aluminium washers to seal the nuts ...
But surely, every single time, on a longish trip, the front covers will leak and cover parts of the head with oil, while the rear will usually weep a bit down its securing nut.
It is not major, it cleans readily but WHY can't I make these covers oil tight? What is it I am missing?
Cheers, Aris

JimC · Jul 7, 2013

Most OEM gaskets are larger than the covers and make for a dam to hold oil at the bottom of the valve cover. Trimming the gasket to size will help stem valve cover leaks.

Kool_Biker · Jul 7, 2013

Thanks for the tip, but I have done this as well, only forgot to mention

Aris

JimC · Jul 7, 2013

Do you have a crankcase breather valve installed?

Flo · Jul 7, 2013

Not sure what you mean by planed, but you can lap the faces on a piece of 240 grit wet & dry emery rested on a piece of glass. You can use a piece of emery held onto a window if you don't have a loose pieces of glass.
I even lap the round face on the rear one that sits under the nut. Place the front covers on the head, without gaskets & see if they rock, if they do, then remove the studs & file away the high spots until they sit properly.

Kool_Biker · Jul 7, 2013

JimC said:
Do you have a crankcase breather valve installed?

Nope!

Kool_Biker · Jul 7, 2013

Flo said:
Not sure what you mean by planed, but you can lap the faces on a piece of 240 grit wet & dry emery rested on a piece of glass. You can use a piece of emery held onto a window if you don't have a loose pieces of glass.
I even lap the round face on the rear one that sits under the nut. Place the front covers on the head, without gaskets & see if they rock, if they do, then remove the studs & file away the high spots until they sit properly.

I now realise I have done ALL things kindly suggested. And somewhere i ma still missing something.
Unless the crankcase breather valve is the answer?

Thanks to all!
Aris

BrianK · Jul 7, 2013

Those orange silicone valve cover gaskets work well. http://www.rockypointcycle.com/p-norton ... -5913.html

ashman · Jul 7, 2013

Could be leaking from the studs, mine did the same but once I sealed the stud and put some sealant in the nuts it stopped the leaking, only a throught.

Ashley

JimC · Jul 7, 2013

Kool_Biker said:
JimC said:

Do you have a crankcase breather valve installed?

Click to expand...

Nope!

There's a pretty good chance if you install a crankcase breather valve your weeping valve covers, as well as any other pesky leaks will stop weeping.

jsouthard · Jul 7, 2013

BrianK said:
Those orange silicone valve cover gaskets work well. http://www.rockypointcycle.com/p-norton ... -5913.html

I use these silicon gasket covers on both of my Nortons. They create a much better seal and are reusable.

DogT · Jul 7, 2013

I used a good amount of silicone on the cover side of the gasket and just a smear on the engine side. Actually, I pretty much glued the gaskets to the covers and I can remove the covers from the engine with the gaskets stuck on the cover and use them again. The other thing as has been said, the studs sometimes leak. I made sure to put silicone on the studs going into the engine, and also on the washers that hold the nut on the cover. It worked for me and mine were pretty leaky with just the gaskets and no sealants.

Kool_Biker · Jul 7, 2013

DogT said:
I used a good amount of silicone on the cover side of the gasket and just a smear on the engine side. Actually, I pretty much glued the gaskets to the covers and I can remove the covers from the engine with the gaskets stuck on the cover and use them again. The other thing as has been said, the studs sometimes leak. I made sure to put silicone on the studs going into the engine, and also on the washers that hold the nut on the cover. It worked for me and mine were pretty leaky with just the gaskets and no sealants.

Hi DogT
When you say you put " ... silicone on the studs going into the engine ..." do you mean you removed the studs, put silicon in the threads, and then re threaded them into the head?
Thanks
Aris

Kool_Biker · Jul 7, 2013

BrianK said:
Those orange silicone valve cover gaskets work well. http://www.rockypointcycle.com/p-norton ... -5913.html

Hiya
Does anyone know where I can get these (or similar) silicone gaskets in the UK and / or the EU?
Thanks
Aris

DogT · Jul 7, 2013

No, I just put some silicone in the stud threads and when it oozed out around the hole, I left some there, but not a lot. Of course you are going to have to de-grease everything so the silicone sticks.

donmeek · Jul 7, 2013

don't know if this would apply to your bike, as I know the MK111 heads are known to be of lessor quality, but on my MK111 I found that the stud holes were actually clear through to the inside of the (exhuast) head. so the oil would work its way up the threads. A little jb weld cured my leakage, as well as the silicone gaskets.

Kool_Biker · Jul 7, 2013

donmeek said:
don't know if this would apply to your bike, as I know the MK111 heads are known to be of lessor quality, but on my MK111 I found that the stud holes were actually clear through to the inside of the (exhuast) head. so the oil would work its way up the threads. A little jb weld cured my leakage, as well as the silicone gaskets.

Good point, definitely worth pursuing. Thanks

1up3down · Jul 7, 2013

get a Dorman 80190 Power Brake Check Valve

it is very cheap and install it in your breather about a foot away from the backside of the timing cover

the breather goes over the big part and then your line to the oil tank goes over the little part so make sure you get the direction flow right

this reduces crankcase pressure as it let it out but not back in, and stops dead almost very minor leak

call a auto parts store for that part or google it online and buy a couple, I put a new on in every year

JimC · Jul 7, 2013

The XS reed type PCV valve does a lot better job and is nearly as cheap, $18. It's an inline installation, as well. Better yet is the CNW valve or Jim Comstock's valve. I tried the brake vacuum check valve, but it didn't work very long, if it worked at all.

Torontonian · Jul 7, 2013

Just to add a thing to the list accumulating here ,overtightening the nuts to stop leakage warps the covers then things will get worse not better. Torque values are important here whatever they are. You absolutely need a reed type crankcase breather installed.

Leaky valve covers

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