Topic: Oil leak advice needed for CB400f

[kajtek]

Hi guys,

I have a persistant oil leak on the left side of the head. the oil is above the head gasket, but not quite reaching the cam cover, a little in the plug hole, then all the way down the fins to the stator cover, then my foot... only leaks when the engine is fully warm and riding harder, revs past 6k (which is most of the time obviously!!)

Doing some reading i understand that if the oil is leaking above the head gasket line it is unlikely to be the gasket? Note that the cam cover gasket has been replaced, and no sign of leakage from there.

Im prety certain of where its coming from though. when i had the cam cover off working on the cam chain/tensioner etc, i realised that one of the head nuts had undone itself while i unscrewed one of the cam cover bolts that thread in to that head nut; after i put it back together and started it and oil poured out of bolt hole... i didnt think much of it and just torqued it back up to specs and left it. after that i didnt notice any leaking but it seems to have come back (albeit a much slower leak..)

My instinct is to open it up and retorque, but i think there was some sort of sealing washer underneath the nut?? maybe this needs replacing too?

Any advice or experience greatly appreciated.

Also, if i undo that particular nut, should i be undoing all the head nuts in the correct sequence then re torquing them? should i consider a higher torque (20nm) to reduce the risk of leaking?

many thanks for any info

Ashley

[trueblue]

A retorque on the head gasket won't hurt. With a head gasket leak you can find the oil slightly above the gasket line. The wind while riding can push it uphill.

[vames]

Watching this. My leak seems to be exactly where yours is. A few years ago I replaced a bunch of copper sealing washers that go under the head nuts. Still the fins around there are wet after I've been riding a while.

Seems like a lot of 400f guys have a leak in the upper left side of the motor. Any intel about fixing them is appreciated.

http://forums.sohc4.net/index.php?topic=86829.msg977929#msg977929

[HondanutRider]

I believe both the 350 Four and the 400 Four have the same head design on both the left and right sides, in that they have oil passages running up the cylinders to spay oil for the head.  These passages have nozzles with o-ring washers sealing them at the head gasket.  These washers tend to either be the wrong size (when replaced) or old and shrunken from age.  Since the oil is under a lot of pressure here due to the nozzles, they tend to leak.

Other people on this forum have documented means of sealing when replacing the head gasket and these washers.  I believe one approach was to coat carefully with copper gasket seal.

[Tim2005]

The head nuts you refer to " head nuts had undone itself while i unscrewed one of the cam cover bolts that thread in to that head nut", with the internal 6mm  thread on top,  have special sealing washers under them, pt no 90442 377 000  - they are a metal washer with a rubber washer in the cenntre of them.

Here's a photo  http://www.cmsnl.com/products/washer-seal_90442377000/

[kajtek]

Thanks for replies, and thanks Tim for the part number.

For now I will give it a go replacing the washers and see what difference it makes.

just to be clear, the head has never been off so original gaskets etc. Can i still retorque all the head bolts?

Has anyone upped the torque to cure a leak? what torques did you use?

many thanks

Ashley

[kajtek]

So, checking the parts fiche there are 2 rubber and 10 copper washers for the head nuts, if i plan to retorque all shall i also replace the copper washers? (im guessing its a crush type washer..)

Im wondering, as im opening it up, shall i just bite the bullet and replace the head gaskets, rubber seals and o-rings? I dont have a workshop so everything would be done at a friends place, which limits my time to around 6 hours ride in ride out... is this doable? should i also lap the valves while im in there or anything else?

I see how this can quickly get out of hand.. next i convince myself i need a 466kit haha

many thanks for any advice

Ashley

[vames]

Im wondering, as im opening it up, shall i just bite the bullet and replace the head gaskets, rubber seals and o-rings? I dont have a workshop so everything would be done at a friends place, which limits my time to around 6 hours ride in ride out... is this doable? should i also lap the valves while im in there or anything else?

I'm in the same place. Tried all the easy stuff -- the copper crush washers, the rubber/metal washers, re-torque all the head bolts. It has to be the o-rings in the head gasket. Just went for a ride yesterday. It's really not a lot of oil but I do have to wipe it down when I park it.

Couple of questions:

1) I've got great compression/no oil burn. Can I pull the head without pulling the block? Will the base gasket stay intact and not start to leak?

2) Are there any components of the cam chain tensioner that can be replaced if I have the head off? It's not bad, but it does make a little noise like every ones does -- especially before it gets warm.

3) If I have the head off, should I have the valves done?

[kajtek]

Vames, after some thought im gonna try the retorque first. If it doesnt change anything i will hold out till winter n do the top end properly, checking rings, bore, valves etc. Dont have the cash to blow at the moment! All the little bits you need add up to a considerable cost, makes owning a single seem much more reasonable...

I will try get a pic of my leak tonight,

Ashley

[Dave Voss]

My CB550 also leaks as you describe, not very bad, but enough at higher rpms and road speeds to be messy and ruin the bottom few inches of whatever pants I'm wearing.  I re-torqued the head nuts, replaced the valve cover gasket, the oil pucks inside, and all eight valve adjustment cap O-rings, but it still leaks.

I'm pretty sure the source is the head gasket O-rings around the pressurized oil passages, sometime this summer I'm going to dismantle and reseal the entire top end, but in the meantime I've just been putting up with the leak, and tucking my pant legs into my riding boots (the oil spatter wipes right off...).

[kajtek]

Couple of pics of the extent of my leaking..

[trueblue]

That looks to me like it is coming from the rocker box gasket.  Mind you it is a little difficult to see from over 10,000 miles away

[iron_worker]

I'd have to agree with true blue but not the greatest pic.

IW

[kajtek]

Thanks for the advice, and sorry for the pics! Done with my phone while wearing stiff leathers and after a long ride...

[Vinhead1957]

You might want to power wash the area, then use a leaf blower to dry the area.    Start the engine and use the talcum powder to isolate the source

[calj737]

You should NEVER increase the torque above manufacturer's specs. If you do, you run the very real risk of shearing bolts in the cases, in the head, or other areas of the engine. Side cover bolts are 6mm and the maximum torque is about 8#. Re-torquing to spec is certainly a good practice, especially on a head with an original gasket. But if you remove the head, you may be required to replace the gasket.

If a seal or washer has failed, more torque won't solve the problem. Strong minds persevere over strong backs where machinery comes into play... Don't be a ham-fisted Previous Owner that we disparage in the future should you ever sell the bike! Fix it properly, the first time, and never look back.

[Jayelwin]

I'm not the Original poster. My leak was coming from the underside of the gasket where the stator cover is on. It's not the original one, it's an eBay shiny polished one. I'm happy with my screw torque and feel it's at spec.  I have a few oil drops on the floor every day. I've always experienced gaskets to really make a good seal over time from heat (we've all scraped them off, right?). And I have not run this bike at all as its still a build.

[trueblue]

I'm not the Original poster. My leak was coming from the underside of the gasket where the stator cover is on. It's not the original one, it's an eBay shiny polished one. I'm happy with my screw torque and feel it's at spec.  I have a few oil drops on the floor every day. I've always experienced gaskets to really make a good seal over time from heat (we've all scraped them off, right?). And I have not run this bike at all as its still a build.

Gaskets don't take up.  If it is leaking now, it will always leak.  What you say is true to a point, that the gaskets grip harder after they have been in place for a while, but they won't fix themselves.  I'm sorry to say it, with machinary there is no such thing as faith healing.

[chewbacca5000]

I am not a 400f expert, but everything I have read indicates that you need to have perfectly flat mating surfaces where the head and cylinders meet also where the head meet the valve cover.  Alot of 750 guys will resurface the heads and / or cylinders to be perfectly flat then resemble with HD studs.