Oil leaking from 3rd fin up on 850 Mk3 head

Mike, there might be other's comments, but I will offer two thoughts on what has worked for me. Yes it is the castings being porous, and with time and age the oil finds its way through at the shortest point being adjacent to the pushrod tunnel at the 3rd fin.

When my RH4 head on my Mk3 started weeping from 'that area' several years ago, I had it sent off for cleaning and vacuum sealer impregnation. I don't know exactly what the sealant was but I am guessing it was part of a commercial casting seal process. That head has been free of any leak since.

On another Commando head we found a leak from exactly the same 3rd fin place. I took the head off, cleaned it in solvent, and then used a leak detector kit to precisely identify the leak point with red dye. This worked and showed the spot deep between the fins. I roughed up the area with a long grinding tool and used a 8mm diameter spot of Devcon high temperature filled epoxy. That repair worked for a year at least, and then the bike went elsewhere and I lost track of any further news.

Norm.

I pretty much agree with what Norman says above as I tried the same as him on 3 cylinder heads, all of which had a crack from the push rod tube to the 3rd find. I tried having one welded by a respected Norton engineer, but he found the aluminium was so impregnated with oil that it could not be welded. I tried the Devcon, but it failed straight away. I tried having it vacuum sealed impregnation, which also didn't work. All this was over a period of 15 years and that leak was driving me mad, ruining the Commando experience, as oil doesn't so much leak, more like pisses out.

My conclusion is that many 850 heads have this crack, and that the problem is crankcase pressure pushing the oil through that damn crack.

So, I found the best way forward is get rid of that crankcase pressure.

If you are sure that your piston/bores, valves/guides are half decent, then the best, cheapest and easiest thing to do is to fit Mikes Yamaha XS650 read valve in the breather from the timing cover.

With a vacuum in the crankcase, air will be pulled from outside the engine through those cracks into the engine. It has worked perfectly for me for many years and also cures many other oil weeps from the engine, like the tacho drive, for about £25. I also felt a slight increase in engine performance as the pistons are now not desending into a pressurised crankcase. I have two friends who have also done this modification with the same results as me.

So, Google Mikes Yamaha XS 650 reed valve, get one, and you can buy me a pint when I see you.

Previously peter_stowe wrote:

I pretty much agree with what Norman says above as I tried the same as him on 3 cylinder heads, all of which had a crack from the push rod tube to the 3rd find. I tried having one welded by a respected Norton engineer, but he found the aluminium was so impregnated with oil that it could not be welded. I tried the Devcon, but it failed straight away. I tried having it vacuum sealed impregnation, which also didn't work. All this was over a period of 15 years and that leak was driving me mad, ruining the Commando experience, as oil doesn't so much leak, more like pisses out.

My conclusion is that many 850 heads have this crack, and that the problem is crankcase pressure pushing the oil through that damn crack.

So, I found the best way forward is get rid of that crankcase pressure.

If you are sure that your piston/bores, valves/guides are half decent, then the best, cheapest and easiest thing to do is to fit Mikes Yamaha XS650 read valve in the breather from the timing cover.

With a vacuum in the crankcase, air will be pulled from outside the engine through those cracks into the engine. It has worked perfectly for me for many years and also cures many other oil weeps from the engine, like the tacho drive, for about £25. I also felt a slight increase in engine performance as the pistons are now not desending into a pressurised crankcase. I have two friends who have also done this modification with the same results as me.

So, Google Mikes Yamaha XS 650 reed valve, get one, and you can buy me a pint when I see you.

This mod worked brilliant on my 850 Mk11a .Still a slight leak Instead of 5.

Hi

I recently had some first class laser welding done on my Norton by EMP Tooling in Havant. Whilst I was there they told me they had repaired a number of leaking Norton heads bythis techniqueand I spoke to a well known Norton engineer who said he had used them.

May be worth a try.

Graham

The XS650 valve is really an exhaust recycle valve, plenty going cheap on eBay with varying pipe configurations so pick the one that suits your breather pipe setup.

Search for EGR valve in motorcycle parts on ebay.

Specifically, a Yamaha 125 EGR valve.

Third fin up is also where any oil leaking from higher up will appear at the front. This can be invisible as it tracks from the rocker spindle covers down inside the casting...or from right at the back if it is from the inlet rocker cover or even the centre nut.

Somehow it seems much more visible when it gets to the front edge.

My first check would be the rocker spindle covers....especially if you've replaced them and they're stainless as they are quite often not truly flat.

RH4 heads don't have to break through / crack. Mine's had several changes of guides etc. and was dry last time I looked...but I have had the odd panic with covers or end plates...

Thank you for the top tip. My MK III 850 had developed some slight weepage from the lower fins on the right side at the front. I fitted the Yam 125 reed valve in the breather line as suggested and it worked like a charm. No more weepage even after a 300 mile run.

Check the top of the nuts in the cylinder head in front of the centre bolt. You will need a little torch to peer in between the fins, you may find the oil leaking up the stud.

Another way of checking where the oil is coming from if you are unsure is to tamp some cotton wool in between the third and fourth fin, having cleaned up the head beforehand. Then go and do 100 miles. On my machine the oil leaking from the crack between the fins did not start to penetrate through the cotton wool for at least this distance. It was clear then where the oil was coming from.

My conclusion is that many 850 heads have this crack, and that the problem is crankcase pressure pushing the oil through that damn crack.

So, I found the best way forward is get rid of that crankcase pressure.

If you are sure that your piston/bores, valves/guides are half decent, then the best, cheapest and easiest thing to do is to fit Mikes Yamaha XS650 read valve in the breather from the timing cover.

With a vacuum in the crankcase, air will be pulled from outside the engine through those cracks into the engine. It has worked perfectly for me for many years and also cures many other oil weeps from the engine, like the tacho drive, for about £25. I also felt a slight increase in engine performance as the pistons are now not desending into a pressurised crankcase. I have two friends who have also done this modification with the same results as me.

So, Google Mikes Yamaha XS 650 reed valve, get one, and you can buy me a pint when I see you.

Hi Peter,

I havebought one of those breather things off a 125 Yam, but notice that the pipe bore is quite small compared to the Norton breather pipe. I may be wrong but I was always under the impression that the larger breather the better ?? I presume that the end of the breather pipe stays connected to the oil tank ? Cheers

Hans Taylor.

The Norton breather needs to cope with 750 or 850 cc's of air which it never does hence the internal pressure as it is 2 way. The Yam valves are 1 way and after the initial start only have to cope with ring blown so can be smaller and work, you can test and find a very small negative pressure inside.

Yes the breather still connects to the oil tank.

Anyone tried one of these?

BSK Speedworks - PCV Valve

Seems to do the same thing, or am I wrong?

Yes same thing, but it does not say what the valve is, on the EGR valves it is a reed valve which is light enough to keep on working well past 7000 rpm, a ball valve will stop moving before 7000 rpm so then stops being a one way valve.

Hi,

The idea of using an XS650 reed valve seems good.........except they do not appear easy to find at the moment. eBay and Google searches have shown differing types; one squarish, with an open, four screw mounting flange (inlet?) and two vee-angled tubes (outlets?), which seems unsuitable to me; one with two offset angled tubes; and one with a rectangular box body, stubby inlet pipe on the long surface and a longer outlet tube at 90 degrees to the inlet on the end of the body. The latter would seem usable, if I could locate one.

Perhaps the benefits of these valves are widely recognised and stocks have dried up?

Any advice on the correct valve to go for and where to find them would be much appreciated.

Regards,

Andy

Widen the search to EGR valve within motorcycle parts on ebay.

Previously mike_steer wrote:

Previously Andy MacKenzie wrote:

Hi,

The idea of using an XS650 reed valve seems good.........except they do not appear easy to find at the moment. eBay and Google searches have shown differing types; one squarish, with an open, four screw mounting flange (inlet?) and two vee-angled tubes (outlets?), which seems unsuitable to me; one with two offset angled tubes; and one with a rectangular box body, stubby inlet pipe on the long surface and a longer outlet tube at 90 degrees to the inlet on the end of the body. The latter would seem usable, if I could locate one.

Perhaps the benefits of these valves are widely recognised and stocks have dried up?

Any advice on the correct valve to go for and where to find them would be much appreciated.

Regards,

Andy

Andy I posted the original thread here. Had a good response as you can see. It came across that this was a sensible modification to help relieve pressure in the crankcases. I also had no luck in getting one on ebay or otherwise in the UK. After countless time searching on-line I was directed to a site in Germany who turned up trumps. Look up XS 650 shop the email address I have is; www.xs650shop.de. I opted for the right angle one. Cost me 36 Euros including tax and packaging. I fitted mine to a Mk3 ES. There is a pre drilled hole in the casing so I fitted it underneath the large plastic airbox in-line on the original breather pipe that goes from the back of the timing crank case to the oil tank. It was fiddly to fit but them again I didn't remove anything to give me a better access. Hope this helps

Seehttps://www.xs650shop.de/en/cylinderhead-cylinder/349/breather-pvc-valve-uni?number=05-0677

Tony

Previously allan_walker wrote:

Specifically, a Yamaha 125 EGR valve.

Hi Allan

I have just got one of these valves and just wanted someone to tell me where the other end of the pipe will go that comes out the other side of the valve and no one has said, but I dont want to put it back into the oil tank where is was going to when I got my MK3 850 so where is the best place for it to go ?

cheers Maurice

The outlet pipe on my MK2a goes back into the oil tank and then a further pipe goes from oil tank into the airbox, MK3 has an oil separator so the routing changed so you should follow this routing even though the oil separator will be doing a lot less work.

Hi John

The thing is that when I got my 850 someone had put the old 750 air box on so the pipe just go`s into the tank from the timing cover outlet is the only thing there is, there is no oil separator like there should be....But I like the way this is now and Dont want to change that set up, the only thing is I got the Yamaha EGRvalve which I was told to get which just has the inlet and outlet but did not want to take it back directly to the tank as before, I have stripped down the engine I found the usual white gunge that gets in the pipe work and then into the oil tank which I dont want, so is there something else I can do with the pipe coming out of the EGR Valve ? someone did say a catch tank but I can not seem to find a nice small and good looking one..any ideas are welcome.

Thanks Maurice

Hi Maurice,

here's a link from Holland Norton Works with photos ofa similarYamaha XS650 PCV valve fitted to a Commando. Open the link and scroll down the page to 'PCV engine breather valve #H14'.

http://www.hollandnortonworks.eu/?lang=EN&page=10

On my 850 MK2 Commando I have a Yamaha XS650 PCV breather connected between the timing cover breather and oil tank.

The oil tank breather which originally was connected to the air filter housing now vents directly to the atmosphere via a rubber hose which exits behind the number plate bracket.

However there is little or no evidence of surplus oil exiting the oil tank breather since I fitted the Yamaha XS650 PCV valve so alternatively you may consider using acatch tank instead. A small 250ml brake fluidcontainer would probably suffice.

BTW

When you say 'EGR', which means exhaust gas recirculation valve I assume you really mean 'PCV'positive crankcase ventilation valve.

Good luck with your project.

Hi Gordon

Well if you look back on this thread that allan saidSpecifically usea Yamaha 125 EGR valve which I think do the same job as a PCV valve as the EGR let flow one way, I had a look at the link but still need to know where the pipe will go from the other side Of the valve.....as I said I don`t want to put it back in to the tank as it just get the gunge and that`s not a good I think to go back into the oil,

I still world like that Idea of a catch tank just need one that is going to do the job but small enough to hide out of the way,

looked on Ebay but a lot of them are to big to fit.

Thanks maurice

The exaust/outlet from my PCV goes into a small shampoo bottle positioned behind the battery. It accumulates a creamy mayonase emulsion which I don't want going back into my oil tank. This oil/water emulsion is the result of combustion water in the piston blow by.

Previous to this conversion my oil would be black within 50 miles of an oil change. It now stays clean for hundreds of miles

Previously maurice_cloud wrote:

I still world like that Idea of a catch tank just need one that is going to do the job but small enough to hide out of the way,

looked on Ebay but a lot of them are to big to fit.

Hi Maurice

I have the XS650 valve fitted inline on the oil tank breather hose, I use a K&N air filter this frees up enough room for a breather catch bottle made from a black plastic PJ1 forkoil bottle to sit out of sight between the Air filter and the battery, a handy feature on this bottle is the opaque measuring strip set in to the side of the bottle makes it easy to keep an eye on the accumulated condensate level. With this setup I have not experienced any emulsion build up in the vicinity of the pcv valve mentioned by others (accessnorton) who have fitted the valve between the engine and the tank. The breather hose is connected in to the neck of the bottle using one of the original steel breather bends, the vent exhausts via a ninety degree hose fitting fixed in to the screw on cap.

Regards

Katherine Scott