Sealing Valve guide bores

pommie john · Jun 5, 2014

I've been chasing a plug fouling problem for a while thinking it was over rich, but I'm thinking now it is burning a little oil. Not enough to make it smoke much, but just enough to soot the plugs.

I had a look down the inlet ports and this is what I saw. A drop of oil on the guide.
Now, if it were coming down the valve stem, I don't think it would sit there on the end of the guide. It would drop onto the valve head. So I'm thinking it is coming around the outside of the guide.
I really don't want to use a bigger oversize guide, they are at least 10 thou over already and I paid a reputable machine shop good money to replace the guides very recently.

What do you guys think is a good fix for this without fitting even bigger oversize guides?

Refit with loctite? High temp silicone? Something else?
Thanks
John

Rohan · Jun 5, 2014

There are grades of some loctites that will "wick into small spaces" for applications like this.
Whether this is one of them you need to investigate. ?

Also check the valve guide seal atop the inlet valve.
I once had one that didn't stay sitting correctly there, and caused a little oil burning, in a new engine like you say.

pommie john · Jun 5, 2014

Rohan said:
There are grades of some loctites that will "wick into small spaces" for applications like this.
Whether this is one of them you need to investigate. ?

Also check the valve guide seal atop the inlet valve.
I once had one that didn't stay sitting correctly there, and caused a little oil burning, in a new engine like you say.

It had come off but I stuck it back on with high temp silicone last week

It may have come off again, you can't see with the valve spring in place.

The head's coming off tomorrow. I want to cover all bases when I put it back together so if I can seal between the guide and its bore, I'll be happy.

Stillreel · Jun 5, 2014

I'm pretty sure those guides are press fit in to the head and therefore there would be zero clearance for oil seepage (I'm dealing with exactly the same issue). I'm thinking its the valve/valve guide clearance to great due to wear. But the weird thing is that I only get the blue cloud of smoke occasionally; as if the position of the valves at shut down allow x amount of oil into the cylinder.

PITA. My next move to new AMALS to see if that resolves the fouling plugs.

BC

pommie john · Jun 5, 2014

Stillreel said:
I'm pretty sure those guides are press fit in to the head and therefore there would be zero clearance for oil seepage (I'm dealing with exactly the same issue). I'm thinking its the valve/valve guide clearance to great due to wear. But the weird thing is that I only get the blue cloud of smoke occasionally; as if the position of the valves at shut down allow x amount of oil into the cylinder.

PITA. My next move to new AMALS to see if that resolves the fouling plugs.

BC

I've read of several cases where the guide bore is damaged by poor installation of the guides. This can score the bores and allow oil down past them.
The guides, valves and seals are brand new on my engine. I don't think it's guide wear.

Stillreel · Jun 5, 2014

The locktite is certainly worth a try. How are your carbs? Any chance that the rich running is a carb issue? Are you running Boyer? The 750 is pulling really well except I have to clean the plugs every 50 miles and the smoke on start up is a little humbling. There is however a stammer between 2000 and 2700 rpm.

BC

pommie john · Jun 5, 2014

Stillreel said:
The locktite is certainly worth a try. How are your carbs? Any chance that the rich running is a carb issue? Are you running Boyer? The 750 is pulling really well except I have to clean the plugs every 50 miles and the smoke on start up is a little humbling. There is however a stammer between 2000 and 2700 rpm.

BC

I've been through everything in the carbs even replacing them with dellortos. Same problem all the time.

kerinorton · Jun 5, 2014

You mention the plugs fouling. Oil contamination on plugs is usually like an ash deposit, although if it is really bad, then they will wet up as well. Modern lead free fuels always tend to make the plug look sooty.
I don't have valve stem seals on either of my 750 or 850. don't have that problem either. I once had a problem fouling up that was caused by bad connections at the Boyer pickup.s

pommie john · Jun 6, 2014

kerinorton said:
You mention the plugs fouling. Oil contamination on plugs is usually like an ash deposit, although if it is really bad, then they will wet up as well. Modern lead free fuels always tend to make the plug look sooty.
I don't have valve stem seals on either of my 750 or 850. don't have that problem either. I once had a problem fouling up that was caused by bad connections at the Boyer pickup.s

I've checked the Boyer pickups impedance at 128 ohms. That was right up where they connect to the box. Also with a strobe it advances smoothly to full advance. I contacted Boyer who were very helpful and prompt. They reckon oil fouling is most likely.

The fact that there's oil dripping down the valve guide is what I'm looking to fix at the moment.

On a fresh set of plugs, it starts first or second kick, pulls cleanly from low rpm to flat out, but within a dozen miles it's fouling the plugs.

Any attempt to lean the mixture makes it run worse.

toppy · Jun 6, 2014

If there is oil on the guides that would seem to be the problem. You could try a different grade of oil but have you contacted the firm that fitted them to see if they are prepared to do something about it.
While the head is off place it at suitable angle so you can poor diesel or some kind of dye in an have it pool around the guide. Then leave it to see if it leaks through, this may not work if the head needs to be hot for the hole to open but if dye flows through when it's cold then it proves the problem an may help prove any repair is successful.

pommie john · Jun 6, 2014

Here a shot of the other guide. You can see where aluminium has been dragged down when the guide was fitted.

i think that tells me all I need to know about the quality of workmanship when the guides were fitted.

pommie john · Jun 6, 2014

toppy said:
If there is oil on the guides that would seem to be the problem. You could try a different grade of oil but have you contacted the firm that fitted them to see if they are prepared to do something about it.
While the head is off place it at suitable angle so you can poor diesel or some kind of dye in an have it pool around the guide. Then leave it to see if it leaks through, this may not work if the head needs to be hot for the hole to open but if dye flows through when it's cold then it proves the problem an may help prove any repair is successful.

Good plan. The head's coming off tomorrow, so I'll try that.

Stillreel · Jun 6, 2014

Please keep us posted as to your progress. As mentioned, I'm dealing with exactly the same issues and following the same resolution path that you're taking.

That said; I still can't get my head around your theory of oil seeping through a press fit. Even if the aluminum is scored, as the photos indicate, it would still result in metal to metal contact rather than a void that the oil would seep down. I used to press fit alum. guides into Honda generator heads for a living and there's no way oil would get between the guide and the head interference fit. It seems more likely to me that the oil would seep down the valve stem. Check the clearance there while you are at it.

It may well be these old bikes are just leaky that way but its a problem; fouling plugs after less than 50 miles.

Good luck.

BC

batrider · Jun 6, 2014

Very common for oil to get sucked down the outside of the guide on a Norton, especially at idle (high vacuum). Do you notice any smoking at idle and when you back off the throttle? On my bike you could smell it.

The machine shop has to know what they are doing with Norton heads.

Torontonian · Jun 6, 2014

Probably the inlet valve guide seals. Once put my head into a reputable shop ( you can easily guess which city..) , mild smoking ,pulled head to find NO seals ! Found several teenageres doing work to learn owner had teamed up with a college and a gov't apprenticeship program. Next time HE does the work only. :!:

Matt Spencer · Jun 6, 2014

Shows it being lubed .

if it were after say two hours from shutdown , it could draindown & form a drop , if it were there ( twixt stem & guide ) perhaps .

Otherwise it sounds like your rideing to slow . :lol: actually , someone who never wound it out could go a grade warmer on plugs , one who never didnt a grade harder .

john robert bould · Jun 6, 2014

Change the seals for the steel ford cosworth type, stock soft rubber are iffy. you will need to machine the guide top to fit them.

Torontonian said:
Probably the inlet valve guide seals. Once put my head into a reputable shop ( you can easily guess which city..) , mild smoking ,pulled head to find NO seals ! Found several teenageres doing work to learn owner had teamed up with a college and a gov't apprenticeship program. Next time HE does the work only. :!:

Cheesy · Jun 6, 2014

While the head is off it would probably pay to check that the oil drain hole in the head/barrel is not blocked as well

pommie john · Jun 6, 2014

Cheesy said:
While the head is off it would probably pay to check that the oil drain hole in the head/barrel is not blocked as well

Done that already with the engine in situ. I poured oil round the valves and took off the timing cover so I could see it coming out . I don't use silicone on the head gasket which is the main cause of blocking that hole.

Anyway. I've just got out of bed and my first task this morning will be to remove the head.

Expect photos later today

pommie john · Jun 6, 2014

OK, the head's off and I found a couple of things. There was some oil on top of the pistons. Maybe that got there while the head was coming off, out of pushrod tubes perhaps.

The exhaust guides are clearly leaking oil quite badly. From the way it's lying it seems to be coming around the outside , between the guide and the head rather than down the valve stem.

From yesterday's photo it seems the inlet guides are doing the same so I need to deal with all four guides.

The question is, how to proceed. I guess I'll have to remove the guides, a friend has offered to machine an o ring groove under the guide's flange which seems a reasonable and not too expensive option.

Any expert opinions would be welcome

Thanks
John

Sealing Valve guide bores

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