Exhaust Valve Guide Seal Question

Britstuff · Nov 9, 2023

Hi:

It would seem that inlet valve guide seals are in place to stop oil being sucked down the guides into the combustion chambers. The question I have is can oil travel DOWN the exhaust valves guides, (via suction, gravity or whatever) to the combustion chambers, or out the exhaust and cause the dreaded Commando white smoke?? Conventional wisdom being that upwards pressure of exhaust gases would prevent such from happening??

The reason I am asking is as follows:

I have a 1974 Commando 850. Recent re-bore and hone with +.020 pistons and rings and rebuilt head with new valves and guides etc. So far have about 100 miles on it. The left hand side cylinder has started to smoke, spark plug is fouled with oil. Right side appears to be fine with a nice brown spark plug tip. I do not use the side stand, and I have an oil tap in place to prevent sumping, (both of which it seems can lead to smoking).

I recently removed the head to see if I could work out what is going on. I thought maybe a wrist pin circlip had come loose and damaged the bore, but no, the bore looks fine. Inlet valves are very clean, inlet valve stem seals are apparently still in place and doing their job. Exhaust ports are oil fouled. I removed the exhaust valves to check for wear etc, both are tight but the shafts were surprisingly oily. No exhaust valve stem seals are currently fitted, (as standard).

Presumably either my piston rings have not bedded in properly, and or oil is running DOWN the exhaust valve guides. Trying to find out if anyone has seen oil fouling caused by oil migrating DOWN the exhaust valve guides.

Thank you,

Kind Regards,

James

Tokay · Nov 9, 2023

The rocker spindles were / are correctly aligned ?

Britstuff · Nov 9, 2023

Yes, rocker spindles correctly aligned / flats are orientated correctly etc. I ran the bike with valve covers off so I could observe oil flow to the head.

kommando · Nov 9, 2023

Are you sure the inlet guides are not leaking around the OD in the head bore, pour some acetone or similar very thin liquid around the guide and see if it appears in the inlet throat. The 73 and 75 heads are very prone to this, 74 less so.

htown16 · Nov 9, 2023

When the old exhaust valve guides were removed possibly the guide bore was scored. As above check with some acetone.

Fast Eddie · Nov 9, 2023

Poor quality piston rings and / or rings fitted upside down are other possible (IMO likely) causes.

baz · Nov 9, 2023

I once had similar
It turned out to be one end of an oil control ring expander was missing
So the oil control rings were not doing there job
Also
You can isolate rocker feed to the head by blocking off the feed pipe to see if it clears up
The valve gear needs minimal oil a couple of miles without feed I guess would be fine for a test
I know lots of people used to do this
I just don't know how long it's safe for? Anyone know?

Britstuff · Nov 9, 2023

I have a feeling the problem may be poor quality piston rings. Previous owner did cut the oil control rings short and the bike made a huge amount of smoke! Thought I had fixed that with the new rings, but perhaps not. If I replace them again I think I am going to go with some pistons and rings from Jim Schmidt. I did so in the past for my dominator and they work great.

Right now I just want to try to eliminate the possibility the issue is with the exhaust valves. Inlet valves are definitely not leaking. I should have tried Baz's suggestion to cut of the head supply for a short while. Oh well, we live and we do not learn!

I think I will experiment with acetone as suggested.

marshg246 · Nov 9, 2023

Britstuff said:
Hi:

It would seem that inlet valve guide seals are in place to stop oil being sucked down the guides into the combustion chambers. The question I have is can oil travel DOWN the exhaust valves guides, (via suction, gravity or whatever) to the combustion chambers, or out the exhaust and cause the dreaded Commando white smoke?? Conventional wisdom being that upwards pressure of exhaust gases would prevent such from happening??

The reason I am asking is as follows:

I have a 1974 Commando 850. Recent re-bore and hone with +.020 pistons and rings and rebuilt head with new valves and guides etc. So far have about 100 miles on it. The left hand side cylinder has started to smoke, spark plug is fouled with oil. Right side appears to be fine with a nice brown spark plug tip. I do not use the side stand, and I have an oil tap in place to prevent sumping, (both of which it seems can lead to smoking).

I recently removed the head to see if I could work out what is going on. I thought maybe a wrist pin circlip had come loose and damaged the bore, but no, the bore looks fine. Inlet valves are very clean, inlet valve stem seals are apparently still in place and doing their job. Exhaust ports are oil fouled. I removed the exhaust valves to check for wear etc, both are tight but the shafts were surprisingly oily. No exhaust valve stem seals are currently fitted, (as standard).

Presumably either my piston rings have not bedded in properly, and or oil is running DOWN the exhaust valve guides. Trying to find out if anyone has seen oil fouling caused by oil migrating DOWN the exhaust valve guides.

Thank you,

Kind Regards,

James

The intakes are much more likely to have the problem than the exhaust. This is because there's only a small drain for the entire intake side the exhaust side has the pushrod tunnels.

Torontonian · Nov 9, 2023

Starve the head of oil for your testings . Plug up the rocker oil feed. This will not hurt anything . Go for a ride and if the smoke has cleared up coming home then it's the head . If not , Piston issue or head gasket or ...
Also do not use OEM Norton intake guide seals . J.S. makes some good ones .

Onder · Nov 9, 2023

I used Kibblewhite valve guide seals. They seem to do well, stay supple for a long time.

Seal, Red Viton, 5/16" Stem x 0.480" Guide Seal Detail, Various Applic

BSA®, B25, 1968-1971 (Pkg. of 2 Required) Norton® 750 1968-1973 (Pkg. of 4 Required) Norton® 850 1973-1977 (Pkg. of 4 Required) Triumph® 500 & 650's 1951-1962 (Pkg. of 4 Required) Triumph® 650 / 750 1963-1983 (Pkg. of 4 Required) Triumph® TRIDENT ™ 1971-1976 (Pkg. of 4 Required) KPMI® Red 100%...

shop.kpmi.us

Shelby-Right · Nov 10, 2023

We used to knife edge our exhaust guides on "some heads" to help shed the oil,exhaust guides need some lube and can seize , the piston is chasing the exhaust valve up the bore and it relys on the spring and the extra piston to valve clearance it should have , also some guide seals can come off and pump oil , generally you need a machined lip or a series little grooves and sometimes you can glue them on , pays to install seals with a protective sleeve on valve, some manufacturers supply them or just cellotape keeper groove .

baz · Nov 10, 2023

Britstuff said:
I have a feeling the problem may be poor quality piston rings. Previous owner did cut the oil control rings short and the bike made a huge amount of smoke! Thought I had fixed that with the new rings, but perhaps not. If I replace them again I think I am going to go with some pistons and rings from Jim Schmidt. I did so in the past for my dominator and they work great.

Right now I just want to try to eliminate the possibility the issue is with the exhaust valves. Inlet valves are definitely not leaking. I should have tried Baz's suggestion to cut of the head supply for a short while. Oh well, we live and we do not learn!

I think I will experiment with acetone as suggested.

You can still try blocking the feed to the head
At least then you will know if it's a guide or ring problem

Madnorton · Nov 10, 2023

Put the bike on the centre stand, leave over night. Remove exhaust pipes and look into the ports. You can now see if the oil is running down the valve stem or dripping of the nose of the guide. Oil coming past the stem or guide in this way usually indicates by smoking or start up which clears after a few minutes. Smoking after this period and during a ride indicates oil is getting into the combustion chamber constantly.

MexicoMike · Nov 10, 2023

YES, oil can be ingested via the exhaust valve guides/seals. Seals on both intake and exhaust valves is common nowadays.

FWIW, the standard practice for automobile performance engine building in the 80's (and maybe long before that) included adding exhaust valve seals. The car (and motorcycle) factories eventually followed. As an example: the original early 1990s Ducati 900ss did not originally come with exhaust valve seals. A year or two later Ducati sent a bulletin to registered owners stating that exhaust seals should be installed. If the bike was under warranty, the parts/work was covered. If not, the seals were free but the owner paid for installation (or did it himself).

marshg246 · Nov 10, 2023

MexicoMike said:
YES, oil can be ingested via the exhaust valve guides/seals. Seals on both intake and exhaust valves is common nowadays.

FWIW, the standard practice for automobile performance engine building in the 80's (and maybe long before that) included adding exhaust valve seals. The car (and motorcycle) factories eventually followed. As an example: the original early 1990s Ducati 900ss did not originally come with exhaust valve seals. A year or two later Ducati sent a bulletin to registered owners stating that exhaust seals should be installed. If the bike was under warranty, the parts/work was covered. If not, the seals were free but the owner paid for installation (or did it himself).

If I remember correctly, on a Norton, there is no groove on the exhaust guide to keep a seal on the guides and I think the pressure to blow them off higher on the exhaust side. Are there guides made for Norton that would accommodate seals?

Also, there should be no standing oil in the exhaust area to seal against. Of course, some splashed oil gets on the valve stem but unless the guides are bad, I can't see that being a problem on a Norton.

A similar engine of the era is Triumph and there is no need for intake or exhaust seals as there is no standing oil in the in either side. To me the Norton has a engineering error by not providing a drain on both sides of the intake area. The one small drain is hidden beside and towards the back on the timing side intake valve - for that reason, installing the rocker spindles incorrectly can easily over oil at least the intake area.

MexicoMike · Nov 10, 2023

FWIW, US v8 OHV engines have plenty of drainage for oil in the heads. There is no possibility of standing oil. Though they didn't many years ago, all the major manufacturers now use/recommend exhaust valve seals and all the major performance-oriented aftermarket suppliers offer them.

I used to participate in the Mopar "Direct Connection" program which was a Chrysler-sponsored program directed at competition engine building. They demonstrated that oil can be drawn past the exhaust valve guide by the venturi effect of the gases leaving the combustion chamber. In that case, it is not "burned" in the cylinder as it would be with intake valve seal issues but still can cause deposits on the the valve stem, disrupting exhaust flow and "burning" oil.

As far as installing them on Nortons, I have no idea what is available/what is necessary to install them. In the old days, when we installed exhaust seals, we had all guides machined to accept PC seals. Intakes at the time usually had umbrella seals.

marshg246 · Nov 10, 2023

MexicoMike said:
FWIW, US v8 OHV engines have plenty of drainage for oil in the heads. There is no possibility of standing oil. Though they didn't many years ago, all the major manufacturers now use/recommend exhaust valve seals and all the major performance-oriented aftermarket suppliers offer them.

I used to participate in the Mopar "Direct Connection" program which was a Chrysler-sponsored program directed at competition engine building. They demonstrated that oil can be drawn past the exhaust valve guide by the venturi effect of the gases leaving the combustion chamber. In that case, it is not "burned" in the cylinder as it would be with intake valve seal issues but still can cause deposits on the the valve stem, disrupting exhaust flow and "burning" oil.

As far as installing them on Nortons, I have no idea what is available/what is necessary to install them. In the old days, when we installed exhaust seals, we had all guides machined to accept PC seals. Intakes at the time usually had umbrella seals.

All interesting but this thread is about an oil burning Norton engine and the OP is asking if that might be due to the lack of exhaust seals. To me there is a very simple answer - NO!

It's very difficult to imagine any effect that will cause oil to be sucked into the combustion chamber via the exhaust valve guides since when the exhaust valves are open there a great deal of pressure in the opposite direction and the oil would somehow have to get in the combustion chamber against that pressure and stay there until the next power stroke. I have no doubt about the deposits you mention on the valve stems but can't imagine that causing oil smoke out the exhaust.

Seeley920 · Nov 10, 2023

I had to work on a Domiracer that a friend owned. It has putting clouds of smoke out of the exhaust. He had had new valve guides fitted, but it still did it, had fitted new rings etc, but nothing cured it. It was bad enough to have him black flagged in races

When I took the head off, the inlets were fine, no seals, none needed. I could feel a wear ridge on the exhaust valves. He had reused the old exhaust valves and the oil just pissed down them and was burned in the exhaust. Fitted 2 new valves and there was never as problem after that.

A common racing mod on racing Triumphs was to knife edge the guides to stop oil from pooling on top of the guides

jseng1 · Nov 10, 2023

marshg246 said:
If I remember correctly, on a Norton, there is no groove on the exhaust guide to keep a seal on the guides and I think the pressure to blow them off higher on the exhaust side. Are there guides made for Norton that would accommodate seals?

Also, there should be no standing oil in the exhaust area to seal against. Of course, some splashed oil gets on the valve stem but unless the guides are bad, I can't see that being a problem on a Norton.

A similar engine of the era is Triumph and there is no need for intake or exhaust seals as there is no standing oil in the in either side. To me the Norton has a engineering error by not providing a drain on both sides of the intake area. The one small drain is hidden beside and towards the back on the timing side intake valve - for that reason, installing the rocker spindles incorrectly can easily over oil at least the intake area.

For a guide without a groove you need a metal ring on the bottom of the seal to keep it from coming off. You also need a spring or ring at the top for a good seal to maintain tension. This combo is not always easy to find. Check the ID of the seal before installing. If they are too loose on the valve stem they will leak oil. Different brand seals may look the same but some don't have enough tension on the valve stem.

Exhaust Valve Guide Seal Question

Similar threads