Causes of a sticking valve?

bertw · L Plate Warrior Joined: 24 May 2006 Karma :

The exhaust valve keeps 'gumming-up' in the guide after about 200 miles of road use. I've had a new guide professionally fitted, de-coked the cylinder head, reemed a good clearance in the guide and lapped-in the valves. Any suggestions as to likely causes would be most appreciated. Many Thanks.
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Regards - Bert.

0ddball · World Chat Champion Joined: 15 Jul 2005 Karma :

I assume you used new stem seals?

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

did you use a new valve? old one bent/damaged? spring not too clever any more?

finpos

bertw · L Plate Warrior Joined: 24 May 2006 Karma :

New valve, uprated valve springs. No valve stem seals used on engine (not missing - they were not specified for use in the design). A friend tried using them on his engine, same make & model as mine, and they melted causing a bit of a mess! (I kid you not).
____________________
Regards - Bert.

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

So how do you fix it when it gums up? Valves not hitting the top of the piston at high revs, is it?

finpos.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Well, I would have though that most likely is either the valve isn't straight or it is too tight in the guide.

I have heard of valves running 'dry' due to top-end oiling issues, especially on older BMW twins. Maybe worth checking the oil pressure?

What bike?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

Which bike is it?

Walloper · Super Spammer Joined: 24 Feb 2005 Karma :

Not reemed correctly.
You have a highspot somewhere.
only takes a little to sieze the valve once it touches the guide.
Wally it out again.
Also re-check the stem is straight.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

bertw · L Plate Warrior Joined: 24 May 2006 Karma :

Thank you all for your responses, this is much appreciated. The bike with the sticking valve problem is a Royal Enfield, 500cc single cylinder 4 stroke. The engine was professionally re-built about 3 years ago and was perfect for about 5,000 miles or so, then last November I had a problem with the (original) exhaust valve guide. I had a new valve guide installed by an Enfield dealer plus installed a new valve as well.
When the valve 'gummed-up' for the first time I stripped-down the top end and head, cleaned and checked everything and polished a little more clearance in the guide as I thought it was just a bit more clearance that was needed. The bike ran fine but after about two hundred miles the valve gummed-up again, so I repeated the procedure and cafefully checked that the oil flow was good (it is), re-lapped the valve and polished a little more clearance in the guide. I then put it back together again and used it but after about another 200 to 300 miles the same thing again. I have now stripped it down for a third time, repeated all the above and put it back together again and have so far used it for about 50 miles or so and it seems OK but if it does gum-up again I'm not sure what I will need to do as the valve is not bent or damaged and is seating correctly, there has been no valve bounce, and there is a good 3 thou (ish) working clearance between the valve stem and guide.
Since last Autumn I have planned a 2000 mile round Britain trip on it this Summer, so really do want to get it sorted once and for all. I'm not sure what to check for next so any suggestions would me most gratefully received.
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Regards - Bert.

map · Mr Calendar Joined: 14 Jun 2004 Karma :

Just curious. Are you using the same oil or have you changed brands?

Just a thought. If changed brands after first gum-up may explain the 200-300 mile issue. Hope you get it sorted.
____________________
...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger? Very Happy

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

British or Indian made Enfield?

If it's British, does it have hardened valve seats? If not, are you using some form of lead replacement? If so, are you always using the SAME sort of lead replacement?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

bertw · L Plate Warrior Joined: 24 May 2006 Karma :

Have not changed brands of oil I use, when I had the engine re-built about three years ago I had the head gas-flowed and hardened valve seats installed at that time.
____________________
Regards - Bert.

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

Certainly very odd, you seem to have covered everything!

If "gummed up" means the valve isn't closing because of oil deposits, I'm not convinced. That's a pretty tough spring, and the valve isn't exactly stationary for long periods. Limited oportunity for gumming up!

If it means the valve is not seating properly, I'm more inclined to think that it is getting distorted slightly. especially as re-lapping it will seem to fix the problem - thus asking if you thought it was possible you get some contact with the head at high revs.

finpos.

bertw · L Plate Warrior Joined: 24 May 2006 Karma :

With both 'gummed-up' and 'sticking valve' I am referring to the valve guide building-up a deposit that looks like a baked-on coat of varnish. These deposits are building-up to the point where the valve literally becomes 'glued' in the guide and has to be driffted-out with rubber-headed mallet. I don't know if it's oil being burnt onto the guide or exhaust gases (carbon) being deposited there, I would imagine it's one or the other. My problem in finding out is that the engine doesn't appear to be burning oil and it has a straight through exhaust system where the gasses are more-or-less totally non-restricted by back pressure so should escape through the system rather than trying to clog-up the valve guide.
____________________
Regards - Bert.

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

That's pretty conclusive, then!

The only things I can think of:
1. valve is leaking allowing hot gas into guide. If you have not already Next time you have the head off, pour petrol through the port so It's held in only by the valve. See if any leaks, perhaps through a crack in your valve seats?

2. wrong type (Solid/sodium filled) of valve fitted?

3. Lack of cooling around that bit of the engine for some reason (fitted a fairing?)

finpos.

tonyyzf · Brolly Dolly Joined: 13 May 2005 Karma :

Definitley a fuel issue here, i've experienced it on industrial kawasaki engines, for some reason the un-leaded fuel deposits a 'varnish' like substance on the valve stems which bakes hard, i've seen me having to knock them back out with a hammer.
You need to do something about changing the nature of the fuel, either by using a lead or sodium additive.
Maybe you're mixture is too rich rich causing some unburnt fuel to pass into the valve port?
Have you checked the inlet side of the fuel system, sometimes this problem starts there and the deposits flow through the engine ending up on the exhaust side, might be worth checking the inlet manifold/valve. The first time it happened to me I missed this and had it happen again almost immediatley, then sussed it out and cleaned the whole system, seems to occur worse if the things been lying a while too.

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Following on from that to make this a true BCF workshop thread. Fuel system, something needing cleaning, could this be the first time in a BCF workshop thread that Redex may be the right thing to use?

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Optimax fuel might be a better bet?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

bertw · L Plate Warrior Joined: 24 May 2006 Karma :

This is good input about my sticky valve problem, thanks once again and do please keep any ideas you may have coming.

To try and answer the latest queries…

Fuel leakage at the valve/valve seat interface: I have recently done a petrol leak test on two separate occasions to check there is no fuel leak after lapping-in the valve(s), the first time was on both inlet and exhaust valves the second time just on the exhaust valve and they are both gas-tight.

The exhaust valve: It is new and specifically made for the 500cc Enfield Bullet engine, so it is definitely the correct type of exhaust valve.

Engine cooling: The bike is in standard trim and there is no fairing (etc.) fitted, so the airflow around the engine is as it should be.

Fuel: I have been using the higher-octane ‘super’ unleaded petrol from Shell & Esso garages in the Enfield for a while now (I avoid supermarket petrol in it), so the quality of the fuel should be OK.

Additive: Tonyyzf raises some pertinent points (thank you) and describes exactly the problem I’m having in his mail about the Kawasaki industrial engines, I will try adding Redex and see if it helps maybe that will do the trick.

Mixture: Yes it is on the rich side but Enfields tend to like to run rich and it has not been a problem before and that’s the puzzle with this point as the gumming didn’t happen before this year, in 17,000 miles of use.

Inlet Side: The inlet side is clean, I gave the cylinder head a full de-coke and thorough clean the first time this happened, since then there has been no appreciable build-up on the inlet manifold or valve.
____________________
Regards - Bert.

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

Are you using one of these Classic type oils in it? Maybe it would help to try one of the new types.

Bloke up the road with very grimey hands and barn full of old triumphs is of the opinion that you should check to see that your valve seat is big enough and that you have a large cut area when lapping in the valves; for to transfer as much heat out of the valve and into the head as possible.

finpos.