Forum

[Graham]

After an hours ride I joined a motorway and within 2 short juntions the exhaust valve on my 1999 500 Bullet seized open. It was a replacement valve, some 18 months old. Examination showed it was a pattern part and the stem was half a mil oversize. I reckon this was why it seized but my good mechanic suggests it is lack of lead in modern fuels. Your views ans experiences please?

[Norm]

Running lean and probably a hot day?

[simon]

I might be tempted to run some two stroke oil or other upper cylinder lubricant in the mix for a while.

[Graham]

Thank you for your ideas. Ir was evening, so cool and the internals do not indiocate it was running lean that I can tell. So maybe an additive is needed, shame ! Graham

[Exile]

I've been advised to use fuel additives while I'm running my bike in.. I don't really know if it makes a difference but I'm using Castrol Valvemaster plus lead replacement. I think it quietens some of the rattle...

[Dennis C]

Is the valve guide Phosphor bronze or cast iron?. A lot of exhaust valves are now made of stainless steel and will pick up if used with cast iron guides.

[Alan R]

Hi guys--------- did I read that correctly ??------ 1/2 mm oversize ??? Isn't that 0,020" approx ??---------how's it managed to operate at all at that oversize ??------------ maybe the rocker arm was pinched by the two enclosing halves of the rocker clamp---it has been known to happen !!

[Dennis C]

With you on that Alan, I thought it best to ignore that bit, at 20 thou oversize it would not fit in the guide.

[Norm]

I think Graham has an Electra so no rocker blocks

[Phil Ashbrook]

Can one still buy bottles of lead anymore ? In the mid 80's I ran a mini with a full race engine and needed 5 star fuel or race fuel ( expensive ) so I made my own by getting a bottle from an motor racing supplier and that stopped the engine running on with the plugs acting like go plugs .
It was very very risky adding to a tank at a petrol station so I wore big industrial rubber gloves that were washed after use , I cant overstate the fact that lead in this form is ultra toxic .
I now use valve master and I'm not impressed with the sooty build up in the combustion chamber and exhaust valve and port .
In your situation you should check that the valve seat is tight and has not moved when hot , do a light valve lap and see if the seat shows evenly , junk the valve guide and get a phospher bronze guide , when pushing out the old guide note how tight it is to remove as you might need oversize external dimention guides .
I now run an oversize valve with the slippery coating and no problems so far , valve guides in Royal Enfields wear faster than most engines for some reason and even faster without the lead and I'm on my 3rd set in 15 years , eventually I want to run on E85 as per Brazil so the engine will run a whole lot cooler and burns very clean and less protection is needed for the exhaust valve .