29 replies to this topic

[weef]

Did you take the valves out for examination to try and find why the valves stick when the cylinder head is off?.

[mini13]

its unusual that they would stick that much, to me it sounds like either incompatible valves and guides have been used, ( some need a plating to work with std Iron guides otherwise they should be used with Bronze guides) or the guides have been replaced, and have closed up whn pressed in and not reamed out, although this normally affects the hotter exhaust valves.

[Turbo Phil]

If the valves are binding in the guide and the valve stem is straight, there’s either incorrect clearance or incompatible material specs.

Phil.

[Steam]

If you are using old fuel or there is residual old fuel in the tank it will stick the valves. the engine will seem to run a bit rough but if you leave overnight they will stick.

the old fuel turns to varnish with heat and solidifies usually around the valve stems,

carby cleaner is the best fix, then drain, wash thoroughly and refill the tank.

[Richard e]

Hi Steam

Yes I agree I think this is it. The fuel in the tank had evaporated. New fuel adde, but as you say the reside will have gone into solution and is leading to the inlet valves only sticking. Tank out and thorough clean.

[Steam]

Hi Steam

Yes I agree I think this is it. The fuel in the tank had evaporated. New fuel adde, but as you say the reside will have gone into solution and is leading to the inlet valves only sticking. Tank out and thorough clean.

I sbould also have mentioned that the fuel lines, pump, float bowl and carbie will also need checking and cleaning

[Cooperman]

It is possible for new valves to seize in manganese-bronze guides if the guides are not reamed correctly. Even with a correct 9/32" reamer they can still come up a bit tight with new valves as well. I had this with a 970 S some time ago and had to open up the guides to prevent valve sticking.
It does not happen with iron guides and that is what I always use now.

[Tones61]

It is possible for new valves to seize in manganese-bronze guides if the guides are not reamed correctly. Even with a correct 9/32" reamer they can still come up a bit tight with new valves as well. I had this with a 970 S some time ago and had to open up the guides to prevent valve sticking.
It does not happen with iron guides and that is what I always use now.

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Prob fitted stainless valves into cast iron guides,they WILL seize,need to be run in bronze guides

[Richard e]

Sorted. It was old fuel that had evaporated over many years. When new fuel was added to the tank the gunk dissolved, resulting in sticky fuel. The inlet valves then stuck open on first crank of the engine when cold.

[surfblue]

Bit of a head scratcher that one.

[Richard e]

Yep. Tank was dry so did not think there would be a residue. Clue, clearly, was only affecting inlet valves and only when cold i.e. when the gum or whatever was thicker. Presumably the valve guides/ stems are a tight fit. I appreciate the suggested solutions.

[sonikk4]

I have to say thats a new one on me. Fair play if thats the root cause.

[Steve220]

I would say a potential contributory factor, but not the prime.

[Spider]

I would say a potential contributory factor, but not the prime.

 

I gotta agree here. Usually with old fuel that's gone gummy in the system, adding fresh fuel dissolves the gum in a few hours. If there is any remnants of the Gum,they just about always cause the Needle and Seat to stick open, causing fuel to leak in a big way from the Float Bowl. With the heat in the head, certainly from a 10 mile run, that would melt any Gum if it made it this far, though granted, it would solidify when cooled down, all the same, the Valve Springs would, even if slowly, pull the valves closed against any Gum. Sorry, but I just can't see that being the issue here.

 

 

I have noted that many, including professional engine builders, assume that cast iron guides can be fitted without subsequent reaming, which is simply not the case. I've always reamed every guide I've fitted and never failed not to remove some material from Iron Guides.

I'd say the issue here is either an incompatibility between the Valve Stem Material and the guides or the Guides haven't been sized after fitting.

[Richard e]

Nope. No valve - stem incompatibility. It was just gummed up and got worse as the varnish in the tank dissolved. It now works.