BMC Valve Gaps ?

[VWNate1]

As valve gaps affect the cam timing , I tend to run them a bit close .

My BMC 'B' series 1500 (think MGA) I'm currently running .010" intake and .015" exhaust .

It seems fine and not overly clattery , what say you all ? .

See you to-morrow on The Martin Swig Drive .

G'night .

[Jimmy]

Since you're practically deaf, why does valve clatter matter to you??

[VWNate1]

I don't care about the valve's clattering , I was thinking about then maybe being too tight or other foolishness .

I'm amazed no one else has chimed in here , I'm not the only mechanic here .

[malcolmr18zoy]

Don't expect too much, Nate. We all have our own ideas, and when I put your engine together, I set the clearances at 0.015" intake and exhaust, as per manufacturers requirements.
Malcolm

[Steve Simmons]

I figured someone more familiar with that engine would chime in first. I tend to run my valves slightly tight as well. 10 sounds too tight to me but it will obviously depend on the type of cam you're running and the geometry of the associated parts in your engine. If memory serves, I usually run a tight 14 all around on my MGBs if that helps. Factory spec on them is 15.

[VWNate1]

Thanx fellas ;

It's all very much stock apart from the modified MGA 1622 cylnder head .

I guess I'll have to check 'em hot just to make sure .

The water pump began to weep a bit in Gleta so now I have to go find where I stashed the new one and swap it out before my back surgery .

[Robb]

Nate,

Someone correct me if I'm wrong, but if your close valve gap isn't causing overheating or loss of power, it isn't doing any harm.

[malcolmr18zoy]

I don't know Robb, I think that if the engineer who designed the engine specifies the required valve clearance, then that is what it should be set to. I can't speak for anyone else, but I don't consider myself superior enough in my knowledge of any engine to argue with the manufacturer.
Malcolm

[Steve Simmons]

I'm no expert, but I believe that setting them too tight can reduce power and cause a rough idle if the valves aren't closing all the way before the next cycle starts, or are opening too early before the last cycle was over. I suppose it could reduce fuel economy for the same reasons.

[VWNate1]

Nate,

Someone correct me if I'm wrong, but if your close valve gap isn't causing overheating or loss of power, it isn't doing any harm.

Correct .

Valves that fully close will never cause overheating and poor idling , by running closer gaps they'll increase power and fuel economy as they increase throttle response .

The designed in gap parameters not only take in the tendancy of some engines to loose clearance as they reach operating temperature but some loosen up , also the tendancy of 90 % of vehicle owners to ignore routine checks and adjustments , this is why the very same engines , when run by factory racing or performance teams , tend to run far smaller gaps , I was just hoping someone here was old enough to remember what they'd be .

I'll just take the time to check in short intervals as I'd hate to burn a valve on this particular $pendy cylinder hear .

Stand by , maybe we'll all learn something new here .

[malcolmr18zoy]

That's strange, because all the engines that I've been involved with are recommended to have larger valve clearances when used in competition. The reason for this, is that the valves usually get hotter during racing conditions, than in normal road use. Yes, intake, and exhaust valves are affected by combustion chamber temperatures, which makes them expand more than the rest of the valve gear. I would definitely not recommend reducing vehicle manufacturers specified valve clearances. The manufacturers always know what the optimum settings are for the engines they design.
Malcolm

[VWNate1]

That's because your Mechanical experiance is so limited (I can't belive I'm saying this) ~ some engines the gaps widen quite a bit as the engine warms up ~ the difference is in the cylinder head and valve train , most notably the push rods , alloy push rods expand quite a bit , OT OH , valves by design , do not lengthen perceptably .

One of many example that come to mind is the 1950's Horex , it was designed to have ZERO valve lash when cold , then upon reaching operating temperature there would be sufficient clearances .

[malcolmr18zoy]

I understand that the coefficient of expansion of an aluminum based alloy is greater than the coefficient of expansion of an iron based alloy, but you'll have to explain to me what design features cause minimal expansion in a component that is located in the hottest part of the engine. I, too, have encountered engines that require zero valve clearance when cold, but they are definitely in the minority, and not in my limited experience, high performance engines. I've never heard of a Horex engine, but AJS does come to mind.
I still maintain that the manufacturers know the best way to adjust their engines, and following their specifications is the best strategy.
Malcolm