7 replies to this topic

[Artful Dodger]

Hi

 

i have just bought a longman race head for my mini7. its built for the championship and has been run making good power. i have just taken it apart and found that under the valves there are roller bearings?

 

i can see how this is a good idea, as when compressed the valve will want to twist, so this reduces friction. 

 

has anyone seen this before, is it a common thing on race engines?  

cheers

 

 

 

 

[Alex_B]

interesting! I havent heard of it but then again im not in the world of mini racing, would love to know why they did it, possibly just an experiment? 

[mk1coopers]

Now that does look trick !

[Artful Dodger]

you should see the valve throats! i can fit two fingers in them!!

 

 

998 mini7 screamer here we come ;)

[Tupers]

I've seen it before but never on a Mini engine.

 

It's not uncommon on high end race cars with coilover's to avoid coil binding. 

[Cooperman]

I don't think they are to avoid coil binding, but to allow the valves to rotate freely which, apparently, gives an advantage in terms of valve seat wear and life.

[Turbo Phil]

I don't think they are to avoid coil binding, but to allow the valves to rotate freely which, apparently, gives an advantage in terms of valve seat wear and life.

 

Agreed. This was what the A+ triple collet was supposed to do better than the single collet earlier design.

Phil.

[tiger99]

Yes, valves are supposed to rotate freely, and the rockers are deliberately set off-centre with respect to the valves, to rotate them slightly each time they open. (I expect that some well-meaning people spend ages shimming their rockers to get them dead central on the valves, but that is a very bad thing to do.) I do agree that a roller bearing will help with the rotation, otherwise most likely the valve will rotate in the collets. The collets will not rotate in the cup, due to the taper causing lots of friction.

 

I would point out that needle roller thrust bearings, although widely used, are an engineering abomination, because the parallel needle rollers must skid, are the outer and inner ends travel rather different distances. I get annoyed every time I see them! At the modest and well-defined maximum pressure applied by a valve spring, a ball thrust race would be better, but that too is a very slight engineering abomination. Think about it carefully, and you will see that it needs the outer and inner sides of the balls to run slightly different distances, can, in theory, be made to run correctly by making the grooves assymetric, although it is rarely done properly. I was once responsible for a very high precision servo mechanism which had to use a best quality ball thrust bearing at one end, and a single ball on a tungsten carbide pad at the other. The mechanical experts deemed a needle roller bearing to be unsuitable, as the skidding of the rollers would have introduced friction and caused erratic operation.

 

Valve spring rotation would also be within the capability of a teflon washer, running on a polished steel cup fitted under the spring, which would be far less likely to result in disaster if valve bounce was to occur. I really would not want lots of hardened needle rollers, or balls, getting loose in the engine. It would almost certainly completely trash every major component of the engine and gearbox, possibly even locking the transmission and causing an accident.