11 replies to this topic

[bikenutmart]

Took the head of the mini today (1275 std) as no 2 exhaust valve had seized in the guide resulting in no compression on no 2, took all 8 valves out, they all had top hat type stem seals fitted, I thought they were only fitted to the inlets, could this be why it seized, ( no lube) I will order a new set of ex. valves, will I need to replace the guides as well, on inspection they all look fine, would the seats need recutting  if new guides were fitted? Thanks Martin.

[grck1]

some engines did have seals fitted to all valves.

 

best way to check if guides need changing is to fit valve and check for play. any movement usually indicates wear.

if the guides are replaced then the seats ideally need recutting to suit the new valves

 

you can not bother with re cutting the seats and get away with it but for best results i would recommend re cutting

[bikenutmart]

Its an early engine 1967,which im told did not have seals on the ex. valves. (12g940 head)Don't want this happening again and reason that no seals on ex. will keep them cooler and lubed and avoid a reoocurrance. What the opinion of other members please. Martin.

[Gremlin]

Sounds like it got too hot, the exhaust valve guide and stem is under pressure from the exhaust being pushed out, so the seal won't stop oil going in as the pressure is pushing it out

[bikenutmart]

Thanks Gremlin, so are you saying to leave the seals off the ex. valves? Martin.

[Gremlin]

I've got none on the exhaust valves, thats why SRE (Slark Race Engineering) did, it's a 295 on my 998

[bikenutmart]

Thanks for that, I will try without any. Martin.

[carbon]

Martin - were the exhaust valve stems smooth or scored when you took them out. Also watch out for the length of the valve stem, as the early S valves were shorter. But if it's a 940 head then chances are you should have later (longer) valves fitted.

 

Also using bronze valve guides may help avoid seizure when using stainless valves.

[ACDodd]

Check to see the stem to guide clearance is not too tight, this happens if the guide has not been sized after fitting.

Ac

Edited by ACDodd, 19 May 2014 - 09:45 PM.

[Gremlin]

What crank case setup have you got? If it's plumbed into the inlet no need to worry but if you've got a catch tank or small breather filter you might find it pushes out a bit more air

[Cooperman]

There have been problems with the phos-bronze guides where there was insufficient stem to guide clearance. I always use the chilled iron guides to prevent this possibility. I also fit stem seals on all the valves, just because I've always done so.

[bikenutmart]

Thanks for all the replies, it was just no 2 cylinder ex. valve  that nipped up, and yes it was slightly scored, they are cast guides. Martin.