Screeching noise ?????

[michael snellin]

Hi, i have taken on board what all you guys have said i have now found the noise that is coming from the rockerbox area,the o/s exhaust valve which i replaced new along with the springs seems to want to jump on closing  causing the valve to make the noise, against the rocker, does look to me though the valve may be bent slightly, before i take the head off appreciate your thoughts  Does any one no what the difference on the three rocker boxes there is three part numbers in the A GROUP parts book.

[chaterlea25]

Hi Michael
To the best of my knowledge the castings are all very much the same
The 650  alloy head models use different springs collars and keepers from the rest
To make room for these the rocker box is relieved by grinding it away in the appropriate place
Attached are 2 pics I saved from somewhere or another (probably here??) showing this

HTH
John

[bsa-bill]

More knowledgeable minds will hopefully comment but I've read that Rocker box with studs is different part number to a rocker box without so two variations would be for the Flash and Rocket as the alloy head requires longer studs.

Ive had the same problem with an EX valve snapping shut, no screech tho, just when I watched it there was a definite hesitation before it went from open to shut and a click, I treated it with ZX ZX1 additive = scooted some around the valve guide and added it to the engine oil, after running it for a few miles I drained it off and the valve seemed fine, however probably you'd be wise to check the valve is not bent first

[A10Boy]

As I mentioned earlier and as John reminds us, the BSA fitters used to grind the rockerbox to give valve spring clearance. They then stamped 1142 over the casting numbers underneath the box. comparing the two boxes, there is only about 15 thou taken out of the front corners in the valve spring locations

[muskrat]

Unless it was done by a previous butcher my 1142 is relieved on the inlet side as well.
A compression test will show a bent valve as it won't seat properly. But if it's sticking because of being tight or bent I'd take the head off to investigate. Don't want it hitting the piston. Was it an oversize valve stem or guide that you changed?
Cheers

[wilko]

Remind me not to take noise descriptions seriously! SCREECHING??