Valve seat recession

I shall keep bumping this one, as surely someone must know? Alternatively, are there other measureable criteria which dictates when valve seat recession is unacceptable? My manuals give all sorts of technical data, measurements etc, including mention of replacing valve seats when they are too worn, or have been ground too much, but no measurements to back it up. Thanks in advance.....

Ian

Anna. Thanks for the reply. What is the datum point from which you measure, and to where? My issue is one I raised in another thread I have running, regarding the length of pushrods supplied by Andover Norton, which appear to be about .070" too long. When I fit them, I can get no valve clearance on the exhaust valves, and not much on the inlets. I can get clearance if I use RGM steel pushrods, which are about .040" shorter than Andovers, although still longer than the published lengths of the original Norton rods. I don't want to use the steel ones, as they are too heavy. Andover say they have never had a problem with their rods, and anyway, the dimensions which Norton published back in the 1960's are wrong.... of course, I should have realised....

Your service tolerance of 3/32"; or .094"; if added to a pushrod additional length of .070" is a massive difference from original manufactured specification. Therefore, I need to know whether my valve seats are getting to the edge of tolerance, or whether the problem is just the pushrods, before I remove the ends of the rods, which I am having difficulty in doing, in order to shorten them.

I have attached a picture, although not as clear as yours.

Thanks. Ian

I have now checked the length of the valves as they protrude through the head, as Mike P. did with the ES2, and the n/s inlet is 42.6mm, o/s inlet 42.1mm, n/s exhaust 42.6mm, and o/s exhaust 42.4mm, so 0.5mm, or .020", covers them all. Likwise the valves are all within .010" of each other in length. Attached is a photo of the inserts with valves removed.They appear different, as the profile of the outer edge of the inlet valve inserts are rounded, protruding slightly into the head, whilst the exhaust insert is chamfered. However, the cut seats appear to be at similar depth, as witnessed by the measurements of the valves through the cylinder head. The valve heads are proud of the combustion chamber, so they don't appear to me to be recessed. Does anyone have a good head and valves sitting on the bench which you could measure?

Gordon. Thank you for your reassurance! That is my belief, but with no data to take measurements, I was feeling a bit stuck. The problem I have, therefore, has to be the over-long Andover Norton pushrods. I will attempt to put the ball back in their court next week. I will take similar measurements of my 750 Commando head today, by way of comparison. The valves are 0.10" longer than the SS ones, but it may give some comparison. Meanwhile, the bike remains dismantled on the bench....

Ian

Yes, those are the measurements which Phil Hannam also posted up in an earlier thread, on a chart of pushrod lengths; no doubt the same one you have.

Andover say they manufacture to original 1964 drawings, which state :-

inlet 8.284"-8.248"; exhaust 7.440"-7.404"; in each case showing a .036" manufacturing tolerance.

The lengths of the rods they supplied me with are:-

inlet 8.263"; exhaust 7.429", which are pretty much in the middle of their stated tolerance, yet 0.053" and 0.063" longer than Hudson's measurements, and even more, when compared with Norton's published figures in their Publication P106/P, workshop manual from the period; see attached.

Whatever; these pushrods will not allow any valve clearance, whilst the shorter, but much heavier, RGM ones will.

Andover, despite acknowledging that they are puzzled by the discrepancy in figures between the 2 lots of data, which they will look into, maintain that I am wrong, they are right, and they will not shorten the rods for me, but will give me a refund. They further said that I am being unreasonable, and should not consider that I am right.

Charming....