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john clark 1212/03/2018 19:28:19
4 forum posts

I am assembling the valve blocks and finding the tappetts tight in the bore, so much so that the spring pressure will not push them back.

The o rings are imperial and all the measurements correct. Any help here will be appreciated.

I have also some extra castings and parts i anybody is interested.

Many thanks john

Brian Wood13/03/2018 12:01:10
1929 forum posts
37 photos

Hello John,

Welcome to the Forum. I am not a modelling man but this sounds very much like standard fitting work to me to get the tight spots out and make things move sweetly. Remove the o rings before you start on these methods

The first thought is of course reaming the bores and the cheat on that is to push a piece of card into the reamer on one side so that the other side is pushed off line to cut slightly oversize. You will have to find the optimum size of card to get a decent result, too thick and the reamer won't enter and too thin it has no effect. You are only taking off a few tenths of thous anyway. The alternative is to use some Scotchbrite pad, the red is the finer grade over green but used green will suffice and polish down the items that fit the bore. I have found a battery powered drill is good for that sort of job and move the job about as it rotates to even out the treatment.

Finally there is lapping where each bore fitting component is lapped to it's bore with something like Brasso until it feels right. Again, the metal removal is very small and having nicely matched polished bores and internals makes a world of difference to the operations later. Be sure to clean up after all these methods to remove all traces of the removed metal so that it doesn't continue the process when in use.

Regards

Brian

john clark 1213/03/2018 19:26:44
4 forum posts

Thanks Brian the card trick sounds great. You are right i need to excessive some patience and fit each one indivually.

I have reamed the bore which is 5/16 the tappetts are 1/4, the o rings 1/16. Its only the o ring in contact with the bore

I did measure 1 tappett again tonight and found it to be dead on 3/16.

I could take say 5 thou off the ring groove?

Or ream the bore oversize as you suggest.

Thanks for all your help and advice

john

Brian Wood13/03/2018 19:54:22
1929 forum posts
37 photos

Hello John,

You might have the o ring groove too shallow and that is the cause of the poor response in tappet closure. Be careful though, you don't want to overdo things. I suggest making a dummy to try out the effects of varying depth on the rings, which of course will have strong influence on the grip in the bore and hence on the springs for the tappets

Regards

Brian

john clark 1213/03/2018 20:26:45
4 forum posts

Thanks Brian great idea i will use a piece of 3/16 rod say 6 inches long, machine one end with nominal grooves and the other end just under. Being that length will enable me to easily push it into the bore. I can gradually reduce the gap until i get the correct fit which will be when the spring pressure can push the tappett back against the cam.

Throwing ideas around always works best.

Regards John

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