Eccentric Question

I am currently engaged in the frustrating exercise of setting valve gear and I have the problem with the eccentrics which keep moving from their set positions on the crank shaft.

I have followed the drawings in that I have used two 4BA grub screws per eccentric but I think because the socket head is very small I cannot get the business end of the screw to bite into the MS shaft with any lasting effect.

My question is - do I position the eccentrics and pin through the shaft using roll pins? I have only seen reference to using grub screws but surely once the eccentrics have been located on the shaft - are you really likely to want to move them?

Put points on the end of the grub screws, one 4BA grub screw should be enough, so check that you havn't got something tight try it without the eccentric to see if it will turn over Ok, then add the eccentric and check that it is still smooth.

Hope this helps

Stew

Quentin,

Use the grub screws for setting up only, when you are happy withe engines performance fit keys to the crank and the eccentrics, ensuring they will never move during use.

I'm building a 6" scale traction engine, on the drawings the eccentrics are shown fitted with grub screws only, No way would I leave it at that ! I will fit decent keys as I have suggested.

Are you building a locomotive or what ?

Richard.

Put a slug of alluminium in the hole below the grub screw so you don't chew up the saft/axle while setting things up. Once you are happy mark the positions and machine flats for the grub screws or sin'ket them in place.

J

Thanks for your help - I discovered that when I shortened the grub screws I hadn't put back the point! _ so that certainly didn't help the situation.

Stew, yes the sheaves are tight when it's all bolted together - I'm not sure how to resolve the situation however, I do not want to remove the eccentrics so pehaps I need to skim the inside of the sheaves - so much for trying to make things a good fit - perhaps I should have gone sloppy fit.

Richard, it's a Stirling Single in 5"

Consensus of opinion seems to be just edging towards grub screws - possibly with a drill tip hole in the shaft when all is set.

Edited By Quentin Reidford on 29/09/2013 18:45:56

Hi Quenton,

I am also building a model traction engine and my eccentrics will be keyed to the shaft.

Richard, what type of engine. Mine is a 6" Ruston Proctor.

Paul.

Hello Paul,

I am building a 6" Burrell , castings by EKP Supplies, been building it for 2 1/2 years now, hopefully get it finished next year,

Richard.

A Burrell is a nice engine. Although mine is also a 6" it is half the size of yours. Been building mine for about 18 months now. Would like to have it finished this time next year. Unfortunately work get in the way.

Good luck with your project.

Paul (Sydney, Australia)

I have used bearing retainer on the shaft with great results - obviously only apply once you have marked the set point, acts as an aid to the grub screw and can be undone.