Hello all

I wonder if you can help me with a query on tiches valve gear, i have notised that some measurements are different in the book to the drawing. firstly the return crank centres are 11/16 in the book and 39/64 on the drawings giving i think 5/64 difference. secondly the combination lever (vertical rod) shows on the drawings to be 8 thou longer between centres with writing saying it has 10 thou lead (this is the two lower hole distances). If i have not explained it well, please say and i could take some pictures of the relivent drawings.

Does anyone know which we should be following?

Your help would be much appreciated

many thanks

Stephen

Please see below photos of the drawings which differ from the book, i purchased them from my hobbies store and i belief they are the same supplied by reeves.

Apologies Ryan for cluttering up your build diary but i am sure it may be of help to us all to make sure we are using the correct dimentions. your diary has been very usefull and interesting by the way

many thanks

Stephen

hi ryan,

i think you would be well advised to consider carefully the drawing uploaded by stephen. at some point the original dimensions have been re-drawn presumably to deal with excessive return crank throw and excessive lead. such errors are not uncommon in the designs of LBSC, martin evans, and don young. the revised drawings will give a slightly smaller lead, and the shorter return crank throw will avoid the valves overrunning when the die block in the expansion link is at top and bottom of the slot, and avoid the dieblock having to be in a partly 'notched-up' position to give the correct valve events.

i should add i havent built a TICH, but i have come across this problem on a number of well known 5"g designs.

it is very little extra work to make up a spare set of combination levers and return cranks to the revised drawings with dummy eccentric rods when trying out the gear and setting it – just dont pin the original return cranks if you fit them first but make a clamp arrangement, and dont finish the eccentric rods.

cheers,

julian

Edited By julian atkins on 14/11/2014 11:59:00

Edited By julian atkins on 14/11/2014 11:59:46

Great job Ryan 😀 Your'e getting there!

Do you have any drawings of the larger boiler version? I think there may be a few missing from ME 1950 and also did you use drawings when you made the brake axle?

Just worked on Tich today. Made the smokebox and smokebox door.

Good luck on your build ahead!

Cheers

Hi all,

Do you know about the 3rd Tich boiler? A Belpaire which has a 9% larger grate than the large boiler, but not as simple a build as the other two.

Dave

I think we should start a TICH discussing thread somewhere.

Edited By MK on 14/11/2014 19:52:34

hi stephen,

to simplify things somewhat the combination lever provides the lap and lead part of walschaerts valve gear, and so lengthening the distance between the bottom and middle holes or their proportions compared to the middle and top hole reduces the lead. the 8 thou difference is frankly immaterial and could easily be negated by the odd slight tolerance error on the valve lap or valve setting.

however the return crank throw alteration is more significant, but wont in any way affect performance, just wear on the valve gear. with the longer return crank to provide the correct cut off in full gear the die block wont be anywhere near the end of the expansion link slot and probably just halfway down from centre. altering the return crank length also alters the eccentric rod length.

cheers,

julian

Thank you Julian, that is most helpful, i have saved many of your posts in the past as they are always worth listening to.

Thank you Dave, i do not have access to E.I.M but will try to get hold of a copy, its all useful information!

Sorry Ryan, back to your build diary…

Many thanks

Stephen

hi ryan,

you are making a very good job of those valves!

going back to the revised return crank drawings, i forgot to add another advantage in that swing of the expansion link will be less and so with the shorter return crank the gear will be easier to change from forward to reverse.

cheers,

julian