Tag Archives: drawing errors

Stud Clash on LP Valve Chest

There is a clash in the drawings between the bolts holding the reversing lever slider pivot (shown in the scrap drawing on page 33 of “the book” entitled “Reversing Arrangements”, and numbered item “2”) and the upper-right stud securing the LP Chest to the LP Cylinder….

Having hit the problem, I moved the pivot in-board about a quarter to miss – I now have an ugly hole to plug 😦

Also take care, I think the original hole locations in the pivot are also incorrect, as they seem to result in the slotted arm (item 3 in above drawing) fouling the studs on the LP valve cover. So I made mine (the 2nd one!) a bit longer and located holes by eye.

The &^*$! reversing gear…

Well, if you’re building this engine then I hope the valve gear goes more smoothly for you than me!

The Draglinks

The Drag Link Bearings

Drag Link Bearing Blanks

A handfull of work, drag link bearing blanks ready for drilling boring, fitting and oil-hole drilling

I cannot believe just how long it has taken to complete the reversing gear on the engine – and it’s still not done.

The multitude of little blocks (drag-link bearings) take an age to make – if you had some 7/16″ sq Ph Bronze bar to hand then it might be OK, but I didn’t so decided to hack the blanks out of a piece of 2-inch square bar I had. However, I discovered that my trusty Warco bandsaw did not cut as straight as I hoped, and half of the resulting blocks were undersize. So then you spend a while silver soldering extra bits back on, to bring them to size, and then (literally) DAYS on the shaper, transforming a set of rough cut rhomboids into little cuboid shapes.

Drag Link Pins

Meanwhile a relatively simple turning and pressing job produces the pins for the lifting arms and eccentric pivots.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

I happened to have some EN1A on the shelf that these got cut from – this is lovely free-cutting (leaded) mild steel, but I must confess I worry that this is so “soft” that it might not last well in service.

BTW – Midway thru the gear building I ran short of 1/4MS bar. So I went off to Metal Super Markets in Southampton (metalsupermarkets.com) and stocked up on a variety of bar and plate, that my “stores” were running short of; (these really are great people, and very helpful and economic – I would recommend them to anyone, over the counter service with a smile, for even small quantities) – But they only had EN3B, and when it came to turning and screw-cutting this stuff you really miss the free-cutting EN1A!!!

The only issue with the manufacture of these pins, is that one of the errors in the drawings means these pins need to be longer than drawn, to clear the bolts and lock nuts securing the Expansion Links and Die Blocks. There’s not a lot of space, so take care – I extended mine to 1.5″ overall (I think).

Drilling and Boring Drag-Link Bearings

drilling the bearingsThe next job was to drill the bearing halves for the rods. I did this by clamping them into a small jig (with tool-makers clamps). My normal approach to this would be to soft solder (“sweat”) the bearing halves together and then drill and bore them as one, separating them at the end. But this was not what the ME articles said – so I followed them… The plan was to create a small jig, drill half the blocks 2BA clearance and the other half 2BA tapping – then tap these and use temporary screws to assemble them into pairs while they are bored, and then open out both sides to clearance for the long rods to be fitted.

Jig Drilling DragLink Bearings

Jig Drilling DragLink Bearings

I think this approach was slower.  A better plan would have been to solder them into pairs while they were all still oversize, drill, bore, finish to size and then separate.

As it was I then discovered that despite machining all the blocks to size, the journals on the pins were too tight (only a few thou, but enough to stop them fitting, so yet more fettling was needed)- At this point I discovered that the relevant reamer has gone missing, so more careful hand work on pins and bores (scrapers and emery tape) was needed to get a good fit….

The Valve Rods

This is about to start sounding like the blog of a complete idiot, but at least it’s improving my patience.

LP Valve Rod

Firstly, while assembling and testing the valve gear (prior to first run on air) I found that the LP valve was fouling something and could not accommodate the full travel of the eccentrics, over a couple of hours of assembly, disassembly, reassembly (repeat as needed) I came to the conclusion that the tailrod was too long and clouting the end of the tailrod guide… there being no opportunity to lengthen the guide, I decided to shorten the tail rod – carefully sawed 1/4″ off, and reassembled again, only to find it STILL DOES NOT FIT!!!!!

Further inspection determined that the valve buckle was actually fouling the nut holding the tail-rod guide – and actually the shortened tail-rod was now falling out of the guide at the lower extent of the valve travel!!! So, it now needs lengthening – more work yet to be completed…

HP Valve Rod

The HP valve rod has a “joggle” on the bottom to line up the valve rod with the eccentrics. I decided to make this as a separate part and screw it to the rod proper. This joggle also serves to further widen the already widened drag-link pins resulting from the error in the drawings. I did measure this and allow for it in the longer pins – but I forgot to take account of the lock-nut on the die-block pin….AAAARRRGGG!!!

I concluded I could shave enough off the joggle to accommodate all this, but the amount of metal left for the thread holding the actual valve-rod into the joggle was going to be a bit thin, so I decided to braze the rod into the joggle – this I did (with no distortion), and decided to use the Linisher (belt sander) to just clean the flux and oxide off the joggle…. What I failed to see as I did the final side was that I was holding the assembly slightly out of square and ground a nice 20thou depression in the bally valve rod – thus rendering the whole shooting match scrap! 😐

Either way it provided me the opportunity to screw-cut the 3″ long 3/8″x26 thread on the new rod, using the off-set compound slide method often recommended (but never tried by me) mechanism – and it does a much nicer job (even on the nasty EN3B!), so I conosoled myself that the extra 3 hours work, had resulted in a nicer job (displays a fixed grin)!

BTW, In this process I again reminded myself that under conditions where you need to take fine cuts on tough material a carefully sharpened carbide or carbon steel tool will outperform a indexable tipped tool – as if you check the specs these are not typically made to make a cut of less than 5thou !

The Result….

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Overall these 16 half bearings and eight rods and 4 pins took more than a 10 days of effort (probably about 30 hours! not including the remaking of the vale rod) – a slog…. assembling the whole sh-bang produced something that worked but was too stiff, so more fettling and adjusting needed!

I am really hoping I can bring this all to a good end – sometimes I wonder!

Eccentric Rod: Part 14

  • BOOK, NEW, OLD?, ME? Colin Sims analysed that the length of the eccentric rods appears to be wrong as follows: “The eccentric rod issue I worked out in the following way: Link radius is 7.5″, with a ‘backset’ (not the right term, I know) to the pin holes of 3/4″, leaves a dim of 6 3/4″ from the pin to the crank centre. If I add the dim from the centre to top face of the eccentric strap to the foot to pin hole dim on the rod, I get 6 5/8″, i.e. 1/8″ short. This will not affect the valve travel, as this is determined by the eccentric throw, but it would affect the quasi-SHM of the valve movement subtly. Yes I know it is not true SHM, as the mechanism is effectively a slider-crank form.editor’s note: I have made the rods to the drawings, and they seem to fit, but I agree with Colin that the math sais they may the wrong length.
  • Having now assembled the valve gear (February 2014) I fear that this is proven – moving the gear from ahead to astern cannot be accomplished without the valves being deflected in mid gear, no matter where the crank is set. I think this is wrong, ah well, time will tell – I have managed to time the engine to run on air, but pretty roughly so far….

Drag-Link Bearings: Part 16

  • BOOK, ME & NEW: From John Olsen (NZ) – “I have built a Leak engine (with mods) from the original 1980-83 ME articles. One mistake in the drawings there was that the pins at either end of the drag links are not long enough. This means that the drag links would foul on the pins in end of the eccentric rods. This is on page 707 (ME). Part 16 “drag link bearing” has a dimension of 1′ between the two grooves. The pins at the end of the eccentric rods is 1.25″ long plus the head, which is not dimensioned. For this to fit between the drag link rods, the 1″ on part 16 must be increased to at least 1.25 inches.” Submitted John Olsen –
  • editor’s notes: Also submitted by Colin Sims, he comments:  “I think the eccentric rod pins that John mentions are overly long too – I think they would work at 1″ if they just needed to fit over the eccentric rods outside dimension o but the heads and lock nuts mean that the pins need to be lengthened, but perhaps not as much.”
  • John Olsen also sais: “Not an error as such, but those drag links are excessively fiddly. They look good when together, but there are a lot of small parts when you have to assemble and disassemble them.”
  • editor’ s notes: Having now completed these parts, John and Colin are certainly correct – the drag-link pins DO need lengthening, I went for 1.25 inches, but actually this proved too tight, as the joggle in the HP valve-rod also clashed, some careful thinning of this component has provided the needed clearance. This is a complex and fiddly assembly, and a pain to work on – but it does look nice!

Front Columns: Part 4

  • Diameter of Columns BOOK, NEW,ME, OLD: There are no diameters for this – while this is not “critical” it does leave one at a bit of a loss as to the size of stock one should start with. I decided on 1.125dia at the top and 1 5/16 at the bottom – IMHO wider is better, as I was surprised at the amount of “flex” in the erected engine, even with everything “dogged up tight” – maybe this is a good thing – who knows…. Submitted by Malcolm D

Cylinder Top and Bottom Covers: Parts 5, 6a & 6b

  • BOOK: The stud locations for the covers are not well dimensioned. Care needs to be taken as they can break into the ports. This is particularly likely to happen as the covers are drilled first and then spotted thru to the cylinders, and the clash is not obvious until it is too late…
  • BOOK: Similarly, the holes in the lower covers to attach the covers to the rear columns are not dimensioned at all! I concluded that the two outer ones should be 1.875″ from the cylinder centerline and the centre one 2″ from the cylinder centreline – this worked OK for me…
  • BOOK: Two of the cover bolt holes on the lower HP cylinder cover (and one on the upper HP valve chest cover) are shown as blind – this can’t be right!

LP Valve Chest: Part 3c

  1. Cover Studs: Colin Sims (another SBA Leak builder) reminded me of this one – The LP Valve Chest Cover is attached to the Chest by 12 studs; and the chest is attached to the cylinder by 8 (EIGHT)…. the two at the top and bottom cannot be attached as the studs clash with the ports. So as I wrote at the time “It may be that my Technical Drawing A-level from the ’70s was to a different standard but only 8 of the 12 holes for the valve chest cover mounting holes should be drilled through. The 8 down each side do carry through to the block, but the 4 at the top and the bottom, should be blind – as they “clash” with the port pockets.“…. Moreover this also means that the stepped studs shown in the drawings should only be used on the sides (the top and bottom are plain studs as the larger ones would (do) clash with the stuffing box and tail rod)… Lastly in the BOOK (at least) only the four right hand holes are shown threaded – in fact the left hand ones need to be too (to take the aforementioned stepped-studs).
  2. The Lap: The ports as shown in the BOOK, have an undimensioned dimension indicating where the “LAP” is/can be measured? There is no indication of what this should be…but see below….Update: I found the lap and lead dimensions at the end of the Book in the valve setting section, Lap is given as 3/16″ and the Lead as 1/32″, but still not sure of the implications of the LP port height issue noted below.
  3. The Port Height: This is dimensioned in two places as two different sizes! I have only just realised this. I noted that the ports on my valve chest were 3/8″ high, and that this did not match the 5/16″ dimension shown on page 10 (of the BOOK) I thought this was just a blunder on my part. But tonight as I am writing this page, I realised I cut them this size because they are shown as 3/8″ high (on page 7 of the BOOK). Lord knows which is right, perhaps they are meant to be tapered! This will mess with the LAP, I guess I am going to find out when I time and steam the engine!