For about a year now I have been saying “Yes, the engine is done, apart from a few bits and bobs” – so the other week I found myself waiting for some timber to arrive and decided to just “knock those bits and bobs on the head” – 10 minutes inspecting the engine revealed that there were in fact (at least) 23 jobs still to be done!!! So so far we have spent two weeks reducing this list to 7…. (and deciding to do some much later!) Herewith some notes on some of this activity… Continue reading
Well as the videos below demonstrate we have the valve gear finished, and I managed to time it reasonably. There is some blowby on the HP, and that might need further investigation, but on the whole it’s OK.
I scratched my head a lot on how to set this gear, and while this might not be the “right way” and the setting is certainly not “perfect” – let me tell you how I did this….
Firstly we set the engine up so I could feed each cylinder from compressed air, with “ball-a-fix” valves to allow me to control the amount of flow, and which cylinder is fed. Also fitted a small pressure regulator to allow me to control the pressure fed to the engine.
This set up allowed me to turn the engine over by hand and feel when the air pressure was assisting or hindering this turning, and thereby determine if the gear was feeding the pressure at the right part of the stroke. Then one could simply say “is the gear ahead of the crank position?” (e.g. the air is being fed too soon, or cut off too soon), OR “is the gear behind the crank” (e.g. the air is being fed too late). It was then quite simple to slack off the allen screw locking the eccentric to the crank, use the key to hold the eccentric in place, and manually move the crank ahead or behind (forwards or backwards) to attempt to correct the error. I did this first in full-forward gear and then repeated the same process for the HP cylinder, and then in full reverse (setting the relevant eccentrics).
Three or four iterations produced the results shown below…
Firstly running in (very) slow forwards
Secondly, a “video tour” providing a more detailed view of the various components?
Well, if you’re building this engine then I hope the valve gear goes more smoothly for you than me!
The Drag Link Bearings
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.
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
The 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.
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 !
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!
Close but no coconut
I have been working on the valve gear completing the expansion links and die blocks. The link slots are longer than designed (due to iffy dimensioning on the drawings), so I made the die blocks longer to match, so I think all should be OK.
Colin Sims and I have been debating if the eccentric rods are too long, and having now assembled the LP Valve gear I can confirm they are!! I have ad to shorten the clevis (?) at the bottom of the valve rod, and also shorten the valve rod to get everything to fit – not a complete disaster, but it seemed to be about 3/8″ long over all…
Worried about LP Valve too
Having now assembled the LP gear I could not resist applying some compressed air to see what happened – and what happened? The valve leaked (a lot). Inspection revealed that the eccentrics and eccentric rods are too close to the valve chest, and so exert some side pressure on the valve rod, and the design of the “buckle” means that this resulted in the valve being held off it’s seat. I am sure this is all as a result of inaccuracies in my machining, but it’s still a bit of a concern.
A normal slide valve buckle allows the valve to settle smoothly onto the port face, but the circular arrangement in the Leak has the opportunity to hold it at an angle in either the vertical or horizontal plane. Disconnecting the expansion link from the valve rod, resulted in the valve seating, so I think it’s just a matter of providing enough “slop” to prevent the crank endfloat from forcing things out of line…
However, I also found if I upped the pressure the balanced valve started to leak. – It seemed to be that the part a the valve bearing on the valve chest cover is forced off it’s seat. (not a good sign). It would appear that there is insufficient surface area on this part of the valve to hold it in contact with the cover, a large change!.. Time will tell…
Some picks of machining the links and assembly…
Over the last few weeks I have been progressing with the HP valve assembly – a greenly long-type piston valve (apparently).
Because the Harrison is showing it’s age (70) the wear on the bed sometimes leads to
trouble you can’t manage… most notably tapers everywhere! The HP Valve chest had to be bored on the lathe, as it was too small/long to be done on the Vertical Mill – as a result it had a taper on the bore of about 3thou. The piston valve liner therefore needed to be similarly tapered, and it was not possible to try the chest on the liner while being constructed – so this just makes it harder.
Machining the Liner
The liner is meant to be a push fit into the valve chest, and my machinery handbook suggests that this meant there needed to be about a 1thou clearance – all a bit tight, but with carefull use of a set of inside micrometers my friend Juliet donated to me (her father’s) and a lot of carefull miking it all came good! The picture above shows the first facing cuts on the liner casting in progress.
The first stage is to cut a small part of the bore at each end, and press in a centre at one end – I happened to have a bit of cast iron bar which was a nice fit – and by the three-jaw (with inside jaws at the other) and then the outside of the liner can be machined. This was carefully made with a taper to match the liner, but you can’t check the fit till you finish, as dismounting it, or removing the centre, would disturb the allignment. Later when the outside was finished I was very pleased to find that it slid in with the last 1-2 inches needing a push.
At the same setting I cut the port grooves. (One of the really pleasant things about the Harrison is that it is so ridgid you can plunge a tipped parting tool in a near full speed without a jot of chatter or other pain). However, it was noticable that the finish I was able to get from the tool on this was no-where near as nice as I had achieved on the cylinders, some difference in the iron I imagine.
Once the outside was ready I transfered the liner to the mill and drilled the port holes using a rotary table and the DRO (to ensure perfect positioning)..
Because of the limited vertical clearance I was worried that I would not have room to get the drill bit in, and guessed that I would have to use a centre drill and then finish the job on drilling machine – but for once the gods smiled and I realised that two of the standard sized centre drills were the size I needed – so just drilled straight thru 🙂
Boring the Inside
Now we are on the home stretch, a simple boring job – first make a plug gauge, but again the dreaded the tapers bite – and I discover the the inner end is about 4 thou larger!!!
The book suggested using the plug gauge to lap out any such problems, but of course it is now too damb small!! So I set to with my trusty sykes-pickavance cylinder hone (three wobbly slip-stones in a hand drill), and carefully reduced the error to about 2 thou, and decided that could be accomodated by a tapered valve and it’s rings… time will tell, but I am starting the “buy Malcolm a newer lathe fund!”.
(yes I know you can see the whitness marks from the chuck jaws, but this surface is the push fit into the liner (secured with Locktite Structural Adhesive) so I am guessing it will not be a problem, and you can also see the less-than-perfect bore, but the hone cleaned this up a lot).
The casting was one of the few parts which had been machined, and I would guess was the point at which the builder threw in the hand towel, as the cored recesses were not well aligned with the outside, and I think they took a starting cut over the outside, aligning things at one end, not realising the recess at the other was so far out that they then had a “scrap” valve… however my inherent tightness and belief in shrink fits took charge! so I cleaned up the errent recess and srunk in a block of cast to provide the meat to effect a repair.
The rest of the job was a nice turning and parting excercise. The final sizing and ring groves being turned with the valve mounted on its spindle (as a mandrel) in the (newly made) collet chuck – buy yourself a set of ER collets NOW… I can’t believe how many years I delayed that purchase, and just how good they are (and mine were second hand of ebay!)
It’s a funny thing, throughout my life I have read constant warnings about breaking piston rings, and the man who started this engine had even got spares for the 6 on the piston valve – now I know I am going to regret saying this – but I have never broken one, not even the ones on the Edgar Westbury Seal I am making (5/8″ bore)…
Fitting the Liner
I used locktite structural adhesive (the yellow stuff) to fit this, I am not sure about it’s high-temperature performance, but the recommended Slow Areldite is much the same, so I am hoping. I had left the liner a few thou long to match the cylinder block, which will get a final skim over the top, and crossing my fingers, just pressed it home with the help of a G-clamp and a pair of plates – and it looks OK… Job Done!