Well, after a long lockdown winter, and a rather cold snap, we decided we were certainly ready to unwrap Befur and get back on the water.
From Experience two other issues to consider
While these are not drawing errors, they have emerged over the first 3 seasons with the engine, and should be considered by builders.
HP Valve Chest to Cylinder Joint
In the BOOK the designer suggests using Araldite? as a jointing/sealing material… its not a solution, particularly for this joint.
The joint between the HP Valve Chest and the HP cylinder is problematic, as the sealing faces are very thin, and the two components are only secured by 4 bolts, which are hard to tighten and not well positioned to ensure a steam tight joint.
My first attempt was using “SteamSeal” jointing compound – this failed quite quickly.
The second attempt was using “Heldite” jointing compound – this failed within a few hours.
My last attempt was using “Oakenstrong” gasket paper, I had resisted this, not wanting to affect the overall block dimensions. However, rebuilding with gasket paper and jointing compound (Heldite) does seem to have cured this problem.
Lubrication of “small ends”
I spent a long time chasing a knock that appeared to come from the LP small end. Rebushing the piston rod and a new pin did not cure this, and it was clear that the pin was suffering.
This was finally cured by increasing the size of the Lubtech pump units feeding these bearings and slide ways. A “black” one (0.1cc/stroke) silenced the knock instantly.
I am sure that a better builder than me might make the sideway fits better, but the lubrication points at the bottom of the piston rods have to lubricate the “small end” and the slide-ways, and so need a heavy oil flow to ensure that both bearings are supplied on each cylinder, as I think the oil preferentially flows to the slide-ways, starving the bush at the lower end of the piston rod.
Timeframe missed a bit
Well, looking back the first post here was on 8th June 2011, and we aimed to finish and launch by 26th June 2015 – planning was never my hot spot! We did change the goal posts in mid-flight (adding a sail, loo, etc, and stretching her from a planned 16ft to almost 27ft to get everything in, but hey we did get there!), and on the 20th July 2020 we took her for a steam and sail on Windermere with a cameraman (Roger Heise from the SBA) on hand to record her 2nd trip under sail (thank you Roger).
Notes on the Steam Bit
Before I inflict an album of sailing photos on you, a couple of notes on the steam side, especially for Leak Compound builders…. Continue reading
This post continues/concludes the story of manufacturing a new crank for Befur from the last post.
Here we can see the re-assembled engine with new crank. We are still to install all the ancillaries (reversing gear, lubrication, condenser and feed/air pump & alternator drive.)
It took 6-man days from receiving the crank back from the grinders to reach this stage.
Once we have tested it on air, we will reinstall it on the boat and undertake this year’s boiler test and check all is as it should be.
Machining Crank Pins
Those of you who have been following Befur’s progress will know that our first year in the water was marred by the failure of the crankshaft in the Leak Compound engine I built.
This post deals with the manufacture of a replacement, and the results of my research/experience into the approaches to building cranks for “small” (<20HP) marine steam plants.
Methods of Manufacture
Well we got Befur’s engine back into the workshop, and stripped it down to see if we could locate the source of the knocking we have been suffering all season.
On lifting the crank out it looked perfect, and did not have any obvious loose or moving joints My heart sank, as this was really my only theory on what was wrong. Continue reading
Having “finished” and tested my engine there were a final set of issues that I suggest you keep an eye on:
- Piston Rod Lubrication Fitting Clash: The drawings show the small-end and cross head lubrication is achieved via drillings at the top of the piston rods. There is no indication of how oil is delivered to these drillings. I have arranged this using small-bore flexible nylon tube and push fittings. I installed a small elbow into the feed hole to allow the push fittings to point between the bores. However, space is very limited here, being close under the lower cylinder covers and stuffing box glands. When I packed the glands I found that as these sat slightly lower they clashed with the oil feeds at TDC. I can see no way to move the oil feeds. So I resorted to machining away some of the bolting flange of the stuffing-box glands next to the columns. This has worked, but clearances here are tight.
- Air Pump Drain Modification: the drawings show a simple drain plug screwed into the bottom of the air pump body. In my design of pump drives this is hard to reach, and having a circulating pump exhausting into the condenser, you can get into the situation where the condenser becomes full of condensate if the main engine/air pump is not running. So I have brought this drain out to a simple taper cock. This just makes things a bit easier.
- Pinning the Drop Arms: During early testing I found the drop arms had a tendency to slip on the weighshaft. So I installed small taper pins to secure them.
- Reversing Lever Clash: This was just me not spotting a problem earlier. I fitted the weighshaft at the top of the column position. On final installation I discovered the level collides with the exhaust pipe in full-ahead. Just keep an eye open. 🙂
An experiment – Steam Operated Combined Drains & Relief
Much earlier in the process I baulked at drilling the cylinder castings for the cylinder drain cocks because they looked hard to drill with out risking damage to some rather expensive castings. Moreover, previous experience with manual cylinder drain cocks on the loco had been poor (leaky, difficult linkages etc.) and on the steam launch most people seem to opt for 4 manually operated cocks which involves a deal of “faffing” in use. Continue reading
So, following some communication with the steam boating forum we are all agreed that the Edwards Air Pump as drawn is missing anything to hold the valve-plate in place, or seal its contact with the pump body. This means that:
- The whole valve tends to move up and down with the piston rod, (and I think this needs to be a “good” fit to prevent leaking round the pump-rod, so this is unavoidable).
- There is nothing to seal the lower valve plate (the one with the holes) where it sits on the ledge of the pump body…
So, my solution is to:
- fit a gasket under the valve plate
- make and fit a nylon block to hold the plate down – made 10 thou too long, so that the top cover provides some “squishing pressure”
As other members suggested this may help pump performance by removing “deadspace” (but it is beyond the valves so I am not sure if this is correct), and secondly it needed to be made in a way that ensured the outlet port is not cut-off if the block rotates; so, as can be seen in the pics below, I have made it with an exhaust annulus and internal ports to the valve chamber cut in the bottom…
I think this approach will also prevent the valve opening too far….. a test in the kitchen sink proves that it all works!
Here are some pics of the block and completed pump assembly.
I think there is a problem with the air pump design/drawings…
This looks like it’s not a problem with the drawings, so much as an oversight in the design…
The outlet flap valve assembly is not fixed/located by anything vertically within the outlet chamber… neither is the lower valve plate – part 3 on P20 of the book – (the one with the holes) sealed against the lip it rests on above the cylinder….so (as I noticed when I completed a trial assembly) the whole valve (both plates and the rubber washer) move up and down with the piston rod, and even if the vacuum held it down, I feel sure any hard won pressure difference would be lost as the air leaked back into the pump round and under the valve plate.
My current plan is to make a nylon “block” which is a light push fit in the outlet chamber, has “ports” to let the air-water out to the delivery port, and is slightly longer than the available space, so that when the top cover is fitted it will press the lower valve plate down onto a gasket I am fitting under the valve plate….
does anyone have any better ideas/opinions? am I missing something?