Asciidv

As you will see, the superior Dennis product has 3 rivets to hold the washer in place to aid alignment whilst the bolt is pushed through. It must be so dispiriting working on a Thornycroft after the magnificence of a Dennis!

Barry.

My Land Rover wheels must be missile proof by now having for years had the daily attentions of half a dozen dogs all determined to be the last to leave his mark

I don't think Degsy should be too confident about the strength of his Land Rover wheels, for here is a picture of a 4mm thick box section post which has had the daily attention of one of our dogs. Maybe it is the breed, - so avoid Belgian Shepherds!

Barry.

Oh look, Mr. Dennis Patent keeps his doorknob very shiny!

 

Seriously, what is that brass thing on the cover? Is it just to lift the cover?

 

Trevor

...here is amother door knob this time on the top of the PTO. As you will see it is just a rather smart 'breather'. The advantage (or sometimes disadvantage) of having a fire engine is that all the brass bits have to sparkle - and yes it is cheating if you laquer it over to save effort later on.

Barry.

This, apparently, was how it was done. There is no separate oil-filler hole in the top, so it seems that the whole top had to come off for filling the gearbox with oil! The wing nuts on it at present are the more modern type but we have just found some older style ones on E-Bay with the correct for the period, "Mickey Mouse" ears!

 

Tony

Tony, surely your Dennis gearbox was just like this with a cover plate and wing nuts?

Barry.

I am still pondering as to how the factory would have machined the pistons. Possibly, they may have started with the bottom of the skirt, facing and boring and then by cutting the gudgeon-pin holes. Next, using a dummy gudgeon pin and a draw bolt through the lathe headstock, the piston could be pulled back onto the faceplate or a locating disc to turn the outside and face the crown. They would not have had a chucking piece like ours as it is a wasted piece of metal. We don't have the facility to bore the gudgeon pin holes and that job will have to be put out. Using the chucking piece, I can complete all of the other machining processes before having the hole bored.

 

Steve

Here are some pictures showing the process that Steve has just described.

The piston skirt has been faced and bored so that a spigot the diameter of the piston may be fitted. A gudgeon pin has been fitted with a block which will have a threaded rod screwed to it. This will pass through a hole in the spigot and pulled up tight against the end of the lathe headstock.

Here the spigot is held in the chuck of the lathe and machining of the outer diameter is taking place. In this instance we are turning down an oversize piston. It was quite easy to make the original piston run true to a 'thou' before machining took place.

Finally a comparison with the new and old. Pistons are never constant diameter, always smaller around the upper ring grooves to allow for expansion. Many pistons are taper turned. Pistons fitted to my 1930's Leyland engine were both tapered and oval. I am sure that would be a challenge that Tony would takei in his stride!

Barry.

Just to show that Steves's patern making skills are equal to any other, here are some photographs of a piston pattern made for the 60HP White and Poppe Dennis engine. This pattern was made for 'Jezebel' the Royal College of Science Dennis fire engine, which had a phase of eating its pistons.

Barry.

Well, I feel a bit more relaxed about keeping fire engine Breathing Apparatus in our dining room, knowing that Steve has a hydraulic press in his lounge!

Barry.

Was all of this fabrication silver soldered? I thought that this picture shows traces of conventional welding of the main boss to the handle plate?

Anyone who has "chewed" through a lump of steel with a small diameter milling cutter will admire Tony's perseverence in milling a nice perfect fit square hole in the end of the handle.

Are the piston patterns underway?

Best wishes,

Barry.

Well, I am going to vote Conservative - leave well alone!

Barry.

I know that this is Steve's Thorneycroft thread, but I am sure he will not mind if I ask you a couple of questions which your very interesting pictures raise. First are you casting these parts yourself in your garden!? The internet has many examples of 'home foundries' but they tend to be more for model parts or decorative plaques not large manifolds. If your are casting these parts I think we would all like to see some pictures of your furnace and perhaps the actual pouring.

My second question relates to your etched plates. I too have made etched plates for my Dennis Fire Engines, but I always find the black infill a problem. After etching the brass I then use a brass blacking solution which is applied all over. I then polish this off the un-etched sections leaving the black in the lower level of etched brass. This can be tricky. What is your equivalent of plaster of paris core boxes for your plates!?

Best wishes,

Barry

Steve, why has the top core print an inverse taper rather than being just parallel like the bottom print? Does this part really need a core at all as you could mill out the water passage?

Barry.

Gordon,

May we have a sketch please? I think what you are proposing all sounds a bit too fanciful!

Barry.

If you increase the clearance beyond 15 thou. ...... rapid wear of the tappet/valve faces will occur.

 

Best wishes. John

Why? On a side valve engine these are co-axial.

Barry.

(...I keep thinking about this, and in practice the larger the gaps the engine does sound more 'tappety'. So there must be extra energy at the point of impact and hence more wear, but I do not really see why this should be case.)

(and thinking a little more, with larger gaps the point of impact occurs at a steeper part of the cam ramp whre the acceleration is also greater, hence the bigger 'tap' and more wear. Perhaps it was too early in the morning to think straight!)

Steve,

When you have the time, I am sure that many of us would like to know your experience with silver soldering/brazing. Do you use the same rod type all the time or do you select a rod depending on the strength of joint that you require? Do you find the flow characteristics of different rods and flux types influences what you use? What combination do you normally use and does it differ for ferrous and non-ferrous parts?

Barry.

Yes - we have thought of that one and Steve has been doing some calculations to take that into account. I am not sure how far he has reached with it and no doubt he will come into comment!

 

Tony

I read this and "m omega squared r", flashed past me and I thought that Steve was going to be brave and put his maths and mechanics to the test, only to be a little disappointed that it was going to be spring rate modification calculation! He ought to let off though, because the bits are beautifully made and I am sure that they will work too.

He gave an example of his friend testing out a similar governor in a lathe, it would be nice to see some photographs or better still a video of this one operating.

Barry.

Steve,

There are many low temperature aluminium 'welding' rods available under different names such as Technoweld, Lumiweld and HTS. In effect it is just like aluminium brazing or perhaps soldering. If you watch this video,

http://www.aluminiumrepair.com/video_new.php

you would think it is the most magic thing on earth and wonder how you could have possibly done without it. In reality it is never that good. Due to its low viscosity it tends to run away, so if you are trying to fill a crack in a casting on a non-planar face as soon as you move away from the level it runs out from the area that you have just completed.

Barry.

Were those bird droppings on the water pump housing from a MIG pigeon or a TIG pigeon?

Barry.

Returning to the question of acceptable crankshaft end float and the observations that John raised, I have included the section on endfloat from a 1930's Leyland engine manual. The size of this engine is simiilar to the Thorny. The suspicion might therefore be that 30 thou float is a little on the large side.

Barry.

John,

I would love to talk to you in detail about the noise from crankshaft end float.

If you go to this You Tube link, you will see (hear!) why.

This link tells the full story

http://www.dennisfire.co.uk/p50.htm

I wonder if you would contact me off the HMVF forum at;

DrBAH999@aol.com

Thanks,

Barry.

......and another question! Does this engine have shell bearings as the text suggests or is it white metalled? Isn't it very advanced to have shells?

Barry.

Were you not making it more difficult for yourself by fitting the crank with the flywheel already attached? Or was there a reason why the flywheel had to be present? When you were fitting the crank could you adjust the end float and what about the main bearings. Did you just repalace the main bearing caps exactly as they came off or did you have to 'juggle' them around? What torque did you use on the main bearing nuts? Was it from a torque wrench or just an appropriately sized spanner and an interpreted number of foot-Steve-pounds?

Isn't it about time you put your mince pies down and made your way to your shed? I have been looking every day to see what you have been up to, but there is nothing!

Best wishes, Barry.

"30 mph", was he hoping it would do 60 ? :-D

 

David

I did laugh at this!!!

Barry.

Steve, on early engines like this, what was the function of the governor in every day use? Was it a mechanical 'cruise control' or just a 'rev limiter' if you were to use today's terminology? Also how exactly does it work, where is the closed loop function?

Why not remake the parts in aluminium? Far easier to do, more original and I doubt that once restored this lorry will ever be abandoned again to decay away.

Barry

Did you consider boring the roller out further so you could fit a thicker wall bush? I know you consider the load on these parts to be negligible but on my Dennis the roller shaft pins have to be nitrided or they last no time at all.

Barry.