Asciidv

"Dave was not happy with the method of Tony’s manufacture of the Valve Guides"..... I have just been longing for someone to ask 'What did Tony do wrong'?!, but everyone has been polite enough not to ask. Were the outer diameters turned first and then the guides drilled and reamed rather than the other way round? Barry.

I am sure if I scroll back through these pages I would find the answer, but I am still going to ask a silly question.... I am sure that I must have missed something but I am only a casual reader to this thread as you are not working on a great engine like the White and Poppe in the Dennis! What now goes over the top of this part (the threaded bit with the hex ) to seal the hole up? Barry.

Steve, to what accuracy do you believe the cylinders have been bored to? Have you tried to measure them? How concentric do you think the recesses are to the main bores (although in this case this isn't really critical)? Do you know how your friend set up to find the centre of the bore before cutting the recess? Another mystery to me that you can perhaps explain is how do they set up the boring bar to the centre of the cylinder when what they are presented with is often a bore which is oval with non-symmetric wear? Barry.

Why just one thou oversize? Obviously a rule of thumb, but was it a Devonian thumb, or a Midlands thumb? Best wishes, Barry.

Whilst a picture of a four jaw chuck is fresh on the page, I just wondered if any of you have any 'trick' for centre'ring up an irregular shaped part. I have always just done it by eye, followed by taking a trial very light cut to see if all is running true. Returning to the 'O' ring I have never really been happy with the homemade glued together type. The junction is always a lot harder than the rest of the ring and never quite seems to seal properly. I an looking foward to seeing the development of the piston pattern set! Is it coming soon? Barry.

....and did it leak?.....

Returning to the radiator, hasn't a little bit of science been skipped as to what makes an anode or a cathode and electrochemical potential? Even, if Tony had an 'earthed' block of zinc in the header tank as a sacrificial anode I bet the water would have weeped out just the same. However, this is all to our benefit, as we can now watch Steve make the patterns for the new tanks :nut:! The header tank is no mean task as more than one core will be required. Barry.

There is a very easy and reliable method of removing pressed in liners and quite possibly 'glued' in liners too. You simply run beads of weld (perhaps 4 or 5 of them) down the length of the liner using a stick welder. When the weld cools it contracts the liner too and then it is loose! I needed to re-liner a Perkins V8 in-situ in a fire engine chassis and was taught this trick by the local Brigade workshops. Barry.

For head and block crack welding I have used Slinden Services twice; http://www.castironweldingrepairs.co.uk/classic-vintage-veteran-motor-vehicle-casting-repairs.php Both times the work was excellent. Their web site shows photographs of some of their more extreme welding jobs. Incidentally I hope Tony is not going to be too distracted from the Thorneycroft restoration by watching his new 32" LCD television!

My own experience of JB Weld is that it appeared to be no better than any of the other epoxies currently available. I used it on the external surface of a White and Poppe engine block which had turned porous. Within a season it had broken away from the surface, possibly due to differential expansion rates.

The cylinder bore coating process which has been referred to is less than 100 microns thick, is depositied electrolytically and essentially is only a plating. Not really suitable for building up such deep corrosion. The most common of this type of coating is 'Nicasil'. Very successful on two stroke racing cylinders where I first used it, but a total disaster for Jaguar when they used it on there V8 car engiines in the 1990's. (High sulphur petrol dissolved the coating resulting in 1000's of engines having to be replaced under warranty). It is a problem, but I am sure Steve will overcome it, even if it means casting a new block!

A question for the Master Stud maker..... I would imagine that the stud holes are a mixture of through holes and blind holes. 1. On the blind holes are you screwing the studs in until they bottom out at the end of the tapped thread? 2. On the through holes are you screwing them in until you bottom out on the end of the thread on the stud? 3. OR, are you taking advantage of something like Loctite 270 'Studlock'? and now a question for the Master Engine Block Painter...... 1. Do you have any reservations about gasketing (if there is such a word) onto painted metal rather than the gasket having direct contact with the metal face? I saw your broken rings and I think we will all be disappointed if you do not make your own replacements. I have just taken the easy way out and had 25 made by the 'Bradford Piston Ring Company' based in Manchester. A superb old style company who made these rings to my specification and only asked for payment once I had received them. They came within 2 weeks too. Looking forward to Brighton 2015 for the Thorny's first run! Best wishes, Barry.

Thanks, for the responses so far. In particular I found Tom's reply very much in line with my own thoughts although I hadn't considered the next logical step forwards and make my own studs in a material that I know the specification of - and hence the torque figure can be accurately specified. Setting torque just by 'feel' is risky I think, especially on cylinder head bolts. Even clamping pressure of the head gasket is important My straight six Leyland engine has always been susceptible to head gasket problems and I would always want to be as precise as possible with the setting of the head bolts. I have a realtively modern big V8 diesel in my transporter. The torque for the head bolts is 240 ft lbs. (Time for the 4 foot spanner....). I would defy anyone to achieve consitent torques (say within 10 percent) without a torque wrench at this level of torque. I do believe in the old ways, but I can guess when a little modern science is better! Barry.

I know that this question has nothing to do with the Thornycroft restoration :-(, but I do know that the kind of people who read this thread are ideal to answer my question about torque'ing down old cylinder head and big end nuts. I will be putting an old Leyland engine back together next weekend and was wondering what torque I should use on the head nuts and the big end nuts. They are both 1/2" BSF. If you look at all the charts available on the internet the suggested torque figure range from 30-120 ft lbs depending on the bolt grade. So the question being is 'What grade of bolt' did they use in the 1930's for this type of application? Barry.

Does the Thorneycroft restoration have an dedicated HMVF thread already? If so where should we be looking? Thanks, Barry,

How did the Dennis start? Are you still with the non-impulse magneto? Hope you had a lovely weekend! Barry.

Does one of the last pictures show that it is a true Dennis, with the characteristic oil drips coming from the gear selector rods indents? Barry

I would cheat! I would weld a bit tube onto the end of the flat spring steel (probably NOT using an Oxford stick welder)... Barry.

"The spring then unwinds giving the magneto a sharp flick producing a good spark in spite of the low engine speed." I would like to point out that magnetos put out a high spark at low speeds" Mathew I don't know whether you are talking in relative terms or absolute terms, but magnetos do produce a poorer spark at low RPM than they do at high RPM, hence the need for an impulse starter. It is all to do with the rate of cutting the magnetic lines of flux. The faster you turn, the greater the rate of cutting, resulting in a larger emf (Faraday's Law). You have to achieve a certain level of voltage before the air gap will break down and a spark is formed. Magnetos do start to fizzle out at very high revs (perhaps greater than 8000 rpm) but this is far in excess of the speeds of the engines which we are concerned with. Barry.

Steve, The secret is to have a 5 cylinder engine or at least 5 sparking plugs! I don't think back feeding HT into the magneto would do it any good and the impedance of the magneto would probably be low enough to reduce the voltage so you couldn't have a spark anyway. All of my valve caps have provision for two plugs. (See above picture). This isn't really a serious suggestion as I am sure the impulse magneto will do the trick. It was just with this particular machine of mine, it doesn't have a trembler or an impulse magneto, just like your lorry. Starting it without help at the farm is impossible, hence the intervention of science. As an emergency 'Get you by fix' until you have your magneto sorted out, a battery and coil in a little box would make life easier.:yay: Barry.

As Tony has explained before, the engine was originally a fire pump engine and was fitted with a trembler coil for easy starting. In lorry guise the engine only had a magneto, hence the desire to fit an impulse magneto to make starting easy. There is a short video here; which describes the starting of a Dennis using science! Barry.

Isn't it awful! You spend 10 years restoring a pile of rust to a magnificent Dennis and then someone 'nitpicks' about a split pin that you have used... Barry.

Please tell me more about your split pins. I have always associated this type of pin (with the large oval head) as being American. Barry.

I hope you don't forget to attach the 'lucky horseshoe' before Brighton! Barry.

I hope with the Powerfile! Barry.