911hillclimber Posted March 5 Author Share Posted March 5 That approach had gone through my mind too, but I'm not sure I can get the pin in square to the crank or indeed to get the right interference fit to get the pin in tight and for it to tolerate the engine running. This is why I had the thought of En8 pin oversize and brazed in (after press fit). Machining the pin as before will get it square as the dia is machined down to a 1/4". If I allow the parts to air cool slowly the En8 should stay reasonably soft. Quote Link to comment Share on other sites More sharing options...
KEITH BEAUMONT 1 Posted March 6 Share Posted March 6 On the last 6 engines I have made, I have force fitted the crank pin into the Disc and have had no problems with them failing. I did make the Sparey from one piece though. My method is to drill.015" undersize, Using a hand reamer,carefully ream using just the taper end until the pin just starts to enter. Remove the leading edge of the pin so that it will not scrape. Then, using a vice with Ali plate in the jaws,set it up square, put some Loctite in the hole and squeeze thhe pin in until it is flush with the back face. I think you are doing a great job! My first lathe, many years ago was a round bed Drummond. Keith 1 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted March 6 Share Posted March 6 On 03/03/2024 at 19:09, jeff2wings said: If you go on e-bay and look for myford accessories they sell a clip together belt,abit like the old motorcycle final drive belts before using chains,this should give you the chance of adjusting the belt length to suit Hi Jeff I bought soome clip together belts for my Myford ML2 . It is i believe a "between the wars" model that uses an over- cemter cam to act as a clutch. The clip together belt was intended for the drive ftom motor to the intermediate shaft. Its noisy (constant clicking) and slips. So its now sitting waiting for a home ! It comes in different section sizes and I obviously have an inappropriate sectionfor the pulley "v" I'll be sticking to fan type belts. The annoying part was it was it comes in 1mtr lenghts and one meter was just too short so bought another 😁 If anyone is interested its going cheap £10 plus postage. Enjoying the trials and tribulation of the build 911Hillclimber. Keep going. Re brazing a pin into the crank web. If its pressed in without clearance then brazing will be inefective as it will only run around the outside and you would then have to clean it off ? A good press fit would be the way id go using a roller bearing as Martin suggested. A lot of the chinese engines use a press fit crank pin( roller bearing)and only occasionally do they come loose ; but then some of the crank shafts were turned from not the best grade steel and bent easily. Fortunately this meant they straighten very easily. Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 6 Author Share Posted March 6 This is very useful real-life experience, thank you all. Just been to Hemmingways for a fresh steel billet, but now home it is too short! Thus, a short ish return tomorrow i hope to swap for the right length. This is an insurance incase the pinning idea fails... I will try the force fit. I have borrowed a 1/4" reamer from my oldest friend (who has now joined this forum to keep abreast of my adventure) so that should fix it. I'll order a ground pin as suggested before from Simply Bearings. That should negate the need to machine the pin I hope. These things are sent to try me!! Mind you, I doubt a Myford Super 7 would help.lol Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 6 Author Share Posted March 6 (edited) Spent a few hours fixing this bloody crankshaft. I've ordered some ground 1/4" pins 3/8" long, so right dia for the con rod big end and right length. Bought 4 for a £5, hope they come soon. I've removed the machined crank pin and drilled the crank web to the right stroke and drilled under the 1/4" reamer size, so best drill I had is a 6mm Dormer new one. Set the crank in the lathe, removed the pin. Set the new/correct centre for the pin and drilled it 6mm dia ready to be reamed. Did this on the compound slide head which worked a treat. Advice is to ream the hole 'just' so the dowl pin will 'just' enter the hole. The reamer has a very very slight taper to the nose to ease the reamed dia to be made. Remove the crank and squeeeeze the pin in, thus an interference fit. Need those pins! As advised, the 4 jaw chuck has been damaged by my clumbsey mishaps, Jeff was right. However, managed to strip it down and after some swiss filing to 3 jaw screws all is working like new. My Vee blocks are going back into storage... I feel like I'm dodging bullets at the moment. Every day I lean something. If I make another crankshaft I will turn the blank to shaft dia for the bushes and turn the crank web to thickness. All 3 jaw stuff. Transfer the machined blank to the cross slide. Pick-up the crank centre to the chuck and then index the stroke on the compound VERTICAL slide as it is fitted with a dial. Drill and 'pin-fit ream' as advised. That would be SO much easier! 73T 911 Coupe, road/hillclimber 3.2L Edited March 6 by 911hillclimber Quote Link to comment Share on other sites More sharing options...
RottenRow Posted March 6 Share Posted March 6 I have a book written by L. H. Sparey (the designer of your engine). He shows the turning of a crankpin in a similar way to your method, except his vee block was designed to bolt on to a faceplate. He refers to the vee block as a Keats plate. They aren’t very clear but hopefully you will be able to see from the pictures below how he did it. Also shown is the book. First published 1948 but reprinted later. Brian. Quote Link to comment Share on other sites More sharing options...
KEITH BEAUMONT 1 Posted March 6 Share Posted March 6 Although I machined the Sparey crankcase to the drawing dimentions, I found on assembly that the con-rod touched the corners and some scraping and filing were needed to get free rotation, so dont be too disapointed if you get the same result. Keith Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 6 Author Share Posted March 6 Thank you for this detail. Not sure if I want to do another! Good to see though, just might make one when done. Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 8 Author Share Posted March 8 Con rod pins came a day early, so got one in the crank after 'just' reaming the hole 1/4". The pin was a force fit, not a very high interference, but a good tight one. Didn't use loctite as i forgot! Thus, i think this crank pin saga is at an end. Collected my new En8 blank yesterday from Hemmingways, so all set nearly to make another (if I fancy to) Social weekend now as my motorsport interests kick-in, so back on the engine next week (dreaded con rod) 73T 911 1 Quote Link to comment Share on other sites More sharing options...
KEITH BEAUMONT 1 Posted March 8 Share Posted March 8 Well done with the pin! Loctite ,in this case has two uses. It lubricates the insertion and,hopefully,does leave some behind to improve grip. Dont forget you need to take metal out of the Disc, to help balance. Keith. Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 8 Author Share Posted March 8 Thank you Keith. The crank has some more work needed yet, the shaping of the web as you say and the prop drive hub. I'm not cutting a taper as the design but using a stepped hub in ally. I can't machine male/female tapers on this lathe! While the pins were arriving i have adapted a home made face plate that came with the lathe to me and have made an adaption of my Vee block. Will detail when I've skimmed the mounting surface clean and added some paint. Quote Link to comment Share on other sites More sharing options...
KEITH BEAUMONT 1 Posted March 8 Share Posted March 8 The taper on a crankshaft is not a good idea and makes it quite difficult to judge the all important gap between Driver and front face of Crankcase, to avoid things binding up when you tighten the prop nut. The best method is to make a brass collet. I know you cannot turn tapers, but the method I use is to use a short taper reamer,that is made for enlarging holes in sheet metal , to put the female taper in the Driver. These are 20 degrees inc and just right for a collet. I am talking about the plain two bladed type, not the stepped variety. Run lathe fairly slow, 50 RPMish, with plenty of oil. Then I am sure it is not beyond your skill to make the male taper on the Collet by rough cuts to shape and then finish with a file,using some Blue to check fit. The step in the crankshaft needs to be .020" in front of case front face, Dont forget a small radius in the corner. Hope I am not telling you how to suck eggs? Keith. Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 8 Author Share Posted March 8 I’m open to all ideas! Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted March 8 Share Posted March 8 It may be possible to find spare parts for current production engines to remove the need to manufacture difficult parts. That is assuming it's not against your philosophy to create something all of your own. Quote Link to comment Share on other sites More sharing options...
Indian Posted March 8 Share Posted March 8 Your lathe should be able to turn short tapers and if you leave your compound set at the taper you can then machine another taper on a piece of silver steel to make a D bit ensuring the two pieces will fit together perfectly. As for allowing for free play between the pulley and the crankcase its a simple matter to skim the pulley to get some. The taper on the crank makes it less likely to give stress risers and therefore failures. Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 8 Author Share Posted March 8 (edited) I doubt anything I've restored mechanically has not been modified! lol The lathe can machine a nice external taper, it is the only function on the Drummond that has a 'gauge' on it, but it is cutting the small long similat taper that gets tricky. The induction inlet 'bell mouth' was tricky enough and that is massive in comparison. I was thinking to machine the prop end of the crank to 6mm dia. This will give a shoulder against which the prop flange can locate. The prop itself at 12 to 16" dia (!) has a hub dia of 8 mm i think, so a prop hub with a 6mm hole and an 8mm dia and then threaded M6 to take the prop 'nut'. Shaping the crank web will be awkward, but i will cut the side scallops out by hand roughly and then mill to true things up using the compound slide. That will be the next job, possibly tomorrow pm if I'm home in time. There is a gap between the crank case and the screw-in rear cover which i left a bit long, so that needs machining down to allow the cover to be tightened andd still give some crank pi clearance. I guess that clearance only needs to be about 1/64" or a 1/32". You could call this crankshaft float. As to borrowing parts from other engines, I am looking for a spare fuel bowl instead of the design's aluminium tank. A nice clear one say. You can buy new Mills 0.75 tanks but they must be minute. Edited March 8 by 911hillclimber Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted March 9 Share Posted March 9 (edited) Re tbhe tank . There was I believe somebody on the net making replica tanks for ED comps ? Worth a search ? Edited March 9 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted March 9 Share Posted March 9 9 hours ago, 911hillclimber said: As to borrowing parts from other engines, I am looking for a spare fuel bowl instead of the design's aluminium tank. A nice clear one say. I have made a few nice vintage style fuel tanks by recycling the clear plastic tops that come with some drink bottles. Check them with your intended fuel before using. Regards * Chris * Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 9 Author Share Posted March 9 I have thought about a fuel filter cartridge as the basis for the clear tank, but not sure is araldite is fuel proof. Quote Link to comment Share on other sites More sharing options...
Indian Posted March 9 Share Posted March 9 As I said before if you turn the outside taper and a d bit blank at the same time they will fit perfectly, same goes for your Venturi and if the material being cut is alu no need for fancy hardening if you are only going to use it once or twice. Quote Link to comment Share on other sites More sharing options...
KEITH BEAUMONT 1 Posted March 9 Share Posted March 9 I made the fuel tank from acrylic tube, with an acrylic bottom screw cut and superglued. The top was as drawing,also screwcut Ali. Keith. Quote Link to comment Share on other sites More sharing options...
911hillclimber Posted March 9 Author Share Posted March 9 Must admit I am trying to avoid the faf of thread cutting! Over the years i have collected a few old engines, all spark ignition and the last one was only £18 with a great fuel tank (diesel though) with a neat filler cap etc. One like that off a dead engine would be perfect. Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted March 9 Share Posted March 9 Thoroughly enjoying this thread even though... a) I only did one year of metalwork in school b) I don't own, and probably never will own, a lathe c) most of it's double dutch to me! Great work guys. Quote Link to comment Share on other sites More sharing options...
Indian Posted March 11 Share Posted March 11 Its a shame you are avoiding screw cutting as it is a necessity on most model engines and a good skill to learn. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted March 11 Share Posted March 11 Yes thread cutting on the lathe is really good once its set up . Some good "how to" vids on youtube once you can filter out all the bodgers and fools on there. I found out how to cut the thread in the rear of a crank case on there as my lathe doesnt have reverse or an index system. An ingenious person made a handle to fit on the mainshaft to reverse to make the next cut so keeping the spacing correct. I adapted this idea by turning the input drive pulley from the motor. I leave the change wheels on my ML2 set at 26 tpi as this suits most jobs i do and was the thread pitch i measured some years ago when msking a replacement screw in backplate. Always more than one way to skin a cat 😉. Quote Link to comment Share on other sites More sharing options...
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