First IC engine design and build

Discussion in 'A Work In Progress' started by retailer, May 7, 2019.

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  1. Jun 17, 2019 #21

    retailer

    retailer

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    bluejets - I've seen that model online somewhere but can't recall where, I do recall though thinking that it is a superb model of a blower Bently, the model is up there with the best of the best.


    Thanks Cogsy that little cutter is quite ingenious and looks to be very similar to an annular cutter or rota broach, I hadn't thought of that. Looks like my failed crankshaft can be put to good use by making a similar cutter out of it when the time comes.
     
  2. Jun 17, 2019 #22

    stevehuckss396

    stevehuckss396

    stevehuckss396

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    If the cap is the big hang up Roy sholl from s/s used to sell caps all the way up to 9 cylinders. Can see if he has one then make a distributor to fit.


    Cncengines.com
     
  3. Jun 18, 2019 #23

    bluejets

    bluejets

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    In the past, I have basically gone for a radius contact/pickup arrangement with a clear lid with the centre ht input for simplicity.

    Plan to make up the next one for the V8 using glass epoxy and plug and mold.
    Have noted in the past that epoxy tends to be rather heat sensitive so perhaps polyester resin instead.

    My mate George is building a very similar design but with a twin overhead cam arrangement.
    Plan there is for dual dizzy.
    Will post eventual outcome. Busy rebuilding the crank grinder feed arrangement.
     
  4. Jun 18, 2019 #24

    retailer

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    bluejets: I have seen those distributors with the radial leads, and they may be easier to make I'll have to see when I get to that point.

    stevehuckss396: Thanks for the info on the availability of distributor caps I'll keep it in mind if I fail to make something that is decent and workable - I think it will be a while before I get to that stage, soon I'll need to temporarily put the V8 project aside for a few months, I promised my son I'd make him a Fender Deluxe reverb copy, I wound the transformers late last year and he keeps asking if I've made any progress.
     
  5. Jun 21, 2019 #25

    retailer

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    My next attempt at a crank went a bit better, roughed it out again in the mill this time with the big end journals in the correct place. I recall seeing a youtube machining tutorial video where a small model engine crank is machined by using an offset hole in a soft collet, I though it looked like a good idea but finding a large enough collet was a problem, I then thought that maybe I could simulate a collet and came up with a crank machining jig that provided support for the crank while allowing all of the machining to be done right up next to the chuck - ideally a square section of MS would have been easy to use but as I couldn't source a suitable 4" length of 2"squ so I machined a couple of flats on a 2.150" diam chunk of 1020, the flats make it easier to be gripped off centre in a 4 jaw chuck. Two holes were drilled and tapped 1/4x20 for grub screws to hold the crank in the jig.

    The jig was set up in the mill with one of the flats parallel to the Y axis two marks were centre drilled at one end - one on centre and the other in the Y direction a distance half of the crank stroke (.312") off centre. In the 4 jaw a shoulder was machined once the centre mark was clocked with a dial gauge - this centre mark would eventually be machined away so the shoulder would then serve the same purpose ie:- reference surface to recentre the jig. The jig was then re-centred this time on the .312" offset and a hole bored through from front to back, the hole must be sized such that the crank fits though with a firm push, the jig is now ready to use. The jig is set up in the 4 jaw using the turned shoulder as a centre reference and the crank is pushed in with the first big end journal just poking out and rotated so the centre mark in the end of the crank for that journal runs true and the grub screws tightened, this can be checked with a bar that has a 60deg taper at one end and a centre in the other, I call it a wobble bar but it probably has an official name, once it is right this puts the bigend journal on the centre line of the lathe and it can now be machined, the unsupported end has no stress put on it but it wouldn't hurt to use a live centre to steady it. The bigend journals can all be done the same way one at a time, with the machining being done up next to the chuck the tendency for the crank to flex would be minimised.

    Once the bigends are done the jig can be recentred this time using the internal bored hole as a reference and the main bearings can be machined in a similar way, although I may do the last few thou of the mains between centres I'll see how it pans out.

    How well does it work and is it easier than other methods? this I don't know as I haven't machined a crank of any sort before and I have only just set it up ready for the first journal to be done, I may find it is a waste of time - my main concern is keeping things square and parallel, and possibly the two grub screws may not hold the crank enough to withstand an interrupted cut - while the jig uses a close bored hole it is not really a collet and so does not have the same precision.

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  6. Jun 23, 2019 #26

    retailer

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    The first big end journal finally finished to size - I found the setup not as easy as I thought. I imagined that I would be able to insert the crank into the offset bored hole, rotate the crank and use a wobble bar to locate the bigend journal on the centre line of the lathe but it proved to be very touchy - just nudging the crank a round a degree or two was just about impossible, it would overshoot one way and then the other, I did eventually get it to within 1.5 thou (about .04mm) but this was probably more blind luck than skill. I had to resort to adjusting the 4 jaw chuck to bring it on to the lathe centre line and the end result was better than 1 thou or about 1.5 divisions of my .01mm dial gauge.

    I read gbritnell's post on another forum about making a crank and duplicated his idea for a lathe tool, I ground mine though from a 1/2" square HSS blank, roughing it out with a side grinder and finishing it off in the T&C grinder to give it side rake and front to back relief, the end of the tool is notched and while I'm not 100% sure of the function of the notch but I included it - I'm guessing it is to reduce the contact area between the tool tip and work to possibly help with chatter. It was slow going low speed small cuts, I did get an occasional hint of chatter and curiously it was at the end of the crank pin journal that is closest to the chuck I would have thought the setup would be more likely to chatter further away from the chuck. Haven't had much shed time these last days so only the one journal finished so far.

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  7. Jun 24, 2019 #27

    retailer

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    I found some time to make a bit more progress with the crank today, the big end journals are around a thou or so oversize so I should be able to polish out the majority of the machining marks same goes for the mains, I did find though that in roughing out the crank on the mill I went a bit deep on one of the big end journals and was unable to cleanup it up fully, if you look closely at the last pic it can be seen as a small flat spot, I don't think it will affect the way the crank works and given the amount of time that hasgone into the crank so far I don't think it is bad enough to scrap the crank.

    I swapped out the plier tightened brass threaded rod that I used to secure the crank in my jig for proper grub screws, they hold the crank tighter which eliminated the occasional chatter I was experiencing, the brass threaded rod stuck out a long way and I was always mindful of it and making accidental contact in which case my fingers would have come off second best.

    Once all of the big end journals were completed I centred the bored hole in the 4 jaw and worked on the mains bringing them to size plus 5 or 6 thou, (about .15mm) so I could finish off the mains between centres. Once between centres I experienced a fair amount of chatter when I tried to finish them off to size, probably should have put in something to support the crank across the big end journals, but it was getting late and a bit cold in the shed so it was slow and steady with very small cuts, I think I have the worst of it done, I still need to bring the ends to size for the ball races, this will be between centres so I'll have to rig up some support across the big end journals as there is more than just a few thou to remove.

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  8. Jun 24, 2019 #28

    minh-thanh

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    Thank you for sharing !
     
  9. Jun 25, 2019 #29

    bigearl91

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    Lots of patience, good job. Thanks for sharing.

    Earl
     
  10. Jun 25, 2019 #30

    Luiz Fernando Pinto

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  11. Jun 25, 2019 #31

    deeferdog

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    Love your patience retailer, something I sadly lack. Would it be a rude question to ask which country you are located? I understand if you don't want to answer this. Cheers, Peter
     
  12. Jun 26, 2019 #32

    retailer

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    I'm in Oz - Adelaide SA to be specific - yes patience is needed, the small stuff is certainly a different ball game.
     
  13. Jun 27, 2019 #33

    retailer

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    I made up some expanding spacers to fit in the big end journal space and taking very small cuts turned the mains to final size, next were the front and rear mains turned down for the 8x16x4 ball races, it all looked quite good. I mounted the crank in the block and it spun over quite nicely, however I noticed what looked like run out on the 3 internal mains, must be an optical illusion I thought, they were turned between centres and I did check them with a DTI, they had no run out. Just to be sure while the crank was mounted in the block I placed a DTI over each main and checked it - almost 3 thou run out ! checking with my calipers two of the 3 mains were tapered by around 2thou I was stumped. No option but to put it back in between centres and rectify the run out and taper, this time I double checked - no run out and no taper.
    Once again back into the block and again I'm sure I can see run out in the mains when the crank is spun over, I check with a DTI and yes there it is, the run out varies from from 2-3thou on each of the 3 mains, the front and rear are fine, time to go inside, have a coffee and give it some thought. I come to the conclusion that in applying some pressure/preload on the crank from the running centre the crank is flexing - perhaps only a thou or so and once machined and the preload is removed it flexes back and we have run out, to check on this I remount the crank and with a DTI on one of the mains I gradually put some preload on the crank, sure enough I get a reading of 2 - 3thou, this is with the adjustable spacers in place, not sure what to do I decided to put minimal preload on the crank so I can cleanup the mains and eliminate the run out, while I did have a hint of chatter before which was most evident if I let the cutting tool rest in the one place, with less preload the chatter was constant and unacceptable making it impossible to get a good finish, I increase the preload bit by bit until I find a satisfactory setting where I can machine out the chatter marks.

    Job done I once again set it in the block and you guessed it there is run out but only around 1.5thou, I was hoping to get it less than 1/2 thou so there would be no tight spots, then I thought that 1.5 thou is not that much and to get it to 1/2 thou I only need to remove 1 thou from 1 side so with a felt tip marker I marked the high side and with the crank mounted in the vice used some 600 emery on the high side gradually working around with less pressure, bit by bit I managed to get it down to around 1/2 thou, I know it's probably not perfectly round anymore but it is round to within 1/2thou. I do the same to the other 2 mains, the good thing is I have all of them with in the spec I wanted but the bad thing is they are now under size which can be compensated for when I make the three split bearings but worse they are all a different size now which means I'll have to number them. I know my method is not exactly precision machining, maybe if I had used a different material rather than an unknown I may not have had these issues.

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  14. Jun 28, 2019 #34

    propclock

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    Absolutely gorgeous.
     
  15. Jun 28, 2019 #35

    deeferdog

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    I've had issues with single throw crankshafts! I think your work is excellent and the results prove that. Thank you for posting all this, I'm pretty sure most will agree with me that reading about other members travails helps us through our own, particularly with crankshafts. Cheers, Peter
     
  16. Jul 8, 2019 #36

    retailer

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    Managed some more time on the V8 - cut a couple of pieces of brass from a odd shaped lump and machined up 2, 8mm x 16mm rectangles that were soft soldered together make up one piece with a 16mm x 16mm square cross section. A centre pop mark was put in the middlle of one end right on the join line and the centre pop mark centred in the 4 jaw chuck. It was then a simple turning job to make each of the 3 split bearings, a few seconds with a small blow torch was enough to separate the bearing halves.
    I'm not sure what is done in the model making world to locate bearings of this type or even if they have them at all but I recall seeing locating pegs on the bearings of my small window VW beetle when I pulled the engine out to fix a dropped valve, so I decided use pegs to locate the main bearings - the centre bearing is also the thrust bearing, with no clutch assembly it is doubt full if it is needed at all.

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  17. Jul 8, 2019 #37

    bluejets

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    Brass or bronze...??? Brass will be too soft for bearing material.
     
  18. Jul 9, 2019 #38

    retailer

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    Brass or bronze that's a good question, I'm not sure and I don't know how to tell them apart, my bearings were cut from a failed attempt to make twin cylinder steam tractor. The engine has ball races at both outer ends so even if the material is brass I don't think that there will be a huge amount of wear for the amount of run time the engine will get, once I get past the initial excitement and all of my mates have seen it, it will probably just sit in one of our bookcase cabinets as a display piece sadly we don't have model engineering shows where people can exhibit and run their creations in my area.
     
  19. Jul 10, 2019 #39

    bluejets

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    Looks very much like brass to me.
    Brass is shiny yellow whereas most bronze is more orangy colour, the exception being copper bronze which is very difficult to machine and very rarely, if ever, used in modelling.
    One can usually get 1/2" bar of standard bearing bronze from just about any bearing shop, not too bad for cost either.
    Might be worth a try for you just to see and learn something new. Works for me.

    Shame it will just sit on a shelf.
    My engines all have work to do in one form or another.

    Even the old Atkinson sits on a bench at the entrance to my workshop as an interest factor when people come to browse.
    Reconnect a battery and a quick flip gets it up and running , always with a favourable response.
    There is nothing like an engine that fires up first flick.
     
  20. Jul 10, 2019 #40

    retailer

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    Having more experience than me you are probably right in that it is brass. I had that material already and the only bronze I have is some cast bar that once machined will be under 0.5", to make some split bushes with 0.512" OD I would need the next size up from 0.5" - I'll probably leave the brass for now as they are already made, I plan to strip the the engine down after the first few runs to see how things are wearing maybe by then my father in law will agree to part with the only bit of his old boat he has left a 1" diam x 40" long bronze propeller shaft.

    Yes it is a shame for working models to spend a good part of their life as display pieces, the only other model engine I have made is a Jenny Wren style mini steam engine I gave it to my adult son as a Xmas present and although it has been almost 2 yrs he has not as yet steamed it even though I packaged it up in a presentation box along with mini oil can and syringe to fill the boiler with, he says he does not want to muck up the polished appearance.
     

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