Author Topic: Dyno compression ignition  (Read 45322 times)

Offline tangler

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Re: Dyno compression ignition
« Reply #120 on: October 30, 2014, 11:15:42 AM »
Guys,

Thanks for the comments.  AS, my first thought was the easy way out and to bush but actually it was only half a piston that I wasted and it was quicker to re-make.

Regarding SG iron.  Most of the bar that our suppliers sell is continually cast grey iron.  SG stands for Spherical Graphite and is the so called "malleable iron".  Is this what you are using?

Cheers,

Rod

Offline Ramon Wilson

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Re: Dyno compression ignition
« Reply #121 on: October 30, 2014, 12:01:08 PM »
Hi Rod - yes it is in this instance. I have used the continuous cast in the past with good results. However I had this slice of 4" diameter bar of SG under the bench and decided to convert that into blanks as it was just thicker than the length of the pistons - which are long at 24.75 mm for 16.5 mm diameter

Personally, when it comes to pistons and rods (well most things I guess) bodging is not really an option - far much better to make again and be certain of what you've got. :ThumbsUp:

Re your Contra Piston fixture Rod - Having struggled with this awkward little item in the past I've settled on turning the inside of them with a slow taper - about 10 degrees inc. A quick taper mandrel to match is turned up and the c.p. pushed in place and held with the tailstock centre with a pad between. More than enough grip to finish turn and size and they're popped off with ease once done.

Just finished lapping the liners - came up very quick indeed, no doubt due to the free cutting steel which left a very good finish after turning. Pistons this afternoon  :)

Regards - Ramon



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Offline Stuart

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Re: Dyno compression ignition
« Reply #122 on: October 30, 2014, 01:13:32 PM »
Spheroidal Gaphite its a long time I have heard of that stuf

Mehite yes but not Sg

It fun to see it made pouring 1600 c molten Iron into a ladle with magnesium ingot in the botom the result flare was something to see . then a sample was taken cut polished etched and look at under a optical microscope you could see the globe shaped graphite particles as posed to the flakes of normal CI

we used it for cast pipes . cast nuts and bolts

this stuff turned like steel and the chips came off like steel , but it had the corosion resistance of CI

small test samples were done with mish metal instead of magnesium

Stuart
My aim is for a accurate part with a good finish

Offline tangler

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Re: Dyno compression ignition
« Reply #123 on: November 10, 2014, 05:33:37 PM »
Nearly there now  :D   I need to remove the cut outs in the crank web.  I marked the positions on the web and then used the Keats fixture to hold the crankshaft on the milling machine and roughed out the shape using an end mill and some XY hand cranking...



...before finishing off the curve with the boring head



The next job was to hack out the crankcase profile.  First, I squared it up in the dividing head.



The aim was to cut the waste away to leave the mounting flanges.  A miscalculation combined with sitting the wrong side of the job resulted in making the first cut too deep. 



 :-[  :censored: :Mad::facepalm::'(  OK I can always re-make it, but tomorrow, or next week or maybe next year.  A bit of sober reflection after I'd calmed down suggested it might be worth breaking out the "putting on tool"

I "tinned" both the patch and the job and put a bit of hand pressure on while it cooled



I'll see what it looks like when it's finished.  So, carrying on,  I cut the rounded base first by facetting in the X direction and then rotating the job under the cutter to get the circular profile



I then used my height gauge to find the correct angle to mill the sloping shoulder between the upper crank case and the mounting flange



and then milled that



before repeating the process for the other side.  I also needed to put a radius on the joint between the crankcase and the crankshaft housing







If you look carefully you can see where the patch is - rather more in the photo than in real life actually but I know it's there.  It was at this point that I decided to re-make the upper crankcase.  As well as the position of the carb inlet in relation to the inlet port, there were some surface finish issues that weren't going to come out and I wasn't happy with the flair on the exhaust ports and decided to do without them.  I used the same method as before except that I used a 2mm endmill, rather than slitting saw and file, to split the clamp.

I've recently managed to procure some metric Myford collets to supplement my Imperial ones.  The  carb body is made from 6mm FC steel which I was surprised to find in my store.  This needs drilling through 3.5mm before opening out one side to 5mm.  I used a 1/8" stub drill to get a good start before drilling through and then turning around in the collet to drill the 5mm hole.



The needle jet and body fit into holes milled across the carb body



The needle jet and body them selves are simple brass turning jobs.  The needle valve has a knurled brass knob.



The carb was assembled using solder paint.  I used the needle to ensure that the 2 parts were correctly aligned



I wafted a gentle flame over the job to melt the solder - even so it probably got hotter than it needed to



The whole thing assembled





There's roughness in the stroke - investigation showed that the con rod is interfering with the bottom of the cylinder.  The contra-piston is not, I suspect, tight enough, there is some evidence at the compression screw of leakage.  I'll try Ramon's heating method to expand the contra piston or make another.  A bit of fettling to do yet.







Online Roger B

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Re: Dyno compression ignition
« Reply #124 on: November 10, 2014, 05:43:46 PM »
Coming along well  :ThumbsUp:  :ThumbsUp: First run soon  :)

Is that the Hemingway quick set Keats you are using that I am currently making?
Best regards

Roger

Offline Ramon Wilson

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Re: Dyno compression ignition
« Reply #125 on: November 10, 2014, 06:06:29 PM »
Looking good Rod - have to dash out - back later
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Offline Jasonb

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Re: Dyno compression ignition
« Reply #126 on: November 10, 2014, 06:30:09 PM »
Looks good Rod, can you expand a littel on what you used to put that bit back on?

Offline tangler

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Re: Dyno compression ignition
« Reply #127 on: November 10, 2014, 09:28:50 PM »
Hi Guys,

Roger, I think mine is the College Engineering Supplies version - I got the castings (and loads of other stuff) together with my S/H S7 lathe and made it 30 odd years ago (a process I have absolutely no recollection of   :old:)

Jason, the stuff I used was this http://www.aluminiumrods.co.uk/.  I used it on the Wyvern.  I'm pretty impressed with it.  Rather than using it just as a bodge, I think it would be good for fabricating ally "castings" with reinforcing filets or perhaps a front mounted carb.

Cheers

Offline Jasonb

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Re: Dyno compression ignition
« Reply #128 on: November 10, 2014, 09:42:56 PM »
Thanks Rod, looks good stuff from their video. Could be handy for silencers and fuel tanks too.

J

Offline Ramon Wilson

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Re: Dyno compression ignition
« Reply #129 on: November 10, 2014, 10:45:14 PM »
Nice save Rod - I know that sinking feeling only to well   :-[

It'll be interesting to see how that stands up for if it does that's a useful bit of 'ammo' to have in your arsenal. There's going to be a strong whiff of diesel in the air next year  ;)

Good luck with the CP

Ramon
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Online Roger B

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Re: Dyno compression ignition
« Reply #130 on: November 11, 2014, 06:17:24 PM »
Rod, I think that the castings are the same in the College Engineering and the Hemingway versions but the Hemingway one has slots and a guide bar to allow easy offsetting. I'm just about to make the saddle clamp shown in your pictures.
Best regards

Roger

Offline tangler

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Re: Dyno compression ignition
« Reply #131 on: November 12, 2014, 07:42:37 PM »
I tried heating up the contra piston but that didn't seem to help enough so I made a new one.  This one is really stiff in the cylinder but seems to work - no sign of leakage but moves up when I slacken off the compression screw.

I've had a go at flicking the prop round.  I don't seem to be getting any suction through the carb with my finger over the air inlet, if anything it is pushing the fuel away.  By squirting a bit of fuel at the exhaust ports I have managed a few 1 second runs, which is encouraging.  Mostly, though,  I get a bang, a puff of smoke and the prop unscrews.  Very frustrating :(

I'll try again tomorrow.

Rod

Offline Ramon Wilson

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Re: Dyno compression ignition
« Reply #132 on: November 12, 2014, 08:22:26 PM »
Rod - 'growing' a piston doesn't always work though I have only had the odd occasion when it didn't.  Just to be sure - did you quench it after heating? If they are going to they will increase if left to cool but nowhere near the amount if quenched. Academic now as it sounds like the new one is just right  :ThumbsUp:.

Hate to say this but, is the piston in the correct way round - the piston step toward the transfer port. (Read below  ::))

If it will fire as you describe it should run once you have the settings right. If the prop unscrews you probably aren't getting enough grip on the knurl - tighten the nut a bit more for a start but if that doesn't help then a disc of wet and dry paper (about 320 - 400 grit) between driver and prop, abrasive side toward the prop face, will usually cure that problem.

 As drawn the needle is quite coarse too so probably doesn't need to be open very much - usually if a needle is open too far then the fuel does tend to fall back toward the tank. The finer you can get the needle point the better control you will get.

Hope that helps - I shall be 'rooting' for you for it to break into a run  ;)

Ramon


Ah! - Just looked at those drawings again and I think I may have just seen the problem - there is no step on the piston as drawn.

If you look in the General Arrangement you will see that the piston is at BDC. The top of the piston at this point is level with the bottom of the exhaust which is above the top of the inlet. As I'm looking at it there is no means to get the fuel in.

The timing diagram gives you the inlet period so you can work out how much step to mill down the side of the piston. The distance from the top will dictate the timing - the step over on diameter is not critical but no more than a couple of mil at most.

If I'm right here - and I'm sure I am - you could flick away for ever - it just isn't going to run  ::) 'Golly Gosh' you could even have flicked your way into convincing yourself that you need an electric starter  :o
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Offline tangler

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Re: Dyno compression ignition
« Reply #133 on: November 12, 2014, 11:08:48 PM »
Ramon,

Many thanks for your input.  I did let the contra piston cool slowly but I guess it must have been really slack   :o.  I've tried putting a coarser knurl on the prop driver but it's almost as if the engine is backfiring!  As you know, my knowledge of these little diesels amounts to zero.  I'm trying to better understand how this engine should work:



Bearing in mind that the top of the inlet ports in the cylinder are level with the bottom of the inlet pipe as shown on the drawing, what I think should happen is:

As the piston goes up from BDC the piston creates a low pressure in the crankcase.  Near TDC the skirt uncovers the inlet port and mixture is drawn in to the crankcase.  After TDC the piston uncovers the exhaust then uncovers the transfer port.  The descending piston is now pressurising the crankcase so the mixture exits via the transfer port into the cylinder ready for the next compression.

This suggests that the crankcase needs to have a good seal at the backplate so perhaps I ought to check that. 

Cheers,

Rod

Offline Ramon Wilson

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Re: Dyno compression ignition
« Reply #134 on: November 13, 2014, 12:23:13 AM »
Oh dear oh bloody dear - who got his inlet from his transfer all ar-- about face er, the wrong way round then :facepalm:

Any piston step, if designed in, will of course face the transfer and not the inlet  :embarassed: Senior moment of course - senility creeps ever closer  :o

Okay - do try the wet and dry paper - it does work. If you haven't got a gasket on the backplate that will help but I do feel one of the big things that may cause you a problem is the needle valve - it will not need to be open very much before flooding becomes a likely problem.

If it does flood - compression will go 'hard' and you'll get black smoke puffing out. Close the needle completely, back the compression off and keep flicking to bring any residual fuel in the case up. Clear that by blowing across the exhaust port - if/when it fires don't open the needle rather keep flicking/letting it fire in bursts as it clears itself. It will suddenly go 'dry' that's the time to crack the needle a tad and prime the exhaust - then keep running in short bursts on exhaust primes gradually cracking the needle until it evens out into a steady run.

Good luck with it tomorrow.

This is the second time I've replied - just went and dumped the last one by mistake ::) - it's one of those nights - time this doddering ol' sod was well and truly in his bed  ;)

Regards - Ramon

Just took a look at your engine pic - try replacing that spinner nut with a washer about two thirds that diameter and an ordinary nut for your testing runs
« Last Edit: November 13, 2014, 12:26:18 AM by Ramon »
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

 

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