Nalon Viper 2.5cc CI Engine

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f2cf1g

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Hi Pat. I'm following your thread with interest because I'm also building one. My scrap bin is far from empty! The drawings show two methods for cutting the transfer ports, the one you are contemplating and another with the flute extending from a hole drilled at rightangles into the bore. I can't think it helps gas flow so maybe it was simply a way to mount a guide for a broach. Any views?
Roy
 

pat_pending

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Playing with cutters some more today but in between I thought I'd have a go at making the needles for the NVAs. I used the procedure outlined on ModelEngineNews How To Grind Needles for NVAs and I'm really chuffed with the result.

I started out with some 1/16" Piano wire. I looked for stuff advertised us 'unrolled' or 'straight' assuming this would be best although I suspect at some point this stuff 'must' have been on a roll (?) keen to hear where people get theirs from and if piano wire is piano wire if that makes sense (in terms of quality/ straitness etc for the job at hand).

I then mounted a rotary tool in the tool post and set the cross slide over to 10degrees. I mounted the wire in an ER14 MT3 collet. Then using a Dremel #85422 Silicon Carbide disk 25/32", i proceeded to gently rough out the taper using the cross slide edging in 0.01mm at a time. The last pass I covered a few times to take the 'flex' out of the wire which had to stick out a bit for clearance.

For all the milling I ran the lathe in reverse at something ridiculous like 2000RPM and the grinding wheel at 20,000. Both got pretty warm after I was done 😬. I also covered the lathe bed for this one to keep all the abrasive dust of my precious cast iron.

After roughing the needles I switched the wheel over to a #425 7/8" Emery Impregnated disk and did some really light finishing passes. After this was done I finished the needles off with WD40d carbide paper going down from 800, 1000, 2000 grades.

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pat_pending

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Hi Pat. I'm following your thread with interest because I'm also building one. My scrap bin is far from empty! The drawings show two methods for cutting the transfer ports, the one you are contemplating and another with the flute extending from a hole drilled at rightangles into the bore. I can't think it helps gas flow so maybe it was simply a way to mount a guide for a broach. Any views?
Roy
Hi Roy, hope your build is going well. In terms of the two sets of plans, I went for the Viper first prototype one since the idea of messing up the whole cast iron head vs just the liner just seemed too risky given my current skill level. I may still have a go at some point to have both versions in the cabinet.

-Patrick
 

Ramon

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Pat, Though either will do there is a distinct difference between 'Music wire' and 'Piano' wire not least that the music comes in imperial sizes and piano in SWG. Piano wire is much harder and springier than music. Most wire sold in model shops from the KS range is music wire and usually has a small label attached to each piece saying so

16 SWG piano wire is just over a 1/16 so won't go into a 1/16 hole unless it drills oversize. A piece of it however can be turned into a reamer quite easily.





This is doing the spaybar parts for the Eta engines- the image makes the thread look truncated but it's not. The wire is just ground at a shallow taper - it's important to constantly withdraw to clear the swarf away as it will soon become crowded and possibly jam. Here are the finished parts. The threaded needle is done by drilling through a 7BA bolt and loctiting on the needle


1/16 Music wire should fit a 1/16 hole if it's very slightly over size but size for size is usually interference. Doing the same thing will ease it but the edges do need to be sharp as only a scrape is coming off.

Hope that helps - Tug
 

Tim Wescott

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Edit: I just realized I responded to an old post. Oh well -- I'm leaving this. Pretty drawing and all that.

If you don't introduce too many errors in deburring, there's a way. Edge-find the exhaust ring, and move in a known offset from that.

An even better way, if you have three or four hands, would be to put a bit of drill rod of a known diameter into the corner between the exhaust ring and the outer cylinder wall, and edge-find off of that.

This all means that the precision of your transfer ports is dependent on the precision of the location of that exhaust ring and the thickness of the cylinder wall, both of which did not used to be controlling dimensions.

But, hey -- driven by needs and all that.
 

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pat_pending

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Pat, Though either will do there is a distinct difference between 'Music wire' and 'Piano' wire not least that the music comes in imperial sizes and piano in SWG. Piano wire is much harder and springier than music. Most wire sold in model shops from the KS range is music wire and usually has a small label attached to each piece saying so

16 SWG piano wire is just over a 1/16 so won't go into a 1/16 hole unless it drills oversize. A piece of it however can be turned into a reamer quite easily.





This is doing the spaybar parts for the Eta engines- the image makes the thread look truncated but it's not. The wire is just ground at a shallow taper - it's important to constantly withdraw to clear the swarf away as it will soon become crowded and possibly jam. Here are the finished parts. The threaded needle is done by drilling through a 7BA bolt and loctiting on the needle


1/16 Music wire should fit a 1/16 hole if it's very slightly over size but size for size is usually interference. Doing the same thing will ease it but the edges do need to be sharp as only a scrape is coming off.

Hope that helps - Tug
Thanks Tug. Yes I'm studying you ETA and Super Tigre builds v carefully! :) .

Any tips on the D-Bit? I guess grinding the width with a Dremel Danger Wheel or bench grinder a 'smidge' under half seems to be the common wisdom and then trying to get a decent finish/sharp edges with a stone?

Thanks,
Patrick
 

pat_pending

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Thanks for the ideas Tim. I have 4 hands so will try the suggestion with the drill rod. Time to brush up on me Trigonometry!... It's been a while! 😬

-Patrick
 

Ramon

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Its not a D bit Pat merely a flat acute angle ground across the wire by holding the wire at such an angle on the side of a wheel - try not to get it too hot as you'll lose the temper. If you can't hold it long enough to get a flat area then clamp it to something that will prevent the wire turning.

Tims idea is how I went about it but without edgefinder just used the cutter but the more I think about it the more I can see the ease of the scribed line technique. Providing the line is fine and accurately placed relative to the top edge of the exhaust port for maximum efffect and the needle point runs true the accuracy is probably as good as you would want.

Tug
 

pat_pending

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Hi all,

bit more shed time today and managed to get the NVAs done. A seemingly easy set of operations with surprisingly many opportunities to cock things up especially on the final operations. My nerves are shot and I'm going to have a beer. I'm happy-ish with the result and Im pretty sure they'll work fine as they are airtight, needle seat is just a smidge under the hole and the places where the needle goes were reamed with the same music wire so no air bypass there.

That reamer made from the music wire worked an absolute treat and was a joy to use. It cut beautifully and pulled out layers of brass swarf that looked like a Vienetta ice cream. yum.

Where I would probably improve things next time is how far the thread goes up the spray bar up to the venturi. The die (obviously) didn't cut a thread to the very edge so I'll need to make a small washer to take up the gap. Not a 'biggie' but far from perfect.

I also seemed to bend one of the spray bars a tiny bit whilst cutting the thread (or being clumsy doing something else). I think that one will be a bugger to turn the thimble as the tolerances between the needle and the bar are so tight. That's in the spares/engine #3 bin for now and I might remake it but need a break from the tiny brass parts for now! The other two are spot on.

Axial accuracy on the lathe is one of my weaknesses also atm. I could really use a DRO. Wheeling that cross-slide and counting at 0.025mm per tick is tiring over longer distances!

Anyway here are some pics. I'm down to the 'hot-end' now (liners, pistons and contras). Tomorrow i will try to finalise the cutters and hopefully get the cylinder blanks turned. Exciting to be approaching the finishing straight although the risk of some mistake made earlier scuppering plans is very real as always.

Thanks,

Patrick
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pat_pending

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Just as I was getting a bit of a 'pace on', disaster struck. The headstock bearings in my trusty Sieg SC6 decided to pack up on me. I noticed more vibration/noise than normal and the case was getting a bit warmer. I thought i'd be able to limp through these Vipers and do a strip-down after but things were too bad and deteriorating rapidly. Turning the chuck by hand, it felt like the shaft was square! I took off the belt and tensioner to see if the problem was there but no such luck. In the end it was the back bearing that had died and not the front angular contact beading which still seemed OK. With al the grief of the strip-down I decided to replace them both. I was on my own in terms of how to do this job so will probably post an Instructables or something (provided I'm successful) for anyone attempting similar.

For those interested to see, look at the surface finish on that cylinder liner I had just started on. The part will be easily salvageable at the lapping stage but a strange pattern on the surface I've definitely never seen before.

Good progress today and home-made puller did the job. The replacement bearings are on order from Simply Bearings and hopefully not too many snags at the point of pressing the bearings back in.

On the bright side, i should have a super smooth running machine replacing the Chinese 'car grade' bearings to Timkin and SKF.

Thanks,
P

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pat_pending

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So, is a claw hammer an approved machinist's tool?
One man's claw hammer and cat litter tray is another man's drift and parts washer :) .

I found some perfect size tubing in my scrap bin to tap out the bearings after using 3 bolts and some shims as a puller as below. When the work started getting more manual, i layered up on the lathe way protection. Worked out very well indeed. Sometimes the outer race of the angular contact bearings can be a pig to get out!

P


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Billitmotors

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Hi Billit, that also sounds like a neat option. What sort of edge did you put on the HSS Bit for this to cut nicely? I might also give this a try.

Thanks for the tip.

P
Gday Pat
if you imagine a very short HSS parting tool with an increased front clearance so that the heel of the cutter does not rub, and minimum side clearance on both sides. I will find my cutter on the weekend and take a photo and post it here. When cutting the ports I I fed it in slowly and gently by hand and it worked just fine.
 

stanstocker

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So, is a claw hammer an approved machinist's tool?
Heck Tim,
Carefully remove, drift out, press out, beat the sucker into submission, wail on that pig. It's all just a matter of words :cool:

Looks like a well battered piece of wood was used between the hammer and the work, so a 16 ounce claw hammer or a 16 ounce ball pein, all the same.
 

777engman

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Hey pat, just wondering why you didn't just purchase a suitable woodruf cutter for doing the ports? Or have I missed something?
Dean
 

777engman

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Also good luck with fixing the lathe mate hope it all goes well, I did a full strip down and rebuild on my raglan 5" over lock down last year, those head stock bearings were a bit of a job so I feel your pain with that one mate.
Dean
 

777engman

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Thanks Dean. Ideally I’d like to be a bit further away from the cutter for sure. I’m sure it’s obvious but you don’t happen to have a pic/description of your process/fixtures ? That would really help.
Patrick
I'll upload photos soonish, just a bit tied up at the moment
 

pat_pending

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Heck Tim,
Carefully remove, drift out, press out, beat the sucker into submission, wail on that pig. It's all just a matter of words :cool:

Looks like a well battered piece of wood was used between the hammer and the work, so a 16 ounce claw hammer or a 16 ounce ball pein, all the same.
hah. Yeah and that approach didn't work anyway. I had to use the bolts as a puller. Made another puller out of 3 bits of M12 threaded rod and a scrap bit of 3.2mm walled 50mm mild steel box section and that worked a charm.
 

pat_pending

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Also good luck with fixing the lathe mate hope it all goes well, I did a full strip down and rebuild on my raglan 5" over lock down last year, those head stock bearings were a bit of a job so I feel your pain with that one mate.
Dean
Thanks. So far so good. Waiting for a separator to arrive from eBay to allow me to remove the tapered roller bearing inner from the shaft. I had the Dremel 'wheel of destruction' in my hand to cut it off but managed to put it down and wait for the proper tool to arrive :)

P
 

pat_pending

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Hey pat, just wondering why you didn't just purchase a suitable woodruf cutter for doing the ports? Or have I missed something?
Dean
I would have loved to! Although learning a new skill is always cool. I searched far and wide and nothing came up 3/32 x 1". There were companies making them to order for £120 and some available in the US which, when you add shipping, comes to about the same. If anyone knows where i could find such a cutter that would be really helpful (although I have cut another two blanks to try some variations on the geometry to see if i can improve on the last ont that already works pretty well).
 

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