First IC engine design and build

[retailer]

Late last year as my Quorn T&C grinder was nearing completion I was planning on starting an O gauge live steam loco but I came across the Demon V8 build log by Steve Huck I must say it impressed me and and I decided then to put off the loco project and swap it for a running V8 - as I had a few months to go on the Quorn I decided to have a go at my own design.
Not having any experience with model engine design there is always a chance that the design will be difficult to build or even worse may not be a good runner. In that event I would simply purchase a set of Little Demon plans, by all accounts Steve had done a great job of the plans and build details, the design is proven with quite a few examples built and running and being a forum member he is always ready to help out with advice.

The Quorn is now finished to the point where it is use able and my plans have reached the point where I could start actual machining. Bore and stroke is .625" - if this sounds like the PeeWee V4and the Steve Huck V8 that is because I copied these sizes from those two engines, mainly because I know rings can be made that size, I have not made rings before and being my first IC engine there is a lot of info in the forum posts on ring making to help me - the rest of the engine is my own design.

I started with the block, a square extrusion about 6inches long, final length will be a bit over 5.25 inches, extrusions may look square but are not good enough to use with out being squared up.

For this I used the lathe checking each time that the newly machined surface was parallel to the lathe bed, once squared up I mounted the block onto a steel back plate that was drilled to be bolted to my rotary table. The idea is that once the block is setup parallel to the mill table I can machine each surface by indexing the rotary table.

Before I set it up in the rotary table I spotted the holes for the crank and cam as I will probably machine away the face I am using as my datum point. Once bolted to the rotary table I set it square and parallel to the mill table with the rotary set on 0 deg. an angle plate clamped to the extrusion was needed to steady it as I could see it wobbling around once I started boring the holes for the cylinder liners. I don't have any sort of CNC setup but I do have the luxury of a DRO on my mill which does take some of the pain out of it.

 

[stevehuckss396]

I'm in! Lets do this! and yes we will be here if there is any questions.

 

[retailer]

Thanks for the encouragement it is much appreciated. I've made a bit more progress and will get a post up shortly.

 

[retailer]

I have progressed a bit further with my engine build, all of the bores for the liners have been drilled bored and countersunk, I plan to have liners a push fit and seal off the water jacket with O rings.
I only have a set of expanding bore gauges for internal measurements and I find they can be a bit hit and miss - in the lathe is usually ok as I can move the saddle back out of the way and get the gauge nice and square, in the mill though the boring tool was partially in the way making in a bit harder to get the gauge square, I ended up turning up a go gauge - making small adjustments to the boring tool until my gauge was a nice push fit.

The cylinder head bolt holes were drilled and tapped metric 3x0.5 and then the cutouts for the push rods were machined - all operations for each cylinder bank were completed before I rotated the block to do the other bank. While drilling the head bolt holes on the left bank I noticed that the holes looked to be displaced towards the front and on checking the front face of the block against my DRO I found it was set at .02" rather than 0" this threw out of the head bolt holes on the left side by .02", not a disaster as it is not a huge amount and I can compensate when I drill the head bolt holes but it is still not great . Theoretically once I shut down for the day as long as I don't move the mill table the settings should be the same next time it is turned on so that sort of thing should not happen, I'll be checking and resetting the x/y zero points each time I start up the mill from now on.

I always thought that machining cast iron was messy but I'm starting to think AL is worse, a lot of the swarfe is thin flakes and when it is brushed away it ends up all over anything that's close by. At the end of the day the piece of AL was starting to look a bit like an engine block

 

[retailer]

Bores, tappet holes and valley cut out all finished the block was rotated 180 deg to cut out the crank web clearances, I did make a couple errors though - the final dimensions were not affected but it looks sloppy and is sloppy, not happy about it. While it won't be seen once the sump is on but I'll still know it's there. The final operation while it is on the rotary table will be to drill the sump bolt holes and also the main bearing cap bolt holes.

 

[retailer]

Family stuff has kept me busy but I have managed to machine and fit the main bearing caps (with temporary screws), I just need to figure out how to bore the cam tunnel and probably more importantly the main bearings, one of the mains will also double as the crank thrust bearing. None of the small boring bars I have will reach to the back of the block so I may experiment and see if I can bore the front and rear holes for the ball races turn up a pair of brass bushes and then use these as supports for a line boring bar to do the 3 central mains or perhaps I'm over thinking it and a plain simple long boring bar will do the job.

 

[retailer]

I decided to mount the block in the mill and bore the rear main first, turn the block over and bore the front main and then turn up two brass bushes for the front and rear mains and use these as guides for a "line boring" set up to do the three middle main bearings - if I could pull it off then all of the mains should be in perfect alignment.

I started out on the rear main first drilling a 0.25" hole, then gradually opening it up to 0.5" with end mills and then continue to the target size with a boring head - my target id size was .708" (18mm) and as I progressed I could see the main bearing cap getting thinner and thinner in the area next to the screw head cut out, by the time I reached an id of .630" (16mm) and realised that if I continued through to my target dimension of .708" the main bearing cap would not have much meat left on it at all, I went back to my cad drawing and found that the thickness would only be .058" or less than 1.5mm - this may or may not be sufficient thickness - but as it doesn't look right and not wanting to risk bearing failure after the engine is running I decided that I would rather make up new front and rear main bearing caps and complete the front and rear main boring with the caps 'in situ'. Adding thickness just means the screw cutouts will not go down so deep. Bit of a nuisance as need the mill to make the bearing caps.

 

[minh-thanh]

Hi retailer !
Do you use water radiators?
If so, can you tell how you sealed it above and below the cylinder?
Thanks !

 

[retailer]

With regard to the water cooling I plan to have 2 O rings one near the top and one near the bottom, I hope I can work out a way to return the coolant back through the heads and to the top of a radiator.

With the block remounted in the mill and my new main bearing cap in place I started to bore it to size and saw that the boring I had done the day before appeared to be the incorrect distance from the cam tunnel, I took some quick measurements as best I could and sure enough it seemed to be out of place - must have made an error when I zeroed in my two datum faces so I zeroed in my two datum faces again and repositioned the block over the boring head with the same result. I decided that the hole I had bored yesterday was out of place around .02" and would continue on - it seemed good fortune was smiling on me as if I had completed the job the day before it would have resulted either in a slightly misplaced crankshaft or even worse the front and rear bearing would not line up.

Got the rear main bored and fitted one of the bearings - perfect fit.

 

[minh-thanh]

"With regard to the water cooling I plan to have 2 O rings one near the top and one near the bottom, I hope I can work out a way to return the coolant back through the heads and to the top of a radiator."

Thanks retailer !

 

[retailer]

The front and rear main bearings holes were bored but not without some drama - to position the holes the left and right cylinder bank were set to be in the X and Y planes - the top of each bank was then used as the zero datum point, moving the mill table 1.847" in both the X and Y plane had the boring head positioned over the main bearings. I did the rear main first and then flipped the block over to do the front main and proceeded to move the mill table from the zero point a distance of 1.874" in both the X and Y directions I finished boring the hole with the main bearing cap in place and congratulated myself for getting the hole the right size - the bearing was a tight push fit in the hole but - on removing the bearing cap I found that the bearing cap would not fit over the bearing - how could that be I had only a minute before pushed the bearing into the finished hole - then it dawned me the hole was not on the centre line of the main bearing cap and block I checked the DRO and saw that I had 1.874" on both the X and Y readouts I silently berated myself over this stupid error. I slunk back inside to check my cad drawings to see if there was a reasonable fix. I was in luck I had bored the hole away from the block not towards it, I just needed to make another main bearing cap and rebore the hole the same diameter but in the correct position, it was done with out drama.

I found the end of a broken end mill and silver soldered it into a short length of 0.5" rod to make a long reach end mill with this I was able to bore out the next two main bearings down, I flipped the block over again and bored out the last remaining main bearing, they are all very very close to final size and once I turn up a test rod and bronze bushes tomorrow I'll be able to see if they are all in alignment, if they are I'll leave them and alter the main bearing bushes to suit if not then I'll need to rig up a line boring tool to bring them into line.

 

[retailer]

Sadly the main bearings did not all align - out by around .003" - .004" not much but still too much, so I had to get to work and make a line boring setup, a bush at each end and a sliding boring bar that carries an adjustable cutter, the boring bar passes right through both front and rear bushes.

The cutter is held with a grub screw in the end and a small diam rod that passes through the boring bar to clamp the cutter. The cutter is a piece of 0.125" diam HSS, being that small it took some patience to grind something close to the correct clearance angles on the cutting edge, I eventually gave up with the bench grinder and dremel and put my new T&C grinder to use, while I didn't bother to get precise angles and only eyeballed them the setup allowed me to hold the small cutter at a constant angle.

Once assembled in the block and mounted in the mill I nudged the cutter up a few thou at a time until all traces of the old bored hole had gone I then gave it a few more thou just to be sure, the size of hole for the main bearing bushes went up from .503" to .513" - once done I turned up another bush at .513" and was able to slide it along the test bar with no binding, so should be all good to get on with the crank.

 

[minh-thanh]

retailer !!
The way and the tool that I need for my project
Thank you very much !!

 

[retailer]

To prepare for boring out the cam tunnel I drilled 1/4" from both ends, as I expected the holes did not quite meet in the middle, looking through from one end to the other I can see it is not much as 1/4" rod will pass right through if the holes do not quite meet in the middle it really doesn't matter as long as the cam will pass through. I will however try to get the cam tunnel true by finishing off the hole with and end mill from one end to the other before I finish off the bearing recesses at each end with a boring bar. I made up a long end mill using the end of another broken end mill silver soldering it into a length of 12mm bar and reground the dull cutting edges on my T&C grinder, hopefully it will run true and nor wander it only has to clean out out around .03" of diameter.

While I was making up the long end mill I came to the conclusion that I may not have left enough room at the rear of the cam tunnel for the bevel gears that drive the distributor. Checking my CAD drawing I found I had less than 0.45" - could I get bevel gears that small ? I decided to cut my own, I haven't cut gears before but thought it can't be that hard so I ordered a set 0.4mod cutters, I believe this translates to around 64DP.

While waiting for the cutters to arrive I poured over Mr. Law's book on gear cutting, it didn't seem to make much sense at first but I eventually realised that I needed to work from the small end of the bevel gear back towards the large end. I found a web site by a company called KHK that has an online spur gear designer and played around with a few sizes until I came up with one that looked like it would fit using the spur gear info as a starting point -I came up with 16 teeth 0.28" at the small end and 0.41" at the large end. After 6 initial failures I eventually had success, the failures were due to my incorrect calculations on the amount to roll the gear back, with a 32 hole index plate on a 72:1 rotary table I calculated a roll back of 5.625deg which is correct, 5 deg is one turn I got that right but came unstuck with the 0.625deg, I assumed it was 0.625 of 32 so I rolled the gear back 1 turn plus another 20 holes which turned out to be an extra 3 deg rather than the required 0.625deg.

I now have the bevel gears for the distributor drive I doubt they are perfect due to my method of calculating the size of the blank, but they do look ok under a magnifying glass and mesh together nicely I set them up to mesh and can't feel any binding and there seems to be minimal backlash, spinning them over with a cordless drill did not show up any problems. The pic shows them next to a 3mm screw.

 

[retailer]

I've been getting to work on the crankshaft and working through how it will be machined - it seems that the crank appears to be one of the most difficult things to do. I started with a 1inch diam length of some sort of carbon steel or possibly tool steel which came from gumtree, the seller thinks it is 4140 or similar, we cut off a small piece and heated to bright red and quenched in water and it did come up hard, a file just slide over the surface. The bar looks like hot rolled MS but has a green stripe painted along it's length so I doubt it is just plain hot rolled MS, it machines nicely with an acceptable finish.

I went back to my cad drawing and dimensioned a few drawings to give me distances from my datum point to the main bearings and big end journals. One end was centre drilled to mark the axis of the main bearings and the other end was also drilled for main bearing axis and also the big end journals, in the lathe the main web diam was roughed out slightly over size and front main bearing machined to give me a datum point, once setup in the rotary table I worked from my drawing and roughed out slightly oversize the centre 3 main bearing, and then the bigends indexing it with the rotary table. I was able to get the main bearings round but still left them slightly oversize and will do the last of the machining in the lathe. The big end journals were left square, it took a while as I kept the depth of cut small .015" near the rotary table and at the other end only about .005" to achieve a full depth of .630". I used a freshly sharpened 3/16" and new 5/16 end mill.

I finished and had a look and at first I didn't see it then it dawned on me I had screwed it up, in case you can't see it the 2nd and 3rd big end journals should be diametrically opposed, chalk it up to experience - I'd like to think I won't make that mistake again, I'd like to lay the blame on something that distracted me but I know it was just my inattention to what I was doing. On the plus side I won't have to wait to start again as I purchased a 1 meter length of bar, it's a shame to waste the material, perhaps it will make a good paper weight.

 

[stevehuckss396]

I agree with you. The crankshaft can be one of the more difficult things to make. Once you get past that, it's all down hill.

 

[bluejets]

If the material is 4140 then it will not require any heat treatment.
A plus as it would more than likely bend the crap out of it.

A real shame about the boo-boo.
I once made an error making a multi cylinder cam.
Had the engine rotation one way, cam the other.
Easy to make the mistake BUT in any future machining operations I always scan for any possible error areas and make LARGE notes on the drawings.

Hope you wedge those cut-out areas when you move to machine adjacent journals.
Could end up with a multiple stroke engine if you don't.

 

[retailer]

Even though the general concensus seems to be that the crankshaft is the hardest part to make it is the distributor that has me most concerned, I feel the crankshaft is quite do-able as long as it is taken slow and steady and without my stupid lapse in concentration it may have been done by now.

I'm still not sure how to tackle the distributor cap - I don't have any form of CNC, but I think it can be done in the mill with the use of the rotary table, it will require multiple setups - one for each diameter so there would be 10 separate setups and if I radius the lugs on the side that are used to hold it down to the distributor body that will be an extra 2.

I've considered making a full distributorless ignition setup using coil paks and an Ardunio or Picaxe type chip and for me it would certainly be easier - but it just would not look right so I'll give the distributor my best shot.

 

[bluejets]

I don't have any form of CNC

Many of us don't but we make do and usually do ok.

If you think a distributor is an unreachable goal, take a look at this engine.
ALL from solid.

 

[Cogsy]

Here's a few pics of a cap that I roughed out without any sort of plan using a rotary table and a quick home-made lug rounding tool. It turned out ok (although the plastic I used wasn't the best for machinability). It wasn't a difficult job and I'm sure I could have done much better if I'd spent a bit more time (soon I have to re-visit this one so I'll see how it goes).