Model Diesel: 32mm bore, 38mm stroke, indirect injection

[Steamchick]

Hi Nerd, I should check cutting speed from standard tables for the tool bits and material combinations. Also, a less pointed tool and slower transition across the metal, so cuts are finer, is the simple way to improve surface finish. And very thin oil lubrication may help - or not?
I one (industrial) job we were machining flat smooth surfaces with a "woodworking machine" @ 6000rpm. (Overhead router?), 5 in diameter fly-cutter head, carbide (?) tool for ALUMINIUM (much sharper and different angles to regular steel tools) but it was on "Pure" electrical aluminium bars. We needed ridges and grooves for the electrical low resistance joints when bolted-up, so used a smaller radius and fast feed - with a relatively fine cut and the confused coils of swarf flew off the machine (up to the guards) and had to be cleared frequently.
I guess you could flatten the surface of your cylinder head - suitable for the head gasket - with a fly-cutter in your vertical milling machine with a larger radius tool and slow feed?
But maybe I am wrong as this guide suggests otherwise?
https://waykenrm.com/blogs/fly-cutt...ze one or,suitable for heavy material removal.

Point Radius​

Professional machinists maintain the point radius of the fly cutter tool to less than 1.5mm. This is because the smaller the point radius, the slower the feed rate, thus giving a fine finish. Thus, make you avoid large tip radiuses as they increase the tool cutting pressure, causing deflections. This eventually results in squealing, chatters, and poor finishing outcomes.

Cheers!
K2

 

[Nerd1000]

A bit more progress on the cylinder head. I've bored out the seat for the pre chamber cup, drilled the valve bowls, and counterbored the head bolt holes.

I'm contemplating various ways I might cut the valve seats. Initially I thought I might make a piloted cutter, but now I wonder if I might just use a countersink with careful positioning.

 

[Lloyd-ss]

A countersink should work fine. You might finish off with the top and bottom relief angles cut with drills re-sharpened to the correct angles to achieve the seat margin you are looking for. If needed, you could probably make a piloted lap that incorporates all 3 angles to improve the concentricity. Then a little lapping compound on the valves themselves to insure 100% contact.

 

[peterl95124]

since you took the head out of the vise before at least using a 90-deg countersink to get a start, you'll have a hard time now getting a concentric seat (don't ask me how I know this :-( !!!)

my advise, for what its worth, is this, put the head back in the vise, do your best to get your quill centered on the existing valve guide holes, make very very light (.005 deep) 90-deg countersink cuts and look with high power magnifying glass to verify a uniform cut all around (IE concentric with existing holes), and then make actual cuts only .015 deep (you want narrow seats for best sealing), finally the magic ingredient is this: lap the valves into the seats with (I use extra fine) 1200 grit alumina abrasive paste. I do this by slotting the valve head with a #202 or #203 woodruff cutter ground down to .031 thickness (so its a #102 or #103 but they don't make them) and using a screwdriver who's end has been ground to the diameter of the woodruff round bottom slot you cut, and twisting the valve while it is in its valve guide, to get everything perfectly concentric. I call it magic because even under magnification I can't see any change to the valve or seat from lapping, but can assure you my experience is this effects a seal nonetheless !. I test the seals by cleaning off the abrasive, putting the head on the engine but without any rocker arms, and putting a stethoscope in the intake or exhaust port and listening for leaks as you compress the cylinder. The other magic ingredient, if you fail at getting concentric seats is to ream the guide holes oversize, that way the valve head can find its way to the seating location (got that good advise from Paul Knapp !)

good luck !, let us know what works for you !

 

[Nerd1000]

Hmm yes I knew taking it out could cause issues even as i did it. Unfortunately my setup didn't have clearance for my 13mm drill so I had no choice

 

[Nerd1000]

We have valve guides and seats, and inlet and exhaust ports. I've made a goose of myself and drilled the exhaust port in the wrong place (it's not a Nerd Build without a comedy of errors!), but I think I can live with the result. I also drilled and tapped the block for the cylinder head bolts.

 

[Lloyd-ss]

Being able to elegantly adapt the project to work well with the mistakes, separates the real machinists from the machine operators.
Have you named your engine yet? "Brutus" might be a candidate.?!

 

[Nerd1000]

Being able to elegantly adapt the project to work well with the mistakes, separates the real machinists from the machine operators.
Have you named your engine yet? "Brutus" might be a candidate.?!

It's Oscar, in fact.

 

[Nerd1000]

A bit more cylinder head work:

This forms the seat for the injector.
The comedy of errors continues, as I broke my tap while threading the holes for the injector hold down bolts. It's a tiny m1.6 tap, so I've no chance of getting it out of there.

So I need a plan B. Currently I'm thinking of milling myself some more space on each side of the injector and putting hold-downs there, with more robust M3 screws. This should also eliminate any worries about whether the tiny screws were strong enough.

 

[Nerd1000]

Here's my planned solution. Basically we have a slot milled across the mounting point, and two hold down blocks with screws fit into it with their 'toes' over the mounting flange of the injector.

 

[ninefinger]

Will your pushrods clear the heads of the new hold down bolts? Looks like you made the injector already, but I was going to suggest just rotating the hold down pattern 90 degrees and you'd be good to continue.

 

[Nerd1000]

Will your pushrods clear the heads of the new hold down bolts? Looks like you made the injector already, but I was going to suggest just rotating the hold down pattern 90 degrees and you'd be good to continue.

Sadly I can't turn the bolt pattern because there's no room under the rocker shaft support. You made a good point with the clearance for the pushrods, so I went back and checked: I can confirm there's plenty of clearance!

 

[Nerd1000]

Hi all,
Here's the next step. New hold down feature milled, holes drilled and tapped. And we're going high-tech, as I've made the pre-chamber cup... from titanium!

The cup pressed in to the head very nicely.

 

[ninefinger]

Any reason for Titanium other than maybe you had some or wanted an excuse to machine it (nothing wrong with that - more than half my projects are excuses to do something like that).

 

[Nerd1000]

Any reason for Titanium other than maybe you had some or wanted an excuse to machine it (nothing wrong with that - more than half my projects are excuses to do something like that).

Titanium has poor thermal conductivity for a metal, theoretically it should reduce heat losses. But mostly I just wanted to try it.

 

[Nerd1000]

A bit more progress on the cylinder head. Valve springs, keepers, hold downs for the injector all made.

I lapped the valves and made a crush washer for the injector. With the head on and some grease as a temporary seal to the block, I was able to test for compression. The good news: there is some. The bad news: the exhaust valve needs more lapping as it leaks slightly. I also found that air was being pushed back through the injector into the pump, so I lapped the needle into the seat. While this did correct the blow back issue, the crush washer did not work perfectly a second time. Despite this, the engine has enough compression to blow the grease out of the gap between the head and the block.

 

[Roger B]

Are you planning to make a compression tester? There is quite a difference between what feels like a lot of compression and enough to reach ignition temperature ~30 bar plus.

 

[Nerd1000]

Are you planning to make a compression tester? There is quite a difference between what feels like a lot of compression and enough to reach ignition temperature ~30 bar plus.

I have a small engine compression tester, but I would need to make some kind of funky adaptor to allow it to connect up to the injector hole.

I think my next mission is the rockers and pushrods. I've been a bit indecisive on this matter, and actually designed two options

Which option do people like more? I see pros and cons to each. The second option might also be altered to omit the side supports and just use the pillar in the middle.

 

[Roger B]

I would remove the centre pillar from the second option and just support from the sides. This would give you more space if you have to modify the injector design (which my experience suggests will be the case).

 

[Steamchick]

I favour the former... as the rockers area straight line of thrust.
K2