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

[minh-thanh]

so today I tried making a test-version of my injection pump barrel and plunger. The plunger helix came out well, as did the barrel with initial lapping. Sadly, I rushed ahead too far and began final lapping of the two parts together before getting the size close enough- the consequence was galling and seizure of the plunger in the barrel, ruining both. Lesson learned, and next time I may try hardening the barrel to minimise the potential for galling.

That's why I said in my thread about the doubt: "lapping a plunger and cylinder with tight tolerances"
With small diameter cylinders and plunger : I Never lapping them together with tight tolerances.
One mistake and it will destroy your hours of work.
Before you put the plunger in the cylinder: clean them with kerosene - so clean , and then put some w20/40 oil in both before you put the plunger in the cylinder.
Your cylinder is 4mm in diameter, so use the shank of a new 4mm drill as the standard gauge. lapping the cylinder to 4mm and then making the piston (on the shank of the drill bit there is usually a a parameter engraving- sharpen it)
Make the plunger larger than 4mm (maybe 4.1mm or 4.05mm and then lapping the plunger until it slides into the cylinder only with w20/40 oil)
Or you can also use a cheap drill shank to make a plunger

 

[peterl95124]

I've often wondered what is the best way to do this, because the way I see it, the size of the abrasive will determine the gap between the piston and the cylinder, so unless the abrasive is micron size the gap will be too large for a diesel injection pump, and if it is micron size it won't do any useful abrading.

my best guess is that you have to lap the piston with an adjustable dummy cylinder (an external lap), and you have to lap the cylinder with an adjustable dummy piston (an internal lap), and keep monitoring the sizes until they "just" fit. and since this is a laboriously manual and skill intensive job be prepared to have lots of throw-aways, or a few workable pairs from a large set of candidate parts.

IIRC, Cox Thimble Drone type model airplane engines' pistons and cylinders are interchangeable and accurately made to within a few millionths of an inch, they never lap a piston with a cylinder, rather they do it as described above with internal and external laps.

and the reason I'm following this thread is because I'm in the process of making a "Find Hansen Diesel" engine myself. I'm working on the big parts currently, waiting on some helical gears from hpcgears.com, and still thinking about how to make the pump and injector.

HTH, YMMV, etc...

 

[Lloyd-ss]

For the fitting (just a generic fitting, not necessarily lapping) of the plunger, Minh-Thanh has been succesful, as have a few others. I have worked at it, but so far, have been unsuccessful, although each attempt is a little better. So take what I say with a grain of salt.

I tend to agree with Peter that lapping the two parts together doesn't work easily.

I question the need for hardened parts. This doesn't have to work for half a million miles.

My closest attempt was using a brass barrel and a hardened dowel pin as the plunger. I reamed the brass out to slightly undersize, then repeatedly drove a hardened dowel pin, coated in oil, back and forth thru the brass. i thought it would eventually fit properly, but I think the walls were too thick and the pin never would slid thru. Thinner walled brass might work.
I tried lapping just the dowel pin spun in a lathe, using a very fine diamond lap lap. This actually worked quite well but because I had to remove maybe .0003" from the dia, it started to get a bit tapered. This method has potential.

On find Hansen's website (not in the videos) he describes a method of filling the pump body with molten solder and then inserting the dowel pin into the solder such that the solder solidifies around the pin without the tiniest of clearance. I am sure there are some secret tricks to making that work.

I am going to re-try the brass barrel and hard dowel pin with a lap again. I think the thinner wall might do the trick.

Here the laps are. The business end is 3/4 x 2-1/2.

 

[ajoeiam]

I tried a lot, these are just the parts I keep, almost like Ithat put them in the trash


Remember one thing: I never say what I haven't done or tried,.
And I have never heard other people speak and repeat or rely on other people's experiences
Remember that

Respectfully - - - I would disagree.
I have reached a stage in life where I have realized that I just do not have enough time left to make all the mistakes to teach myself everything that I might want or need to know.
That's one of the reasons that I'm on this forum - - - - I can share my experiences (some very hard one!!!) and then I get to learn from what doesn't work for someone else - - - sorta like I'm peering over his (or her as the case may be) shoulder - - - if that saves me effort (and especially time) - - - I am all for it!

 

[Nerd1000]

Bummer. Its all a learning experience and sometimes the journey is the real prize of the project. How big is your reject box? Each item in there will have its own story.
Keep at it!

Haha, I have a 'shelf of shame' full of assorted parts, mostly created by my own absent-mindedness.

I was contemplating hardening one part not for wear resistance but because hardened steel is much less prone to galling. That being said, as Minh-Thanh says the 'lapping together' approach may not be the best option. It's worth considering other ideas. I've also put a little thought into a design that would need no precision fitting of the plunger at all (instead the seal would be provided by a stuffing box) but haven't drawn it up yet.

 

[peterl95124]

I tend to agree with Peter that lapping the two parts together doesn't work easily.

I question the need for hardened parts. This doesn't have to work for half a million miles.



On find Hansen's website (not in the videos) he describes a method of filling the pump body with molten solder and then inserting the dowel pin into the solder such that the solder solidifies around the pin without the tiniest of clearance. I am sure there are some secret tricks to making that work.

I am going to re-try the brass barrel and hard dowel pin with a lap again. I think the thinner wall might do the trick.

the reason for using hardened steel is that it is easier to lap just as hardened steel is easier to grind than mild steel on a grinding wheel, and oversize abrasive grains will get embedded in the lap rather than gouge out the steel so you'll get a better finish.

the purpose of the lead solder in Finn's method is to create a lap made of soft metal so that abrasive grains embed in it rather than the metal you're trying to polish so you can get a finer surface finish. But I'd recommend looking at commercially made laps for very small diameters holes, they look like a rod with a section near one end where the rod has been split lengthwise and widened a bit, its that widened part that does the lapping. I'd get (or make) some of them before I tried lead solder cast into the cylinder and onto a rod - in that case there's no place for the abrasive to go, compared with the split-rod type where there's lots of space since the lap doesn't contact the cylinder all the way around, so this style can't jam and can't cause galling.

the secret to getting a piston/plunger that isn't tapered is to constantly measure with a "tenth" reading micrometer at the ends and in the middle, they should all be identical, if not apply more pressure on the part that's oversize compared to the rest. also make sure you're always moving the lap around in a circular motion while the piston/plunger is rotating in the lathe to get a perfectly flat/level result rather than one that follows any irregularity in the lap itself.

HTH, YMMV, etc...

 

[Nerd1000]

To be clear, I did the majority of my lapping with an aluminium split-lap. I think the main issue is that I tried to final lap with the two finished parts, rather than fitting the barrel and plunger by lapping them separately.

Minh-Thanh, a question: what grit did you use for lapping? I tried initially with 600 grit silicon carbide powder, then for the final pass I changed to 1500 grit aluminium oxide. Lapping was very slow and I wonder if I could use a coarser grit for roughing.

 

[minh-thanh]

Respectfully - - - I would disagree.
I have reached a stage in life where I have realized that I just do not have enough time left to make all the mistakes to teach myself everything that I might want or need to know.
That's one of the reasons that I'm on this forum - - - - I can share my experiences (some very hard one!!!) and then I get to learn from what doesn't work for someone else - - - sorta like I'm peering over his (or her as the case may be) shoulder - - - if that saves me effort (and especially time) - - - I am all for it!

Because I'm so tired of arguments and informations like this :
" lapping plunger and cylinders with tight tolerance " , yes , it fits large diameter cylinders and pistons , but not for 2.3 , 2.4 .... to 4 mm diameter cylinders . Advice that can destroy many hours of work and a lot of effort
......
I'm trying to put information that's fine with my engine
And when I said 1mm diameter is fine and he tried to find a picture and video of me - That's just a small part of my many tests - several dozen times?? I do not remember , instead of asking me: "do you have a picture of your injectors?" or what similar sentence.

 

[minh-thanh]

This actually worked quite well but because I had to remove maybe .0003" from the dia, it started to get a bit tapered. This method has potential.

I can tell you : " my cylinder is 100% straight ., no taper "
But that is the info: Impossible for me.

 

[minh-thanh]

Minh-Thanh, a question: what grit did you use for lapping? I tried initially with 600 grit silicon carbide powder, then for the final pass I changed to 1500 grit aluminium oxide. Lapping was very slow and I wonder if I could use a coarser grit for roughing.

Silicon carbide powder .
I have 2 options: 400 or 600 grit to start with.
Because in my opinion the first step is just to remove scratches caused by drilling or reaming, if I want to be fast, I use 400, 600 is also ok but longer.
If I use 400, then 800 and 1800
If I use 600 then just 1800 is enough

 

[Nerd1000]

Silicon carbide powder .
I have 2 options: 400 or 600 grit to start with.
Because in my opinion the first step is just to remove scratches caused by drilling or reaming, if I want to be fast, I use 400, 600 is also ok but longer.
If I use 400, then 800 and 1800
If I use 600 then just 1800 is enough

Ok, so my choice of abrasives was in the ballpark. Just need to refine my technique

 

[Lloyd-ss]

Nerd,
I am enjoying following your progress. Your candid observations are refreshing.
At the beginning of the thread you mentioned using Delrin for some seals and gaskets. Watch out for high temps (over 180F) with Delrin. PEEK is more expensive but MUCH tougher and is good for 480F.

I have made lots of small parts with both Delrin and PEEK. Both are excellent, but I always use the PEEK when I need the strength or heat resistance.

Also, please consider using copper for seal-washers and gaskets, and crush-rings. I have several sizes of soft copper tubing on hand and with a little practice, they can be cut nicely with a good tubing cutter, with only minimal clean-up needed. If you want them super annealed, just heat to red hot and let air cool or quench in water. If the heat-tarnish is a problem, just dip in a little muriatic acid (brick acid) for several seconds and they will brighten right up. I really like functionality of the diy copper seal-washers.
Lloyd

 

[peterl95124]

To be clear, I did the majority of my lapping with an aluminium split-lap. I think the main issue is that I tried to final lap with the two finished parts, rather than fitting the barrel and plunger by lapping them separately.

and also to be clear, I'm being wordy because I too will be embarking on this challenge when I finish the frame and cylinder for my Find Hansen Diesel, and the more I learn from your endeavors the less trial-and-error I'll have to go through, so
many thanks for sharing.

 

[Lloyd-ss]

Here is a barrel lap from the junk box. The lap is drilled and tapped all the way thru. The gashes were cut thru with a Dremel thin cut-off wheel. The screw in the picture threads in to align and expand. The drive rod threads in from the other end. I have tried many ways to expand the lap, including a rubber plug in the middle that gets compresses by the two screws. Many methods work.
Nerd, you are correct about "technique." Anyone can get it to "work." But getting it to work WELL requires technique, or what I like to call, knowing the "tricks".

 

[Lloyd-ss]

I have a retired diesel fuel injection mechanic kind of mentoring me, and he is a walking encyclopedia of hands-on knowledge. The method that he uses, is to do the barrel first and the plunger last. He uses a piece of wood with a V-notch in and loads it with compound and then spins the plunger in the lathe and monitors it closely. That is his "trick."

 

[Steamchick]

For fine abrasives - much finer than some of the grades mentioned here, try jewellers' polishing pastes?
https://www.cooksongold.com/Jewelle...4583176802198819&utm_content=PLA-All Products - Or the polishing solutions used when making sections for microscopic study? - You really need to try to achieve a mirror finish and clearances smaller than 1000 grade grit for diesel injectors to work.
Lapping your parts together will make the gaps bigger than the grit size.
In industry, working to such fine tolerances, (as happens on millions of engines made every week!) the way is by making a lot of parts and selecting the best fit from the distribution of manufacturing sizes.
So make 1 of the complex parts, and 5 times more of the "simple" parts - then select "best fits". Measuring by using the complex part as the gauge is the only way. You need to measure just a micron or so variation between parts - greater accuracy than "tenths of a thou". (0.0001" = 2.54mu). A single tenth of a thou variation is the difference between good and bad.
Does this help?
https://www.buehler.com/uk/blog/grinding-and-polishing-guide/K2

 

[Steamchick]

I would not use WD40 as any form of lubricant. It is a water dispersant. But use watch maker's lube oil, or sewing machine oil. - Even the very light olive oil you would use for salad dressing is good, light (small molecules!). But the BEST is simply diesel fuel (the most obvious and best for this application) ... as the final job will run in diesel fuel anyway! - DERV contains special lubricant additives to hugely increase the LUBRICITY and AVOID SCUFFING... and detergents to aid washing the grit away from surfaces. (Central heating oil is specifically lacking these detergents and lubricity additives! - so don't use non-"road-use" oils).
I have been using DERV for washing dirty engine parts etc. for 50 years or more.... much healthier and safer than petrol! - and leaves parts with a very light oiling on the surface that resists overnight corrosion from condensation when the workshop cools... (Paraffin and petrol can both permit overnight condensation corrosion!).
Hope that is useful?
K2

 

[Nerd1000]

Nerd,
I am enjoying following your progress. Your candid observations are refreshing.
At the beginning of the thread you mentioned using Delrin for some seals and gaskets. Watch out for high temps (over 180F) with Delrin. PEEK is more expensive but MUCH tougher and is good for 480F.

I have made lots of small parts with both Delrin and PEEK. Both are excellent, but I always use the PEEK when I need the strength or heat resistance.

Also, please consider using copper for seal-washers and gaskets, and crush-rings. I have several sizes of soft copper tubing on hand and with a little practice, they can be cut nicely with a good tubing cutter, with only minimal clean-up needed. If you want them super annealed, just heat to red hot and let air cool or quench in water. If the heat-tarnish is a problem, just dip in a little muriatic acid (brick acid) for several seconds and they will brighten right up. I really like functionality of the diy copper seal-washers.
Lloyd

I'd use PEEK if I could afford it! it's extraordinarily pricey stuff. I think if I need more heat resistance than delrin can provide I might try glass-fiber filled PTFE.

I'm planning to use a copper crush washer as the injector tip seal, IMO there's few alternatives for handling the heat and pressure. Same for the head gasket. As for the HP fuel line to the injector, this will be copper 'capillary' tube sold for use in refrigerators, I have some with a 1mm ID and 3mm OD. It can be brazed to the injector body at one end, but the other will need a fitting for assembly, was thinking of making miniature versions of 37 degree flare fittings for this.

 

[minh-thanh]

I have a retired diesel fuel injection mechanic kind of mentoring me, and he is a walking encyclopedia of hands-on knowledge. The method that he uses, is to do the barrel first and the plunger last. He uses a piece of wood with a V-notch in and loads it with compound and then spins the plunger in the lathe and monitors it closely. That is his "trick."

That's exactly what I did
Make the cylinder first, make the plunger later
But I use aluminum 50. and drill holes

 

[minh-thanh]

Hi Peter !

my best guess is that you have to lap the piston with an adjustable dummy cylinder (an external lap), and you have to lap the cylinder with an adjustable dummy piston (an internal lap), and keep monitoring the sizes until they "just" fit. and since this is a laboriously manual and skill intensive job be prepared to have lots of throw-aways, or a few workable pairs from a large set of candidate parts.

I've been thinking a lot about this method - it's the best method, but with the small diameter it seems impossible - it's like an impossible task, and I'm also trying to find one solution to do it but it seems 1% is successful