Indeed, I have in the past done this sort of thing by putting wet and dry sandpaper on the surface plate.
Model Diesel: 32mm bore, 38mm stroke, indirect injection
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Worth testing surfaces with a surface plate, or other flat plate (gauge plate) and Engineers' blue. It may sound "old fashioned", but it was how we checked for flatness or high spots in the 1960s workshop. - I guess today you have a laser thingummy or something.... but if old methods work, why not use them?
Have you tried a steel rule across the surface? (Use a light source and look for light bleed beneath). Or roll an old car piston gudgeon pin (or other ground steel parallel pin), with marking blue on it, across the surface? - 2 directions, perpendicular....
Sounds to me as if the milling was not as flat as you need?
K2
Have you tried a steel rule across the surface? (Use a light source and look for light bleed beneath). Or roll an old car piston gudgeon pin (or other ground steel parallel pin), with marking blue on it, across the surface? - 2 directions, perpendicular....
Sounds to me as if the milling was not as flat as you need?
K2
A grooved or ridged copper gasket has gotten me out of some bad situations. The grooves or ridges can be on the gasket or the mating surface(s).
Have you tried tightening up the lash on the exhaust valve a little to keep the pressure from getting high enough in the cylinder to push the fuel back into the injector? I am half way expecting this same scenario in my engine.
Have you tried tightening up the lash on the exhaust valve a little to keep the pressure from getting high enough in the cylinder to push the fuel back into the injector? I am half way expecting this same scenario in my engine.
I'll give it a check with some engineers blue.
ruben
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Hola
Me podrías mandar si quieres los planos de la bomba de combustible
muchas gracias
ruben
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Today I blued up my scraping master and checked the head and block top.
The head isn't too bad for a milled part, but the top of the liner has two low spots that correspond pretty closely to where I've been having leaks. Also there's no contact on the prechamber cup, so it could be forming another leak path. It should be easy enough to sand both surfaces, the question is whether I should wait and try a more conformable gasket first.
The head isn't too bad for a milled part, but the top of the liner has two low spots that correspond pretty closely to where I've been having leaks. Also there's no contact on the prechamber cup, so it could be forming another leak path. It should be easy enough to sand both surfaces, the question is whether I should wait and try a more conformable gasket first.
Personal opinion...I would grind the surface really well before I even think about gaskets.
Roger B
Well-Known Member
I agree.
Klrskies
Well-Known Member
Do you have a good, flat surface plate you put a sheet of abrasive on and flatten the surface?
Very fine "wet and dry" paper with 600 ~1000 grade carborundum, on some plate glass (a second-hand mirror is good) on the surface plate, both protects the surface plate from being abraded out of true, and gives a disposable abrasive surface that is pretty accurate for heads and blocks. With Wet and Dry paper you can use a light oil (even fuel oil/paraffin) when polishing in a figure of 8 pattern, which helps clear the grit from clogging with aluminium. When I was a lad in the machine shop we had a few "old mirrors" from second-hand furniture that we used. The mirrors showed any distortion in the glass, so we knew they were pretty true! We NEVER used anything abrasive directly on the surface of the surface plate - It was sacrosanct! - Normally kept beneath an oiled cloth with wooden cover. - Always used for measuring with slip gauges, etc. so surface polishing was done on the glass placed on the surface plate. I was amazed how a large mirror from a dressing table bent when handled, but was as true as we could judge when resting on the surface plate and a steel rested upon the glass. = no gaps! But we only polished surfaces to minimise machining marks from aluminium heads that were turned in the lathe (24inch swing - A big beast!). Cast iron and steel items were ground on a table/face surface grinder. (Not aluminium as it clogged the stones which then needed very frequent dressing).
K2
K2
The tempered glass windows from toaster ovens also work great.
Tempered glass... toaster ovens.... beyond my experience! My memories are of workshop practice in 1960s... When Victorian furniture was scrap! And Ladies had demanded perfect mirrors needing the best glass....
K2
K2
I'll get you some Tollens' reagent so you can silver up a toaster oven window and feel nostalgic.
Today I did the sanding thing on both block and head. Didn't help in the slightest!
Thankfully, I think what I did next has revealed the source of the trouble. I decided to try making a soft gasket, so I cut one out of a manila folder. This gasket produced stronger compression, but upon testing with stater fluid I once again had a leak, in the same spot. Removing the head revealed a very thin black circle on the paper gasket, right under the edges of the pre chamber cup. When I parted the cup off I deburred it, and it seems this has resulted in a very narrow groove around the perimeter of the bore it seats in which forms a leak path past the raised top of the cylinder liner. I'd not have seen it were it not for the light coloured paper.
The solution will be to set the head up in the mill and skim just enough material off to remove this groove. There's a good chance that the copper gasket will work once this is done, but I also played around with forming fire rings from the metal that you get on top of Milo tins. That method seems promising so I'd like to explore it further.
Thankfully, I think what I did next has revealed the source of the trouble. I decided to try making a soft gasket, so I cut one out of a manila folder. This gasket produced stronger compression, but upon testing with stater fluid I once again had a leak, in the same spot. Removing the head revealed a very thin black circle on the paper gasket, right under the edges of the pre chamber cup. When I parted the cup off I deburred it, and it seems this has resulted in a very narrow groove around the perimeter of the bore it seats in which forms a leak path past the raised top of the cylinder liner. I'd not have seen it were it not for the light coloured paper.
The solution will be to set the head up in the mill and skim just enough material off to remove this groove. There's a good chance that the copper gasket will work once this is done, but I also played around with forming fire rings from the metal that you get on top of Milo tins. That method seems promising so I'd like to explore it further.
Roger B
Well-Known Member
Glad you found the problem 
NapierDeltic
Well-Known Member
Do you have a link to Milo tins solution? I believe is a quite soft iron. Can it be found in something else? Is enough for purpose?
Leak detection and repair, especially in a high pressure dynamic condition can be extremely frustrating to trouble shoot and repair. I really, really, know.
Your use of the manilla folder gasket for detection is excellent!
Also, putting a few drops of food coloring in the cylinder before doing the compression test can help reveal a leakage path.
Lloyd
Your use of the manilla folder gasket for detection is excellent!
Also, putting a few drops of food coloring in the cylinder before doing the compression test can help reveal a leakage path.
Lloyd
I once looked very closely at nozzle and droplet size. Specifically for fuels you need a liquid mass of some amount because vapor alone can not give enough mass for the energy that is delivered. The smaller the sphere the more surface area is available for the chemical reaction and it goes faster. Injection into high pressure systems poses a theoretical problem as the engines get smaller say on model systems. It is more difficult to get the fuel to shear properly because it is difficult to machine the geometry required at very small sizes. The injector systems become a design process in itself. I have often thought that maybe at a certain size vapor will be the only way to deliver the fuel. I have seen where some model engines the fuel is mixed with a highly volatile fuel such as ether to get them to run.
I think it's some sort of very soft aluminium, sort of like a very thick foil or maybe shim stock. Easy to bend into shape, I was able to cut out a circle and draw the ID of the hole downwards, then sort of wrap it around the inside of the paper gasket. Result wasn't too great but I feel with some practice and maybe turning up a wooden former I can probably get a neat result.
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