Engine Doctor Posted January 12, 2023 Share Posted January 12, 2023 Here's something for those of you who are paid up members of the "Oily Hands Society " (OHS) and may be interested . is a I was recently given a rather sorry Frog 150 diesel by a forum member as a project , It has Zero compression and when stripped it looks as if its had a sort of replacement piston fitted in the past ! The machining marks look like piston rings . Pic is of the cleaned crank case ( sorry , I got carried away and didn't do a before pic) and the piston -con rod assembly. Other bits will be cleaned properly before they are worked on Fortunately the cylinder looks ok . I might have to give that a light lapping before fitting a new piston . I'll start the piston shortly and post progress . If all goes well I'll also re anodise the Cylinder head as it a bit scratched and will look much better . 1 Quote Link to comment Share on other sites More sharing options...
J D 8 Posted January 12, 2023 Share Posted January 12, 2023 Funny, nothing but code coming up on my screen. My first engine Frog 100 mk3. Not been in a plane for many years but gets a test stand run now and then just because. 1 Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted January 12, 2023 Share Posted January 12, 2023 Hi Ed, sounds interesting, no pictures yet... Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 12, 2023 Author Share Posted January 12, 2023 Hello Rich , Pictures should be on there ? They are on my page ? I'll try re posting the pics tomorrow . Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 13, 2023 Author Share Posted January 13, 2023 (edited) It appears that pics are not showing ? Rich can you confirm if pics are now visible ? Pics re -sent Edited January 13, 2023 by Engine Doctor 1 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted January 13, 2023 Share Posted January 13, 2023 ED, We can see them now. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 13, 2023 Author Share Posted January 13, 2023 👍 Thanks. Quote Link to comment Share on other sites More sharing options...
jeff2wings Posted January 14, 2023 Share Posted January 14, 2023 Don't know what's going on with that piston, but it's definitely out of service limits! 😄 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 14, 2023 Author Share Posted January 14, 2023 Hi Jeff . I think it was a new multi ring low friction experiment ........😉not. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 27, 2023 Author Share Posted January 27, 2023 (edited) Ok so new piston started . Ive bored the inside out to match original piston and reduced the blank so as its very near to fitting the liner . The blank has also been blacked with a marking pen and marked for piston hight gudgeon pin centre line . Next I will drill the holes for the Gudgeon pin but need to fit it in the mill on a rotary table . I tried drilling straight through from one side but the drill always wanders off so Ill drill through both sides the ream to a final fit for pin . When happy with fit I'll finish fitting piston to liner. Normally I would make a new piston and contra-piston(CP) and lap the cylinder but cylinder is good and CP is a good fit so just a piston it is . Edited January 27, 2023 by Engine Doctor 1 Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted January 27, 2023 Share Posted January 27, 2023 Hi Ed, may I ask, are the gudgeon pin and crank pin the same diameter please ? Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 28, 2023 Author Share Posted January 28, 2023 No Rich , not on the Frog 150 . The gudgeon pin is 1/8 inch . All £.s.d and imperial measurements back when they were made or 3.17 mm in modern . Big end is a bit bigger approx 5/32 I think . Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted January 28, 2023 Share Posted January 28, 2023 Cool, was wondering as picture suggests Conrod may be on wrong way. Gudgeon pin may be pressed in ? Anyways good to see stuff being made to bring old engine back to life. Respect. Quote Link to comment Share on other sites More sharing options...
jeff2wings Posted January 28, 2023 Share Posted January 28, 2023 Normally when I drill for the gudgeon I start with a centre drill then a new quality drill, although I have used a slot mill but always under size and then ream with a D bit made from silver steel Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 29, 2023 Author Share Posted January 29, 2023 Hi Jeff . Yes started with a centre dril then an undersized new drill . I believe that had I drilled the gudgeon hole before boring the piston internally it would have been OK? Haven't been in the ws for a few days and have mates wanting some workso piston may have to wait a few days . Next step is to mount it in a rotary table and drill through from both sides before reaming to fit. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 1, 2023 Author Share Posted February 1, 2023 I started again with the piston blank. It has been machined so that it almost fits the bottom of the cylinder. As already stated the cylinder is in very good condition so no machining or lapping required. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 1, 2023 Author Share Posted February 1, 2023 (edited) The blank was then finished to be a snug fit into the bottom of the cylinder but below the the exhaust ports being careful to keep it parallel . Starting with 400 grit placed on a cutting tool for a flat finish . As I get closer change to 1200 grit and finish with 2000 grit wet and dry with a drop of oil . The grinding is done very gently and checked often for fit in the cylinder . I also use a micrometer to check the blank for parallel between each grinding . The cylinders are slightly tapered and become slightly smaller above the ports . Edited February 1, 2023 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 1, 2023 Author Share Posted February 1, 2023 The piston blank is now a nice snug fit in the cylinder but too tight to go any further past the ports . Next I will remove to the mill to drill the gudgeon pin hole . Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 1, 2023 Author Share Posted February 1, 2023 As usual I forgot my phone when I fitted the blank into the milling table so no pics of the drilling . Here its been drilled and re mounted into my lathe and is being parted off . Before the parting off is finished the bank is given a very light grind to remove any burrs . The stud is used just catch it when its parted. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 1, 2023 Author Share Posted February 1, 2023 (edited) The finished item is now fitted to the con rod . Compared to the old piston it look pretty good and the compression is really bouncy . it may look grainy but its the coating of oil and the grain of the cast iron. Edited February 1, 2023 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 9, 2023 Author Share Posted February 9, 2023 (edited) The Frog has now been assembled and test run after re-anodising the Head and prop spinner nut . The engine feels very smooth after a short run with nice bouncy compression . Members of the "Honourable Oily Hand Society" will also know what I'm talking about when I say the smell of it is great 😃. For those interested in anodising , the blue dye used is blue inkjet printer ink mixed 50:50 with distilled water. The needle valve used (not in pic) is one of the generic one available from the 1960/70's so currently looking for a Frog NV to complete it. Thanks again to the Forum member who donated the tired engine . It should grace the skies again at some point in a 2 ch type model . An enjoyable winter project even if heating the Workshop is more expensive now-days . Thank heavens for the Diesel heater ,now run on kerosene as its a bit cheaper Edited February 9, 2023 by Engine Doctor 6 1 Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted February 9, 2023 Share Posted February 9, 2023 Lovely... Could you please talk us thru the anodising process please, maybe in a new thread ? Do any other printer ink colours works as well ? Thanks. Quote Link to comment Share on other sites More sharing options...
brokenenglish Posted February 9, 2023 Share Posted February 9, 2023 Congrats! What a super result. +1 for the anodising process suggestion. Quote Link to comment Share on other sites More sharing options...
J D 8 Posted February 9, 2023 Share Posted February 9, 2023 Very nice.👍 Quote Link to comment Share on other sites More sharing options...
Robert Cracknell Posted February 10, 2023 Share Posted February 10, 2023 Agree to the previous posts. I would like to learn more about home anodising please...... Quote Link to comment Share on other sites More sharing options...
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