Jonathan W

I'm somewhat late, but have clicked "Like" to add myself to the order list way back on page 6 or so.

Looking good now! I'm wondering though if you lapped the piston, or only turned it to size? Anyway, will see what happens when you fire her up.

Thank you Keith, I have sent you a personal message 😄

Also, if the piston pin bore in the piston is not exactly perpendicular. All these things can cause the piston to bind in the cylinder.

Your Viper looks fantastic, Keith. Where can one find plans for this? Internet search came up with lots of promising leads which ultimately all came to nothing.

Frustrating! Milling is a lot easier in a vertical milling machine than in a lathe. For one thing, you have better visibility of what you are doing without a large lathe chuck being in the way. I think even a practised machinist would find it a challenge with the equipment you are having to use. That has to be the model engine world's longest piston. The amount of friction will be considerable. Something of a detail I know, but I'd be tempted to relieve the skirt below the gudgeon pin by a thou. At least that ensures that the crown is the biggest diameter.

The other option is a redesign to use a brass contra-piston with o-ring seal. I guess they did not have o-rings in 1946, or whenever it was. If the brass contra is made to a close transition fit in the cylinder, at running temperature it should expand to be a tight fit.

I can't speak to the Laser 80 specifically, but generally you would go up in diameter and down in pitch if you wanted to "calm things down".

To give you an idea how things have changed, my father and I used to go to Benson's Chemists on the A6 in Stockport to buy methanol, castor oil and nitro-methane to mix our own fuel. Imagine doing that now!!!

Yes, I think fuel and glow plugs will ultimately be the show-stopper for us glow die-hards. Nobody in UK is making plugs anymore. Optifuel did not continue with the Model Technics plugs. Southern Modelcraft had supposedly sold their fuel business, but the new owner appears to have done nothing with it, as far as I know. That leaves Optifuel and Weston. Alan at Weston is no spring chicken, so who knows how much longer he will continue?

When I have expanded pistons in my impecunious youth, it was just to heat up and allow to cool naturally. So probably the quenching has caused the cracks. Sounds like you are on the right track with the lapping now though. What kind of finish did you have before lapping? Was it from lathe boring tool marks or did you use a reamer?

Also see HERE At least this is a UK company you can phone up and talk to 😏 Listing diamond paste in the same range 1 -40 which you seem to have. They are saying W1 = 15000 to W40 = 400, so the "W" numbers are apparently not the same as microns then. If your paste conforms to this system, I would have thought the difference between 1 (super fine) to 40 to be obvious.

It might be that the numbers are the micron size of the diamond grit??? In which case 1 to 40 = fine to coarse. Just to add that I never used this diamond stuff myself and your Chinesium product might be using a different system, who knows? I do have some silicon carbide lapping compound at 600 grit which I use to good effect on model 4 stroke valve seats, but the manufacturer of this product has unfortunately disappeared. Equivalents of FEPA F grain numbers to microns are 400 = 17, 600 = 9, 1000 = 5, 1200 = 3 etc. See HERE It would surely be helpful if your man Keith would point you towards the specific products he has successfully used. 😊

Just my opinion, but I don't think you should get too hung up on the finish. If you look at a brand new PAW, the bore is as ground while the piston has very coarse honing marks. The honing marks promote oil retention and allow some bedding in to occur. You won't get that if everything is to a mirror finish. I think dimensional accuracy with a slight "pinch" at TDC is far more important.

I have some of the smaller New Power servos (9g, 17g) installed in foam models. I found that the few faulty ones failed very soon in testing and the remaining ones have lived on without issues. Still, I wouldn't buy them again personally because of those few initial failures.